# Tyre and Inner tube sizing - confused!



## Lambchop (17 Jun 2009)

Hi guys,
Could someone please clarify as to what exactly the sizing means on tires and inner tubes?

I have 27" wheels on my road bike, just purchased some new tires which are 23-622 or 700x23c - what do those numbers mean?

The inner tubes I have are 27x3/4-1 or 700x18c-25c - are these the right ones and what do the numbers mean again?!

Many thanks.


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## Will1985 (17 Jun 2009)

Don't worry - lots of confusing numbers but you have the right stuff. 622 and 700 are basically synonymous with a 27" wheel.


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## garrilla (17 Jun 2009)

These are the important numbers for you...

27inch = 700mm

The tyre is 700 x with 23mm width for a 'c' (crotchet type) rim

The inner tube will fit a tyre 700 x anything between 18mm to 25mm (after 25mm, its likely to be a bit stretched)


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## Lambchop (17 Jun 2009)

Thanks to you both for clearing that up for me! Can't think why I didn't realise 27" = 700mm - doh!


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## Lambchop (17 Jun 2009)

garrilla said:


> These are the important numbers for you...
> 
> 27inch = 700mm
> 
> ...



Sorry but what is a crotchet type rim?


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## garrilla (17 Jun 2009)

Its the standard type, there is a slight hook on the inside of the rim to keep the tyre on. Unless you have different types of wheels you will have 'C' as a defacto

Mostly its irrelevant, its just saying how the tyre is kept in-place.


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## HJ (17 Jun 2009)

For all you ever wanted to know about tyre size and more, consult Sheldon Brown (RIP)...


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## threefingerjoe (18 Jun 2009)

are you SURE that your rims are 27"? That is a different size. A 700c is 622mm and a 27" is 630mm. A 700 or 622, also called a 28", or in mountain bike terms, a "29er" is too SMALL to fit on a 27" rim. How old is that bike, that it has 27" rims? Tubes, however, will fit. They are often marked for both the old fashioned 27" size, and the current 700c or 622.


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