Car Physics: When You Can't Help But Wander (Wonder?)

Hi all, in a time I should be doing completely different things, my mind can't help but wander back to car physics. Here's two questions that have been bugging me for a while. The first is the question of toe out/in at the front. It has often been said that a bit of toe-out at the front will destabilize the car, helping on turn in. I can't help but think that this should be exactly the opposite; when you turn in, the outside wheel begins to weigh up, meaning that you are making the tyre that points relatively more to the outside of the turn more dominant, making the car turn in less. The way I see it, it is actually toe-in that should create better turn-in, as weighing the outside tyre which points more in the direction of the turn would in this case push the nose even further into it. Any ideas? The second question concerns oval stock car racing. There's always talk of inside and outside lines, and even real drivers don't take the outside-apex-outside line even when there is no cars on the inside. I'm not talking about restrictor plate races, as the cars don't even run at the limit there, but super speedways. In, say, Nascar 4, trying anything else than the geometrically ideal line will make you much slower. Is there generally more rubber on the other lines that may make you almost equally fast in other lines as well, or am I missing something here? Enlighten me! :) -Gregor

I can't speak to the to-in vs. toe-out question - your thoughts mirror mine. As for oval lines though, the key to speed on an oval (on any track really, but ovals emphasize it more) is to minimize the amount of turning that you do. There is a good discussion of this either on Richard Nunnini's site or in the Steve Smith book that comes with GPL - they compare it to sailing where any movement off straight ahead slows you down. So on an oval, the goal is to keep the turns as gentle as possible. This keeps the amount of steering to the minimum. So if you take a smooth curve around the corner, that is less steering input than if you cut in sharp to get to the apex. So even though you may be in the corner longer, you scrub off less speed and are therefore faster overall. Plus, you minimize tire wear which is the main factor in stock cars anyway: keep your tires in good shape for more laps than the other guys. Or I could be completely wrong in which case RAS will politely (or not) set me straight ;-) "Gregor Veble" <[email hidden]> wrote in message news:[email hidden]...

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> Hi all, > > in a time I should be doing completely different things, my mind can't > help but wander back to car physics. Here's two questions that have been > bugging me for a while. > > The first is the question of toe out/in at the front. It has often been > said that a bit of toe-out at the front will destabilize the car, > helping on turn in. I can't help but think that this should be exactly > the opposite; when you turn in, the outside wheel begins to weigh up, > meaning that you are making the tyre that points relatively more to the > outside of the turn more dominant, making the car turn in less. The way > I see it, it is actually toe-in that should create better turn-in, as > weighing the outside tyre which points more in the direction of the turn > would in this case push the nose even further into it. Any ideas? > > The second question concerns oval stock car racing. There's always talk > of inside and outside lines, and even real drivers don't take the > outside-apex-outside line even when there is no cars on the inside. I'm > not talking about restrictor plate races, as the cars don't even run at > the limit there, but super speedways. In, say, Nascar 4, trying anything > else than the geometrically ideal line will make you much slower. Is > there generally more rubber on the other lines that may make you almost > equally fast in other lines as well, or am I missing something here? > > Enlighten me! :) > > -Gregor >

Gregor Veble <[email hidden]> wrote in message news:[email hidden]... > I see it, it is actually toe-in that should create better turn-in,as > weighing the outside tyre which points more in the direction of theturn > would in this case push the nose even further into it. Any ideas? This general thing has puzzled me for a while (and continues to do so, to some extent!) However, one possible explanation is that toe-out makes the (lightly loaded) inside wheel run at a higher slip angle, forcing it to do its 'fair share' of the work. Haven't run the thought experiment properly, but you might like to consider this. HTH, Jonny

Gregor Veble wrote:

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> > Hi all, > > in a time I should be doing completely different things, my mind can't > help but wander back to car physics. Here's two questions that have been > bugging me for a while. > > The first is the question of toe out/in at the front. It has often been > said that a bit of toe-out at the front will destabilize the car, > helping on turn in. I can't help but think that this should be exactly > the opposite; when you turn in, the outside wheel begins to weigh up, > meaning that you are making the tyre that points relatively more to the > outside of the turn more dominant, making the car turn in less. The way > I see it, it is actually toe-in that should create better turn-in, as > weighing the outside tyre which points more in the direction of the turn > would in this case push the nose even further into it. Any ideas?

Ok, I'll have a go :-) With toe out, you will always have one tire trying to turn more than the dominant tire, helping the turn in, even at a very small wheel lock, with toe in, it will work against it from the outset, even if it's lightly loaded, so even if the dominant wheel is now pointing in the right direction, you have an opposing force So not only do you not have the inside wheel helping, you have it actually working against you My theory anyway, I really should be brushing up on this stuff, but al my books on the subject is neatly packed away in boxes, besides, vehicle dynamics were never my strong point anyway, I could read and learn what worked, never could understand much about why it worked, except for weight transfer and dialing in shocks, springs and anti roll bars :-), but that doesn't seem to apply much here Doug ? :-) Beers and cheers (uncle) Goy http://www.theuspits.com http://www.teammirage.com "A woman is an occasional pleasure but a cigar is always a smoke" --Groucho Marx--

