how to understand the physics of car tuning?

[tony2411]

if you increase front suspension stiffness and lower rear stiffness, you obtain more surface area of the front tires in contact with the road, thus increasing the amount of centripetal force available on the front end, but wouldn't this mean that the front end would let go later, thus increasing over-steer? however in the game it increases under-steer.
That reasoning agrees with the down-force tuning in the game... increase rear down-force, more centripetal force in the rear, the front let's go first = more under-steer...
What is lacking in my understanding? (is the game correct?)

Also, are the principles the same, in terms of available centripetal force, for tires, suspension, and down-force? Or does down-force work differently to suspension stiffness in providing grip? (I know down-force is proportional to the square of velocity, i mean in terms of under-steer vs over-steer balance)

 

[Exorcet]

You need to think of springs while the car is in dynamic motion. In steady state, stiffer front springs could act like you suggest. If instead the car is decelerating, the stiffer front springs push the weight of the car on to the rear wheels, which increases rear wheel traction. The springs aren't really there to control tire grip directly. They control weight transfer.

The reason why downforce works differently is because it directly increases traction and has nothing to do with weight transfer.

 

[Speedster911]

Exorcet explains it well. *thumbs up*

OP, without getting too technical, if you want to experiment with grip, I'd suggest playing around with tyre pressures, negative camber, toe in/out and particularly, dampers. Dampers play a major role in how your car behaves around turns, keeping the track surface in mind.

General example:

Lets say a track like Indianappolis. Flat and smooth track surface throughout, practically no elevation changes. What you'd want is lowering the car as much as possible, without the suspension bottoming out. Stiff suspension and the dampers relatively soft.

On a track like Camino or Infineon, where there are lots of elevation changes and a bumpy track surface, you need to raise the ride height to allow sufficient suspension travel. In order for the suspension to absorb bumps on an uneven track surface with elevation changes, you'll need to soften it up, whilst slightly stiffening up the dampers to minimize the spring oscillation.

Now, a word on toe, anti-roll bars and negative camber:

Softer anti-roll bars will allow your car to change direction quicker, but it will also increase it's tendency to lose grip while cornering, IF you're too hard on the steering or aggressive with the throttle. Having stiffer a.roll bars on the other hand, will keep the car more stable throughout the corner/turn, but may diminish a car's ability to consistently grip the road (this varies again, depending on the track surface). With the result, that you'd flat out go unto understeer, or may have to tap the throttle to get the rear to slide out just enough, to control the understeer. Hope this makes sense.

Toe out in the front, and toe in in the rear, allows sharper turn in, and more grip, when exiting under acceleration, out of corners. Couple this with negative camber (say, between 4 and 3 Front, 1 and 2.5 Rear) and you'll be getting a lot of good use out of your tyres! However, if you've softened up the suspension and raised the ride height for a bumpy track with elevation changes, don't go into extreme negative camber angles.

This is what I prefer. Different drivers with varying driving styles, prefer other tuning parameters. I'm a precision driver, so this kind of set up works well for me, just to give you an idea. Of course, a lot of these parameters need to be thrown around, when were talking cars with different powertrains. I.e in a rear engine, RWD car, I'd keep the front anti roll bars and suspension, softer than the rear. Same goes for camber. Why? Because I don't want the front to understeer around corners. Similarly, I'd reverse this set up completely for a front engine RWD car. Or an entirely different set of tuning paremeters for a front engine FWD car.

Experiment with whatever works best for you. Although I'd like to see a heckuva lot of tuning options in a Forza game, the current one gives you a pretty good idea of how these cars would behave IRL. Comparing my real world driving experience, I'd say the tuning options get cars to behave the way they should.

Sorry for the lengthy post!

 

[SlyNine]

The way I picture it in my head, and I could be way off.

Tires work better as pairs, and when you stiffen the suspension on one end of the car the other end is looser in comparison. What this does, I think, is keep the looser end of the car in better contact with the road.