Re: [ST] after 7 months, a bunch of stuff

[kwh@xxxxxxxxxxxxxxxxxxx (Ken Haylock)]

Tyre profiles front-to-rear are weird science. I put the old BT56, as fitted 
stock to Fireblades and suchlike, on my old VFR-750FL once and then 
convinced myself by examination of the profile that I'd never be able to use 
all the front because I'd run out of rear long before I ever got there and 
crash. Indeed, the first time I took that bike on a track day I 'confirmed' 
this theory to myself, having burred the rear up to the edge whilst still 
leaving a nice wide chicken-strip on the front. 

A couple of years or so later a club-racer mate of mine turned up at a 
track-day I was at on his incredibly sexy Ducati 748R road-bike, with boring 
old BT56 tyres mounted front and rear and exhibiting the same potential 
problem, I assumed. Except that by the time he'd finished razzing (and he 
was seriously flying) the Ducati round the track, the front tyre was 
feathered right up to and beyond the edge, which defied all logic. The 
tortured rubber was just over the edge of the front tyre, but at the rear it 
was hanging right over the edge in big burrs all round, most impressively. 
It seems that three factors were at work...

1. The tyre manufacturers know that if you are going to lose an end you want 
it to be the rear, so that make sure you lean off the edge of the rear tyre 
first.

2. The rear tyre is wider and deforms more under weight, cornering and 
accelerative loads while you are cranked over so that whilst if it was cast 
in ferro-concrete you'd be off the edge already, in fact it just squishes 
out a bit.

3. My mate Nigel is a complete animal.  

Fast forward another couple of years to me on the same track on my 
BT010-shod TT600 this summer, after a couple of days of California Superbike 
School, knee down cornering and WFO throttle action. Tyre profiles are 
fairly similar to those of the old BT56, but this time by the end I'd 
managed to mullah the front tyre right to the very edge on the right hand 
side, and the rear was feathered past the edge. I've got a big digital 
picture taken of me mid-corner on the only left-hander on the track (a 
smaller version is on the front page of my website) with my knee hovering 
above the surface, but a quick look at the tyre contact patches shows how 
much the rear deforms mid-corner, and shows how such things happen.

Oh, and fitting an oversize rear to a rim simply results in the profile 
being too tall which will, I'm led to believe, both knacker the handling and 
result in a /smaller/ rear contact patch, less grip etc...


- - --

Ken Haylock - Sprint ST + TT600 - MAG Life Member #93160

- --------------------- http://www.cix.co.uk/~kwh ------------------------
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