I'm not very good at explaining things in a technical term, so bear with my attempt at an explanation I read in a magazine many years ago. When cornering, the outside wheel is the one which is weighted and does most of the steering, so the amount of steering input you give is directed mainly to this wheel. If you have toe in, the inside wheel with its limited grip will try and stop the outside wheel from turning ie. its not steering as much so is pushing against the outside wheel. With toe out, the outside wheel is again doing most of the steering, but this time, the inside wheel is steering more into the direction of the turn so is in effect helping the outside wheel to corner. Hope that helps, if you understood any of my giberish ;) -- Ian P <email invalid due to spammers> "Gregor Veble" <[email hidden]> wrote in message news:[email hidden]... > Hi all, > > in a time I should be doing completely different things, my mind can't > help but wander back to car physics. Here's two questions that have been > bugging me for a while. > > The first is the question of toe out/in at the front. It has often been > said that a bit of toe-out at the front will destabilize the car, > helping on turn in. I can't help but think that this should be exactly > the opposite; when you turn in, the outside wheel begins to weigh up, > meaning that you are making the tyre that points relatively more to the > outside of the turn more dominant, making the car turn in less. The way > I see it, it is actually toe-in that should create better turn-in, as > weighing the outside tyre which points more in the direction of the turn > would in this case push the nose even further into it. Any ideas? > Enlighten me! :) > > -Gregor >

Toe out (and Ackerman steering) are a big help because the RF tire is the dominant tire on an oval. It is turned the number of degrees to handle the corner. However, if there were no toe out, the LF would turn the same amount. Think of a circle. The LF tire has to make a smaller circle than the RF, hence, a sharper angle. With toe out and ackerman steering, the LF turns just a bit more than the RF creating more overall grip...... Hope this helps. BH "Gregor Veble" <[email hidden]> wrote in message news:[email hidden]...

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> Hi all, > > in a time I should be doing completely different things, my mind can't > help but wander back to car physics. Here's two questions that have been > bugging me for a while. > > The first is the question of toe out/in at the front. It has often been > said that a bit of toe-out at the front will destabilize the car, > helping on turn in. I can't help but think that this should be exactly > the opposite; when you turn in, the outside wheel begins to weigh up, > meaning that you are making the tyre that points relatively more to the > outside of the turn more dominant, making the car turn in less. The way > I see it, it is actually toe-in that should create better turn-in, as > weighing the outside tyre which points more in the direction of the turn > would in this case push the nose even further into it. Any ideas? > > The second question concerns oval stock car racing. There's always talk > of inside and outside lines, and even real drivers don't take the > outside-apex-outside line even when there is no cars on the inside. I'm > not talking about restrictor plate races, as the cars don't even run at > the limit there, but super speedways. In, say, Nascar 4, trying anything > else than the geometrically ideal line will make you much slower. Is > there generally more rubber on the other lines that may make you almost > equally fast in other lines as well, or am I missing something here? > > Enlighten me! :) > > -Gregor >

On your question about lines....... There are many reasons for this... if you remember at New Hampshire, they put down a sealer. When the sealer wears off, the cars lose grip and the drivers search around for more grip... and if I remember correctly, some even put the lefts on the arpon. Some of it is rubber. Rubber sticks to more rubber better I would think. At my local track, I like to run the middle groove in 1 and 2 just because it seems to be banked just a few degrees higher. That is one thing too. At Michigan, I've heard a lot of guys say the bottom 8 or so feet aren't banked as much as the rest of the track, maybe my 2 or 4 degrees. A lot of guys run the middle there quite often. There's so many variables that make up the "groove"... and N4 just doesn't really have any of them... it was programed that the absolute low groove is always the fastest, which a lot of times isn't true. BH "Gregor Veble" <[email hidden]> wrote in message news:[email hidden]...

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> Hi all, > > in a time I should be doing completely different things, my mind can't > help but wander back to car physics. Here's two questions that have been > bugging me for a while. > > The first is the question of toe out/in at the front. It has often been > said that a bit of toe-out at the front will destabilize the car, > helping on turn in. I can't help but think that this should be exactly > the opposite; when you turn in, the outside wheel begins to weigh up, > meaning that you are making the tyre that points relatively more to the > outside of the turn more dominant, making the car turn in less. The way > I see it, it is actually toe-in that should create better turn-in, as > weighing the outside tyre which points more in the direction of the turn > would in this case push the nose even further into it. Any ideas? > > The second question concerns oval stock car racing. There's always talk > of inside and outside lines, and even real drivers don't take the > outside-apex-outside line even when there is no cars on the inside. I'm > not talking about restrictor plate races, as the cars don't even run at > the limit there, but super speedways. In, say, Nascar 4, trying anything > else than the geometrically ideal line will make you much slower. Is > there generally more rubber on the other lines that may make you almost > equally fast in other lines as well, or am I missing something here? > > Enlighten me! :) > > -Gregor >

