GPL: regarding ramp angles

Something that I can't understand. Why would *anyone* want to have a low power-side angle and a high coast-side angle? All that the setup guides say about it is that this setting is not recommended for newbies, but they fail to mention why even an experienced player should bother with it. +Cinquo [handicap 68.08]

Ok, allow me to delve into my archive of posts produced for another, private forum again. <start quoted text> Like I promised at the driver debriefing after the Rouen event, I now post my thoughts on setting up the rear differential in GPL. I offer this information as is and I hope it will be appreciated as such. In other words: don't blame me if your driving gets worse once you decide to give this a go. ;-)) Here goes: I will skip on explaining the actual technicalities of the limited slip differential modeled in GPL. Suffise to say it allows for, depending on the amount of "lock", different rotation speeds on each of the rear wheels as to facilitate taking bends (where the outside wheel has further to travel). The amount of "lock" can be set separately for trailing throttle (the "coast" side) and neutral to full throttle (the "power on" side) conditions and is controlled by the "ramp angle". The steeper the angle, the greater the independence of the driven wheels. Differential settings are always quoted "power_on_ramp_angle / coast_ramp_angle", so a 45/85 differential setting has a ramp angle of 45 degrees on the power on side and a 85 degree angle on the coast side. This convention is reflected on the GPL Drivetrain setup screen. So far so good, but what are the correct settings? Common consensus, as shown by most GPl setups, are 85/45 angles, while 45/85 is also generally believed to be more realistic. Hmmm... diametric opposites, let's ask the expert. This combined quote is Carroll Smith's wisdom on the subject from his "... To Win"-series (sly ol' Carrol has scattered pearls of wisdom across his 4 books to make us buy them all): "If pressed to use a limited slip differential I run 45/80 angles, except on very twisty, heavily cambered or crowned tracks, where I run 80/80. I see no reason to ever lock up the coast side." Carroll doesn't explain why though, which is what I will attempt to do now. Let us consider a car traveling through a corner with a locked rear differential (it doesn't matter which "side" is locked, as I will explain later). The outside rear wheel will be on a bigger arc than the inside one and thus rotate at greater speed. Because of the locking between the two wheels the inside one will thus be dragged along at a speed higher than it's road speed. This sets up a turning moment through the chassis (totally rigid in GPL) which works against the turn (if you don't believe me, try it with a toy having a solid rear axle). So, theoretically, from a pure cornering point of view, we should keep the wheels as loosely coupled as we can afford to do. This is consistent with Carroll's twisty-cambered-crowned theory, as in the latter cases (camber and crown used to advantage) the inside wheel bears a higher load and the adverse effect of the locking is therefore more pronounced. Note that it indeed does not matter which side you lock as that only affects the phase of the turn where you will feel the effect. With coast side lock up you will notice the effect at turn in, whereas with a locked up power on side you will notice it most in the constant throttle / exit phase of the turn. So, in closing, no locking = maximum cornering power. Hold up! How come so many real life guys run a locked up power side then? -Well, as with maximum constant radius, the ideal situation to benefit from this maximum cornering ability doesn't exist. Tracks aren't circular, corners are preceded and followed by straights. We want to be at top speed or at least accelerating to top speed for as much of a given lap as possible. We want to brake late, make our turn in a little later and sharper, clip past the geometric (constant radius) apex of the turn and get back on the power as soon as possible. Consider the 45/85 solution: the unlocked coast side indeed allows us to delay our turn in and turn a little sharper (it does not add to turn in understeer). As we get to the constant throttle phase the locking on the power side kicks in (more or less smoothly according to the number of clutches; more clutches = more abrupt), introducing some midcorner understeer. If you've read any discussion about the friction circle cornering method you will have noticed this is a requirement to create excess tractive capacity in order to begin your acceleration early. Notice we're getting this free, without affecting the overall balance of the vehicle. As we accelerate the locking stays, obviously, but becomes less and less of a problem as, on the exit arc of our turn, steering lock is taken off progressively. Another benefit of the locked power on side approach is in the prevention of spin up on the inside wheel. Otherwise the diff will send the engine torque to the wheel that's spinning the fastest which is as such wasted and not used to propel the car down the next straight. Powerslides also become easier to manage as does putting a driven wheel off the track (something you shouldn't do anyways, but still...). Note this effect is neutralized in an adverse cambered turn as spin up will occur and the almost completely unloaded inside rear will pull the heavily stressed outside one into snap oversteer. Again our little twisty-cambered-crowned rule takes over. What of our beloved locked up coast side then? -Wrong, all wrong I'm afraid. As we have seen before a locked up coast side leads to turn in understeer, a condition to be avoided like the plague. For we will have to brake harder to make a clean apex or risk running out of road either on entry or exit of the corner. From personal experience it also necessitates too stiff a rear bar and dramatically increased tire temps on tracks of the twisty-cambered-crowned variety. Also, I've yet to experience it's fabled "quasi ABS" effect. <end quoted text> I'm not sure where I stand on the role of the clutches nowadays (other than that I tend to use fewer than before), but the principle behind this text still holds, IMO. I've been using 45/85 and 85/85 for just about 18 months now and I'm faster and more consistent everywhere... whether this is due to my ramp angles or to just having driven more, I don't know, but I've certainly gotten used to it. Any thoughts? Jan. =--- Ville V Sinkko wrote...

