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Re: [ST] Backing it in (was ABS)



On 11 Oct 2005, at 20:46, Nathan Maher wrote:

>  how exactly it serves to benefit the rider in terms of lap times

It can (or should) make laptimes faster, but tyre wear goes up.

The reason it is useful is to do with cornering forces.  To get  
around a corner a body needs to find a way of providing enough  
centrepetal force to stop it carrying on in straight line (Newton  
style).  The amount of force needed depends upon the weight of the  
body (i.e. it is harder work to turn a supertanker than a bike) and  
its speed (the faster you want to turn, the greater the force you  
apply).  One way of doing this on a bike is to use a combination of  
gravity and lean angle, but for this to work it relies on the tyres  
to provide the pivot point for this system to work.  Therefore the  
fastest you can go around a corner depends upon the maximum grip the  
tyre / road contact can give you.  But it is not the only way -  
another is to angle the bike relative to the line of the corner and  
provide some or all of the necessary cornering force from the drive  
off the back wheel.  This is particularly important where the road /  
tyre grip is low (think how bikes go round corners in speedway).

In the MotoGP context, the tyres are really grippy, and lean angle is  
sufficient to provide cornering forces for most people most of the  
time.  Spinning up the rear tyre (if done properly) is a way to  
increase the available cornering force above that available from  
simple lean angle - with more force, and no change in bike weight,  
cornering speed can be increased and (in theory) lap times reduced.   
As you point out, there is a penalty to pay in form of increased tyre  
wear - so presumably the best MotoGP riders use this extra speed  
thoughtfully etc.

Best regards

Gavin Lawrie
ST'03
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