Engine Braking : One for the physics guys I think

There a bunch of clever guys in this newsgroup, so I though I'd pose a question that's been bothering me. OK, first thing, what do "I" mean by engine braking. Essentially I mean using the engine, via the gearbox, diff, drivetrain to exert a braking force on the rear wheels (I know it can be front wheels but we will just consider a RWD car). We accomplish this by changing down to a lower gear and re-engaging the clutch at a higher speed than the gear and current revs would equate to. Thus if we were travelling at 170mph in 5G, at 9,500 revs and we changed down to 4G we would get engine braking (and perhaps breaking!). We wouldn't normally do the above of course, the correct way to USE engine braking is to brake and change down to a lower gear at aorund the speed you would be going at max revs in the lower gear, thus you get good engine braking but shouldn't damage the engine and shouldn't lock the wheels. I've used engine braking, in real-life and GPL. I know there are current F1 drivers using engine braking. The thing is, does it really help? Surely if we are braking optimally already, the tires will not accept any more braking force than we are giving them. I know engine braking was used in the past as brakes in those days where simply not powerful enough to give maximum braking force, that generally is not true of today cars/brakes. Also, I know that under braking the weight balance of the car shifts forward considerably. We'd generally set the brake bias to compensate for that, but we may be able to alter this weight transfer (as was discussed in gas+brake posts) by using engine braking, allowing the rear (wider) wheels to come into play more. Also of course, having engine braking doing some of the slowing down will alleviate some of the load from the brake pads which at under very heavy braking will reach very high temperatures at which they are less efficient. All that said is there ANY DIFFERENCE, in physics terms between brakes->pads->disk->hub->wheel->tire than engine->drivetrain-> axle->hub-wheel->tire. The sort of thing I'm thinking off is, we know that adding power under braking will negate some of the weight being thrown forward as we brake. Would braking via the axle lead to a difference in weight transfer than conventional braking. Is there any other reason, other than those mentioned above why engine braking might be more efefctive than conventional braking? TIA Maxx

> All that said is there ANY DIFFERENCE, in physics terms between > brakes->pads->disk->hub->wheel->tire than engine->drivetrain-> > axle->hub-wheel->tire. >One thing engine braking would do would be to effectively change your brake balance rearward for a second. This could be good and bad.. I know my down habitual shift points from the Honda resulted in me putting the Brabham backwards into the hedging at parabolica..

This doesn't really answer your question, but I've heard many racers and mechanics state that brakes and brake pads are cheaper than transmissions and engines. When racers use heel-and-toe clutch/brake/throttle techniques to match the engine's RPMs to the the speed of the drivetrain/wheels, this effectively removes engine braking from the equation all together. -- JB F1CS2K Rank 68.354 http://f1cs2krank.dhs.org In article <[email hidden]>, Maxx <[email hidden]> wrote: > > There a bunch of clever guys in this newsgroup, so I though > I'd pose a question that's been bothering me. <SNIP> Sent via Deja.com http://www.deja.com/

On Wed, 31 Jan 2001 17:43:12 GMT, [email hidden] wrote: >This doesn't really answer your question, but I've heard many racers >and mechanics state that brakes and brake pads are cheaper than >transmissions and engines. When racers use heel-and-toe >clutch/brake/throttle techniques to match the engine's RPMs to the the >speed of the drivetrain/wheels, this effectively removes engine braking >from the equation all together. No, Heel & Toe removes BAD engine braking from the equation, hence damaged engines and transmission. H&T is actually a requirement of correct engine braking. Bad engine braking is when you drop it into the lower gear at low revs (as you've let the engine rev down under braking) and it will create all sorts of stresses in the engine and transmission, also likely lock the wheels. Good engine braking is using H&T to match the engine revs AND changing down at what would be the speed = Max Revs in the gear you are changing to. This way you get the same level of engine braking you get when you just lift off at Max Revs (which is more than if you lift off at lower revs). GPL effectively does H&T for us. But by changing down later (say at a speed equal to 1/2 of max revs in the target gear) you are probably getting some small amount of engine push as the revs are still dropping from max revs (blip) and may well be over 1/2 max revs when the gear is engaged. It's not terribly significant in itself as an "aqnti-braking" force, but it will unsettle the car a little. I'm glad you raised the point however as it allows me to explain what I'm meaning in a little more detail. Maxx

My theory on engine braking.... It's all pants:-) I hate comparing racing to road cars but in this instance I will. If you are driving your road car simply try engine braking and then not doing it... You usually use engine braking over a longer stretch of road like coming to a junction at the end of a dual carriageway. You use brakes to stop you quickly. Yes engine braking works, but I cannot see how it can aid you to brake faster. The only way I can brake very efficiently in GPL is to stay in a high gear until I have a very low speed for the next corner then shift, overwise the momentum in the engine is carrying me forward. As I say you can use engine braking is real life, I just believe personally that it's not beneficial in racing... I'm sure someone will try to prove this wrong though, i have no solid evidence only my interpretation. Maxx <[email hidden]> wrote in message news:[email hidden]...

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> > There a bunch of clever guys in this newsgroup, so I though > I'd pose a question that's been bothering me. > > OK, first thing, what do "I" mean by engine braking. > > Essentially I mean using the engine, via the gearbox, diff, drivetrain > to exert a braking force on the rear wheels (I know it can be front > wheels but we will just consider a RWD car). > > We accomplish this by changing down to a lower gear and > re-engaging the clutch at a higher speed than the gear and current > revs would equate to. Thus if we were travelling at 170mph in 5G, > at 9,500 revs and we changed down to 4G we would get engine > braking (and perhaps breaking!). > > We wouldn't normally do the above of course, the correct way > to USE engine braking is to brake and change down to a lower > gear at aorund the speed you would be going at max revs in > the lower gear, thus you get good engine braking but shouldn't > damage the engine and shouldn't lock the wheels. > > I've used engine braking, in real-life and GPL. I know there are > current F1 drivers using engine braking. The thing is, does it > really help? > > Surely if we are braking optimally already, the tires will not accept > any more braking force than we are giving them. > > I know engine braking was used in the past as brakes in those > days where simply not powerful enough to give maximum braking > force, that generally is not true of today cars/brakes. > > Also, I know that under braking the weight balance of the car > shifts forward considerably. We'd generally set the brake bias > to compensate for that, but we may be able to alter this weight > transfer (as was discussed in gas+brake posts) by using engine > braking, allowing the rear (wider) wheels to come into play more. > > Also of course, having engine braking doing some of the slowing > down will alleviate some of the load from the brake pads which > at under very heavy braking will reach very high temperatures at which > they are less efficient. > > All that said is there ANY DIFFERENCE, in physics terms between > brakes->pads->disk->hub->wheel->tire than engine->drivetrain-> > axle->hub-wheel->tire. > > The sort of thing I'm thinking off is, we know that adding power > under braking will negate some of the weight being thrown forward > as we brake. Would braking via the axle lead to a difference in > weight transfer than conventional braking. > > Is there any other reason, other than those mentioned above > why engine braking might be more efefctive than conventional > braking? > > TIA > > Maxx >