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> Something that I can't understand. Why would *anyone* want to > have a low power-side angle and a high coast-side angle? All > that the setup guides say about it is that this setting is not > recommended for newbies, but they fail to mention why even an > experienced player should bother with it. > > > +Cinquo [handicap 68.08]

Jan Verschueren <[email hidden]> wrote in message news:[email hidden]... <lots of snippage> > > I'm not sure where I stand on the role of the clutches nowadays (otherthan > that I tend to use fewer than before), but the principle behind this text > still holds, IMO. I've been using 45/85 and 85/85 for just about 18 months > now and I'm faster and more consistent everywhere... whether this is dueto > my ramp angles or to just having driven more, I don't know, but I've > certainly gotten used to it. > > Any thoughts? > > Jan. One, or sometimes two clutches, will suffice (with the Eagle, anyway) as anything more prompts the dreaded turn-in understeer and general lack of cooperation from the car in corners, and then a rather sharp diff lock-up on exit. I usually run an 85/45, but some tracks neccesitate an 85/60, and at Mosport I find a 60/60 with 2 clutches works really well. The 60/xx diff makes pointing the car with the throttle easier, but is not as forgiving as an 85/xx. For race setups I have to keep the power side angle high regardless, as I'm not always too smooth with the throttle when trying to catch someone :-). Regardless, the days of 3 clutches and the 85/30 are gone forever. -- -Ace- (GPLRank -14.01) **remove BRAIN before replying**

great post Jan, makes a lot of sense , clear and to the point ... I'll give it a go and see what the results are. I have always hated the turn in understeer and can see that it may be accentuated by the mechanical side of things. groovy Shane Jan Verschueren <[email hidden]> wrote in message news:[email hidden]... > Ok, allow me to delve into my archive of posts produced for another,private > forum again. > > <start quoted text> > Like I promised at the driver debriefing after the Rouen event, I now > post my thoughts on setting up the rear differential in GPL. I offer this > information as is and I hope it will be appreciated as such. In otherwords:

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> don't blame me if your driving gets worse once you decide to give this a > go. ;-)) > > Here goes: > > I will skip on explaining the actual technicalities of the limited slip > differential modeled in GPL. Suffise to say it allows for, depending on

the > amount of "lock", different rotation speeds on each of the rear wheels asto > facilitate taking bends (where the outside wheel has further to travel).The > amount of "lock" can be set separately for trailing throttle (the "coast" > side) and neutral to full throttle (the "power on" side) conditions and is > controlled by the "ramp angle". The steeper the angle, the greater the > independence of the driven wheels. Differential settings are always quoted > "power_on_ramp_angle / coast_ramp_angle", so a 45/85 differential setting > has a ramp angle of 45 degrees on the power on side and a 85 degree angleon

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> the coast side. This convention is reflected on the GPL Drivetrain setup > screen. > > So far so good, but what are the correct settings? Common consensus, as > shown by most GPl setups, are 85/45 angles, while 45/85 is also generally > believed to be more realistic. Hmmm... diametric opposites, let's ask the > expert. This combined quote is Carroll Smith's wisdom on the subject from > his "... To Win"-series (sly ol' Carrol has scattered pearls of wisdom > across his 4 books to make us buy them all): "If pressed to use a limited > slip differential I run 45/80 angles, except on very twisty, heavily > cambered or crowned tracks, where I run 80/80. I see no reason to ever

lock > up the coast side." > > Carroll doesn't explain why though, which is what I will attempt to donow. > Let us consider a car traveling through a corner with a locked rear > differential (it doesn't matter which "side" is locked, as I will explain > later). The outside rear wheel will be on a bigger arc than the inside one > and thus rotate at greater speed. Because of the locking between the two > wheels the inside one will thus be dragged along at a speed higher thanit's > road speed. This sets up a turning moment through the chassis (totallyrigid > in GPL) which works against the turn (if you don't believe me, try it witha > toy having a solid rear axle). So, theoretically, from a pure cornering > point of view, we should keep the wheels as loosely coupled as we canafford > to do. This is consistent with Carroll's twisty-cambered-crowned theory,as > in the latter cases (camber and crown used to advantage) the inside wheel > bears a higher load and the adverse effect of the locking is thereforemore > pronounced. Note that it indeed does not matter which side you lock asthat

