Jump to content
Sign in to follow this  

80 - 90

Recommended Posts

What's the differences I would experience in corner handling between a 120/80 and a 120/90 ?

(XR650L 18" x 2.5" rear wheel)

I swear after this I won't ask another tire question till next week.... (j/k)

xr650L street use...

Being newer to bikes than alot of you, it's just hard for me to judge the profile differences of the tire, and what advantages or disadvantages. I know how well the 120/90 works, I just can't figure out what the pros/cons would be with an 80 vs. a 90.

I probably should have just asked my question that way the first time. Sorry to be repetative, I just want to learn these things...

I tried the dual-sport section and someone posted tonight:

"A dirtbike on the street permanently? I'd go buy a streetbike."

Now some of the guys like you all that have been around awhile, did respond like some of you did. And I am definitly going with the 120. (Thank you all for your suggestions !!) I just don't know what is more beneficial.. the 80 profile or the 90? (120/80 vs 120/90)

Thanks for your patience.. Bri :cry:

Share this post


Link to post
Share on other sites

Hi there,

I will try to explain what I know as easily as I know how.

Tire size designation go's like this:

120/70/17

(or in your case: 120/80/18 or 120/90/18)

The "120" is the "sectional width" (aproximately 120mm for a 120 tire)

The "80" or "90" is the "aspect ratio" of the tire which is a measure of the angle of the profile when viewed from the cross section of the tire, properly inflated, mounted on a rim size (width) designed for that tire size.

Now, there really is no correct answer to your question, unless you are MAINLY concerned about keeping within the (tire) manufacturers guidelines as they pertain to safety and liability issues etc.

HOWEVER, these couple things can be taken into account when deciding for yourself which is right or better for you:

If you are "shoe horning" a wider tire (90 series) on a narrower rim you will be DECREASING the aspect ratio, which means you are forcing the tire to have a shorter height, which makes the contact patch slightly larger, but will also make the "turn in" portion of any corner feel sluggish and inconsistent, with a 80 series tire you are starting with a steeper angle which means the tire is more "pointy" in the middle (when viewed from the cross section) for the correct rim width so by squeezing it (the tire) onto a narrower rim you are not growing the contact patch as much as you would a 90 series tire so the steering will feel quicker when the bike is verticle (as in the initial "turn in").

Now since this tire is going to be your rear tire, the steering sluggishness I describe will be less noticable than if it were a front tire, the bigger contact patch may be the mark you are shooting for and would be a better choice, it will also look slightly wider than the 80 series for example.

The biggest issue is the 2.5" width of the rim, that is small for a rear rim with a street tire on it.

P.S.

The aspect ratio is not a measured using the sectional width (the 120 part) alone. It MUST include the bead height as well which is usually around 20mm on most tires.

Think of a tires dimensions as a triangle when viwed from the cross section, the "120" is the width of the base of the triangle and the "80 or 90" is either of the remaining sides ANGLE and NOT height HOWEVER you increase or decrease the angle by increasing or decreasing the height of the centermost portion of the tire accordingly (when mounted on a rim designed for the tire and having the tire properly inflated).

I know that was long winded, but I hope it gives you an idea of how these numbers are relevant.

Dauv

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×