Maxx, I'm no physicist, but I clearly remember Carroll Smith dealing with this topic in one of his " ... to Win" books; probably Drive to Win. His basic point after a long preamble about car physics was something like... "engines are for acceleration, brakes are for braking...". I'd have to sift through it to provide details. I'm not sure about 1967, but in modern racing it makes sense to allow the brakes to handle all the decceleration (unless there is some wierd turn which requires heavier rear braking (bias) to maintain speed and control compared to the rest of the track). But as has been mentioned brakes are cheaper to replace; a point also made by Smith I believe. A side note about your question of the physics of how the slowing down is accomplished: in the late 70's or early 80's Ferraris had inboard rear brakes, near the gearbox. The half-shafts would carry all the acceleration and braking stresses to the wheels. I think the key advantage was the reduced "unsprung" weight of the wheel assembly. I suspect they dropped the design due to cooling issues or broken half- shafts. Or the higher weight of reinforced half-shafts. Cheers, Ray Sent via Deja.com http://www.deja.com/

Maxx <[email hidden]> schreef in berichtnieuws [email hidden]... > All that said is there ANY DIFFERENCE, in physics terms between > brakes->pads->disk->hub->wheel->tire than engine->drivetrain-> > axle->hub-wheel->tire. Look at it from the tyre contact patch up: it doesn't matter what causes the slow down, or where it comes from - it all starts before the bearing (I hope this makes sense) so the effect on grip will be the same. The effect on car behaviour of course is very different <g> It seems I can't drive without engine braking anymore (in GPL that is). Bye, Leo

>Thus if we were travelling at 170mph in 5G, >at 9,500 revs and we changed down to 4G we would get engine >braking (and perhaps breaking!). Breaking, yes! lol >Surely if we are braking optimally already, the tires will not accept >any more braking force than we are giving them. Exactly. If your brakes can lock all four tires already, engine braking is pointless, unless you are trying to decrease brake wear. >I know engine braking was used in the past as brakes in those >days where simply not powerful enough to give maximum braking >force, that generally is not true of today cars/brakes. > Right. Once the brakes are strong enough, there's no point to engine braking in regard to slowing the car more rapidly. The car will only slow down as quickly as the tires allow.

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>Also, I know that under braking the weight balance of the car >shifts forward considerably. We'd generally set the brake bias >to compensate for that, but we may be able to alter this weight >transfer (as was discussed in gas+brake posts) by using engine >braking, allowing the rear (wider) wheels to come into play more. > >

What really ends up controlling weight transfer in the end is the vehicle's acceleration. Whether the acceleration is caused by the brakes, the engine, or both at the same time shouldn't matter. The end "g" is all that counts. >Also of course, having engine braking doing some of the slowing >down will alleviate some of the load from the brake pads which >at under very heavy braking will reach very high temperatures at which >they are less efficient. Right. >All that said is there ANY DIFFERENCE, in physics terms between >brakes->pads->disk->hub->wheel->tire than engine->drivetrain-> >axle->hub-wheel->tire. No difference whatsoever. >The sort of thing I'm thinking off is, we know that adding power >under braking will negate some of the weight being thrown forward >as we brake. I know you've all been on that subject for a long time, so much so that I've not read nearly all the posts, but from what I've been able to gather, the only reason adding some throttle will decrease the amount of weight thrown forward is because we're reducing the vehicle's acceleration by hitting the gas. The car's weight transfer is determined solely from one thing: Acceleration. Of course, you claim from experience that it does indeed happen anyway, so I won't argue with you about that :0) You might be getting some transient effects that are different from steady state deceleration weight transfer stuff. I haven't raced anything but go-karts for $13.50 for 8 minutes at a time, so there may be something I'm not thinking of here. In the end, the only thing that effects steady-state weight transfer is acceleration. By steady-state, I mean once the weight has all transferred, and you're decelerating at a constant rate. (Not the first instant when you hit the brakes, that's a transient condition.) Whether this is coming from a combination of brakes and throttle, or either of these seperately, one acceleration/deceleration should always result in a constant weight transfer: Load transfer = Acceleration (g) * (Weight * cg_height / wheelbase) The acceleration is determined by force via: Acceleration = Force / Mass To find the acceleration, and thus, the load transfer, I'd add together the forward/rearward forces at all four tires. If you've got 1000 lbs of braking force at all four tires, and 200 lbs of throttle input at the rear (800 lbs net for each rear tire), you should end up with 3600 lbs of force. Let go of the throttle, and you should have 4000 lbs of force (more weight transfer, and more deceleration if the rears don't lock.) Divide that by the mass, and you've got the acceleration. Divide that by 32.16 to get the acceleration in g's. Then, run this result through the first equation as (g) to get the load transfer. Your experience seems to indicate otherwise, but unless there's something I'm missing here (quite possible), load transfer is really only influenced by acceleration. >Would braking via the axle lead to a difference in >weight transfer than conventional braking. > Nope. Steady-state weight transfer is only influenced by acceleration, regardless of what force or combination of forces cause it. >Is there any other reason, other than those mentioned above >why engine braking might be more efefctive than conventional >braking? Not that I can think of. If you've got enough braking power to lock the rear tires, adding more torque by including engine braking won't help. The only use I can think of for engine braking is, as you mentioned, taking some load off the brake pads to reduce heat and wear. Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com

