I have a tire that reads “700 x 32c / 32 – 622“ which according to this chart should equal 29", but when I measure with a tape measure it's exactly 27.5".
in a calculator 27.5" converts to about 700mm and 29" to 736mm so is this chart just wrong? does 700c not mean 700mm?
is there a road tire in existence that actually measures 29"?
any help is appreciated and I'm sorry if this question has been asked before. if it has, I couldn't find it.
by abso_lut
8 Comments
622 is mm. 700c is with tire I think.
For mtb, add 2 in to rim diameter to get rim size.
If you have a week, i can explain the absolutely absurd inch sizing stuff.
Short version: 28, 29 and 700 fit the same rims. 27″ is bigger than 28 and 29 and 27.5 is smaller than all.
There are at least 5 different non-interchangable tires labeled as 26 inch.
The solution is to ignore the inch stuff and use the metric ISO sizing which is labed on all tires. 622-50 is a tire that fits any 28/29/700 rim. That is the 622 part. The 50 is the width of tire in mm which equates to 2″
The first and second columns are how tires are marketed. Based on a rough approximation of the tire diameter when inflated.
The third is the tire seat on the rim in mm. That’s the one which absolutely has to match when getting new tires.
https://www.sheldonbrown.com/tire-sizing.html
The problem is that wheels are measured assuming the outer diameter with a tyre so a 622mm wheel with a skinny road tyre is 700mm(ish) across, with a hybrid tyre could be 28″ (usually only schwalbe) or with a MTB tyre 29″(ish)
As above, using all metric etrto sizes is best to be sure.
If you want to be confused look at including older imperial sizing with fractions – all the tyre sizes had the same nominal diameter but a thicker tyre used a slightly smaller wheel as a result leading to the multiple 26″ and similar
>but when I measure with a tape measure it’s exactly 27.5″.
That’s your first mistake. Physically measuring tires will never give you the correct info. Always go with what is printed on the tire/rim
For every tire/rim, the ISO is the most important number
ISO is also called bead seat diameter and the true measure of a tire’s diameter and what tires are compatible with what wheels. You also have width of tire and rim, but there is some tolerance for what widths any rim can take.
Mtb/inch and French sizing are essentially marketing terms. They aren’t real measurements of anything.
29 sizing nomenclature came from Gary fisher, this gist of the story is, they were experimenting making mountain bikes and used road 700c wheels they had available, they got mtb tyres made up and pumped them up to a fairly high pressure and measured the outer diameter which was 28’ something so rounded it up to 29.
The measurements that actually matter are the ETRTO numbers, ie 622mm