120/60 and 120/70 front tires, What's the difference?

[BenDover]

Ok, I'm in need of new tires and I was planning on going with the Pirelli Diablos because of the buy one rear and get one 120/70R17 front.

Well, I just looked at my bike and my front tire is a 120/60. So, how would it effect it putting a 120/70 on there?

Or, should I just stick with the 120/60?

:cry: :cry: I want a free tire!!! :cry: :cry:

[Anonymous]

70 will be a little bit bigger. The 60 will turn a bit quicker. Up to you, for a street bike it probably doesn't matter anyway...

[BenDover]

That number is the measurement of the sidewall, or what?

Do you think that you would really be able to tell alot of difference on the turn in? at the track vs in the canyons?

[Tech Ninja]

That difference amounts to an half an inch difference in height as well, if I did the math right.

120/70 = 84mm = 3.307 inch sidewall
120/60 = 72mm = 2.835 inch sidewall

Not much I know, but for a short inseam rider like me, every little bit counts :D

[BenDover]

:o That is quite a bit of difference in sidwall.

[Anonymous]

In case you were wondering, to calculate actual tire size...

120/70R17

120 = section width of tire. This tire is 120mm wide.
70 = aspect ratio. 70% of the section width is the height of the tire.
17 = rim diameter.

First, let's convert everything to the same units. millimeters to inches will be best for this. mm/25.4 = inches, so 120/25.4 = 4.7244 inches section width.

So... (4.7244 * 0.7) = height (remember, width x percentage) of tire, which is 3.3071 in. high.

Now we add rim diameter, 17 inches, plus 2xsec-height. 17+(3.3071*2)=23.6142 inches.

To do this for your 60-aspect tire, we do the same math over again...

(((120/25.4)*0.6)*2)+17) = 22.6692 inches.

So, the total difference in tire height is 0.945 inches, or half of that (about 1/2") is how much higher the bike will sit with a 70 vs a 60.

This should explain the math to you a little better so you can see how a given tire may affect your bike. Remember, raising the front end has a slowing effect on turning, by increasing the rake angle of the forks to the pavement. You can counteract this by simply raising the forks in the triple clamps (i.e. "dropping the forks"), which then steepens that angle again. This is a trick used by racers to quicken handling; just be aware that if you go past the factory angle, the front suspension will be more susceptible to head shake and tank slappers.

[KooLaid]

Not really much of difference. Average street riders wont even notice a difference. It's all in your head more than likely if you do. Get the free tire. If it truely is noticable, give it a week or two of riding first to see it's mental, then raise the legs in the triple clamps a few millimeters.