>This doesn't really answer your question, but I've heard many racers >and mechanics state that brakes and brake pads are cheaper than >transmissions and engines. When racers use heel-and-toe >clutch/brake/throttle techniques to match the engine's RPMs to the the >speed of the drivetrain/wheels, this effectively removes engine braking >from the equation all together. There are two different things here that people need to look at (not picking on you, this is for everybody :0) ). One is actual engine braking, caused by low pressure in the cylinders. This will exist when the throttle is closed regardless of whether heel-toe downshifting is used or not. Then what's the point of heel-toe downshifting? Because of the other effect: A reaction torque. When we heel-toe downshift, we're trying to get the engine speed to land exactly where it should be (as we all already know). In other words, if the clutch is spinning at 5000 rpm's, we want the engine to be spinning at 5000 rpm's when we let off the clutch. If we let the engine idle, then let off the clutch, we all know that we get a big lurch forward and sometimes the rear wheels lock/break loose when combined with some real braking. This effect is seperate from engine braking. The friction at the clutch causes the engine/flywheel and the clutch disk itself to try and match speeds. The result is, in a downshifting scenario, the engine speeds up and the clutch/drivetrain/wheels slow down. There's an additional torque or "reaction" sent through both ends during that short period of time when the clutch disk and flywheel are not locked together. Once they are locked together, the effect is done, but the engine, running at high rpm now and with no throttle, is still running very low cylinder pressure, causing a "negative" torque to run through the drivetrain, acting *exactly* like a brake. This is what I consider to be engine braking. So engine braking isn't removed from the equation when heel-toe downshifting is used, however, the reaction torque, which is usually several times larger than any actual engine braking torque, *IS* removed from the equation, as you said :0) Just wanted to make sure folks know there are two different issues here. Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com

>As I say you can use engine braking is real life, I just believe personally >that it's not beneficial in racing... I'm sure someone will try to prove >this wrong though, i have no solid evidence only my interpretation. I agree with you here. I think what racers are talking about when they are "engine braking" is operating under "trailing throttle." Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com

How does the differential work when you use engine to brake? Doesn't it help to distribute braking power between inside and outside wheels? Btw, another unrelated observation. While driving FWD car on the snow using throttle and brakes at the same time has some benefits. It allows to lock rear wheels before front, and turn the car nicely. Same as using handbrake, but more control. Alex (alexti) [email hidden] (Maxx) wrote in <[email hidden]>:

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>There a bunch of clever guys in this newsgroup, so I though >I'd pose a question that's been bothering me. > >OK, first thing, what do "I" mean by engine braking. > >Essentially I mean using the engine, via the gearbox, diff, drivetrain >to exert a braking force on the rear wheels (I know it can be front >wheels but we will just consider a RWD car). > >We accomplish this by changing down to a lower gear and >re-engaging the clutch at a higher speed than the gear and current >revs would equate to. Thus if we were travelling at 170mph in 5G, >at 9,500 revs and we changed down to 4G we would get engine >braking (and perhaps breaking!). > >We wouldn't normally do the above of course, the correct way >to USE engine braking is to brake and change down to a lower >gear at aorund the speed you would be going at max revs in >the lower gear, thus you get good engine braking but shouldn't >damage the engine and shouldn't lock the wheels. > >I've used engine braking, in real-life and GPL. I know there are >current F1 drivers using engine braking. The thing is, does it >really help? > >Surely if we are braking optimally already, the tires will not accept >any more braking force than we are giving them. > >I know engine braking was used in the past as brakes in those >days where simply not powerful enough to give maximum braking >force, that generally is not true of today cars/brakes. > >Also, I know that under braking the weight balance of the car >shifts forward considerably. We'd generally set the brake bias >to compensate for that, but we may be able to alter this weight >transfer (as was discussed in gas+brake posts) by using engine >braking, allowing the rear (wider) wheels to come into play more. > >Also of course, having engine braking doing some of the slowing >down will alleviate some of the load from the brake pads which >at under very heavy braking will reach very high temperatures at which >they are less efficient. > >All that said is there ANY DIFFERENCE, in physics terms between >brakes->pads->disk->hub->wheel->tire than engine->drivetrain-> >axle->hub-wheel->tire. > >The sort of thing I'm thinking off is, we know that adding power >under braking will negate some of the weight being thrown forward >as we brake. Would braking via the axle lead to a difference in >weight transfer than conventional braking. > >Is there any other reason, other than those mentioned above >why engine braking might be more efefctive than conventional >braking? > >TIA > >Maxx >

Maxx wrote: >.... > > I've used engine braking, in real-life and GPL. I know there are > current F1 drivers using engine braking. The thing is, does it > really help? FWIW, I use it in GPL. On tracks that like lots of trail braking or braking when going over hills, I set the brake bias a few clicks further forward than usual. This makes the car more drivable and less likely to bite back. With the unbalanced (inefficient) bias, straight line braking suffers. To reclaim it, I just downshift a bit earlier than usual. It makes for a noticeable improvement in stopping power. > Surely if we are braking optimally already, the tires will not accept > any more braking force than we are giving them. I'd think so. Does this count as e.b.? - Use the engine to power an oversized, reversed radiator fan for aero braking! > Also of course, having engine braking doing some of the slowing > down will alleviate some of the load from the brake pads which > at under very heavy braking will reach very high temperatures at which > they are less efficient. If If the brakes are overheating, they are poorly designed/configured or something had broken. > All that said is there ANY DIFFERENCE, in physics terms between > brakes->pads->disk->hub->wheel->tire than engine->drivetrain-> > axle->hub-wheel->tire. I can think of one issue: During engine braking, the drive train channels torque back into the engine. In a longitudinally mounted motor, this may cause chassis flex and other undesirable reactions. > The sort of thing I'm thinking off is, we know that adding power > under braking will negate some of the weight being thrown forward > as we brake. Would braking via the axle lead to a difference in > weight transfer than conventional braking. No. Weight transfer is proportional to deceleration. It doesn't matter where that wheel does the braking. There may be some 'extra' forces involved, but I don't think they will add up to anything worth worrying over. Adding power just reduces your deceleration and, therefore, subsequent w. transfer. > Maxx -Greg

"engines are for acceleration, brakes are for braking..." I remember reading this also, although for the life of me I can't remember where. Mike

"Alex" <[email hidden]> wrote ...

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> > How does the differential work when you use engine > to brake? Doesn't it help to distribute braking > power between inside and outside wheels? > > Btw, another unrelated observation. While driving > FWD car on the snow using throttle and brakes > at the same time has some benefits. It allows > to lock rear wheels before front, and turn the > car nicely. Same as using handbrake, but more control. > > Alex > (alexti)

It's not unrelated, the opposite is true for a RWD car - engine braking allows more braking to be done by the rear tyres, leaving the front tyres to be used for steering. Think of the traction circle. -- Tony Whitley GPLRank +10.65

Maxx <[email hidden]> wrote: <snip> > create all sorts of stresses in the engine and transmission, also > likely lock the wheels. <snip>

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> GPL effectively does H&T for us. But by changing down later > (say at a speed equal to 1/2 of max revs in the target gear) > you are probably getting some small amount of engine push > as the revs are still dropping from max revs (blip) and may > well be over 1/2 max revs when the gear is engaged. It's > not terribly significant in itself as an "aqnti-braking" force, but > it will unsettle the car a little.