There was some discussion of this in a debate in the letters section of Race Tech magazine on Ackerman/Dynamic Toe. In a (large) nutshell, the stabilising effect of toe in is due to the rearwards drag of the tyres. If you consider a small left steering movement with toe in, the left tyre now has zero slip and a small rearwards (rolling drag) force. The right tyre is pointing to the left with a leftwards slip angle, has rearwards rolling drag and sideways (axial) "slip angle" force. This axial force points to the left and slightly rearwards. So, in car coordinates, the left wheel has only rearwards rolling drag force while the right wheel has rearwards rolling drag force plus the rearwards component of the slip angle force. With toe out the effects are reversed and it is destabilising. This was gleaned from the Oct/Nov 200 issue with thanks (or apologies) to Erik Zapletal who wrote the letter and Alan Staniforth who had written the original article (and approved the letter as a plain English explanation of Ackerman). The letter continues to discuss the amplified effect with Ackerman as the difference between wheel angles reaches several degrees whereas static toe is usually tenths of a degree. An interesting conclusion is that while positive Ackerman (dynamic toe out) is destabilising during turn in, sharpening dynamic response, it is stabilising "at the limit" because the rearwards force at the inside wheel is the first to drop. Hopefully I didn't butcher that too much! Ben

I've also wondered about the origins of this. Maybe the toe-in thing started back when most cars had flexible steering systems and lots of steering compliance? This makes a good brain twister-- which way will the front wheels point, with compliant steering and with the influence of trail, tire aligning torque, etc? I have not worked through this myself... and depending on the front end geometry the answer(s) might differ?? There is one car that I did a lot of development testing on. It was a pretty strange car (sorry, no details today...), but it responded very well to toe-out for straight-running stability. On oval lines, here are two things that make it different from typical road race cornering. Just food for thought, not meant to be a complete list<grin>: - When does the banking start getting steep, relative to the turn? Little point in turning in until you get help (download) from the banking. - Since ovals are usually run in one gear, sometimes keeping a peaky motor up on the torque curve (by going around the outside on the high line) may be quicker for the whole lap. On Tue, 28 Aug 2001, Gregor Veble wrote:

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> Hi all, > > in a time I should be doing completely different things, my mind can't > help but wander back to car physics. Here's two questions that have been > bugging me for a while. > > The first is the question of toe out/in at the front. It has often been > said that a bit of toe-out at the front will destabilize the car, > helping on turn in. I can't help but think that this should be exactly > the opposite; when you turn in, the outside wheel begins to weigh up, > meaning that you are making the tyre that points relatively more to the > outside of the turn more dominant, making the car turn in less. The way > I see it, it is actually toe-in that should create better turn-in, as > weighing the outside tyre which points more in the direction of the turn > would in this case push the nose even further into it. Any ideas? > > The second question concerns oval stock car racing. There's always talk > of inside and outside lines, and even real drivers don't take the > outside-apex-outside line even when there is no cars on the inside. I'm > not talking about restrictor plate races, as the cars don't even run at > the limit there, but super speedways. In, say, Nascar 4, trying anything > else than the geometrically ideal line will make you much slower. Is > there generally more rubber on the other lines that may make you almost > equally fast in other lines as well, or am I missing something here? > > Enlighten me! :) > > -Gregor > > >

"Jonny Hodgson" <[email hidden]> wrote in message news:j4Ui7.36005$[email hidden]... > > However, one possible explanation is that toe-out makes the (lightly > loaded) inside wheel run at a higher slip angle, forcing it to do its > 'fair share' of the work. This is probably the first thing that I would suspect, but I'm not at all much of an expert. Ryan

Hi! Indeed, but on the other hand it makes the outside wheel do less work than is necessary. If there is no weight transfer present (c.g. at the ground, impossible, but one can get away with it in a thought experiment), and let's assume a large radius turn so that Ackermann effects are negligible, both in the case of the toe-in and toe-out you are away from the ideal, as in both cases the wheels fight each other equally, at least in the linear regime. If you introduce weight transfer, then the more loaded tyre becomes dominant, and that's why toe-in should be more unstable. -Gregor Jonny Hodgson wrote: > > However, one possible explanation is that toe-out makes the (lightly > loaded) inside wheel run at a higher slip angle, forcing it to do its > 'fair share' of the work. >

Hi Ben, Ah, there's an interesting aspect I haven't thought about! Basically, the torque produced by the turned outside wheel is much different than for the inside. It's the same reason why sometimes turning into further the spin will save your car instead of opposite locking. If the track width is wide enough, and the c.g. low enough, this effect just might be more than the weight shifting one, and probably there exists a geometry setting where the ammount of toe-in and out is actually irrelevant under some assumptions. I'll need a pen and paper from this point on, but thanks for the clue! Cheers, -Gregor Ben Coleman wrote:

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> > There was some discussion of this in a debate in the letters section of Race > Tech magazine on Ackerman/Dynamic Toe. > > In a (large) nutshell, the stabilising effect of toe in is due to the > rearwards drag of the tyres. If you consider a small left steering movement > with toe in, the left tyre now has zero slip and a small rearwards (rolling > drag) force. The right tyre is pointing to the left with a leftwards slip > angle, has rearwards rolling drag and sideways (axial) "slip angle" force. > This axial force points to the left and slightly rearwards. So, in car > coordinates, the left wheel has only rearwards rolling drag force while the > right wheel has rearwards rolling drag force plus the rearwards component of > the slip angle force. > > With toe out the effects are reversed and it is destabilising. > > This was gleaned from the Oct/Nov 200 issue with thanks (or apologies) to > Erik Zapletal who wrote the letter and Alan Staniforth who had written the > original article (and approved the letter as a plain English explanation of > Ackerman). > > The letter continues to discuss the amplified effect with Ackerman as the > difference between wheel angles reaches several degrees whereas static toe > is usually tenths of a degree. An interesting conclusion is that while > positive Ackerman (dynamic toe out) is destabilising during turn in, > sharpening dynamic response, it is stabilising "at the limit" because the > rearwards force at the inside wheel is the first to drop. > > Hopefully I didn't butcher that too much! > > Ben

Hi Doug! Thanks for replying. So, you can indeed confirm that toe-out can be a stable thing, just as I thought? There is another post by Ben that gives great insight into the phenomenon a bit more. Could you please tell what the test car you mention was like in terms of wheelbase, track width and the center of gravity? Thanks for the suggestions about oval racing, I might try and test some in one of my favourite simulators! -Gregor Doug Milliken wrote:

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> > I've also wondered about the origins of this. Maybe the toe-in thing > started back when most cars had flexible steering systems and lots of > steering compliance? This makes a good brain twister-- which way will the > front wheels point, with compliant steering and with the influence of > trail, tire aligning torque, etc? I have not worked through this myself... > and depending on the front end geometry the answer(s) might differ?? > > There is one car that I did a lot of development testing on. It was > a pretty strange car (sorry, no details today...), but it responded > very well to toe-out for straight-running stability. > > On oval lines, here are two things that make it different from typical road > race cornering. Just food for thought, not meant to be a complete > list<grin>: > > - When does the banking start getting steep, relative to the turn? > Little point in turning in until you get help (download) from the banking. > > - Since ovals are usually run in one gear, sometimes keeping a > peaky motor up on the torque curve (by going around the outside > on the high line) may be quicker for the whole lap. >

Hi Billy, some interesting suggestions you put there. If the banking is being altered, that may indeed explain it. On the other hand, Nascar 4 seems to have constant banking along the width, but due to the curvature of the track the lower line actually has a smaller 'vertical' radius w.r.t. car, meaning that the car is pushed down more in the low groove and hence has more grip. -Gregor Billy Hutson wrote:

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> > At my local track, I like to run the middle groove in 1 and 2 just because > it seems to be banked just a few degrees higher. That is one thing too. > > At Michigan, I've heard a lot of guys say the bottom 8 or so feet aren't > banked as much as the rest of the track, maybe my 2 or 4 degrees. A lot of > guys run the middle there quite often. >

Doug, In a word: Ackerman. --Steve "Doug Milliken" <[email hidden]> wrote in message news:[email hidden]... > > I've also wondered about the origins of this. Maybe the toe-in thing > started back when most cars had flexible steering systems and lots of > steering compliance? This makes a good brain twister-- which way will the > front wheels point, with compliant steering and with the influence of > trail, tire aligning torque, etc? I have not worked through thismyself...

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> and depending on the front end geometry the answer(s) might differ?? > > There is one car that I did a lot of development testing on. It was > a pretty strange car (sorry, no details today...), but it responded > very well to toe-out for straight-running stability. > > > On oval lines, here are two things that make it different from typical

road > race cornering. Just food for thought, not meant to be a complete > list<grin>: > > - When does the banking start getting steep, relative to the turn? > Little point in turning in until you get help (download) from thebanking.

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> > - Since ovals are usually run in one gear, sometimes keeping a > peaky motor up on the torque curve (by going around the outside > on the high line) may be quicker for the whole lap. > > > > On Tue, 28 Aug 2001, Gregor Veble wrote: > > > Hi all, > > > > in a time I should be doing completely different things, my mind can't > > help but wander back to car physics. Here's two questions that have been > > bugging me for a while. > > > > The first is the question of toe out/in at the front. It has often been > > said that a bit of toe-out at the front will destabilize the car, > > helping on turn in. I can't help but think that this should be exactly > > the opposite; when you turn in, the outside wheel begins to weigh up, > > meaning that you are making the tyre that points relatively more to the > > outside of the turn more dominant, making the car turn in less. The way > > I see it, it is actually toe-in that should create better turn-in, as > > weighing the outside tyre which points more in the direction of the turn > > would in this case push the nose even further into it. Any ideas? > > > > The second question concerns oval stock car racing. There's always talk > > of inside and outside lines, and even real drivers don't take the > > outside-apex-outside line even when there is no cars on the inside. I'm > > not talking about restrictor plate races, as the cars don't even run at > > the limit there, but super speedways. In, say, Nascar 4, trying anything > > else than the geometrically ideal line will make you much slower. Is > > there generally more rubber on the other lines that may make you almost > > equally fast in other lines as well, or am I missing something here? > > > > Enlighten me! :) > > > > -Gregor > > > > > > >

