I read the story about the Viper service disaster, and had a lengthy discussion with greg stevens about it, and I was wondering if anyone could explain the physics of it. Oversteer leads to spinning out, and apparently giving gas in the turn gives you oversteer. However, doesn't giving it gas shift the weight to the back of the car, therefore theoretically giving more grip to the rear wheels? Could someone please explain this to me? Thanks in advance!

 

Rear weight transfer is merely one piece of the puzzle... There are other factors at work. In the lower gears, the limited slip diff makes oversteer happen. When the inside wheel gets light (natural in a corner) the diff transfers torque to the outside wheel. Imagine the outside wheel providing more forward 'drive' than the inside wheel... instant oversteer. Another factor is the loading of the tires. Yes, you are transferring weight when accelerating but you are also asking the tires to handle both cornering force and positive drive. In a FWD car, the rear tires only have to deal with cornering and braking. That's why you can kick the rear out on FWD while braking... You are not only transferring weight off the rears, you're asking them to corner and brake.

In a RWD you are asking the rear tires to handle braking, accelerating and cornering. The same corner entry case applies, but now when accelerating out of the corner you are adding acceleration forces to the cornering forces. It's always best to gradually apply the throttle as you unwind the steering wheel exiting a corner.

If you stomp on the gas, you'll get a large initial weight transfer and the rear will 'stick'. But then as the rear shocks let the springs unload, and weight slowly evens back out the car will oversteer violently. This is the cause of the 'snap' oversteer in our cars... It's driver induced. Try this exercise:

In a 2nd gear corner that you know well, get to full throttle quickly and early. You'll most certainly get a big snap soon after. Now try this: Apply the throttle gently and squeeze it more as you exit the corner. The car will drift and you'll be able to control where the tail of the car goes.

Try the same exercise in 1st gear. Part throttle in 1st makes lurid, controllable powerslides possible... very impressive to look at, though hard on the tires!

HTH

 

Very detailed explanation...thanks a lot Jason!

 

Interesting description Jason, it certainly explains the theory behind what happens but I think that Jay-Li is talking about something more fundamental.

Jay-Li, it is not really true to say that

 

Thanks for all, jason, great knolegde...
Filipe Jesus

 

Great info by Jason and 2kturkey. They basically covered all the angles.

On 2kturkey's opnion about over being better than understeer, that depends on the driver capacity. Recovering from understeer is easier than from oversteer for most drivers.

On understeer getting off the gas will cure the problem most of the times as you unload weight from the front tires and let them regain some traction back (making them work less).

This is a more natural reaction for most drivers compared to having the back end loose traction (oversteer) and adding more gas smoothly to correct while unwinding the steering wheel or counter steering.

The worst thing you can do on oversteer is let the gas go or hit the brakes. Unless you are header for loosing it completly and I recomend also putting in the clutch.

 

My advice: Play lots of Sega Rally 2. You will learn to accelerate through oversteer in a controlled manner. I'm kind of kidding, but the truth is that no one knows how to reign in oversteer better than the Colin McRae's of this world.

 

As the great Buddy Baker has said about the difference between UnderSteer and OverSteer;

"With UnderSteer you get to see the wreck"

 

Pepe, have to agree with you re most driver's capability. I have had a couple of instances though on tight hairpin bends where I just did not have the opportunity to slow down and drifted wide into oncoming trafic.

There is a great road just outside Melbourne that goes up to the top of a small mountain known as Arthur's seat. It is a series of very tight bends speed signed at 15 - 30 km/h linked by 50 - 100 metre straights.
The very first day I bought the Stook I went up Arthur's Seat. I knew I had to keep the revs below 5000 but that didn't stop me enjoying the full handling capabilities of the car.

Normally what most guys do is put their female partner on the chairlift to the top so they can enjoy the drive even better (no complaining passenger).

Anyway, the last time I took this drive (pre Stook) was in a front wheel drive Nissan and that's where I got into trouble


[This message has been edited by 2kturkey (edited November 28, 2000).]