<snip> *What*? I could never have imagined that the matching of downshifts with the engine revs could have anything at all to do with car balance! I've always been downshifting at as low revs as possible in places where you need balance and 100% control of the car (like Nouveau Monde and Mexico T1), because it feels safe. Eg. Approaching Nouveau Monde at G4 I start braking normally, but only start shifting down when I'm halfway through the last bit of straight that leads to the hairpin itself. So, if I'm not entirely mistaken, what you're saying is that I should do exactly the *opposite* to keep the car in control? Please elaborate further... +Cinquo [GPLRank 30.19] +Cinquo

Alex wrote:

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> > Btw, another unrelated observation. While driving > FWD car on the snow using throttle and brakes > at the same time has some benefits. It allows > to lock rear wheels before front, and turn the > car nicely. Same as using handbrake, but more control. > > Alex > (alexti) >

Yup, that sure is true! You can try it in the Mini in Colin McRae 2.0; great fun! Also, the FWD example is the easiest one to clear the misconception that adding the throttle directly effects any weight transwer (which Todd Wasson already explained nicely). Adding throttle in a FWD car under braking actually increases oversteer. -Gregor

Greg Campbell wrote: > > I can think of one issue: During engine braking, the drive train > channels torque back into the engine. In a longitudinally mounted > motor, this may cause chassis flex and other undesirable reactions. > > -Greg That bit sure is true; I'm waiting for the day when this will actually be an issue in the PC based racing sims (not soon it seems)! Also, another thing to consider is that, in the case of outboard brakes (the usual configuration), when using the brakes the torque is transmited through the suspension links, while in the engine braking case this is done via the drivetrain. Any flexibility in the suspension links may thus lead to a different wheel attitude in the two different braking cases. -Gregor

On Wed, 31 Jan 2001 17:03:32 GMT, Maxx <[email hidden]> wrote: Thanks for all the replies guys, just what I wanted, please keep em coming. A few observations. 1) In real-life I used engine-braking (by which I mean taking advantage of the drag caused by decellerartion from max revs in each gear) in saloons. In this case, under high speed braking I could not lock the wheels no matter how much pressure I applied, so thats probably why it worked for me there. 2) I also used it in FFord type cars (Formula Vauxhall Junior) I think more out of habit, generally unless it was hard braking from 5th Gear I think the brakes would have been good enough to lock up under rmaximum pressure although I don't ever recall doing so. 3) I felt I had to use it in Formula Vauxhall Lotus, these are much more powerful cars with wider, slick tires, plus I felt I also needed to use gas+brake. The main reason for doing both of these was that I found it made the car much more stable under braking, I'd thought that this was down to this technique negating some of the forward weight transfer, hence allowing the rear tires to play a bigger part in braking. I think in terms of pure physics, this has been shown perhaps not to be the case, or at least not in isolation. The other thing that occured to me, which I think is also the reason a car feels more stable going through a corner at high revs in a low-gear, rather than low-revs in a high gear, is that I am getting some benefit from the centrifugal force of the engine spinning, rather like a gyroscope. Is this true? I can imagine it might be quite significant, anyone who's ever "played" with a gyroscope will know that these things take a lot of force to move when they are spiinning. That being the case, have Papy modelled that in GPL? It certainly feels like it to me, unless there are other forces at work here. Maxx

Maxx wrote:

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> > The other thing that occured to me, which I think is also the > reason a car feels more stable going through a corner at high > revs in a low-gear, rather than low-revs in a high gear, is that > I am getting some benefit from the centrifugal force of the > engine spinning, rather like a gyroscope. > > Is this true? > I can imagine it might be quite significant, anyone who's > ever "played" with a gyroscope will know that these > things take a lot of force to move when they are spiinning. >

This is true, but my guess is it's not the reason why you feel your car to be more stable. The simpler explanation is that you have far more torque available on demand at high revs, and, perhaps even subconsciously, you can use it to stabilize from over to understeer in the middle of a corner. Besides, if the gyroscopic effects were important, it would only stabilize the car in, say, left hand corners, but destabilize it in the right hand ones due to the different sign of additional weight shift that rotating the engine axis in different directions would bring. -Gregor

On 1 Feb 2001 09:19:45 GMT, Ville V Sinkko <[email hidden]> wrote:

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>Maxx <[email hidden]> wrote: >> GPL effectively does H&T for us. But by changing down later >> (say at a speed equal to 1/2 of max revs in the target gear) >> you are probably getting some small amount of engine push >> as the revs are still dropping from max revs (blip) and may >> well be over 1/2 max revs when the gear is engaged. It's >> not terribly significant in itself as an "anti-braking" force, but >> it will unsettle the car a little. > ><snip> > >*What*? I could never have imagined that the matching of downshifts >with the engine revs could have anything at all to do with car >balance! I've always been downshifting at as low revs as possible in >places where you need balance and 100% control of the car (like Nouveau >Monde and Mexico T1), because it feels safe. Eg. Approaching Nouveau >Monde at G4 I start braking normally, but only start shifting down when >I'm halfway through the last bit of straight that leads to the hairpin >itself. > >So, if I'm not entirely mistaken, what you're saying is that I should do >exactly the *opposite* to keep the car in control? Please elaborate further...

Well you won't be getting any engine push, and thinking about this further, the revs die so quickly that I doubt this is a real-effect anyway. I've been thinking about this since my initial question. I know what I can feel and what works for me but I've no real idea why. I can postulate but they would be uneducated guesses. Thanks to some of the posters in r.a.s. I have a better grasp of the basic physics but there are a lot more things in play here, all the various suspension items, the diff, etc, etc. Certainly the cars "attitude" will be very different in both scenarios (i.e. late, trailing throttle (coast) change downs v. the method I describe. I've posted another possible theory just now to do with centrifugal force (gyroscope effect). Much depends on your speed and your brake balance and probably also your setup, specifically your diff. I BELIEVE I can carry more speed into Noveau Monde using the method I describe, although I havent done any comparative tests. I am certainly in 3G as I turn in and often changing to 2G well before half-way down the short straight after. Here I am most definitely using the engine revs as a stabilising force rather than a brake (although as braking is so tricky here I do think it helps braking also). I think I'll leave any explanation as to why adn indeed if to the vehicle dynamacists. Maxx

