Quote:
Originally Posted by FReSh
It all comes down to the available traction at the tires. A tire can only provide so much grip.
In a cornering situation, a FWD car splits the available traction of the front wheels between turning the car and accelerating. The rear tires only focus on keeping the back of the car from sliding out.
In a RWD car in the same turning situation, the front wheels can focus completely on turning to prevent understeer. Meanwhile, the rear tires split the available traction between turning (holding the back end in) and accelerating.
The question is 'Which is better?'
The answer lies in the weight transfer when power is applied. When a car applies power, it partially unloads the front wheels and transfers that load to the rear wheels. This lowers the peak amount of traction available to the front tires, and raises the peak traction of the rear tires.
In many FWD cars, this causes the front tires to expend all of their traction much earlier than the rears, causing understeer. As a result of this, the rear tires may be "underchallenged" (they have more grip available than what is being used). In this scenario, not all of the available grip is being used.
In a RWD car, the weight transfer under acceleration gives more peak traction to the rear wheels which have to split their traction between turning and accelerating. This allows them to hold the road better than the front tires of a FWD car. This allows for a higher corner speed before traction is broken. The front tires' grip is also used completely for turning (due to increased corner speed and the partial unloading). This allows all 4 of the tires to contribute all of their available traction.
These things give the advantage to a RWD car. It's better to have the turning/acceleration split occur at the tire with the higher total amount of available traction.
The imbalance of traction in a FWD car can be tuned out through suspension adjustments. However, in the best case scenario, no weight is transferred to the rear tires and the front tires maintain their original amount of grip to split between turning and accelerating. This is better than unloading the front tires, but still doesn't perform quite as well as a RWD car using weight transfer to load the rear tires.
Then of course you could add in the torque steer issues and the fact that RWD is more controllable at the limit since you can adjust the car's angle with both the steering and the throttle, rather than just the steering.
RWD wins.
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This is not quite true. I don't dispute the essence of what you say but it isn't as straightforward as you may imagine.
For underpowered fwd the front tires can actually utilize some of their traction to pull the front of the car in the direction of the turn. Only if enough torque is available to overwhelm the front tires is this advantage lost.
Secondly, rwd cars use up some front wheel steering grip because the rear driving wheels are pushing the front of the car straight on, the turned front wheels can't use all their grip for turning.
Awd cars always understeer for these two reasons combined: some front wheel steering grip is used up driving the car and some is used to counter the sideways push from the rear driving wheels.
Before modern tires became so good rwd with excess torque could be driven sideways a bit so as to utilize the rear driving force to push the car towards the apex. The ideal line in the 50's and 60's was a good four wheel drift but remember in that drift the front tires are hardly doing any work. The rear tires were using a lot of their grip to, in effect, steer the car round the corner. Modern racing cars do not do this, the rear drive wheels just accelerate the car and the front wheels just steer the car. Modern race cars are much quicker for driving in a slight understeering attitude. Only the are all four tires delivering maximum force to turn and accelerate the car.