Gregor, the toe-in effect has an effect at the very initial part of turn-in. It doesn't change the grip level, and certainly not what goes on when the turn is being taken, only the feel of the very initial turning in. The toe-in controls the aligning force, the force trying to force the front wheels to go straight forward. Toe-out has little aligning force, so there is less force trying to keep the car going straight, meaning that the car feels lighter or eadier to turn. The self alignment forces determine how the front wheels are perceived through the wheel more than the actual grip available. So when you have a race car with toe-out, the turning the wheel will feel light and weird, and it feels like the car turns more easily. More easily in terms of how much force you need to apply to the wheel, NOT how fast you can go through the turn. How to explain it from a contact patch point of view is quite difficult I think. I have to give that some though. :-) And it needs to be seen in relation to the toe-in of the rear tires. A car with toe-in at the front and toe-out at the back will be very unstable, and will turn easily... In fact it will be quite unstable. I have been experimenting with my own car, and the difference between toe-out and toe-in is striking. The wheel feels all different going from one to the other. ---Asgeir--- Gregor Veble wrote:

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> Hi all, > > in a time I should be doing completely different things, my mind can't > help but wander back to car physics. Here's two questions that have been > bugging me for a while. > > The first is the question of toe out/in at the front. It has often been > said that a bit of toe-out at the front will destabilize the car, > helping on turn in. I can't help but think that this should be exactly > the opposite; when you turn in, the outside wheel begins to weigh up, > meaning that you are making the tyre that points relatively more to the > outside of the turn more dominant, making the car turn in less. The way > I see it, it is actually toe-in that should create better turn-in, as > weighing the outside tyre which points more in the direction of the turn > would in this case push the nose even further into it. Any ideas? > > The second question concerns oval stock car racing. There's always talk > of inside and outside lines, and even real drivers don't take the > outside-apex-outside line even when there is no cars on the inside. I'm > not talking about restrictor plate races, as the cars don't even run at > the limit there, but super speedways. In, say, Nascar 4, trying anything > else than the geometrically ideal line will make you much slower. Is > there generally more rubber on the other lines that may make you almost > equally fast in other lines as well, or am I missing something here? > > Enlighten me! :) > > -Gregor

Gregor Veble <[email hidden]> writes: > Hi! > > Indeed, but on the other hand it makes the outside wheel do less work > than is necessary. If there is no weight transfer present (c.g. at the > ground, uh. if you have cg at ground level, you'll still have weight-transfer, no? -- Gunnar #31 SUCKS#015 Tupperware MC#002 DoD#0x1B DoDRT#003 DoD:CT#4,8 Kibo�: 2 "Det er nok ingen ovn, men fartsm�leren v�r."

"Gunnar Horrigmo" <[email hidden]> wrote in message news:[email hidden]... > uh. if you have cg at ground level, you'll still have > weight-transfer, no? Nope. Weight transfer is caused by the torque exerted on the car by the wheels - or specifically, the components of the torque that attempt to make the car dive or roll. If the CG is on the ground, those components are not present - hence, no weight transfer. Of course, like Gregor said, it's impossible for a car to have a CG on the ground or below it anyway. Think about a car that, for the sake of argument, has its body (and therefore its CG) below ground (no collision detection :-) In this case, the car would actually behave more like a boat: it would lean into the curve, and weight would be transferred to the inside wheels. Petri Blomqvist

"Petri Blomqvist" <[email hidden]> writes:

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> "Gunnar Horrigmo" <[email hidden]> wrote in message > news:[email hidden]... > > > uh. if you have cg at ground level, you'll still have > > weight-transfer, no? > > Nope. Weight transfer is caused by the torque exerted on the car by the > wheels - or specifically, the components of the torque that attempt to make > the car dive or roll. If the CG is on the ground, those components are not > present - hence, no weight transfer. Of course, like Gregor said, it's > impossible for a car to have a CG on the ground or below it anyway. > > Think about a car that, for the sake of argument, has its body (and > therefore its CG) below ground (no collision detection :-) In this case, the > car would actually behave more like a boat: it would lean into the curve, > and weight would be transferred to the inside wheels.

At least for small outboard boats. Taller boats will have the CG above sea level and lean outwards when turning :) -- Olav K. Malmin remove .spam when replying

"Olav K. Malmin" <[email hidden]> wrote in message news:[email hidden]... > > Think about a car that, for the sake of argument, has its body (and > > therefore its CG) below ground (no collision detection :-) In this case,the > > car would actually behave more like a boat: it would lean into thecurve, > > and weight would be transferred to the inside wheels. > > At least for small outboard boats. Taller boats will have the CG above > sea level and lean outwards when turning :) I just knew I shoulda been more specific. :-) Petri Blomqvist

"Petri Blomqvist" <[email hidden]> writes:

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> "Gunnar Horrigmo" <[email hidden]> wrote in message > news:[email hidden]... > > > uh. if you have cg at ground level, you'll still have > > weight-transfer, no? > > Nope. Weight transfer is caused by the torque exerted on the car by the > wheels - or specifically, the components of the torque that attempt to make > the car dive or roll. If the CG is on the ground, those components are not > present - hence, no weight transfer.