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> only affects the phase of the turn where you will feel the effect. With > coast side lock up you will notice the effect at turn in, whereas with a > locked up power on side you will notice it most in the constant throttle / > exit phase of the turn. So, in closing, no locking = maximum cornering > power. > > Hold up! How come so many real life guys run a locked up power side > then? -Well, as with maximum constant radius, the ideal situation to

benefit > from this maximum cornering ability doesn't exist. Tracks aren't circular, > corners are preceded and followed by straights. We want to be at top speed > or at least accelerating to top speed for as much of a given lap as > possible. We want to brake late, make our turn in a little later and > sharper, clip past the geometric (constant radius) apex of the turn andget > back on the power as soon as possible. Consider the 45/85 solution: the > unlocked coast side indeed allows us to delay our turn in and turn alittle > sharper (it does not add to turn in understeer). As we get to the constant > throttle phase the locking on the power side kicks in (more or lesssmoothly

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> according to the number of clutches; more clutches = more abrupt), > introducing some midcorner understeer. If you've read any discussion about > the friction circle cornering method you will have noticed this is a > requirement to create excess tractive capacity in order to begin your > acceleration early. Notice we're getting this free, without affecting the > overall balance of the vehicle. As we accelerate the locking stays, > obviously, but becomes less and less of a problem as, on the exit arc of

our > turn, steering lock is taken off progressively. Another benefit of the > locked power on side approach is in the prevention of spin up on theinside > wheel. Otherwise the diff will send the engine torque to the wheel that's > spinning the fastest which is as such wasted and not used to propel thecar > down the next straight. Powerslides also become easier to manage as does > putting a driven wheel off the track (something you shouldn't do anyways, > but still...). Note this effect is neutralized in an adverse cambered turn > as spin up will occur and the almost completely unloaded inside rear will > pull the heavily stressed outside one into snap oversteer. Again ourlittle > twisty-cambered-crowned rule takes over. > > What of our beloved locked up coast side then? -Wrong, all wrong I'mafraid. > As we have seen before a locked up coast side leads to turn in understeer,a > condition to be avoided like the plague. For we will have to brake harderto > make a clean apex or risk running out of road either on entry or exit ofthe

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> corner. From personal experience it also necessitates too stiff a rear bar > and dramatically increased tire temps on tracks of the > twisty-cambered-crowned variety. Also, I've yet to experience it's fabled > "quasi ABS" effect. > > <end quoted text> > > I'm not sure where I stand on the role of the clutches nowadays (other

than > that I tend to use fewer than before), but the principle behind this text > still holds, IMO. I've been using 45/85 and 85/85 for just about 18 months > now and I'm faster and more consistent everywhere... whether this is dueto

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> my ramp angles or to just having driven more, I don't know, but I've > certainly gotten used to it. > > Any thoughts? > > Jan. > =--- > Ville V Sinkko wrote... > > Something that I can't understand. Why would *anyone* want to > > have a low power-side angle and a high coast-side angle? All > > that the setup guides say about it is that this setting is not > > recommended for newbies, but they fail to mention why even an > > experienced player should bother with it. > > > > > > +Cinquo [handicap 68.08] > >

Do you trailbrake much? I can't trailbrake for shit when I use setups like that. Wayyy too much oversteer for me. I wonder if that's where the quasi-ABS effect comes into play. Mid-corner braking. I think it would help keep the inside rear brake from locking up. Of course you might use that brake-and-throttle-at-the-same-time technique to prevent that least-loaded wheel from locking. Is that how you do it? I use that technique just a little bit myself, but I sometimes wonder if I'm really getting the most out of it. I trailbrake all the way to the apex in most corners, and I still feel compelled to use those unrealistic 85/30 or 60/30 setups. They just feel a million times better to me. They feel neutral to me, but I suppose they would feel very pushy if I didn't trailbrake. I've experimented with other settings, but every time I've met with success, going back to my usual diff settings saw my laptimes improve even further. -Aubrey "Jan Verschueren" <[email hidden]> wrote in message news:[email hidden]... > Ok, allow me to delve into my archive of posts produced for another,private > forum again. > > <start quoted text> > Like I promised at the driver debriefing after the Rouen event, I now > post my thoughts on setting up the rear differential in GPL. I offer this > information as is and I hope it will be appreciated as such. In otherwords:

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> don't blame me if your driving gets worse once you decide to give this a > go. ;-)) > > Here goes: > > I will skip on explaining the actual technicalities of the limited slip > differential modeled in GPL. Suffise to say it allows for, depending on

the > amount of "lock", different rotation speeds on each of the rear wheels asto > facilitate taking bends (where the outside wheel has further to travel).The > amount of "lock" can be set separately for trailing throttle (the "coast" > side) and neutral to full throttle (the "power on" side) conditions and is > controlled by the "ramp angle". The steeper the angle, the greater the > independence of the driven wheels. Differential settings are always quoted > "power_on_ramp_angle / coast_ramp_angle", so a 45/85 differential setting > has a ramp angle of 45 degrees on the power on side and a 85 degree angleon

