Hey guys,

Ive read plenty about rear wheel sizes, and was essentially under the impression that both 18" and 19" rear tyres had the same external diameter, and the difference in rim size was accounted for in sidewall hieght, which essentially explains why mx and enduro bikes have there respective rim sizes. 

So, being an enduro rider on a mx bike, i sorted an 18" rear wheel to convert it over. But much to my horror when i picked up my 18 wheel from the dealer the tyre didnt look the same size as a 19. So after getting into the shed, i measured the side wall on both the 18 and 19 (same tyre dunlop 952) they were same!, shoudnt really have been suprised, when both tyres were 110/90 (sort of expected that the 18" should be 110/100?)

where does everyone get these ideas on tyres? ive seen it everywhere?

is it just dunlop who do this? (they only offer 110/90 in either wheel size)


The whole idea of getting the 18 rear wheel was to get a bigger sidewall.......


advice would be greatly appreciated

It's unclear form your post what size the 18" tire in question is.  You also have to be careful how/what you measure for comparison.  Tire sizes are composed of 3 numbers: nominal tire body width when mounted on a specified rim width, aspect ratio, and rim diameter.  Thus, a 110/90x19 is expected to have a tire body (carcass) width of 110mm measured from somewhere, is 90% as tall as it is wide, and fits a 19" rim.  The width number is highly variable because there is no universal standard as to whether this should be from inside to inside, or outside to outside on the tire, for one thing, and the rim width at which the tire was spec'd out may be different from the one it's mounted on by enough to make a pretty big difference.  The result is that often times, two tires marked at the same size might look quite differently.


A 110/90x19 should nominally be 680.6 mm tall ((.9x110)x2+482.6) or  26.79" ((.9x4.33)x2+19).  A 110/90x18 is automatically an inch (25.4mm) shorter because the only difference is the smaller rim diameter.  OTOH, a 110/100x18 should be closer to 677.2mm tall (110x2+457.2, again, not considering the height of the tread), or 26.66" (4.33x2+18).  Only 3mm different.

^ +1

Yup. In a 110/90---110 is the width, 90 is the PERCENTAGE of the width. So a 110/90 on an 18" wheel is TECHNICALLY 1" shorter than the same tire on a 19" wheel. So, when buying tires for an 18" wheel, you must size it according to the TOTAL height that you want to obtain (go with a bigger side wall).

Yes this is what I was saying, It just seemed strange, as they are 'supposed to be' the same overall height, looks like I'll be changing tyre choice unfortunately , metzeller perhaps

Yeah I've never heard that they were "supposed to be" the same overall height. If that were the case then you wouldn't an option to have different sizes

Well you would have the option to have different sizes, the 19 is for mx, smaller side wall means less flex and better handling

The 18 slightly heavier has more sidewall which allows for more deflation, for less flats and more traction

That's the theory anyway

Create an account or sign in to comment

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

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now