I'm getting ready to order new shoes for the SS and noticed the existing front tire is a 120/60-17 but the manual calls for a 120/70-17. Will I notice a difference between the two?
Same goes for the rear. It has the recommended 170/60-17 now but some people say go with a 180/55.
???
Definitely go for the 120/70 up front. In case ride height was adjusted for the 120/60 you will want to check that. Won't be much of a difference anyway. Go for the 180/55 in the back.
If you have a 5.5" rear wheel then you want a 180 rear. If you have a 4.5" then stick with a 170.
120/70 is the way to go in the front.
the stock 96 900SS was a 5.5" rear
The higher aspect ratio tires (larger "ab" number in the xyz/ab-...) will on sport tires tend to have more crown angle, part of how they get to the higher aspect ratio, which means when fitted to the right wheel width that the full contact patch is maintained to a greater lean angle (i.e. the when your leaned far enough to draw rubber snot off the edge of the tire angle is leaned closer to the ground).
now, at less than extreme lean angles, the higher tread width, or "xyz" number, on the same width rim, will give you a larger contact patch.
Another note - so, 180/55-17 is typical (and stock) for a 5.5" Ducati rear, but if you went 180/60-17, you would do two things:
1) slightly increase the degrees radius of the crown, allowing full traction to a slightly higher lean angle
2) raise the rear slightly, resulting in a less stable feel on the controls and quicker turn in.
Likewise, on the front the stability thing works backwards, so going from your current front 120/60-17 to a 120/70-17 will result in a more stable bike with full traction on the front to a higher lean angle.
Higher wheel width essentially reduces the extent angles of the tire's crown, so this is where we talk about a rear 4.5" wheel with a 160/60-17 tire having the same overall diameter and full contact patch lean angle as a 180/55-17 tire on a 5.5" wheel... However the 180/55-17 tire on the 5.5" will have a larger contact patch at *any* lean angle, and if we were to put the 160/60-17 tire on a 5.5" wheel the full contact patch lean angle would be greatly reduced...
So, quick answer, I believe spec for your bike is 180/55-17 for the rear and 120/70-17 for the front, and going from the current 120/60-17 on the front to a 120/70-17 will gain you a little bit of both stability and traction, but deviate wisely from the spec...
And as Howie mentions, double check the chassis geometry for the front end profile change (basically, is it comfortably unstable now for your taste? If so, when going to the 120/70-17 on the front, your front end will raise slightly making the bike more stable, so raise the rear a smidge to maintain the desired level of instability, to taste of course ;D )
[beer]
Excellent.
Just ordered Dunlop Q2's in 120/70-17 and 180/55-17. Never been a Dunlop fan but the reviews and price are just too good to ignore.
Thanks all !