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> the coast side. This convention is reflected on the GPL Drivetrain setup > screen. > > So far so good, but what are the correct settings? Common consensus, as > shown by most GPl setups, are 85/45 angles, while 45/85 is also generally > believed to be more realistic. Hmmm... diametric opposites, let's ask the > expert. This combined quote is Carroll Smith's wisdom on the subject from > his "... To Win"-series (sly ol' Carrol has scattered pearls of wisdom > across his 4 books to make us buy them all): "If pressed to use a limited > slip differential I run 45/80 angles, except on very twisty, heavily > cambered or crowned tracks, where I run 80/80. I see no reason to ever

lock > up the coast side." > > Carroll doesn't explain why though, which is what I will attempt to donow. > Let us consider a car traveling through a corner with a locked rear > differential (it doesn't matter which "side" is locked, as I will explain > later). The outside rear wheel will be on a bigger arc than the inside one > and thus rotate at greater speed. Because of the locking between the two > wheels the inside one will thus be dragged along at a speed higher thanit's > road speed. This sets up a turning moment through the chassis (totallyrigid > in GPL) which works against the turn (if you don't believe me, try it witha > toy having a solid rear axle). So, theoretically, from a pure cornering > point of view, we should keep the wheels as loosely coupled as we canafford > to do. This is consistent with Carroll's twisty-cambered-crowned theory,as > in the latter cases (camber and crown used to advantage) the inside wheel > bears a higher load and the adverse effect of the locking is thereforemore > pronounced. Note that it indeed does not matter which side you lock asthat

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> only affects the phase of the turn where you will feel the effect. With > coast side lock up you will notice the effect at turn in, whereas with a > locked up power on side you will notice it most in the constant throttle / > exit phase of the turn. So, in closing, no locking = maximum cornering > power. > > Hold up! How come so many real life guys run a locked up power side > then? -Well, as with maximum constant radius, the ideal situation to

benefit > from this maximum cornering ability doesn't exist. Tracks aren't circular, > corners are preceded and followed by straights. We want to be at top speed > or at least accelerating to top speed for as much of a given lap as > possible. We want to brake late, make our turn in a little later and > sharper, clip past the geometric (constant radius) apex of the turn andget > back on the power as soon as possible. Consider the 45/85 solution: the > unlocked coast side indeed allows us to delay our turn in and turn alittle > sharper (it does not add to turn in understeer). As we get to the constant > throttle phase the locking on the power side kicks in (more or lesssmoothly

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> according to the number of clutches; more clutches = more abrupt), > introducing some midcorner understeer. If you've read any discussion about > the friction circle cornering method you will have noticed this is a > requirement to create excess tractive capacity in order to begin your > acceleration early. Notice we're getting this free, without affecting the > overall balance of the vehicle. As we accelerate the locking stays, > obviously, but becomes less and less of a problem as, on the exit arc of

our > turn, steering lock is taken off progressively. Another benefit of the > locked power on side approach is in the prevention of spin up on theinside > wheel. Otherwise the diff will send the engine torque to the wheel that's > spinning the fastest which is as such wasted and not used to propel thecar > down the next straight. Powerslides also become easier to manage as does > putting a driven wheel off the track (something you shouldn't do anyways, > but still...). Note this effect is neutralized in an adverse cambered turn > as spin up will occur and the almost completely unloaded inside rear will > pull the heavily stressed outside one into snap oversteer. Again ourlittle > twisty-cambered-crowned rule takes over. > > What of our beloved locked up coast side then? -Wrong, all wrong I'mafraid. > As we have seen before a locked up coast side leads to turn in understeer,a > condition to be avoided like the plague. For we will have to brake harderto > make a clean apex or risk running out of road either on entry or exit ofthe

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> corner. From personal experience it also necessitates too stiff a rear bar > and dramatically increased tire temps on tracks of the > twisty-cambered-crowned variety. Also, I've yet to experience it's fabled > "quasi ABS" effect. > > <end quoted text> > > I'm not sure where I stand on the role of the clutches nowadays (other

than > that I tend to use fewer than before), but the principle behind this text > still holds, IMO. I've been using 45/85 and 85/85 for just about 18 months > now and I'm faster and more consistent everywhere... whether this is dueto

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> my ramp angles or to just having driven more, I don't know, but I've > certainly gotten used to it. > > Any thoughts? > > Jan. > =--- > Ville V Sinkko wrote... > > Something that I can't understand. Why would *anyone* want to > > have a low power-side angle and a high coast-side angle? All > > that the setup guides say about it is that this setting is not > > recommended for newbies, but they fail to mention why even an > > experienced player should bother with it. > > > > > > +Cinquo [handicap 68.08] > > >

