Help me understand tire sizes

[endurotuff]

In a 300 cc 2T motorcycle I've seen that tires used are:

140x80 - 18"
120x90 - 18''

What are the differences between them and how do I know which one to use for enduro/woods racing? :ride:

 

[_JOE_]

1st number=width in millimeters

2nd number=aspect ratio(sidewall height as a % of tread width)

3rd number=rim size


Those two tires are similar in overall diameter, however the 140 is wider(some mfg. size tires a bit differently ie. Michelin).

 

[endurotuff]

Thanks Joe! How would I know which to choose from? Depends on terrain type? I know I would't use one of these on a 250F for example.

 

[Tom68]

Don't think anyone uses the 140's, they come std for reg purposes in some countries.

 

[_JOE_]

It's usually a good idea to stick with the stock size. There can be some clearance issues with the chain or swingarm if the tire is too big.

I run a 100/90 on the 250f. I had a 120/80 on my old rm250 (was110 stock) and it got skinned up a bit by the chain. I wouldn't think a 140 would be too happy on a stock mx bike.