I was tricked by my own head. I was thinking that if you introduce a sentripetal force to turn the car, you also have a sentrifugal force, which wouls cause weight transfer. that whole "this is of course impossible"-thing went flying over my head. :) -- Gunnar #31 SUCKS#015 Tupperware MC#002 DoD#0x1B DoDRT#003 DoD:CT#4,8 Kibo�: 2 DE RECTIS NON TOLERANDUM EST

"Gunnar Horrigmo" <[email hidden]> wrote in message news:[email hidden]... > I was tricked by my own head. Now what was that saying again..? "Trick me once, shame on you, trick me twice, shame on me, trick myself once, DOUBLE shame on me." :-) Petri Blomqvist

I always thought the track curved upwards to the wall, like a horizontal section of a cereal bowl. In this way, the roll angle of the car increases as it moves higher (towards the wall). Thus, using the same tyres, a larger horizontal force can be generated the higher up the track you go, meaning the speed is higher. So you get the effect of a clock face: the tip of the second hand goes further than the middle of it, but they both take the same time to do a complete circle. So the tip must go at a faster speed. This is what I always thought, which would explain why two lines are used much more at a place like Bristol than a flatter oval like Michigan. Maybe I just assumed this, coz I also thought that curving the surface upwards towards the wall would slow the cars down a little bit more if they are out of shape and heading to the wall.

Gee I thought it was "F" me once.. Ooops wrong newsgroup :) "Petri Blomqvist" wrote:

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| Now what was that saying again..? | | "Trick me once, shame on you, trick me twice, shame on me, trick myself | once, DOUBLE shame on me." :-) | | Petri Blomqvist | "Gunnar Horrigmo" wrote: | > I was tricked by my own head.

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Gregor Veble wrote in message <[email hidden]>...

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>Hi Ben, > >Ah, there's an interesting aspect I haven't thought about! Basically, >the torque produced by the turned outside wheel is much different than >for the inside. It's the same reason why sometimes turning into further >the spin will save your car instead of opposite locking. > >If the track width is wide enough, and the c.g. low enough, this effect >just might be more than the weight shifting one, and probably there >exists a geometry setting where the ammount of toe-in and out is >actually irrelevant under some assumptions. I'll need a pen and paper >from this point on, but thanks for the clue! > >Cheers, > >-Gregor >

I think that the stabilising or destabilising effect of toe in/out is what I would call an immediate effect - it occurs immediately on turning and is probably rapidly overshadowed by the effects of weight transfer affecting geometry etc., although still playing some role. A similar effect is found in (at least model) aeroplanes. If both ailerons are deflected equal amounts up and down, a yaw _away_ from the desired turn is initiated due to the increased drag from a lifting surface. Although the magnitude of the difference in longitudinal force is small, its effect will be felt most while the car is unstable (changing accelerations? as opposed to twitchy), such as immediately on turn in and at the limit. The letter I quoted gave the examples of fiddle brakes, differential steering and "active stability control systems" as practical examples of the longitudinal forces exerting a moment on the vehicle. One other point made by many contributors (it became quite a debate) was the tuning of the geometry to give the desired toe in/out in a given situation - ie the tuning of dynamic toe, as each situation (fast, slow, braking, accelerating yadda yadda) calls for different amounts of toe in/out. The static toe in setting as found on most simulators would seem to be a gross (if necessary) over-simplification once ackerman, bump steer, roll steer and ride steer (? what's that?) are factored in, each able to alter the toe in/out more than the static setting. Perhaps this explains the success of dramatic toe-out settings in some sims. BTW this post is my musings only! Ben

Not so, boats with a V section, such as most power boats, lean inwards because of the yaw of the hull as they turn causing a low pressure under the side of the V to the inside of the turn. This low pressure is caused by the angle at the bottom of the V. The position of the CG, unless extreme, is a minor force (whcich causes a moment!) compared to this hydrodynamic force. Andrew. "Olav K. Malmin" <[email hidden]> wrote in message news:[email hidden]...

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> "Petri Blomqvist" <[email hidden]> writes: > > > "Gunnar Horrigmo" <[email hidden]> wrote in message > > news:[email hidden]... > > > > > uh. if you have cg at ground level, you'll still have > > > weight-transfer, no? > > > > Nope. Weight transfer is caused by the torque exerted on the car by the > > wheels - or specifically, the components of the torque that attempt to

make > > the car dive or roll. If the CG is on the ground, those components arenot > > present - hence, no weight transfer. Of course, like Gregor said, it's > > impossible for a car to have a CG on the ground or below it anyway. > > > > Think about a car that, for the sake of argument, has its body (and > > therefore its CG) below ground (no collision detection :-) In this case,the > > car would actually behave more like a boat: it would lean into thecurve,

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> > and weight would be transferred to the inside wheels. > > At least for small outboard boats. Taller boats will have the CG above > sea level and lean outwards when turning :) > > -- > Olav K. Malmin > remove .spam when replying