I do trailbrake, but not as much as most GPL drivers. Certainly not down to the apex, which I tend to think is counter-productive. IMO, once you get to the apex you should already be working on getting out of the turn asap. But, as always, in GPL everyone can have an individual style and still go like the clappers. ;-)) I don't left foot brake and compensate with the throttle at all('cept for the occasional tap on an oval). Trouble with this stuff is you can't just change the differential setting and start using a locked up power side. Chances are one's made his/her setups too oversteering in order to make 85/45 turn, especially the rear anti-roll bar. I've now got the spring set according to weight distribution (see Ricardo Nunnini's site) and the bars 2/3 total front and 1/3 total rear (eg. 160 front/80 rear). Another thing to watch out for is excessive rear suspension damping, especially on the long wheelbase cars. From a driving point of view, the 85/45 diff "dogma" (no settings are "the correct setting" in race car setup, it's about what works best for you) has made the technique of povoting the car into the turn on the brakes very popular. As you will have experienced yourself, the different settings require you ease yourself into it as the car seems more nervous at first. I can now lean as hard on the car as I was used to doing, I just lean a little differently. ;-) Changing the diff settings requires both changes in the rest of the car's setup and to some extend in driving technique (if you were overusing the brakes as a steering device before), maybe I should have pointed that out in my original post, I'm sorry. Took me about two weeks to adapt (but I don't race/practise _that_ much), but I feel it was worth it, if only from an accuracy point of view. The trouble with GPL is, while it's possible to hone the car to a personal style and realise your driving potential, this also means setups and setup technique don't port easily from one person to the next (or from rig to rig for that matter... I once found I couldn't drive my own setups for shit on another guy's rig). The best we can hope for is try explain how and why we do certain things and hope the other person can apply it to his personal situation in a positive manner (i.e. a couple of secs off that GPL Rank!! ;-)). Cheers, Jan. =--- Aubrey wrote...

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> Do you trailbrake much? I can't trailbrake for shit when I > use setups like that. Wayyy too much oversteer for me. I > wonder if that's where the quasi-ABS effect comes into play. > Mid-corner braking. I think it would help keep the inside > rear brake from locking up. > > Of course you might use that brake-and-throttle-at-the-same- > time technique to prevent that least-loaded wheel from locking. > Is that how you do it? I use that technique just a little bit > myself, but I sometimes wonder if I'm > really getting the most out of it. > > I trailbrake all the way to the apex in most corners, and I > still feel compelled to use those unrealistic 85/30 or 60/30 > setups. They just feel a million times better to me. They > feel neutral to me, but I suppose they would feel very pushy > if I didn't trailbrake. I've experimented with other settings, > but every time I've met with success, going back to my usual > diff settings saw my laptimes improve even further. > > -Aubrey >

<snip>

Aubrey wrote:

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> > Do you trailbrake much? I can't trailbrake for shit when I use setups like > that. Wayyy too much oversteer for me. I wonder if that's where the > quasi-ABS effect comes into play. Mid-corner braking. I think it would > help keep the inside rear brake from locking up. > > Of course you might use that brake-and-throttle-at-the-same-time technique > to prevent that least-loaded wheel from locking. Is that how you do it? I > use that technique just a little bit myself, but I sometimes wonder if I'm > really getting the most out of it. > > I trailbrake all the way to the apex in most corners, and I still feel > compelled to use those unrealistic 85/30 or 60/30 setups. They just feel a > million times better to me. They feel neutral to me, but I suppose they > would feel very pushy if I didn't trailbrake. I've experimented with other > settings, but every time I've met with success, going back to my usual diff > settings saw my laptimes improve even further. > > -Aubrey >

Indeed, trailbraking is hard (impossible?) with such settings. There is a reason for this. Not only does a locked axle make the car push in the middle of a corner, but it also dampens the yaw response. Imagine a car travelling in a straight line, and then disturbed so that it acquires a yaw rotational velocity. If the rear axle is open, the only thing countering this motion are forces produced due to slip angles, the first component being produced due to the yaw angle of the whole car, which only builds over time, and another one where the tires acquire an additional (transversal) slip velocity due to the sideways velocity components that the rotation of the car contributes, which dampens the yaw motion. However, if the rear axle is partially locked, another effect comes into play, namely that the rotation of the car also produces longitudinal velocity components on the tires, which point in opposing directions on the left and right sides of the car and are proportional to the track width on the axle. This difference in velocity produces a torque in the differential, which in effect results in another moment acting on the car that opposes the rotational velocity and hence additionally dampens the yawing motions. A locked coast angle hence produces a stabilizing effect not only during the turn but also when the yaw angle is being altered, which is happening when you are transitioning from braking to cornering during the trailbraking exercise. -Gregor

Gregor Veble wrote: > Ok, lots of good stuff has been written here now, and I agree on most of it, but, as far as I can tell, we have been talking about a car cornering well within the traction limits of the rear tires, at least under "coast", I would have thought that a "locked" axle would actually break the traction of one of the rear wheels and pitch the car into an oversteering condition, assuming that we are now so close to the traction limits of the rear end that one wheel isn't enough to "keep it in line" ? Or am I totally off base here, because this is how I setup my car, with a car this light and with such a powerful engine, I feel that this gives me the option to suddenly lift the throttle to get more weight to front at the same time as I'm breaking the traction of the rear end, which I feel is useful when you're going just a little bit too fast in a medium speed corner as it scrubs off speed and gets the nose to "tuck in" at the same time....? Beers and cheers (uncle) Goy "Team Mirage" http://www.teammirage.com/ "The Pits" http://www.theuspits.com/ * Spam is for losers who can't get business any other way * "Spamkiller" http://www.spamkiller.com