On Thu, 01 Feb 2001 11:26:43 +0100, Gregor Veble <[email hidden]> wrote: >Besides, if the gyroscopic effects were important, it would only >stabilize the car in, say, left hand corners, but destabilize it in the >right hand ones due to the different sign of additional weight shift >that rotating the engine axis in different directions would bring. Is that really the case? I imagined it as a gyrosope on the end of a stick, (i.e the engine on the back of the chassis). I'm fairly sure if you have a gyroscope on the end of a stick it will be as hard to move left as it is right (also up and down) irrespective of the spin direction. Bear in mind the last time I had a gyroscope I was 10 so I could be wrong. If my feeling is correct, then this gyroscopic effect COULD make the car more stable in the up and down direction also .. could it .. boy this is confusing stuff! Maxx

Maxx wrote:

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> > On Thu, 01 Feb 2001 11:26:43 +0100, Gregor Veble > <[email hidden]> wrote: > > >Besides, if the gyroscopic effects were important, it would only > >stabilize the car in, say, left hand corners, but destabilize it in the > >right hand ones due to the different sign of additional weight shift > >that rotating the engine axis in different directions would bring. > > Is that really the case? > I imagined it as a gyrosope on the end of a stick, (i.e the engine > on the back of the chassis). I'm fairly sure if you have a gyroscope > on the end of a stick it will be as hard to move left as it is right > (also up and down) irrespective of the spin direction. > > Bear in mind the last time I had a gyroscope I was 10 so I > could be wrong. If my feeling is correct, then this gyroscopic > effect COULD make the car more stable in the up and down > direction also .. could it .. boy this is confusing stuff! > > Maxx

The gyroscopes are really funny, and really gard to comprehend! Besically, the gyroscope will try to rotate in the direction that is both perpendicular to its axis of rotation and the direction in which you're tring to push it. Lets say that the gyroscope such as our engine is pointing forward in our car, and if you look at the car from behind, let's consider the case when the engine is rotating in the clockwise direction. Now, to move the gyroscope (engine), say, to the left, it would require a change of it's angular momentum, which in the case considered points forward along the axis of the engine, towards the left as well. Physics would tell you that the torque required to do so would point in the direction of the change of the angular momentum (to the left), and be proportional to the size of this momentum and the rate of rotation (how fast the nose of the car is turning). In a left turn, the torque needed would then point to the left relative to the nose direction. The torque needed to turn the rotating engine is provided by the car body, so an equal but opposite torque acts on the car body by the engine. Therefore, apart from the torques produced by the tires, there now exists an additional torque on the body that points to the right. Any torque tries to rotate the body anticlockwise around the direction where it is pointing. In the case of the torque on the body pointing to the right, there is therefore an additional shift of the weight to the rear, stabilizing the car. In the case of a right hand turn, the above analysis repeated will give you an additional torque on the body pointing to the left, which, on the other hand, gives an additional weight shift to the front and as such destabilizes the car. For transversally mounted engines, one would get similar weight shifts, but they would be left to right instead of back to front. Come to think of it, perhaps this could even be of use for cars racing on ovals to better ballance the weight? I demand a patent on this solution :)! I hope all of this was at least half comprehensible :). -Gregor

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> >Besides, if the gyroscopic effects were important, it would only > >stabilize the car in, say, left hand corners, but destabilize it in the > >right hand ones due to the different sign of additional weight shift > >that rotating the engine axis in different directions would bring. > > Is that really the case? > I imagined it as a gyrosope on the end of a stick, (i.e the engine > on the back of the chassis). I'm fairly sure if you have a gyroscope > on the end of a stick it will be as hard to move left as it is right > (also up and down) irrespective of the spin direction. > > Bear in mind the last time I had a gyroscope I was 10 so I > could be wrong. If my feeling is correct, then this gyroscopic > effect COULD make the car more stable in the up and down > direction also .. could it .. boy this is confusing stuff!

It's all immaterial anyway, as the speed of the engine is just a function of how fast you're going and what gear you're in, negating clutch/differential/wheel slip. As you wouldn't be spinning the rear wheels under braking (I hope!) all this is just a function of what gear you're in whilst going through the corner, rather than how much throttle you apply. Andy

On Thu, 01 Feb 2001 01:30:21 GMT, [email hidden] (Alex) wrote:

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> >How does the differential work when you use engine >to brake? Doesn't it help to distribute braking >power between inside and outside wheels? > >Btw, another unrelated observation. While driving >FWD car on the snow using throttle and brakes >at the same time has some benefits. It allows >to lock rear wheels before front, and turn the >car nicely. Same as using handbrake, but more control.

When all the "left-foot braking" was discussed in GPL it kind of threw me off. Here in rally-infested Sweden when you say "left-foot braking" you mean the above. The technique was developed here for gravel and snow rallyes for the SAAB's(started with two stroke 92's) which for some odd reason was very popular for rallying. As any one that has driven a SAAB knows they're _MASSIVELY_ understeered(esp. pre-9-3). Besides that, they have the handbrake on the _front_ wheels together with FWD so the only way to get the car into something reminding a sliding state is to throw the car into the corner with almost floored throttle and brakes. Worked great, though. The SAABs racked up victories in the 60's... /Magnus GPLRank hcp: -40.04

From Drive to Win by C. Smith, chapter 6: "The purpose of the engine is to accelerate the car. The purpose of the brakes is to decelerate the car. The purpose of downshifting is to select the proper gear for the forthcoming corner, and, sometimes, to stabilixe the car - not to slow the car. The sequence of downshifting is brake and then downshift. If you are near max. engine revs on a straight and downshift, you will over-rev the engine." and earlier in chapter 4: "The Other Side of the Coin" - " A large number of exceedingly competent and accomplished drivers disagree with the idea of skipping gears. Thier numbers include Mario and Michael Andretti and for a while, our son, Christopher (Smith). They feel that particularly in long braking areas - from very high speed to very low speed - the retardation of the rear wheels by the friction of the engine exerts a stabilizing influence on the back of the car (somewhat like a sea anchor) and gives them both better control and more retardation." TJ Maxx wrote:

