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RWDboy
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South Australia
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July 2002

Re: Countering Understeer....???	Mon, 30 December 2002 13:20

I'm not much of a racer, more a bit of a beginner/weak attempt at a rally-driver, but I'm a bit of a cornering performance fanatic, and not all of this is truly technical (I've yet to go through Race Car Vehicle Dynamics), it may help a little. Sounds to me like you asked a bit too much of your tyres. Cars will turn in on wet roads to a certain degreee, but it's much lesser because of the fact that the water acts as a cushion between the rubber and the road, on top of that, the friction co-efficient between water and rubber, is pretty darn low. It's basically just what people call aquaplaning. When a car aquaplanes it's tyres wont get any more rubber back on the surface until either the speed slows down enough that the rate of water dispersion through the tread is enough to allow for contact between the rubber and the road, or the tyres return to an angle that allows for more efficient water dispersion. Most tyes nowadays have circumferential grooves, and other water dispersion tread pattern catch-phrases. However the theory behind the circumferential grove is simple. Firstly it reduces the contact area of the tyre, which means that the same weight is being applied to a smaller area resulting in greater pressure being exerted on the road/water by the tyre and also - more importantly - it is an easy channel for the water to run through rather than having to disperse the water all the way to the outside of the tyre. When you turn the wheel, the circumferential groove is then at an angle to the direction the water comes in, which reduces it's efficiency. The other tread patterns are supposed to help out with this, but there's only so much they can do before they let go, and I think you might know what happens then.... The best thing when a car aquaplanes to all hell, or understeers even slightly in the wet (especially if you find yourself just turning more and more and getting nothing), is to actually reduce the amount of turning you are doing, back off and brake whilst you have some decent longitudinal grip, and then turn again. Booting the car in this circumstance will not make it oversteer, more than likely it'll just reduce your rear-end grip, and make your car slide off the road in a straight line. My personal preference to all of this is to buy some kick arse tyres, because some moron in a car with 300+ bhp at the wheels will crap his dacks around every corner in the wet and be slow as all hell as opposed to a guy in toyota echo or something gutless with good tyres on it. I personally use Bridgestone RE711s, but they are kinda cheap in some respects, and too soft for decent longevity. Bridgestone S0-3s or something like that are good I hear. Any top of the range tyre is good. Anything from a reputable manufacturer. Yokohama A008s, Dunlop LeMans 7000 (or some number like that, can't remember), whatever is expensive. To counter understeer in general, depends on the type of understeer. Terminal understeer like the case above, is best served by trying to get control of the front wheels again. Lifting off the brake if you've locked them up is a good idea, or lessening the amount of steering you are asking the car to do can help so you can back off a bit. My personal technique is left foot braking, works best on front and four wheel drive cars, although it can be done to an extent on rear wheel drives. (This technique won't save terminal understeer, might make it worse, or if you are really sensitive, might help a tiny fraction). When keeping your foot on the accelerator, pull your left foot over and brake a little. Or even lift off the accelerator at the same time if you get better at feeling when the tyres are on their limit. This is a weight distribution trick, but on wet/slippery surfaces you can use it to partially lock up wheels as well. In a front wheel drive you can use it to partially lock the rears to send the rear end around a bit (don't fully lock them though, that'll slow your corner right down as you wrestle the car back), same with four wheel drive. In rear wheel drive you mostly do it to play with the weight, but you can "drift" the car in with left foot or "trail" braking (possibly even with your right foot). This may not seem related, but watch Valentino Rossi on a MotoGP bike when he goes into a corner, he's using the resistance to rotation from the engine to make the rear end kick out a little into a corner, same thing with rear wheel drive, adding a little bit of resistance can make the tyres just step over their limit a little bit without locking, just enough to drift the rear end out and get some good turn-in. Although, none of these techniques are at all useful without practise. It may seem crazy, but the best place to practise is on a dirt road. Not quite as crazily deadly as a soaking wet tarmac road, but it'll let you feel out the limit of the tyres but also what the tyres and the car does when they are on the limit. It's also alot slower, everything on a dirt roads happens slowly. Getting sideways on tarmac requires an incredible amount of speed to break the traction you have on that surface (unless you are being a bit of a show-pony), whereas dirt you can get sideways going 30km/h. Also you can practise recovering from the many brake lock-ups you'll encounter with your first forays into driving on dirt. The only problem is the trees along the sides of the road. A good idea is to try to oversteer through the corners, that way if you do stuff it up, you'll probably just spin to a halt in the middle of the road. If you understeer, you're screwed [Report message to a moderator]

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