tire sizing inches to mm

Brad William /

Fitment charts list a 2.75-17 as equivalent to a 80/90-17. Sounds about right.

But I took a sec to do the math and 80mm is 3.15in. 70mm almost exactly 2.75in. ??

80/80 is 80mm wide and 80percent of 80mm tall. 80mm wide and 80mm tall would be 80/100.

When a tire is marketed in inches 2.75 indicates 2.75 inches wide and the profile is never specified so we can only guess how tall the tire is. correct so far?

Can someone find me a better explanation to this than the ones I've found so far? (edited)

Re: tire sizing inches to mm

Brad William /

Often, older motorcycle tires have a Standard Inch System. These tires do not have an aspect ratio designation marking. The cross-section tire height is 100% of the width. An inch-sized tire is bias-ply construction and is not belted. However, these are being phased out and are not used on newer motorcycles.

That's from Denniskirk.com.

Dennis Kirk does list the inch/mm crossover more correctly.

Re: tire sizing inches to mm

I have some Michelin pilots that are 70/90, 80/90, and 90/80 all 17" and the 70/90's are pretty small, close to some 2.5" Hutchison tires I have.

The 80/90's are wider than the 2.5" tires and a bit taller and the 90/80's are massive. Unmounted they are around 3.5-3.75" wide and much taller than the 2.5" tires.

Hope this helps.

Re: tire sizing inches to mm

Dirty30 Dillon /


Meant for truck tires, but input some Moto sizes and give you an imperial measurement set

Re: tire sizing inches to mm

I was gonna post that Tacoma world link, I have it favorited. I use it all the time like, what tires can I put on a 10" wheel to match the same OD as the 12 inch stickers on an arrow. Or whatever.

Re: tire sizing inches to mm

There is no real direct conversion because the sizes do not always match up to an existing size, so you basically have to go with what would fit/not fit with a close size so you do not have interference from forx, frame, trailing arm, shocks, fenders or chain(s). This is my "closeness" chart with sizes that actually exist (though some sizes are hard to find) and you need some goodly wise rims for the 80 ratio.

2.25=70/90 or 80/80

2.50=80/90 or 80/80

2.75=80/90 or 90/80

3.00=90/90 or 100/80

3.25=90/90 or 100/80

3.50=100/90 or 110/80

4.00=110/90 or 120/80

Re: tire sizing inches to mm

The other handy thing on the Tacoma calculator is how the tire size change or even a wheel size changes final drive ratio

Re: tire sizing inches to mm

Brad William /

Ive been running Michelin m29s 2.75-17 on two of my puchs for years. Ive loved them. But they're no longer available. Id like to stay as close to this profile as possible and there are a number of brands that offer options in mm sizes. Thats why I'm trying to get to the bottom of this. Guess I'll just order Michelin Pilot Streets in 2.75-17 and hope I love them as much as the m29s.

Jesse do you like the pilot streets? (edited)

Re: tire sizing inches to mm

Too bad the m29 are discontinued. I thought I found some but the scooter shop in Florida that listed them in stock hadn't updated their website for a very long time.

I haven't run the pilots yet but they look and feel solid.

If I ever get around to finishing the new bike I can comment on the ride quality.

They are supposed to last a long time and they are cheaper than good moped tires at around $30 each.

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