Metric to imperial bicycle tyre size

[rcx132]

I bought new tyres for my wife's mountain bike, size is quoted as 37-590 (26x1 3/8). But the tyre diameter is too big to fit on her 26" rims. Have just compared size to a spare 26x2.10 tyre and definitely a size difference. Am I missing something here?

 

[a111r]

That's 'Dutch bike' size, in Imperial, seller may have made a mistake.
Using the ETRTO nomenclature is the most reliable way to get the right size, e.g. 37-590.
Metric and imperial may seem equivalent, 1.5 = 1 1/2 but never are.
Her rims will be 559 (dia. mm)

 

[a111r]

Tyre Sizing Systems

Several different systems of size markings for bicycle tires are in existence. The modern ISO system is not as familiar as it should be, this article explains it.

sheldonbrown.com

 

[CompoSimmonite]

I had similar problem with 20" tyres. It depends on the rim size rather than the tyre size. The old tyre will have the correct sizes marked

 

[mr haynes]

Yes a metric 26 is quite a bit different from an imperial one.
Who said bicycles were simple...

 

[RWD3M]

I bought new tyres for my wife's mountain bike, size is quoted as 37-590 (26x1 3/8). But the tyre diameter is too big to fit on her 26" rims. Have just compared size to a spare 26x2.10 tyre and definitely a size difference. Am I missing something here?

Now, I'm no expert on bicycle tyres, but 26" is, give or take a gnat's, 660mm and 1 3/8", to the same level of accuracy, is 35mm. Now if I understand what you have written (and there no gaurantee that I have!) then the tyres you have bought are 26" in diameter, but the size quoted (37-590) appears to be a little over 23". If the rims are definitely 26" then I suggest you might need a 37 - 660 tyre (in metric speak)

Hope you get what you need

Richard,

Edit:

Ooh, I've just found this:

A guide to cycle tyre sizes | Cycling UK

26×1.5, 26×1½ , 700×25C – trying to work out what tyre sizes your cycle needs can be confusing. Richard Hallett, Cycle magazine technical editor, explains what all those numbers mean so you’ll always be able to find the right tyres

www.cyclinguk.org

Makes no sense to me but maybe it'll help you?

 

[grim_d]

Yes a metric 26 is quite a bit different from an imperial one.
Who said bicycles were simple...

It's not the bicycles but rather those that ride them.

 

[rcx132]

Yeah I still don't get it. The article @RWD3M and @a111r posted says to use the ISO sizing to avoid confusion. The shop couldn't explain it either, said something about these tyres being "very old imperial" (an imperial that came before imperial?). Sending them back, they said they'll send me other 26" tyres that this time will fit on the 26" rims.

 

[a111r]

Yes it is confusing. It took a similar incorrect purchase for me to look into it. Car tyres sizes are so straightforward, comparatively!

The old 27" wheel size (fitted to racers up to the '80s) is another interesting one. There's only a few mm difference in diameter to the 700c size that took over.
So a tyre size error here means either they can blow off the rim, or they are so tight that the tube gets damaged, either on fitting or the next time the tyre is removed.

Then there's bottom brackets. Another area in which to fall foul easily.

 

[Sbc]

Schwalbe do label there tyres odd sometimes but 26 1 3/8 is a traditional tyre size and completely different from a modern 26". A 26 1 3/8 will be in a more classic bike with slick Town style tyres. A normal 26" is way more common and have massive variety of tread patterns.
The ETRTO size is the only real way if you unsure. The ETRTO size is TIRE WIDTH in mm - RIM DIAMETER in mm (from where the tyre seats) ish.

So all standard 26" mountain bikes will have be xx-559 ETRTO wheel. So a 26x2.10 will be 54-559. Or a slimmer 26x1.75 will be 47-559.