I recently put a 70s series tire 207RR Dunlop on the front and wondered the same thing. 65 is stock on the D207 for the ZX6R US Model. Haven't adjusted a thing, not really noticeable. But some guys on Yamaha R6 Messagenet talk about going from 60 to 70 series and have many discussions on adjustment.
when i bought my 6R, it had a 120/70 on the front.... when i purchased my first set of rubber, i got a 120/60 on the front because 120/70 was out of stock on the tyres i wanted. to me, it felt like a HUGE difference, it honestly felt like a different bike. i can get through corners faster now, but i changed tyres when i was still learning to ride, so i'm just becoming a better rider, i don't know if the tyres really had much to do with it.... i know this won't help much, but wanted to share my story.
I moved to 120/70 , in addition dropped my triple clamp down approx. 1/2 inch. Huge difference, broke in my pucks on the second ride. riding sportec M1's/ They are awesome for street use, vs. running on racing compound.
I was thinking about dropping my front end a little. How much can I get by with without running in to stability or interference problems? I have got my preload cranked all the way down to get 1 3/16" sag.
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