jbrennen
None taken.
In my setup, in a steady-speed medium-speed corner (medium speed for autocross being about 40-50 MPH), the outside rear tire is the tire which is closest to its traction limit, and -- like you mentioned with FF cars -- the inside rear tire may actually be off the ground at times. This is achieved by running the rear with less negative camber than the front, and with relatively stiffer springs than the front (actually both front and rear are 10kg/mm springs, but with 60/40 weight distribution, the rear springs are actually 50% stiffer than the front on a pound-for-pound basis).
So when I get on the throttle, even with a 50-50 torque distribution, the outside rear tire is going to lose relatively more lateral grip than the front tires -- oversteer.
Ok. I think I understand now. Is the implication then that this car always has oversteer, throttle on or not? I'm imagining a car that basically always rotates on demand, but since it's AWD, the amount of oversteer doesn't vary so dynamically so it's controllable. That could be quite handy in the typically low speed, highly technical turns of an autocross but it might get pretty unruly on a high speed road course. This is theoretical conjecture... am I right?
Hmm... the thing that's throwing me off is... starting from the scenario you describe... when you apply more throttle, it shifts more of the car's weight from the front to the rear tires. That _should_ push the car in the direction of understeer... hmmm... but the rear tires could go off faster than the added weight helps them. So whether or not it actually oversteers or understeers could be more dynamic... depending on how hard a turn and how much gas it could understeer or oversteer.
Perhaps the real key is the cambers. Giving it more gas also causes it to lean more. With a lot more negative camber up front than the rear... the rear tires could lose traction from running on the outside edges faster than the weight transfer adds traction... Again, whether it oversteers or understeers can be a more dynamic function...
Ok. I think I'm coming to an understanding that the equation can be more complex than that. It seems to me that the natural effect of 50/50 AWD... just that piece of the equation by itself... is to push the car toward understeer when its on throttle, but the combination of other factors can still produce oversteer instead.
Hmmm... well, I'm just theorizing, and you've got the real car. Am I way off here?
In fact, the first time I let somebody else drive my car in competition, it was a guy who normally drives a RWD Camaro. He thought that because it was AWD, that the correct response to a loose rear end is to get on the throttle. He promptly proceeded to spin the car out less than 10 seconds after leaving the starting line.
Yeah. I race a RWD Corvette so my knowledge of AWD cars is theoretical, not practical.
Btw... I haven't meant to imply that I think RWD is inherently better than AWD. Actually, my assessment is that whether RWD or AWD is better is dependent on the track design and road conditions. RWD has inherent balance advantages in regards to traction circles during a turn... with the front tires taking on the task of primarily turning the car and the rear tires taking on the task of primarily accelerating the car. But AWD has an advantage in stability and a HUGE advantage in turns with traction limitted (versus torque limitted) acceleration.
It all makes it clear, I think, why formula cars are RWD and rally cars are AWD. Different tools for different circumstances.
Someone will probably beat me up for this... but I can't see where FWD has any advantage over either one. Or is in any way equal, actually. Well, other than being easier to control. It seems to me that FWD is an inherent disadvantage.
Oh, btw... I do think your Lancer is a cool car.
I'm an American sports car junkie, but the Lancer is one of the imports I have admiration for.
Heh. I guess we'd never face eachother RL since I'm SM2, not SM.
As for the turning with 3 wheels instead of 4, I see a lot of BMWs (M3s mostly) cornering on 3 wheels when autocrossing. The difference is that they are lifting the inside front tire. Just an interesting observation that FWD/AWD cars are not the only "tricycles" out there.
Heh. That's true. But FWD is the only one where it's standard practice. I think it's pretty obvious that having 4 tires on the ground is inherently better than 3. Any car that actually handles better by lifting a tire like that is compensating for a substantial balancing problem.
At least with AWD, you're getting very substantial gains in other areas. Like exploding off the line from a standing start! Argh! I hate that about facing an AWD car in a drag. I may blow by them a little further down the road, but the first 60 feet are theirs no matter what I try.
- Skant
(I have an Impreza 2.5RS with upgraded cams.)
