09-04-2005, 11:43 AM
A local racer who routinely gets podium finishes on an 05 636 set up my suspension for me at my last trackday. He asked what I'd done already and I mentioned that I'd raised the forks 5mm up in the tubes to compensate from going from a 120/65 to a 120/70 front tire. He mentioned that he put a 5mm shim on the rear shock (that's like raising the forks 13-15mm) and runs dunlop 195/50 slicks. The slick lowers the rear by 1.5mm making the combined geometry change 5mm + 15mm - 4.5mm = 15.5mm. So this guy effectively has his forks raised 15.5mm from factory default geometry.
I didn't get a chance to ask him why make such a severe change? I was too busy enjoying my new setup. My 636 corners on rails w/ Power Race tires and the setup work he did. Anyone here know exactly what the benefit of such a huge geometry change would be? I heard you don't want to go that far since the bike would get squirrely when hard on the gas. Not sure what the effect would be in a turn. Maybe it lets you carry more corner speed w/ lower risk of tucking the front?
09-04-2005, 06:34 PM
Because of the 106mm of trail slowing the steering, people load the front to speed the steering. This setup will chatter a bit under braking. I think the better option (but not SS-legal) is to reduce the offset at the triple - but Attack, for example, doesn't list a reduced-offset triple (or at least not yet).
Now, I don't pretend to be an expert, and I don't ride hard enough to chatter the front (and my geometry is a whole lot less steep - I can muscle the front around pretty well), but one of the local guys is having fits with the front of his 636.
The other thing - don't use Dunlops if you're in this extreme a geometry - try Michelins, is a word floating around the pits... I run Michelin DOTs, but again, my geometry is not steep.
edit - I reread your post, and you're using PR's too.
09-04-2005, 07:05 PM
Yeah, dunlop is getting pretty upset with track/raceday sales seeing that almost EVERYBODY runs power races now.
09-04-2005, 07:18 PM
Generally speaking racers as a whole want a bike to turn so the geometry changes they perform are focused as such even though they know the stability will be sacrificed.