Help solve an argument about understeer and possible solutions.
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AudiWorld Super User
Joined: Apr 2001
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Help solve an argument about understeer and possible solutions.
When a car is understeering it's because the front wheels increase slip angle before and/or more than the back wheels, straightening the trajectory.
On an AMG/C32 forum, someone has suggested reducing rear contact patch as a solution. My argument is that reducing traction may cause the rear slip angle to increase at lower speeds, so there will be the perception of balance, but to get the balance, you are at the same or even lower speed in the corner. So, the understeering car driven at the limit (little or no understeer) will have the same entry/exit speed as the car with narrower rear tires.
Can you improve TIME (not feel or balance) by reducing traction at the rear? If the answer is "no" then can the same argument be made regarding a firmer rear stabilizer bar (it may increase rotation, but solely by robbing traction from the rear end).
On an AMG/C32 forum, someone has suggested reducing rear contact patch as a solution. My argument is that reducing traction may cause the rear slip angle to increase at lower speeds, so there will be the perception of balance, but to get the balance, you are at the same or even lower speed in the corner. So, the understeering car driven at the limit (little or no understeer) will have the same entry/exit speed as the car with narrower rear tires.
Can you improve TIME (not feel or balance) by reducing traction at the rear? If the answer is "no" then can the same argument be made regarding a firmer rear stabilizer bar (it may increase rotation, but solely by robbing traction from the rear end).
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Joined: Nov 2000
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is this a total hypothetical, or are we talking about a specific car?
it's hard to render an opinion on an unknown starting point.
are the tires staggered F/R to begin with?
what happens if you reduce the corner entry speed to the point where there's no understeer, and then get on the gas once the car is turned most of the way? Can you put the power down?
absolute grip is only part of the game; if you can't get the car rotated, you're not going to be able to get on the gas early in the corner at that entry speed. For a momentum car, this is a bad thing. There's a reason momentum RWD cars almost always run the same tire size F/R.
But on a RWD car with tons of power, the understeer might just be telling you to back off the entry speed a bit so you can get the car turned and on the throttle earlier. And in that case, you'd probably the wider rear tires to put the power down.
Between the setup and driving style there are tons of variables....
are the tires staggered F/R to begin with?
what happens if you reduce the corner entry speed to the point where there's no understeer, and then get on the gas once the car is turned most of the way? Can you put the power down?
absolute grip is only part of the game; if you can't get the car rotated, you're not going to be able to get on the gas early in the corner at that entry speed. For a momentum car, this is a bad thing. There's a reason momentum RWD cars almost always run the same tire size F/R.
But on a RWD car with tons of power, the understeer might just be telling you to back off the entry speed a bit so you can get the car turned and on the throttle earlier. And in that case, you'd probably the wider rear tires to put the power down.
Between the setup and driving style there are tons of variables....
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AudiWorld Super User
Joined: Apr 2001
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It's the Benz C32 AMG. Lots of HP, RWD and staggered setup. Front suspension sucks.
Very little ability to go negative camber. I've already de-staggered the car, but it still understeers mightily. One guy suggested reverse staggering (and he actually tracks the car with a mix of tires putting more grip in the front).
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A stiffer rear bar reduces rear traction, but it also increases front traction.
A stiffer rear bar increases the load distribution across the rear tires, which reduces total grip because of the non-linear behavior of a tire's grip versus load. Increasing the load distribution across the tires at one end of the car reduces it on the other end, therefore a stiffer rear bar also increases total grip available from the front tires.
<img src="http://pictureposter.audiworld.com/17157/tiregrip.jpg">
<img src="http://pictureposter.audiworld.com/17157/tiregrip.jpg">
Elder Member
Joined: Mar 2001
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I was the S8 at RA, audios was an A8.
The FJ's a hoot. My only real complaint is that the gas tank is too small. With the the aerodynamics of a brick and the low gearing of the 6-speed manual, I rarely get 250 miles on a tank (versus 400+ from the S8).
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