by Ruth Wolf

Race cars will and do understeer in one portion of a corner and oversteer in another. During corner entry we want mild understeer to stabilize the transition from brake to throttle. During the corner exit phase we want just enough oversteer to get directional control without sacrificing throttle application. We then want to have the car stable and balanced to apply maximum power coming out of the corner all the way down the straight.

UNDERSTEER
In a constant radius turn, when the slip angle of the front tires is greater than the slip angle of the rear tires the car will understeer as speed increases. A race car driver will say the car 'has a push' or 'is tight'. (Most production cars are designed with mild understeer, the rationale being that street cars driven by distracted drivers will move away from on-coming traffic to the outside of the road.)

From behind the wheel, a driver senses understeer when the car is running wider than steering input, and increasing the steering angle does not make the front end turn in. This means the front tires need more download to generate more grip. To transfer weight to the front means giving up the acceleration you just worked so hard to achieve. Reduced cornering speed means reduced corner exit speed, and a loss of rpm's all the way down the next straight, or driving off the road!!!

Determine the problem. Test for understeer
Tape the top of the steering wheel when the wheels are pointing straight. Note how much steering angle is used through a given corner at a moderate speed. If there is more steering input with increased speed, the car is pushing. Determine if what seems like exit oversteer is really the car's reaction to too much steering input through the corner because of tight entry.

OVERSTEER
In a constant radius turn, when the slip angle at the rear tires is greater than the slip angle of the front tires the car will oversteer as speed increases. A race car driver will say the car 'is loose'.

From the drivers seat, when you recognize that the front of the car is turned too far into the apex, you are sensing that the car is going into oversteer. Your first reaction should be to dial in opposite lock, steering into the direction that the rear is moving. Then settle the rear by adding a little throttle. When you lift off the throttle, weight shifts from the rear to the front, reducing rear tire adhesion. This is commonly known as 'trailing throttle oversteer'. With just a slight lift, the driver can help the car rotate into a smooth transition to oversteer; with too abrupt a lift the car will snap into a spin.

DRIVER INFLUENCES
The driver influences tire loading by throttle application. Adding throttle transfers load on to the rear, giving additional grip for acceleration, but reducing grip for cornering. With a gradual application of throttle understeer will result. Remember smoothness. Too abrupt on the throttle will throw the car into oversteer.

THE CAR
What we are looking for in car set-up is balance. If you are doing a lot of steering, something is wrong. Start soft - soft tire pressures, soft springs, soft shock - so you can feel what is happening with the car. Stiffen to the point where any gain in tire adhesion results in a loss in balance and controllability. It's a compromise.

WHAT DOES THE CAR SENSE
Let's take a brief look at how the car responds:

• Too much front brake bias and the front end will not turn in (understeer).
• Too abrupt off the brake as you steer into the apex and the rear will continue its rotation past the apex while the front is pointed at the apex (oversteer).
• Shift gear and underrev, the rear will lock, and slide.
• Too stiff front roll bar and understeer increases through mid point and into exit.
• Too stiff rear roll bar, inner tire unload, and oversteers through corner.
• Too soft rear roll bar, the car will not rotate.
• Both roll bars too soft and there is excessive roll .
• Both roll bars to stiff and the car will tend to slide and dart.
• Too soft front spring, the nose drops, understeer, will not turn in.
• Too stiff front spring, and the front will brake loose over the bumps.
• Too soft rear spring and there will be excessive squat.
• Too stiff rear spring, the car will oversteer on acceleration.
• All springs too stiff and the car looses contact with the road surface in bumpy corners.
• Too stiff shocks, the car will unload abruptly.
• Too soft shocks, the car floats, rolls and oscillates.
• Too much toe out and the inside tire will bite before weight is transferred.
• Too much negative camber and the outside front is overloaded (corner exit understeer).
• Too little negative camber and the full footprint is not being used.
• Unequal front cornerweights and the car will understeer one direction, but not the other.
• Unequal rear cornerweights and the car oversteers in one direction.
  

In subsequent articles, I will get into the specifics of these suspension components, how they work and are interrelated. The goal is to balance the car for smooth weight transfer - how the weight is being transferred, how much and the rate at which it is moving and where.

As always, do one change at a time and record results. Remember quick fixes at the track will not improve overall vehicle performance, and may only be helpful for a few laps.

Again, I'm describing car performance from my point of view behind the wheel of a rear wheel drive formula car designed for road racing. The theory is common to all car designs, and since we are not looking to relocate suspension geometry in this article, keep the chassis design of your vehicle in mind when you are reading this. What will work for you will not necessarily work for another.

I would be interested in hearing from drivers about cars set up for oval tracks, for the drag strip, and front drive cars.

I'll be looking for your feedback, your experiences, and techniques that have worked for you. Respond to the discussion group at

ThunderValleyDiscuss@listbot.com