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Old 06-18-09, 04:39 PM   #1
nbru
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tire widths

Quick question.

How wide is a 27" x 1-1/8" tire, as compared to a 700c 25mm?

Mathematically, 1-1/8" = 28.5 mm, but I'm not sure if the translation is that direct or accurate when it comes to sizes in bike tires ...

Some insight into whether or not 25's are wider than the 1-1/8's that would be helpful.
I'm curious as to how the two different tire sizes compare ...
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Old 06-18-09, 04:50 PM   #2
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Bike tire sizing is an imprecise thing. For one, the actual width of your tire will vary according to rim width. More importantly, manufacturers do not always provide the real width, but rather some approximate value. Two 700x25c tires may not have the same width.

But yes, 1-1/8" should be around 28mm. Could be a bit narrower, could be a bit wider. The ETRTO size for those tires is 28-630, that is, 28mm wide and 630mm Bead Seat diameter. It is 25-622 for 700x25c tires, and 28-622 for 700x28c tires.
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Old 06-18-09, 05:04 PM   #3
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Some 700 X 25C tires measure 23C. And some 23C tires measure 25C. When you get a tire, having a digital-caliper is very good indeed. The tire should be inflated to it's suggested pressure before measuring it.

These are very same ones that Park Tool offers (with their name on them) for a lot more money:

Amazon.com: 6 Inch LCD Digital Caliper with Extra Battery and Storage Case: Home Improvement Amazon.com: 6 Inch LCD Digital Caliper with Extra Battery and Storage Case: Home Improvement
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Old 06-18-09, 09:37 PM   #4
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Right-on Panthers007. I have measured the mounted width of an older Vittoria folding tire as narrow as 20.5mm yet the ETRTO marking was 622 x 25. It used to be that undersizing bike tires was very common so that the manufacturers could claim a lower weight. Not as bad as it used to be apparently though I am judging by recent 700 x 25 and 700 x 28 tire buys. I do not know about current narrow road tires.
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Old 06-18-09, 10:40 PM   #5
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Just measured a very good 23C - 23.5C - which is mm. And a 27C - it was actually 28.65mm(C). Both of these tires were top-of-the line quality and price - too. Get a digital-caliper. Find out what's really out there!
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