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> > On Wed, 31 Jan 2001 17:03:32 GMT, Maxx <[email hidden]> > wrote: > > Thanks for all the replies guys, just what I wanted, please keep > em coming. > > A few observations. > > 1) In real-life I used engine-braking (by which I mean taking > advantage of the drag caused by decellerartion from max revs > in each gear) in saloons. In this case, under high speed braking > I could not lock the wheels no matter how much pressure I > applied, so thats probably why it worked for me there. > > 2) I also used it in FFord type cars (Formula Vauxhall Junior) > I think more out of habit, generally unless it was hard braking from > 5th Gear I think the brakes would have been good enough to lock > up under rmaximum pressure although I don't ever recall doing so. > > 3) I felt I had to use it in Formula Vauxhall Lotus, these are much > more powerful cars with wider, slick tires, plus I felt I also needed > to use gas+brake. > > The main reason for doing both of these was that I found it made > the car much more stable under braking, I'd thought that this was > down to this technique negating some of the forward weight transfer, > hence allowing the rear tires to play a bigger part in braking. > > I think in terms of pure physics, this has been shown perhaps not > to be the case, or at least not in isolation. > > The other thing that occured to me, which I think is also the > reason a car feels more stable going through a corner at high > revs in a low-gear, rather than low-revs in a high gear, is that > I am getting some benefit from the centrifugal force of the > engine spinning, rather like a gyroscope. > > Is this true? > I can imagine it might be quite significant, anyone who's > ever "played" with a gyroscope will know that these > things take a lot of force to move when they are spiinning. > > That being the case, have Papy modelled that in GPL? > It certainly feels like it to me, unless there are other forces > at work here. > > Maxx

On Thu, 1 Feb 2001 13:33:23 -0000, "Andy Laurence" <[email hidden]> wrote: >It's all immaterial anyway, as the speed of the engine is just a function of >how fast you're going and what gear you're in, negating >clutch/differential/wheel slip. As you wouldn't be spinning the rear wheels >under braking (I hope!) all this is just a function of what gear you're in >whilst going through the corner, rather than how much throttle you apply. Absolutely, we are talking about (primarilly) changing down gears at such a point as to get the engine revving at high revs, maybe getting some increased stability from that. I think the diff/clutch aspect comes in when we consider gas+brake, although again, I'm sure the car will "react" differently under engine braking dependent on the configuration of ramp angles and number of clutches. I'm sure the diff guru's will help us out here. Maxx

On Thu, 01 Feb 2001 14:42:12 GMT, Thomas JS Brown <[email hidden]> wrote: Hey Thomas, glad to see you back! Interesting stuff there. Someone told me that CS didn't "believe" in engine braking. I think it's more down to the definition of engine braking than the effect itself. It's a fact that it exist, lift off at max revs in any gear and you will see it for yourself (versus dipping the clutch at max revs). Certainly changing down to a lower gear whilst at max revs in the higher gear is plain dumb, the trick is to change down at the speed at which you would be pulling max revs in the gear you are changing down to, this gives you "safe" engine braking. Whether it actually helps of not is debatable and certainly would be vehicle specific. If you can't lock the wheels by applying the maximum pressure on the brakes then maybe it will help. I know it's used in all formula, including F1 which I would say is renowned as having the best brakes there is.

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>From Drive to Win by C. Smith, chapter 6: > >"The purpose of the engine is to accelerate the car. The purpose of the >brakes is to decelerate the car. The purpose of downshifting is to >select the proper gear for the forthcoming corner, and, sometimes, to >stabilixe the car - not to slow the car. The sequence of downshifting is >brake and then downshift. If you are near max. engine revs on a straight >and downshift, you will over-rev the engine." > >and earlier in chapter 4: > >"The Other Side of the Coin" - > >" A large number of exceedingly competent and accomplished drivers >disagree with the idea of skipping gears. Thier numbers include Mario >and Michael Andretti and for a while, our son, Christopher (Smith). They >feel that particularly in long braking areas - from very high speed to >very low speed - the retardation of the rear wheels by the friction of >the engine exerts a stabilizing influence on the back of the car >(somewhat like a sea anchor) and gives them both better control and more >retardation." > >TJ

Maxx wrote:

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> > Hey Thomas, glad to see you back! > > Interesting stuff there. Someone told me that CS didn't "believe" in > engine braking. I think it's more down to the definition of engine > braking than the effect itself. It's a fact that it exist, lift off at > max revs in any gear and you will see it for yourself (versus > dipping the clutch at max revs).

Oh yes, it certainly does exist, if I had a proper clutch setup for my rig I'd probably use engine braking much more... I forgot to put this part in my previous post...this is the bottom part of the Chapter 4 paragraph "The Other Side Of The Coin": "The diversity of opinion among the very best practitioners of the art merely confirms that there are no absolutes in motor racing. My job is to point out the options and thier possible advantage. It is up to you to determine what is best for you. Bear in mind that what proves best in one situation may not be best in all situations." -Carrol Smith- "Drive to Win" TJ

In article <[email hidden]>, Maxx <[email hidden]> writes:

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> On Thu, 01 Feb 2001 11:26:43 +0100, Gregor Veble > <[email hidden]> wrote: > >>Besides, if the gyroscopic effects were important, it would only >>stabilize the car in, say, left hand corners, but destabilize it in the >>right hand ones due to the different sign of additional weight shift >>that rotating the engine axis in different directions would bring. > > Is that really the case?

I'm no physicist, but I know I have read that the WWI Sopwith Camel was famous for the fact that the torque of its engine gave it a strong tendency to turn right. This made it tricky to fly, and apparently it killed quite a few beginners, but it also meant that in the hands of a skilled pilot who was familiar with it, it could out-turn anything else to the right, which made it a formidable opponent in a dogfight. Now, I'm not sure why this was only true of this one plane, and not of its other contemporaries. Perhaps it simply had the most torque of any plane at the time, making the effect more noticeable? But at any rate, it certainly does seem to imply that gyroscopic engine effects are directional. Oh, right, I almost forgot-- this is why helicopters have tail rotors. If they didn't, they'd just spin around and crash. And on the topic of engine braking, wasn't there a famous British GP driver (I forget exactly who) who once said "Engines used for br[e]aking usually do". :-) Marc

The Camel also had a rotary engine, meaning that the entire engine spun with the propeller, this is one of the reasons for the gyro effect. TJ

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> > I'm no physicist, but I know I have read that the WWI Sopwith Camel > was famous for the fact that the torque of its engine gave it a strong > tendency to turn right. This made it tricky to fly, and apparently it > killed quite a few beginners, but it also meant that in the hands of > a skilled pilot who was familiar with it, it could out-turn anything > else to the right, which made it a formidable opponent in a dogfight. > Now, I'm not sure why this was only true of this one plane, and not > of its other contemporaries. Perhaps it simply had the most torque of > any plane at the time, making the effect more noticeable? But at any > rate, it certainly does seem to imply that gyroscopic engine effects > are directional. > > Oh, right, I almost forgot-- this is why helicopters have tail rotors. > If they didn't, they'd just spin around and crash. > > And on the topic of engine braking, wasn't there a famous British GP > driver (I forget exactly who) who once said "Engines used for br[e]aking > usually do". :-) > > Marc

I'm no physicist or pilot but I do know from my pilot buddies that all single-prop planes have a tendency to roll in the opposite direction to prop travel. It's just more pronounced in some planes and I'm sure that's primarily due to the amount of torque, as you say. However, I think most modern single-engine planes are also trimmed to counter (or at least minimize) this effect. "Marc Fraioli" <[email hidden]> wrote in message news:95c617$377$[email hidden]...

