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Hi 200 & Bob,
Quote 200; Going to a larger (stiffer) front bar reduces understeer. A larger rear bar reduces oversteer.
Quote Bob; Generally adding on a rear bar or stiffening an existing bar will increase understeer.
If the references cited above by Kenny are valid, & I think they are, increasing a front bar will increase understeer. Likewise, adding a rear bar or stiffening one, will increase oversteer.
D
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That's correct, Larger front bars on rear wheel drive cars will induce/create more understeer. An understeering car is tight and easy to control, an oversteering car is loose and on the edge of out of control. Understeer is deemed safer than oversteer because it is easier to control and correct through driver control. When understeering you turn the wheel but the car keeps going staight. Oversteer is when the rear of the car no longer follows the front but comes around on its own. Oversteer is considered less safe because it is very easy to lose control of the car when oversteering. If you lose control while oversteering, the driver becomes a passenger and a whole lot of physics start happening. The 911 problem, before they engineered it out, was "snap oversteer", sometimes referred to as 'exiting a corner backwards'. Though this is primarily a 911 (or other rear engined cars) trait and has to do a lot with weight transfer from lifting off the throttle too quickly while deep in a corner. 911 drivers often call it "chickening out". Spend some time at a PCA event and you will see plenty of rookie 911 drivers doing just that. /ubbthreads/images/graemlins/grin.gif
Cars are designed to understeer from the factory as a safety measure. Sway bars/Anti-roll bars increase roll stiffness. Anything you do to increase rear roll stiffness will reduce the designed in understeer. This includes adding rear sway bars but can also be done by stiffening the rear springs, reducing chassis/body flex in the rear (as in rear strut bars etc...) or increasing rear axle placement and control (panhard bars etc...).
When understeer and oversteer balance out you achieve a neutral handling car. Which can be really fun but can also be a nightmare under common street driving conditions, especially if roads are wet. Race cars are rarely set up absolutely neutral. The particular race course determines the amount of understeer/oversteer in the set up and is why they try to have as much adjustability as possible.
Front wheel drive cars have strong understeer characteristics. So strong that the factory often places equal size front and rear bars or slightly larger rear bars on the car to reduce the understeer by inducing a small level of understeer. They will still be understeer biased but much more driveable.
Tony, on your GRM car, since you have already altered so much of it you can only really start by guessing. For Auto-Xing you might think that an oversteering car would help you rotate around the cones better, which it would, but could make chicanes a nightmare. Ideally you would want a more neutral car. With the lighter car and the increased torque you should be able to induce oversteer with your right foot on the vertical pedal and steer the rear of the car with the throttle (throttle steering /ubbthreads/images/graemlins/thumbsup.gif). If you have ever heard someone refer to balancing the car with the throttle, it means they can transiton the car from understeer to oversteer and back simply through throttle control.
Tire Pressure is another large contributing control factor in this and something you should test as well. Variances as little as a pound or two can make all the difference in fastest time of the day or losing control in a corner. Some auto-Xers will gaurd their tire pressures like top secret knowledge.
If you have time, try taking the car to some local auto-X events. By practicing on competitive courses you can learn so much more and you will probably get plenty of advice from more experienced auto-Xers. You will only really find the answer to your question through application. Auto-Xing is a different enough form of motorsport that circle track and road course set ups might give you a good starting point but will be far from ideal for the short low speed coned course of auto-X.
Also, keep in mind that ulitmate Auto-X set ups are not ideal for 1/4 mile times either.
BTW, I think it's awesome that your doing this and allowing us to live vicariously through your exploits. Keep it up and keep us informed. /ubbthreads/images/graemlins/driving.gif
If anyone is wondering, my knowledge on the subject comes from much research, some practical application and instruction from professional racing drivers, mechanics and engineers.
/ubbthreads/images/graemlins/cheers.gif