Tyre Pressures

Been having a mooch around tyre websites, & noticed something that's
baffled me a bit. Take Pirelli for example; they recommend the Diablo
Corsa III for the MV, with 2.3 bar front & rear. Yet for the same tyre
& size on the Jap 750s (GSX-R, R7 & ZX-7R) they say 2.5 bar front & 2.9
bar rear.

I can't figure out why there'd be such a big difference on the rear for
the MV, bearing in mind the fairly similar weight & power output. Any
ideas?

 

Stupid boy.

 

Jap bikes are ridden by fat(ter) bastards?

 

Wild guess #1: it's lighter/carries its weight further forward than
other comparable bikes;

Wild guess #2: it's more powerful and more likely to run the rear tyre
hot;

Wild guess #2a it's even more of a sports toy than other bikes and
likely to be ridden harder, thus more likely to run the rear tyre hot;

Really Wild guess #3: the rear suspension needs to work with a softer
tyre spring rate for some reason.

 

2a - unlikely imo. 1, 2 & 3 had all crossed my mind (3 because the
standard suspension settings are harder than typical Jap bikes), but it
just seems like too big a difference, even taking all of the above into
account.

 

Different wheel/rim material? Or profile?

Quote from Ducati SS owner's Manual: "To avoid front wheel rim
distorsions when riding on bumpy roads, increase tyre pressure by
0.2-0.3 bar"

Yes, it was _front_ rim distorsion, but it may have to do with different
profiles; the Duc 750 SS should have a 60 profile and the 900 a 70 one
on the same wheel dimension. Several 750 SS owners I know of have had to
have their front rim straightened.

 

That's gender reassignment surgery, right?

 

Me and Bruce, for starters.

 

I suspect it's all about wheel rate. Tyre pressures make a big difference to
what forces the suspension recieve. Same thing as some tyres suiting some
models fine whilst being naff on others - the carcass strength affects the
wheel rate.

IIRC Caterham found several seconds a lap after trying their stock tyre and
wheel combo on a chassis dyno, and getting some tyres that actually suited
the suspension.