I would be more inclined to believe (in a real car) that having a more closely locked diff on the coast side would give you so much in the way of corner entry and mid corner understeer that you'd probably never get going fast enough to get the rear end to break away unless of course you simply threw the car at the apex of the corner and crossed your fingers. This of course would probably cause your tires to degrade pretty quickly, and also would be pretty hard on the differential as well. What makes spooling the coast end of the diff so effective in GPL IMO is the extreme slip angles allow you to take advantage of what in the real world would be a disadvantage, more corner entry and mid-corner understeer...which in GPL translates to stability and thusly allows you to carry a lot of speed through corners when you perfect the techniques of "riding the coast side". TJ > under "coast", I would have thought that a "locked" axle would actually > break the traction of one of the rear wheels and pitch the car into an > oversteering condition, assuming that we are now so close to the > traction limits of the rear end that one wheel isn't enough to "keep it > in line" ?

Hmmm... yes, that's another way of putting it, nice post. Like I said, whatever suits the individual driving style. Still puzzled as to why this works in the game, but apparently not in "real life", though. I'm sure they tried it... if I remember correctly Carroll even commented on an "embarrasment" with an incorrectly assembled diff (swapped power and coast sides) and actually recommends the higher ramp angle for trailbraking. Maybe the drawback/pay-off balance is more pronounced in the physical world. Sure would like to see some hard data on this... anyone got a Salisbury diff manual lying around? Jan. =--- Gregor Veble wrote...

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> <snip> > Indeed, trailbraking is hard (impossible?) with such settings. > > There is a reason for this. Not only does a locked axle make the car > push in the middle of a corner, but it also dampens the yaw response. > > Imagine a car travelling in a straight line, and then disturbed so that > it acquires a yaw rotational velocity. If the rear axle is open, the > only thing countering this motion are forces produced due to slip > angles, the first component being produced due to the yaw angle of the > whole car, which only builds over time, and another one where the tires > acquire an additional (transversal) slip velocity due to the sideways > velocity components that the rotation of the car contributes, which > dampens the yaw motion. > > However, if the rear axle is partially locked, another effect comes into > play, namely that the rotation of the car also produces longitudinal > velocity components on the tires, which point in opposing directions on > the left and right sides of the car and are proportional to the track > width on the axle. This difference in velocity produces a torque in the > differential, which in effect results in another moment acting on the > car that opposes the rotational velocity and hence additionally dampens > the yawing motions. > > A locked coast angle hence produces a stabilizing effect not only during > the turn but also when the yaw angle is being altered, which is > happening when you are transitioning from braking to cornering during > the trailbraking exercise. > > -Gregor

Yes, whatever suits or as Carrol Smith says, "different horses for different courses". I saw a scca event on Speedvision last week and one of the participants dropped out after awhile due to differential problems. The cause?? They'd packed the diff. full of clutches to give them better traction in and out of the corners...the plates began to gall, the oil in the diff. overheated and the unit failed. The commentator (Dorsey Schrader also a driver) mentioned that lots of folks have tried this one time or another and more often than not it causes more problems than its worth. I think there a several reasons that reversed ramp angles work so effectively in GPL. These are a few that I can think of... 1. Due to the extreme slip angles you can drift the car through the corners with a diff. that in the real world cause more understeer that would make it a disadvantage rather than an aid to stability. 2. Tire wear is not modelled, which means the above mentioned drifting won't ruin your day in the long run. 3. Damage to the differential is appearantly not modelled so that you can pack the thing full of clutches and never worry about the unit failing. Anyone else got any hunches?? TJ Jan Verschueren wrote:

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> > Hmmm... yes, that's another way of putting it, nice post. Like I said, > whatever suits the individual driving style. > > Still puzzled as to why this works in the game, but apparently not in "real > life", though. I'm sure they tried it... if I remember correctly Carroll > even commented on an "embarrasment" with an incorrectly assembled diff > (swapped power and coast sides) and actually recommends the higher ramp > angle for trailbraking. Maybe the drawback/pay-off balance is more > pronounced in the physical world. Sure would like to see some hard data on > this... anyone got a Salisbury diff manual lying around? > > Jan. > =--- > Gregor Veble wrote... > > <snip> > > Indeed, trailbraking is hard (impossible?) with such settings. > > > > There is a reason for this. Not only does a locked axle make the car > > push in the middle of a corner, but it also dampens the yaw response. > > > > Imagine a car travelling in a straight line, and then disturbed so that > > it acquires a yaw rotational velocity. If the rear axle is open, the > > only thing countering this motion are forces produced due to slip > > angles, the first component being produced due to the yaw angle of the > > whole car, which only builds over time, and another one where the tires > > acquire an additional (transversal) slip velocity due to the sideways > > velocity components that the rotation of the car contributes, which > > dampens the yaw motion. > > > > However, if the rear axle is partially locked, another effect comes into > > play, namely that the rotation of the car also produces longitudinal > > velocity components on the tires, which point in opposing directions on > > the left and right sides of the car and are proportional to the track > > width on the axle. This difference in velocity produces a torque in the > > differential, which in effect results in another moment acting on the > > car that opposes the rotational velocity and hence additionally dampens > > the yawing motions. > > > > A locked coast angle hence produces a stabilizing effect not only during > > the turn but also when the yaw angle is being altered, which is > > happening when you are transitioning from braking to cornering during > > the trailbraking exercise. > > > > -Gregor

