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Older Rim and Tyre Size Compatibility

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Older Rim and Tyre Size Compatibility

Old 02-27-13, 01:06 AM
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umogem
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Older Rim and Tyre Size Compatibility

Hey everyone

Im very new to the cycling side of life, so you can assume i know nothing. I have found this pretty old road bike lying around which i thought i might try get going. First port of call is the tyres, they have written on them 27 x 1 1/4. Now ive tried reading up on this and most things come up with something about 700c and things like that and ive just assumed mine wont fit those. But am i right in saying 27 is the rim size in inches? and the other number is width? and if so can i use any different width tyre (eg: 1 3/8 or 1)? And is there any other different named tyre that would fit?

Any help would be appreciated. Thanks heaps.

Ben
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Old 02-27-13, 01:23 AM
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27" is the size.

You can use 27 x 1 1/8 in some cases, typically 27 x 1 1/4, and 27 x 1 3/8 in some cases. If you are not sure, have and LBS test the 1/8 and 3/8 ones for you.

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Old 02-27-13, 01:34 AM
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Current system adds metric numbers; 27" is 630, the bead seat diameter..
an agreement between rim and tire makers ... so things fit.

700c is 622
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Old 02-27-13, 01:55 AM
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Originally Posted by umogem View Post
.. I have found this pretty old road bike lying around which i thought i might try get going. First port of call is the tyres,
A must-read for those facing a tire conundrum:https://sheldonbrown.com/tire-sizing.html

Originally Posted by umogem View Post
....they have written on them 27 x 1 1/4. Now ive tried reading up on this and most things come up with something about 700c and things like that and ive just assumed mine wont fit those.
Correct. If we translate into the less confusing ETRTO standard of tire sizing, a 27"-something road bike wheel/tire will usually have a bead seat diameter(where the tire and rim begin to overlap) of 630 mm, while a 700C-something wheel/tire will have a bead seat diameter of 622 mm. These don't mix well, if at all.
And just to keep us on our toes, the industry is now beginning to launch the 27" MTB standard, which is another beast entirely.

Originally Posted by umogem View Post
.. But am i right in saying 27 is the rim size in inches?
No.
27" is the kinda-sorta, approximate, once-upon-a-time-relevant outside, or effective diameter of the tire when mounted and inflated on the rim - which is the main reason why this is such a silly sizing system.
They started with one tire size, matched to one tire, which resulted in one outside diameter of the finished wheel. Then someone said "hey, I want to fit a narrower tire to the same rim." Now the original reference to outside diameter is shot, as a narrower tire makes a smaller overall wheel, but it's kept b/c it defines the rim size, in a bass-ackwards way.

700C is based on the same principle.

Originally Posted by umogem View Post
.. and the other number is width?
Kinda-sorta, but yeah.
First there's a lot of dishonesty among makers, and if you were to press it flat and measure across you'd see plenty of differences for the same given size. Not only differing among makers, but also differing between models from the same maker.

Then there's the fact that tires are round-ish when inflated, and rim with will affect the final result.

Originally Posted by umogem View Post
.. and if so can i use any different width tyre (eg: 1 3/8 or 1)?
Depends on clearance of frame and fork, and to a lesser degree on the internal width of your rim. 27" road bikes usually are roomier than modern bikes, so you're probably OK to go up a notch. But have a look first at how much air you have between tire and fork crown, tire and brake bridge, tire and chain stays by the bottom bracket.
You may also dig up the Sheldon Brown article on tire widths, check that you're not going crazily out of spec - unlikely for a 27" but who knows.

Originally Posted by umogem View Post
...And is there any other different named tyre that would fit?
Any tire with a 630 ETRTO is likely to be possible to fit to your rim, width around 32 mm should work. Going bigger, you have to judge clearance first. Smaller, consider your rim with. It's not only width you're changing, but also height. A narrow tire on a wide rim will give a really low air chamber and high risk for snakebite punctures.

Last edited by dabac; 02-27-13 at 01:59 AM.
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Old 02-27-13, 03:28 AM
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Thanks heaps for all your answers. So just to make sure i should stick close to 1 1/4 width but might get away with 1 1/8 or 1 3/8?
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Old 02-27-13, 04:58 AM
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Hi,

You say it is a "road" bike, and that nowadays means a very specific
type of bike that usually has limited clearance for the tyres and
mudguards (if they are possible at all).

If its a "roadster" then it will have plenty of room for tyres and mudguards,
and your best best is probably the fattest road tyres that will easily fit.

rgds, sreten.
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Old 02-27-13, 05:04 AM
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Originally Posted by umogem View Post
Thanks heaps for all your answers. So just to make sure i should stick close to 1 1/4 width but might get away with 1 1/8 or 1 3/8?
Yepp !!
Search the internet for a better selection of 27", than most bike stores would have .
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Old 02-27-13, 05:42 AM
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dabac
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Originally Posted by umogem View Post
Thanks heaps for all your answers. So just to make sure i should stick close to 1 1/4 width but might get away with 1 1/8 or 1 3/8?
w/o seeing your frame/fork, with a reference wheel/tire in place, it's all assumptions. Well-based ones, but still assumptions.
1 1/8" is narrower than 1 1/4" so it will fit. 1 3/8 is wider by 1/8", or roughly 3 mm, and will most likely fit. If you have a pencil's worth of air between tire and fork/frame with your 1 1/4", an 1 3/8" will fit.
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Old 02-27-13, 06:47 AM
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"If you have a pencil's worth of air between tire and fork/frame... "

Check all around for clearance, including under the brakes. I have a bike where the front derailleur mechanism is the tight spot for the rear tire.
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Old 02-27-13, 07:13 AM
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You should have no problem finding that tire size on the Internet. Below is just one example:

Kenda K35 27x1 1/4 Inch Tire (ISO 32-630), ~13.00 USD.

https://www.biketiresdirect.com/produ...FQeznQodrmUA6w

And here are a couple of bike maintenance and repair links:

https://www.parktool.com/blog/repair-help

https://sheldonbrown.com/repair/index.html

Welcome to the Bike Forums and good luck with your restoration!
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Old 02-27-13, 07:43 AM
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Check your tubes and rim strips for condition before you order tires; old-style rubber rim strips may be hardened or cracked so you may as well get everything you need. Many folks swear by Velox tape; I like Continental Easy Tape myself; the thin, slick plastic helps when mounting tight-fitting tires. The 700c (ISO622) size should fit your ISO630 wheels.
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Old 02-27-13, 07:57 AM
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Ben, another thing to consider when purchasing tires is the rim bead. A lot of the old 27" rims don't have a "hook" on the rim's sidewall. Modern rims use a hook which engages the tire's bead. This positive engagement allows for higher pressures on new tires without the tire blowing off the rim. If you have a non-hooked rim, don't expect to pump your tires to the full rating written on the tire's sidewall. Many people recommend you don't go higher than 75psi. I would go with an old school tire like the Michelin World Tour. These tires have been around forever and work great on the non-hooked rims as they were most likely designed for that type of rim in the first place.
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