"Andrew Hollom" <[email hidden]> writes: > Not so, boats with a V section, such as most power boats, lean inwards > because of the yaw of the hull as they turn causing a low pressure under the > side of the V to the inside of the turn. This low pressure is caused by the > angle at the bottom of the V. The position of the CG, unless extreme, is a > minor force (whcich causes a moment!) compared to this hydrodynamic force. LOL! You're right. How stupid of me to forget that :)

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> Andrew. > > "Olav K. Malmin" <[email hidden]> wrote in message > news:[email hidden]... > > "Petri Blomqvist" <[email hidden]> writes: > > > > > "Gunnar Horrigmo" <[email hidden]> wrote in message > > > news:[email hidden]... > > > > > > > uh. if you have cg at ground level, you'll still have > > > > weight-transfer, no? > > > > > > Nope. Weight transfer is caused by the torque exerted on the car by the > > > wheels - or specifically, the components of the torque that attempt to > make > > > the car dive or roll. If the CG is on the ground, those components are > not > > > present - hence, no weight transfer. Of course, like Gregor said, it's > > > impossible for a car to have a CG on the ground or below it anyway. > > > > > > Think about a car that, for the sake of argument, has its body (and > > > therefore its CG) below ground (no collision detection :-) In this case, > the > > > car would actually behave more like a boat: it would lean into the > curve, > > > and weight would be transferred to the inside wheels. > > > > At least for small outboard boats. Taller boats will have the CG above > > sea level and lean outwards when turning :) > > > > -- > > Olav K. Malmin > > remove .spam when replying > >

-- Olav K. Malmin remove .spam when replying

On Wed, 29 Aug 2001 23:19:47 GMT, "Andrew Hollom" <[email hidden]> wrote: >Not so, boats with a V section, such as most power boats, lean inwards >because of the yaw of the hull as they turn causing a low pressure under the >side of the V to the inside of the turn. This low pressure is caused by the >angle at the bottom of the V. The position of the CG, unless extreme, is a >minor force (whcich causes a moment!) compared to this hydrodynamic force. It's time you start on BoatSim 2001, Andrew! Have often thought about a sail sim, but it would be too damn boring on a computer (and it is). :) That's where a lot of senses are neglected on a computer. Ruud van Gaal Free car sim : http://www.marketgraph.nl/gallery/racer/ Pencil art : http://www.marketgraph.nl/gallery/

Ackermann doesn't do much until the wheels have been turned quite a bit. Initial toe settings probably swamp any Ackerman correction until you are on a pretty tight and slow corner... On Wed, 29 Aug 2001, Stephen Smith wrote:

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> Doug, > > In a word: Ackerman. > > --Steve > > "Doug Milliken" <[email hidden]> wrote in message > news:[email hidden]... > > > > I've also wondered about the origins of this. Maybe the toe-in thing > > started back when most cars had flexible steering systems and lots of > > steering compliance? This makes a good brain twister-- which way will the > > front wheels point, with compliant steering and with the influence of > > trail, tire aligning torque, etc? I have not worked through this > myself... > > and depending on the front end geometry the answer(s) might differ?? > > > > There is one car that I did a lot of development testing on. It was > > a pretty strange car (sorry, no details today...), but it responded > > very well to toe-out for straight-running stability. > > > > > > On oval lines, here are two things that make it different from typical > road > > race cornering. Just food for thought, not meant to be a complete > > list<grin>: > > > > - When does the banking start getting steep, relative to the turn? > > Little point in turning in until you get help (download) from the > banking. > > > > - Since ovals are usually run in one gear, sometimes keeping a > > peaky motor up on the torque curve (by going around the outside > > on the high line) may be quicker for the whole lap. > > > > > > > > On Tue, 28 Aug 2001, Gregor Veble wrote: > > > > > Hi all, > > > > > > in a time I should be doing completely different things, my mind can't > > > help but wander back to car physics. Here's two questions that have been > > > bugging me for a while. > > > > > > The first is the question of toe out/in at the front. It has often been > > > said that a bit of toe-out at the front will destabilize the car, > > > helping on turn in. I can't help but think that this should be exactly > > > the opposite; when you turn in, the outside wheel begins to weigh up, > > > meaning that you are making the tyre that points relatively more to the > > > outside of the turn more dominant, making the car turn in less. The way > > > I see it, it is actually toe-in that should create better turn-in, as > > > weighing the outside tyre which points more in the direction of the turn > > > would in this case push the nose even further into it. Any ideas? > > > > > > The second question concerns oval stock car racing. There's always talk > > > of inside and outside lines, and even real drivers don't take the > > > outside-apex-outside line even when there is no cars on the inside. I'm > > > not talking about restrictor plate races, as the cars don't even run at > > > the limit there, but super speedways. In, say, Nascar 4, trying anything > > > else than the geometrically ideal line will make you much slower. Is > > > there generally more rubber on the other lines that may make you almost > > > equally fast in other lines as well, or am I missing something here? > > > > > > Enlighten me! :) > > > > > > -Gregor > > > > > > > > > > > > > > >