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> I'm no physicist, but I know I have read that the WWI Sopwith Camel > was famous for the fact that the torque of its engine gave it a strong > tendency to turn right. This made it tricky to fly, and apparently it > killed quite a few beginners, but it also meant that in the hands of > a skilled pilot who was familiar with it, it could out-turn anything > else to the right, which made it a formidable opponent in a dogfight. > Now, I'm not sure why this was only true of this one plane, and not > of its other contemporaries. Perhaps it simply had the most torque of > any plane at the time, making the effect more noticeable? But at any > rate, it certainly does seem to imply that gyroscopic engine effects > are directional. >

I think there is a bit of confusion in this thread, and you'd need a true physicist to clarify the many aspects of this topic. For the planes/helicopter examples I think this is merely (as stated) a torque effect, but does not clarify the issue of a gyroscopic (or is it Coriolis acceleration?). It's been 16 years since I took Physics/Statics/Dynamics courses in university. All I can remember is if you take the front wheel off your bicycle and hold the axle ends with both hands and have someone spin the wheel, you can rotate one hand over the other easily but not the other way around without having the wheel spun in the opposite direction. That, I think is the essence of the gyroscopic question, but does not get to the bottom of the engine braking problem. As mentioned earlier, outboard brakes apply stresses to the suspension which may affect the handling under braking differently than engine-assisted braking. A side note: if you mount free-spinning wheels (or flywheels) to your bicycle and spin them fast in the opposite direction of the standard wheels, the bike looses all stability and you will quickly fall to the ground no matter how fast you go. C.Smith mentions also that engine friction and not compression within the cylinders accounts for the braking force. But I'm not sure about that. Bottom line is the physics are actually quite complex and may have a lot to do with the specific car, engine and suspension design. But I stand by the theory that all braking ought to be done by the brakes. Cheers, Ray "Rob Adams" <[email hidden]> wrote: > I'm no physicist or pilot but I do know from my pilot buddies that all > single-prop planes have a tendency to roll in the opposite directionto prop > travel. It's just more pronounced in some planes and I'm sure that's > primarily due to the amount of torque, as you say. > > However, I think most modern single-engine planes are also trimmed to > counter (or at least minimize) this effect. > Sent via Deja.com http://www.deja.com/

Well, as C. Smith is a mechanical engineer and has been involved in motorsport since 1955 (as a driver and engineer), I would think he knows what he's talking about. TJ > C.Smith mentions also that engine friction and not compression within > the cylinders accounts for the braking force. But I'm not sure about > that.

Maxx, Interesting discussion you started. However, IMHO engine braking does not necessarily involve downshifting or double clutching or heel & toe. You obtain engine braking merely by letting off the accelerator. The compression of the engine (more than engine friction) causes the braking effect. This affect is more pronounced at higher revs (I think because there are more compression cycles for a given distance traveled than at lower revs), but still exists at middle revs and sometimes even at low revs (depends on the car or truck). Downshifting, double clutching, and heel & toe are sometimes used in conjunction with engine braking, but are not, per se, engine breaking. In fact some cars/trucks require double clutching for up shifting. I think C. Smith (as quoted by Thomas JS Brown) explains it well when he describes " A large number of exceedingly competent and accomplished drivers disagree with the idea of skipping gears. Thier numbers include Mario and Michael Andretti and for a while, our son, Christopher (Smith). They feel that particularly in long braking areas - from very high speed to very low speed - the retardation of the rear wheels by the friction of the engine exerts a stabilizing influence on the back of the car (somewhat like a sea anchor) and gives them both better control and more retardation." I believe engine breaking is just one of the tools used in slowing and controlling the car. A very precise tool because you can use the accelerator to slow, be neutral, or accelerate (move the center of gravity where you want it using one input device). But what do I know, I'm slower than Eldred. Sorry Eldred, just kidding, I couldn't resist. Claude

>C.Smith mentions also that engine friction and not compression within >the cylinders accounts for the braking force. But I'm not sure about >that. That's probably quite possible. I haven't done any work simulating engines at part throttle. (This should be coming by the year 3050.) Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com

On Thu, 01 Feb 2001 13:01:37 -0800, Claude Beaudouin <[email hidden]> wrote: >Maxx, > >Interesting discussion you started. Thanks

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>However, IMHO engine braking does not necessarily involve downshifting >or double clutching or heel & toe. You obtain engine braking merely by >letting off the accelerator. The compression of the engine (more than >engine friction) causes the braking effect. This affect is more >pronounced at higher revs (I think because there are more compression >cycles for a given distance traveled than at lower revs), but still >exists at middle revs and sometimes even at low revs (depends on the car >or truck). > >Downshifting, double clutching, and heel & toe are sometimes used in >conjunction with engine braking, but are not, per se, engine breaking. >In fact some cars/trucks require double clutching for up shifting.

