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Road Bike Tire Width

Old 06-13-19, 06:27 PM
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Road Bike Tire Width

What exactly is a (for example) 25mm tire width measuring? What is it that is supposed to be 25mm? Is it the maximum with of a mounted and inflated tire? If so it appears that Conti 4000ii 23mm tires are really very slightly oversized 25's.

Thanks.

dave
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Old 06-13-19, 06:47 PM
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It is SUPPOSED to be 25mm when mounted on a specified width rim, per ERTRO specs. However, in practice they are all over the map both bigger and smaller. Of course they will measure differently when mounted on a wider or narrower one.
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Old 06-13-19, 06:57 PM
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DS, thanks.

And the following is relevant and consistent with what you said.

https://www.velonews.com/2016/05/bik...sistent_406275

And that brings up the question, is a 23mm tire that measures 25.5mm pretty much the same tire (WRT air pressure) as a 25mm that also measures 25.5mm? Or is there also a height change as nominal width changes?

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Old 06-13-19, 07:18 PM
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From what I've gathered, most brands who care spec their 700c tire widths off of a 622x17c wheel, so your tire should mount to the mfr. stated if it has a 17mm internal width. Mostly.

I wish Schwalbe had chimed in with their answer. I've seen a 700x28 Schwalbe One mount to a hair under 32mm wide. They just make up the numbers as they go along. Continental is close behind.
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Old 06-13-19, 07:56 PM
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I guess it's all about the rim width and profile. I've been using Michelin Pro-Tek tires on my some of my bikes. The Pro Teks are larger than the listed dimension. Good for a hybrid style frame with plenty of clearance. But, I wouldn't try putting them on my race bikes. I've used Bontrager tires that run large too.
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Old 06-13-19, 08:11 PM
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I always thought most mfr's said that was the width of the tire casing which does not include the rubber or material covering the casing.
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Old 06-13-19, 08:29 PM
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Originally Posted by DaveLeeNC
What exactly is a (for example) 25mm tire width measuring? What is it that is supposed to be 25mm? Is it the maximum with of a mounted and inflated tire? If so it appears that Conti 4000ii 23mm tires are really very slightly oversized 25's.

Thanks.

dave
It is a nominal sizing statement. Simplicity in exchange for some inaccuracy. And ballpark 10% error isn't awful, unless you're riding a paved-road racing bike. Generally, most lay-people can stand to be riding wider tires anyway.

The alternative is car-tire sizing. Which has no fewer than 5 alpha-numeric descriptors in order to get exactly what you need possibly, 10 depending on the purpose...Which if you're a gear-head is no biggie. You know you need"LT275/70R18 125/122R E" set of tires, then great for you you can go and get it....for the other 99.99% who are not gear heads it is beyond unwieldy and they leave it to a shop to spec something "right" or "close enough"
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Old 06-13-19, 09:26 PM
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Originally Posted by DaveLeeNC
Is it the maximum with of a mounted and inflated tire?
Yes, this.

It is the width of the tire at its widest point.


-Tim-
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