Doug Milliken <[email hidden]> wrote in message news:<[email hidden]>... > Ackermann doesn't do much until the wheels have been turned > quite a bit. Initial toe settings probably swamp any Ackerman > correction until you are on a pretty tight and slow corner... Awwww, I was going to be all flash and implement full steering geometry adjustment but if it won't actually improve anything (unless I'm going really slow, which I never do !?!?!) I don't think I'll bother, apart from the fact that it is another cool feature to put in the engine. When I say 'fully implement', I'm talking about allowing adjustment of the tie-rod / hub connection points in relation to the hub and the position of the steering rack. Would there be any other benefits from implementing all of this? Colin

Doug, I see a lot of guys changing the ackerman in road racing and solo II only cars. I was thinking about it, but it seems a bit lenghty to actaully do. Would it really help that much on a Solo II only car? Dave Doug Milliken <[email hidden]> wrote in message news:[email hidden]... > > Ackermann doesn't do much until the wheels have been turned > quite a bit. Initial toe settings probably swamp any Ackerman > correction until you are on a pretty tight and slow corner... > >

Unfortunately, there were no numbers (calculations with tire data, etc) supplied with that article. Put some numbers in, then you will find out if this new premise is correct or not. On Wed, 29 Aug 2001, Ben Coleman wrote:

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> There was some discussion of this in a debate in the letters section of Race > Tech magazine on Ackerman/Dynamic Toe. > > In a (large) nutshell, the stabilising effect of toe in is due to the > rearwards drag of the tyres. If you consider a small left steering movement > with toe in, the left tyre now has zero slip and a small rearwards (rolling > drag) force. The right tyre is pointing to the left with a leftwards slip > angle, has rearwards rolling drag and sideways (axial) "slip angle" force. > This axial force points to the left and slightly rearwards. So, in car > coordinates, the left wheel has only rearwards rolling drag force while the > right wheel has rearwards rolling drag force plus the rearwards component of > the slip angle force. > > With toe out the effects are reversed and it is destabilising. > > This was gleaned from the Oct/Nov 200 issue with thanks (or apologies) to > Erik Zapletal who wrote the letter and Alan Staniforth who had written the > original article (and approved the letter as a plain English explanation of > Ackerman). > > The letter continues to discuss the amplified effect with Ackerman as the > difference between wheel angles reaches several degrees whereas static toe > is usually tenths of a degree. An interesting conclusion is that while > positive Ackerman (dynamic toe out) is destabilising during turn in, > sharpening dynamic response, it is stabilising "at the limit" because the > rearwards force at the inside wheel is the first to drop. > > Hopefully I didn't butcher that too much! > > Ben > > > >

Doug Milliken wrote in message ... > >Unfortunately, there were no numbers (calculations with tire data, etc) >supplied with that article. Put some numbers in, then you will find out if >this new premise is correct or not. > > I'm in the unfortunate position of having no way to verify or otherwise these kind of assertions. I read the articles and try to decide whether or not I agree with them based on a combination of the arguments presented, the author's and editor's credentials and the credibility of the publication. Is RaceTech generally repected for its articles? Ben

On Thu, 6 Sep 2001, Ben Coleman wrote:

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> Doug Milliken wrote in message ... > >Unfortunately, there were no numbers (calculations with tire data, etc) > >supplied with that article. Put some numbers in, then you will find out if > >this new premise is correct or not. > I'm in the unfortunate position of having no way to verify or otherwise > these kind of assertions. I read the articles and try to decide whether or > not I agree with them based on a combination of the arguments presented, the > author's and editor's credentials and the credibility of the publication.

Well, if you are going to act on the advice of tech articles (and in the case of a real racecar, this often means spending hard-earned money), I'd strongly recommend getting enough of a self-education so that you can run some simple numbers yourself. Or, find someone that can do it for you. Really, most of the math in our book is high school algebra & geometry (but there is a lot of it, because cars are complex!) > Is RaceTech generally repected for its articles? Um, I don't know (I have only seen a few issues). But I'm generally annoyed by people that put forth technical articles with no data to support their thesis. That's speculation (or journalism??<grin>), not engineering.

Doug Milliken wrote in message ...

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> > >Well, if you are going to act on the advice of tech articles (and in the >case of a real racecar, this often means spending hard-earned money), I'd >strongly recommend getting enough of a self-education so that you can run >some simple numbers yourself. Or, find someone that can do it for you. >Really, most of the math in our book is high school algebra & geometry (but >there is a lot of it, because cars are complex!) >

The numbers aren't a problem (I'm an engineer) but I don't have the resources ATM to start running suspension calculations. At some point I would like to but I'll have to cull another hobby first - perhaps after I bolt my own car back together. I appreciate what you are saying about the articles. A demonstration of the theory would give some easily-verified credibility to it. Thanks, Ben

Ben Coleman <[email hidden]> wrote in message news:[email hidden]... > The numbers aren't a problem (I'm an engineer) but I don't have the > resources ATM to start running suspension calculations. At somepoint I > would like to but I'll have to cull another hobby first - perhapsafter I > bolt my own car back together. > > I appreciate what you are saying about the articles. Ademonstration of the > theory would give some easily-verified credibility to it. IIRC the website www.racetechmag.com does have some Ackermann software available for download, if anyone wants to play... whether the results would be easy to plug into a whole-vehicle model is another matter ;-) Jonny