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Tire width: a black art?

Old 11-26-18, 02:12 PM
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Tire width: a black art?

When I saw this I wondered how many mm's 1.4" would be .... You've guessed it. Not 35mm. Not 37mm either. I've so much yet to learn ....


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Old 11-26-18, 02:19 PM
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The first spec printed on your sidewall is the ETRTO one. In theory, the width spec is not actual width but distance between beads (when the tire is flattened out) divided by 2.5. That might be the most accurate you will get.
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Old 11-26-18, 02:21 PM
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when I use google to do the conversion I get 35.56mm. am I missing something?

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Old 11-26-18, 02:28 PM
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Originally Posted by rumrunn6 View Post
when I use google to do the conversion I get 35.56mm. am I missing something?

No. My physics teacher taught me that would be 36mm ...
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Old 11-26-18, 02:29 PM
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Originally Posted by noglider View Post
The first spec printed on your sidewall is the ETRTO one. In theory, the width spec is not actual width but distance between beads (when the tire is flattened out) divided by 2.5. That might be the most accurate you will get.
Thanks, Tom. I didn't know that.
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Old 11-26-18, 02:53 PM
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Originally Posted by non-fixie View Post
No. My physics teacher taught me that would be 36mm ...
Strictly speaking, since the tire width in inches was specified as 1.40 and the formula is multiplying by 25.4, the answer should be rounded to 35.6 to keep the correct number of significant digits.

I worry more about the fact that the wheel used for a 27" tire has a larger diameter than the wheel used for a 28" tire or a 29" tire but that the wheel used for a 27.5" tire is smaller than all three of the others.
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Old 11-26-18, 03:11 PM
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Originally Posted by Andy_K View Post
Strictly speaking, since the tire width in inches was specified as 1.40 and the formula is multiplying by 25.4, the answer should be rounded to 35.6 to keep the correct number of significant digits.

I worry more about the fact that the wheel used for a 27" tire has a larger diameter than the wheel used for a 28" tire or a 29" tire but that the wheel used for a 27.5" tire is smaller than all three of the others.
Let me see if I can get this right: 28 x 1.40 would be 711 x 35.6? Since we're talking outside diameters this could actually be correct. I'll see if I can hold a tape measure next to that particular tire.
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Old 11-26-18, 03:33 PM
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What problem are you looking to solve?
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Old 11-26-18, 03:49 PM
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Originally Posted by noglider View Post
What problem are you looking to solve?
Just a lack of comprehension on my part. I had expected 37 x 622 to be the same as 700 x 37c, but it appears I was wrong there. Thanks again for the explanation.
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Old 11-26-18, 04:05 PM
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Originally Posted by non-fixie View Post
Just a lack of comprehension on my part. I had expected 37 x 622 to be the same as 700 x 37c, but it appears I was wrong there. Thanks again for the explanation.
I had a Specialized Touring from way back that was labeled by Specialized as a 700 x 25c "touring width" tire - while the manufacturer had marked it as 622-20. And yes, it was that narrow.
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Old 11-26-18, 04:13 PM
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Yes. It is most certainly a black art.
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Old 11-26-18, 04:20 PM
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(Dare we mention the thrills of 26" tire sizes?.....)
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Old 11-26-18, 04:27 PM
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At this point this needs to be said:

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Old 11-27-18, 04:57 AM
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Originally Posted by madpogue View Post
(Dare we mention the thrills of 26" tire sizes?.....)
Yeah, I just received my new tires for a 1953 Schwinn, sidewall says 26 x 1-3/8 x 1-1/4. I guess they'll be oval....
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Old 11-27-18, 07:35 AM
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Originally Posted by jj1091 View Post
Yeah, I just received my new tires for a 1953 Schwinn, sidewall says 26 x 1-3/8 x 1-1/4. I guess they'll be oval....
They're all a little bit oval at the very bottom while being ridden, right? Didn't know there was a measurement for that.
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Old 11-27-18, 04:04 PM
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Originally Posted by speedevil View Post
They're all a little bit oval at the very bottom while being ridden, right? Didn't know there was a measurement for that.
Northern European designation for 700C is "28 x 1 5/8 x 1 1/4" per Sheldon's site
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Old 11-27-18, 04:17 PM
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One inch equals 25.4 mm. Or put another way, 1 mm equals .03937 inch. You do the math.
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