As far as trailbraking goes, when I say "apex", I'm referring to the slowest part of the corner, which is not neccessarily the "clipping point" where you touch the edge of the track. So all I really meant is that I brake gently up until the point where I get on the gas. Come to think of it, there aren't many corners where I stay on the brakes all the way to the clipping point. So our driving styles might not be that different. I agree with everything else you said, but I see you're using a very soft (probably realistic) rear bar, so I would think that eliminates much of the oversteer I have trouble with. I imagine you must use a slightly higher rideheight than most folks to accommodate the softness. I've tried setups like that, and I find them fairly nice to drive, although I still go slower than usual. What I actually had in mind was the sort of setup the hotlappers use. Just out of curiosity I downloaded all the current WR setups from Schubi's site, and remarkably, the majority have made the transition to the 45/85 diff with 1 or 2 clutches. But even more remarkably, they are still running with very stiff rear bar and springs. Around 160 and 100 respectively. I imagine they're doing this so that they can set the rideheight to it's minimum without worring about the rear suspension bottoming too much. The problem with setups like this is extreme oversteer, probably much more than what we're talking about with your setups. So in a sense, it's a whole 'nother can of worms. Until GH had abandoned his 85/45 diff, I had thought that an 85/30 or 85/45 diff was an absolute must for a low-rideheight setup because of the rear suspension stiffness requirement. So in a nutshell, I'm still left scratching my head as to how the quickest guys deal with the oversteer in their driving. I can nurse the car cleanly around the track with one of their setups, but I do it much slower than usual, and my rear tires overheat to the extreme, even if I don't have any big slides. -Aubrey "Jan Verschueren" <[email hidden]> wrote in message news:[email hidden]... > I do trailbrake, but not as much as most GPL drivers. Certainly not downto > the apex, which I tend to think is counter-productive. IMO, once you getto > the apex you should already be working on getting out of the turn asap.But, > as always, in GPL everyone can have an individual style and still go like > the clappers. ;-)) I don't left foot brake and compensate with thethrottle > at all('cept for the occasional tap on an oval). Trouble with this stuffis > you can't just change the differential setting and start using a locked up > power side. Chances are one's made his/her setups too oversteering inorder > to make 85/45 turn, especially the rear anti-roll bar. I've now got the > spring set according to weight distribution (see Ricardo Nunnini's site)and > the bars 2/3 total front and 1/3 total rear (eg. 160 front/80 rear).Another > thing to watch out for is excessive rear suspension damping, especially on > the long wheelbase cars. > > From a driving point of view, the 85/45 diff "dogma" (no settings are "the > correct setting" in race car setup, it's about what works best for you)has > made the technique of povoting the car into the turn on the brakes very > popular. As you will have experienced yourself, the different settings > require you ease yourself into it as the car seems more nervous at first.I > can now lean as hard on the car as I was used to doing, I just lean alittle > differently. ;-) > > Changing the diff settings requires both changes in the rest of the car's > setup and to some extend in driving technique (if you were overusing the > brakes as a steering device before), maybe I should have pointed that outin

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> my original post, I'm sorry. Took me about two weeks to adapt (but I don't > race/practise _that_ much), but I feel it was worth it, if only from an > accuracy point of view. > > The trouble with GPL is, while it's possible to hone the car to a personal > style and realise your driving potential, this also means setups and setup > technique don't port easily from one person to the next (or from rig to

rig

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> for that matter... I once found I couldn't drive my own setups for shit on > another guy's rig). The best we can hope for is try explain how and why we > do certain things and hope the other person can apply it to his personal > situation in a positive manner (i.e. a couple of secs off that GPL Rank!! > ;-)). > > Cheers, > > Jan. > =--- > Aubrey wrote... > > Do you trailbrake much? I can't trailbrake for shit when I > > use setups like that. Wayyy too much oversteer for me. I > > wonder if that's where the quasi-ABS effect comes into play. > > Mid-corner braking. I think it would help keep the inside > > rear brake from locking up. > > > > Of course you might use that brake-and-throttle-at-the-same- > > time technique to prevent that least-loaded wheel from locking. > > Is that how you do it? I use that technique just a little bit > > myself, but I sometimes wonder if I'm > > really getting the most out of it. > > > > I trailbrake all the way to the apex in most corners, and I > > still feel compelled to use those unrealistic 85/30 or 60/30 > > setups. They just feel a million times better to me. They > > feel neutral to me, but I suppose they would feel very pushy > > if I didn't trailbrake. I've experimented with other settings, > > but every time I've met with success, going back to my usual > > diff settings saw my laptimes improve even further. > > > > -Aubrey > > > <snip> > > >

