I'm going to get some Diablo Stradas for my 600 F3. I want to put a 170 on the back do I need to go up in the front or keep it 120?

 

Stock is 160 i take it (wrong forum btw)? you shouldn't have a need to change the front.

any reason you want to bump your tire size?

 

Yes, stock is 160 and we've been here before. Bigger tire on a smaller wheel only makes the tire taller. The wheel will still be the same size so the tire will not be wider.

 

soooo many people want to go bigger tires ...dumbest thing you can do, screws up your handling ..because the bike wasnt designed for the bigger tire

 

also consider that the larger tires weigh more so you'll lose accleration with larger tires

 

A wider than stock tire (for the rim) will cause the tire to lose its designed profile because it gets pinched in a tad too much. You might have ok contact when leaned way over, but I wouldnt
feel confident on them.