GPL physics bug?

Can someone please explain if this is correct. In whatever formula car you want, you're driving down the track and start to loose it on a turn. At this point I put my foot down (gas) with the intent of continuing the spin past 180 deg all the way around to 360 deg, or straight ahead again. The idea of course is to kill rear traction by spinning the tires, only it doesn't seem to work! Over and over I've had the car start to spin, I react by flooring it, and the spin continues as it should... THEN, at 180 deg (pointing backwards) the stops spinning, even though I still am spinning the rear tires. This seems really wrong. The car has a certain rotational inertia at that point and nothing has happened that should cause the spin to end. Thoughts? -- Thanks, Kurt, who's sick of spam. Change "server" to "servr."

Rear engine car....the old lead-tipped missile, going backwards!

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>Can someone please explain if this is correct. >In whatever formula car you want, you're driving down the track and start >to loose it on a turn. At this point I put my foot down (gas) with the >intent of continuing the spin past 180 deg all the way around to 360 deg, >or straight ahead again. The idea of course is to kill rear traction by >spinning the tires, only it doesn't seem to work! Over and over I've had >the car start to spin, I react by flooring it, and the spin continues as it >should... THEN, at 180 deg (pointing backwards) the stops spinning, even >though I still am spinning the rear tires. This seems really wrong. The >car has a certain rotational inertia at that point and nothing has happened >that should cause the spin to end. >Thoughts? >-- >Thanks, >Kurt, who's sick of spam. Change "server" to "servr."

The car is spinning around the longitudinal balance point, but the majority of weight is at the back of the car. As the car comes around through 180 deg. all that weight suddenly has to start moving back the way it has come - often the rotational inertia isn't enough to overcome that. I tend to use the steering to induce the car to continue the turn, turning away from the direction of rotation to get the front to move. Cheers! John PS - Whether the above is the correct reasoning or not it works on the track and it works in GPL. If the above explanation is bollocks it would be interesting if someone could explain why it works :-)

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> Can someone please explain if this is correct. > In whatever formula car you want, you're driving down the track and start > to loose it on a turn. At this point I put my foot down (gas) with the > intent of continuing the spin past 180 deg all the way around to 360 deg, > or straight ahead again. The idea of course is to kill rear traction by > spinning the tires, only it doesn't seem to work! Over and over I've had > the car start to spin, I react by flooring it, and the spin continues as it > should... THEN, at 180 deg (pointing backwards) the stops spinning, even > though I still am spinning the rear tires. This seems really wrong. The > car has a certain rotational inertia at that point and nothing has happened > that should cause the spin to end.

I suspect this is correct behaviour. Anyone car to try it out in their real car to confirm? ;) But seriously, I think what's going on basically the same thing as when you lock up your front wheels in a normal braking maneouver while the rear wheels are rolling freely: the car plows straight ahead. But while you're spinning your car around, the rear wheels are the ones with no grip due to the wheelspin, and the front wheels are rolling freely, but the car is going backwards so the car just plows straight backwards... if you get what i mean:) My solution: try hitting the brakes at the same time you are flooring the accelerator so that the front wheels are locked up while the rear wheels are wheelspinning and then the car will quite happily come right around - once you have passed 180 degrees and are coming back around to pointing forwards again you ease off on both throttle and brake and let the wheels spin up (or down) to match the road velocity and "catch" the spin as it reaches 360 degrees. if the car still has too much rotational momentum and goes around for some more, repeat and try to catch again at the 720 degree mark. I've had the occasional 1080 degree spin which i have caught quite well, before:) hehe Grant.

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>Can someone please explain if this is correct. >In whatever formula car you want, you're driving down the track and start >to loose it on a turn. At this point I put my foot down (gas) with the >intent of continuing the spin past 180 deg all the way around to 360 deg, >or straight ahead again. The idea of course is to kill rear traction by >spinning the tires, only it doesn't seem to work! Over and over I've had >the car start to spin, I react by flooring it, and the spin continues as it >should... THEN, at 180 deg (pointing backwards) the spinning stops, even >though I still am spinning the rear tires. This seems really wrong. The >car has a certain rotational inertia at that point and nothing has happened >that should cause the spin to end.

The modelling of this behaviour is completely accurate. It's as simple as feathers on an arrow. The end of the vehicle with the least traction is the arrowhead. The end of the vehicle with the most traction is the feather. You can demonstrate the effect by purposely mis-adjusting your fore-aft brake balance. With too much FRONT brake bias, the front wheels will lock first under braking. The locked and sliding front wheels (the arrowhead) provide less traction than the rolling rear wheels (the feathers). In this case the car is considered "stable". It will understeer straight ahead, usually straight off the track and nose-first into a tree. "Stable" is when you never lose sight of the object you're trying to avoid, right up until you hit it. With too much REAR bias, the rear wheels will instead lock first. The locked and sliding rear wheels (now the arrowhead) provide less traction than the rolling front wheels (the feathers), and unless you do something *quickly* to correct the situation the car WILL turn 180 degrees until the arrow is flying as nature intended it to. This is considered an "unstable" car. It will try to swap ends during braking with the result that you usually hit the fence going backwards. "Unstable" is when you need your rearview mirrors to see what you're going to hit. Unstable is a big no-no when designing street cars for the use of grandmothers, pregnant women, and 99% of other drivers. When you try to spin the car at speed using too much throttle, you have in effect turned the spinning rear wheels into the arrowhead while the solidly planted contact patches of the rolling front tires become the feathers on the arrow. If you keep the rear wheels spinning, the car *SHOULD* "weathervane" around so that it spins 180 degrees and then continues going straight backwards down the track. Once you're flying backwards down the track like this, the trick to completing the 360 is to regain traction on the rear tires and simultaneously kill the traction on the front tires (put feathers on the rear tires, arrowhead on the fronts). You first need to get the rear tires rolling again at the right speed (backwards now) so that the contact patches are planted firmly on the road (not sliding). You *cannot* do that by adding more throttle. That only spins the tires faster in the wrong direction. The quickest way to get the tires rolling again in full contact with the road surface is to dip the clutch to disconnect the engine from the drivetrain! Unless you're sliding square sideways, the wheels should be free to roll and should almost immediately hook up again. Simultaneously, turn the steering wheel to force the nose of the car to continue swinging around (The Rockford Turn mentioned in an earlier thread). You can practice this part separately by driving quickly in reverse, and then suddenly turning the steering wheel in either direction. The nose will immediately swing around. The tricky part here is that as the car swings through the 90 degree position, the wheels will stop rolling backwards and instead begin rolling forward. This will do bad things to your drivetrain unless you remember to keep the clutch pedal depressed, or unless you're really clever and can switch gears from reverse into the proper forward gear at the exact same moment as the wheels go from rolling backwards to rolling forward. If you're thinking of practising this in your street car, I recommend using a snow-covered parking lot (NOT DRY PAVEMENT). -Ferdinand-