[snip] I'll leave the compression v. friction argument to the experts. I think there is still some confusion over what I mean by "engine braking" and I think it's because the term is so broad. I suspect that what C. Smith is referring to is downshifting in manner which stresses the engine/transmission i.e. To change down at such a point that the engine is travelling slower than the wheels, such that the wheels will then try to "drive" the engine, which, via friction or compression will resist this, causing a braking effect at the driven wheels. I also suspect that this is what most people will regard as engine braking. This is NOT what I meant but have not really read about it or discussed it before so I can appreciate now that using that terms is confusing. I think I could rephrase my question as "Optimum Downshifting under Braking (ODUB) : One for the physics guys I think". To re-iterate, I am taking about timing ones downshift such that one arrives in the lower gear at maximum revs in that gear, thereby taking maximum advantage of the decellerative forces of the engines "rev drop off". It certainly makes sense. As Claude says, lift off at 9,500 revs and you will get a greater decellerative force than if you lift off at 6,000 revs. My initial point was, if you are braking to the maximum capacity of the tires already, then does this ODUB have any "additional" effect/benefit. I think it does as rarely is a driver able to brake at the maximum capacity of all four of his tires. It may not even be possible to do so as it needs to brake bias and weight balance of the car to be perfect to exatracct the maximum from all four tires. Whilst this might be possible under heavy braking on a flat approach, it would not be under lighter braking, not if there was an incline of if we were slightly off balance from the exit of the previous corner. The rule about braking and setting up brakes is that the fronts should lock up first under normal conditions (of course we should avoid any lockup). So we are always going to have a slight bias on the front brakes. I think what ODUB might give us is a very small window of rear braking bias as we approach brake. Even to the point of split-second lock-up (almost an ABS/Cadence Brake effect). I should stress that IMO ODUB is kind to engines and transmissions, and puts no more stress on them than the act of accelleration and change up at maximum revs. I wanted to try and ascertain whether a decellerative force (I'm sounding more like a physicist daily :-)) acting on the tires via ODUB would be different in any way that that acting on them via conventional brakes. I suspect not at the tire end, but I just get the "feeling" there is elsewhere, does the suspension behave differently?, is the weight transfer different? Certainly by using ODUB you are changing the way the car brakes as you are dynamically altering the brake bias. I think this is the reason it works (dependent on setup and driver timing). Certainly I see many driver laps, and my own where I am changing down to say 2G, as I brake for a corner, then putting it in 3G to actually take the corner. I've (They've?) done this to get that extra bit of ODUB at the end of braking. The next thing I thought was that the actual centrifugal force of the engine at high revs was perhaps giving me some extra little bit of stability under braking. I don't notice it in GPL much but one of the biggest problems in real-life under very heavy braking is keeping the car stable, avoiding that slight fishtail effect. You often see this in F1 under braking for chicances and very much in F3/FF etc. etc. OK, sorry for the long post, but theres been some great feedback to my original post. I just wanted to make sure there weren't those with a misconception of what I was saying. I'm still very intrigued with this gyroscope effect and if if does havae an effect and if I really can go faster adn be more stable turning left than turning right (or vice-versa). Interestingly, most oval racing in the UK (short track, none-banked mostly) is done clockwise, whereas it appears that it is the opposite in the US. Maxx

Thomas JS Brown wrote:

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> Well, as C. Smith is a mechanical engineer and has been involved in > motorsport since 1955 (as a driver and engineer), I would think he knows > what he's talking about. > > TJ > > > C.Smith mentions also that engine friction and not compression within > > the cylinders accounts for the braking force. But I'm not sure about > > that.

An interesting biographical note for the airplane guys about Carroll Smith is that he was a naval aviator briefly before he got into racing cars. - Matt

Time for me to chime in with my non-technical, non-engineering, sim-based thoughts on the subject. (And if you tell me I don't know what I'm talking about, I'll be neither offended nor surprised ;-) Maxx wrote ... > > 1) In real-life I used engine-braking (by which I mean taking > advantage of the drag caused by decellerartion from max revs > in each gear) in saloons. In this case, under high speed braking > I could not lock the wheels no matter how much pressure I > applied, so thats probably why it worked for me there. It's the wheel lock that's the key for me. Maximum slowing force comes just before wheel lock. On a number of circuits/turns, I just have not developed the skill yet to drive as deep as others and not lock the wheels when I apply brake. That could be partly a controller issue, but it's more likely a me issue. My theory is that there's some ratio between slowing power of brakes and slowing power of engine braking, such that perhaps on a given piece of road 80% brake depression without downshifting would be equivalent to 60% brake depression with engine braking. I can't tell you why, but I suffer wheel lockup much less often with the latter arrangement. > The other thing that occured to me, which I think is also the > reason a car feels more stable going through a corner at high > revs in a low-gear, rather than low-revs in a high gear, is that > I am getting some benefit from the centrifugal force of the > engine spinning, rather like a gyroscope. I believe the reason a car feels more stable (easier to balance) in the turns at high revs has to do with throttle response. When you're in the upper quarter of the rev range of a gear, the throttle response is fairly direct and predictable. It's quite easy to tip the car forward or back with slight throttle movements. At the low end of the gear's range, the throttle response is not nearly as uniform and as a result, much less predictable. At the extreme low end, for example, when the engine is actually "lugging", too much throttle can momentarily choke the engine and cause a decrease in rpm's, and you have to back off and bring it up slowly. It's very tricky getting just the right revs at the moment you need them when you're at low revs, and a fairly simple matter at high revs.

Nice post Don. What you describe is exactly what I've experienced. I agree that it seems to be delicate balance of engine braking and brakes that is the most effective in GPL. -- Chris "Ambulater" Lee "Don't Bother Running.........You'll Just Die Tired." Reviews at www.sim-arena.com "Don Jennings" <[email hidden]> wrote in message news:969nbn$jm1s4$[email hidden]... > Time for me to chime in with my non-technical, non-engineering, sim-based > thoughts on the subject. (And if you tell me I don't know what I'm talking > about, I'll be neither offended nor surprised ;-) > > Maxx wrote ... > > > > 1) In real-life I used engine-braking (by which I mean taking > > advantage of the drag caused by decellerartion from max revs > > in each gear) in saloons. In this case, under high speed braking > > I could not lock the wheels no matter how much pressure I > > applied, so thats probably why it worked for me there. > > It's the wheel lock that's the key for me. Maximum slowing force comes just > before wheel lock. On a number of circuits/turns, I just have not developed > the skill yet to drive as deep as others and not lock the wheels when I > apply brake. That could be partly a controller issue, but it's more likely > a me issue. My theory is that there's some ratio between slowing power of > brakes and slowing power of engine braking, such that perhaps on a given > piece of road 80% brake depression without downshifting would be equivalent > to 60% brake depression with engine braking. I can't tell you why, but I > suffer wheel lockup much less often with the latter arrangement. > > > The other thing that occured to me, which I think is also the > > reason a car feels more stable going through a corner at high > > revs in a low-gear, rather than low-revs in a high gear, is that > > I am getting some benefit from the centrifugal force of the > > engine spinning, rather like a gyroscope. > > I believe the reason a car feels more stable (easier to balance) in the > turns at high revs has to do with throttle response. When you're in the > upper quarter of the rev range of a gear, the throttle response is fairly > direct and predictable. It's quite easy to tip the car forward or back with > slight throttle movements. At the low end of the gear's range, the throttle > response is not nearly as uniform and as a result, much less predictable. > At the extreme low end, for example, when the engine is actually "lugging", > too much throttle can momentarily choke the engine and cause a decrease in > rpm's, and you have to back off and bring it up slowly. It's very tricky > getting just the right revs at the moment you need them when you're at low > revs, and a fairly simple matter at high revs. >