Well, I've noticed that G Huttu has worked around the tendency of a 45/85 diff. to oversteer during throttle transitions by some clever means. One is when he downshifts sometimes he keeps his foot buried in the throttle and also tends to turn the wheel past the point of adhesion to induce understeer. This is most noticeable on quick corners. I've been driving 45/85 for more than a year, and I generally don't overheat the rear tires, but rather more often than not have a fairly close balance between front and rear. If I get a little too throttle happy on corner exit I definately get hotter rear readings though. TJ GPL Rank -5.42 > So in a nutshell, I'm still left scratching my head as to how the quickest > guys deal with the oversteer in their driving. I can nurse the car cleanly > around the track with one of their setups, but I do it much slower than > usual, and my rear tires overheat to the extreme, even if I don't have any > big slides.

Aubrey wrote...

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> As far as trailbraking goes, when I say "apex", I'm referring > to the slowest part of the corner, which is not neccessarily > the "clipping point" where you touch the edge of the track. > So all I really meant is that I brake gently up until the point > where I get on the gas. Come to think of it, there aren't many > corners where I stay on the brakes all the way to the clipping > point. So our driving styles might not be that different.

Ok, difference in termimology there, no prob. We might drive alike, I don't know... very hard to tell from a newsgroup posting, isn't it? ;-) > I agree with everything else you said, but I see you're using a > very soft (probably realistic) rear bar, so I would think that > eliminates much of the oversteer I have trouble with. I should hope so. That's what I use the rear bar for... set the amount of response with the front and balance with the rear. I'm sort of confused about rear toe... I can't seem to get a feel for exactly how it affects the handling, so at the moment I just set it at 0.050 and deal with the result. An avenue I'll maybe start exploring next, if I can manage another "track day". > I imagine you must use a slightly higher rideheight than most folks > to accommodate the softness. Well, I don't know about most folks, but I usually run between 2.75" and 3.75", depending on the track... bump stops lowered to 0.5" using the GRE. Even at the Ring I found I lose less time lifting for a compression to stop the chassis from grounding (I go into the bumps as a matter of course at some places) than dealing with the raised centre of gravity all the way around the track (strong tendency to "rock" out of control in places). > I've tried setups like that, and I find them fairly nice to drive, > although I still go slower than usual. Yes, high setups are comfortable to drive, but as motion is exaggerated you tend to back off too early. You're welcome to try some of my setups. I'm always curious as to what people can do with/think about my setups.

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> What I actually had in mind was the sort of setup the hotlappers use. > Just out of curiosity I downloaded all the current WR setups from > Schubi's site, and remarkably, the majority have made the transition > to the 45/85 diff with 1 or 2 clutches. But even more remarkably, > they are still running with very stiff rear bar and springs. Around > 160 and 100 respectively. > > I imagine they're doing this so that they can set the rideheight to > it's minimum without worring about the rear suspension bottoming too > much. The problem with setups like this is extreme oversteer, > probably much more than what we're talking about with your setups.

Definately... I have tried hotlapper setups too and after tip-toeing around a track with them for a little while my own setups feel quite sluggish at first... that changes as I lose the trepidation the hotlapper setup imprinted on me. ;-) > So in a sense, it's a whole 'nother can of worms. Until GH had > abandoned his 85/45 diff, I had thought that an 85/30 or 85/45 > diff was an absolute must for a low-rideheight setup because > of the rear suspension stiffness requirement. Well, I don't know if it's all to do with bottoming/grounding... with combined thottle and brake control, the weight shift tends to travel along the diagonal of the car. If the rear is soft this actually makes the tendency to pivot around the outside front stronger (the torque in the chassis loads it even more). > So in a nutshell, I'm still left scratching my head as to how the > quickest guys deal with the oversteer in their driving. The difference between the alien and the mere mortal... talent, acute sense of balance and bags and bags of practise, combined with a driving style/setup approach that's honed to an extra-ordinary level. IMO, of course. > I can nurse the car cleanly around the track with one of their > setups, but I do it much slower than usual, and my rear tires > overheat to the extreme, even if I don't have any big slides. Two things: 1) the car's only got to last for a few laps at most. 2) the setup and driving style go hand in hand. To go as fast as them you have to drive as them. There's more to that than meets the eye. We have the means (the game and the setup) and the result (the replay), but it's hard to see what they actually did to produce that fast time... maybe one of the fast guys could video himself driving for us to dissect? I actually learned a lot from watching a faster friend driving. My driving used to be pretty physical: wrestle the FF-wheel and the on-screen car into submission. He, on the other hand was very economical in his movement, guiding and slightly correcting the car as he finessed it along. As a result he could get away with a more "knife-edge" car. I couldn't emulate his style completely, so, over time, I struck a happy medium, where my style is moderately flamboyant, with a touch of finesse added. All in all I believe the only thing you can "get" from another driver is his/her "approach", both in driving line and setup. It's up to the individual to then fit the approach in his own "plan". Jan. =--- <snip>