Quote:
Originally Posted by KoenG
Ovekwam, You did a really nice write up until this part... There is a transversal vector, which is orthogonal to the length ax of the car, and a longitudinal vector in the length of the car. the front tires on a RWD car leave the longitudinal vector rather unexploited. The AWD version will exploit it by pushing torque on the front tires.
When you check what the tire is going to do, you have to vectorial combine the longitudinal and transversal components together. When the combined forces exceed the grip of the tire, it slides.
When you check the grip "oval" of a front tire, you'll see that max g's are exploited when you combine transversal and longitudinal components. Assume theoretical that limits transversal and longitudinal are the same (they aren't since longitudinal are better, but anyway), you could converse 1.4142 times the transversal force to the FWD.
I agree that the transversal component will be a bit smaller on AWD, but the longitudinal one is clearly bigger. The overall G force on the AWD will be bigger during all circumstances. This will convert the AWD to a winner during circuit driving conditions while providing a comfort of mind to the one's not trying to set lap records.
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You seem to assume that there is always a longitudinal component of the force on the contact patch. That is not the case. If you maximize the transverse component, there is no grip left for forward traction. If you choose to sacrifice the transverse force by adding forward traction on an AWD car, the overall force will not be any higher. The more forward force you add, the more transverse force you have to take away. If both components are the same, they will both be around 70 percent of the maximum transverse force. The vector sum is still not higher.
At this point, the cornering ability is down to 70 percent, and the car is accelerating. This combination indicates that the race line straighens a lot, so you can not do this before the very end of the corner. A RWD car can start feeding in power earlier and still keep a tighter line, since it is still using the maximum cornering ability by by not reducing the bottleneck transversal force up front.
In very tight corners, the AWD works well, since you need to use a lot of power and straighten the line quickly. In a long sweeper corner, RWD is more suitable, since it can corner better while accelerating moderately.
Quote:
Originally Posted by KoenG
Oh yeah, I brought it up... an xDrive AT will certainly lap faster on the Nordschleiffe than the RWD AT. Certainly with less swet involved, agree on that. But when you state, the max attainable lateral g's are best on the RWD, I agree but the difference is really small (about 1 percent) and not compensating enough for the lack of traction.
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Lap records are set with good tires on a dry day. In those conditions, I am pretty sure the RWD version would set the best time. The average speed around the track is quite high, so the cars will not be traction limited except for the slow corners. The traction advantage will not make up for the 70 kg extra weight on the AWD car and less optimal weight distribution.
On a wet lap, the AWD car would probably win.