Would it be ok to run a 120/60/17 tire in the front of my bike? Any positive or downside to doing this?

 

When you change the profile to higher I belive it give the front tire a sharper turn in. Don't quote me on thats just what i think.

 

What year and make? Actually doesn't some of the 636 have a 65 series tire? So then he would be going to a lower profile right?

 

its a 2005. Im pretty sure i have a 65 series on right now so ya, it would be a lower profile. What are the effects to this?

 

A lower profile helps the bike turn in sharper. My husband went with a 60 series also and he actually prefers it now. I used to change tires at Cycle Gear I had to learn about all this kinda stuff here is a quick run down...the first number 120 is the width, the 2nd number is the height and the third number is the rim size. That second number represents the percentage of the width so 60 means it is 60% of the width of the tire (your profile) this directly affects how your bike handles. Always keep your tires properly inflated it really makes a big difference on performance. my 2 pennies.

 

The difference will affect your geometry. Whether that geometry change is for you? kinda depends on your riding style and on how you set up your suspension also. SKG is correct on the tire nomenclature