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Cornering, fast

"In recent messages to the Mini list there have been a number of messages advocating the spinning of wheels as the fastest or the safest way to go round a corner or the best way to get of an understeer problem. Well I am sorry to be so harsh but you are WRONG.

There is something called the circle (it's not actually a circle more of an ellipse) of friction, a commonly heard term within racing books and training schools and the world of vehicle modelling. What this means is there is a limit to the amount of force that can be generated by the tyre in the ground plain.

If we take the pythagorus (you remember the length of the longest side of a right angled triangle is equal to the square root of the squares of the other two sides c^2 = a^2+b^2) of the two basic forces generated it will be within this circle.

What are these two basic forces of which I speak:

Right so what does this mean for the wheel spinners of this world by spinning the wheel you are trying to develop the maximum longitudinal force so therefore using the circle of friction rule, you have to lose out some where and you lose out due to a drop in lateral force (why you have to apply more lock).

But the story gets worse the amount of force generated by the tyre is non-linear in proportion to slip.

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          |       __
          |      /  \ <The best place to be at the top of this peak
          |     /    \-------------
    Force |    /                   \_____________
          |   /        Wheel spin way over there>
          |  /
          | /


Therefore as you can see from the graph (hopefully) by spinning the wheels or by braking to hard so they lock up or turning the wheels at to tight an angle so they slide you are generating far less force than your tyres are capable of therefore losing out big time.

So what is the fastest way to drive? The fastest way to drive is to carefully balance the tyre at the very top of the peak, not especially easy but it is possible to feel it going over through the steering or notice it through a reduction +/- acceleration (- is braking) so you drive by carefully cycling back and forth over the peak top there by being continuously aware of its level. This is what ABS and Traction control do and why they have both been banned from most race series.

Mind you having said all this wheel spin and skidding is FUN I can't deny that. But those of you who are racers would do well to keep this in mind next time you are chasing down Ian Curley and Martin Bell, both if you watch them very good at keeping their tyres just at that optimum balance point.

Best of luck all of you in your crusades to go as fast as you can.

READ THIS BIT IF NOTHING ELSE: the best way to get out of an Understeer situation according to the laws of physics is LIFT OFF!!! (you dedicate more of your circle of friction to turning), and reduce the amount of lock until the tyre stops slipping then carefully begin to re-apply, keeping in mind the non-linear profile above. (I think this is called cadence steering in motorcycle racing)


Ps sorry to be so brief you could write several books on the behaviour of the tyre and many people have. Race Car Dynamics, Pub; SAE is a good place to start. a snip at 75, cheaper in America."

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