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I fitted a pair of Continental Grand Prix 4 Season 700x28 tyres at the weekend. Thinking that they looked a bit narrow I measured them with calipers and found that they are 25.5 mm wide. Measuring a Michelin Krylion Carbon 700x25 on another bike I found that it is 27 mm!

Do Continental tyres tend to come up narrow? I thought I was buying a fatter tyre which would be better on the occasional diversion along bridleways and gravel roads.

5 comments

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Fringe [1047 posts] 5 years ago
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it may depend on how much 'psi' you put into 'em.. i spose.

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cat1commuter [1420 posts] 5 years ago
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The rim width can effect tyre width, but pressure shouldn't. The threads in the carcass prevent tyres from stretching.

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dave atkinson [6201 posts] 5 years ago
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Sheldon Brown he say:

"Competitive pressures have often led to inaccuracy in width measurement. Here's how it works: Suppose you are in the market for a high performance 700 x 25 tire; you might reasonably investigate catalogues and advertisements to try to find the lightest 700-25 available. If the Pepsi Tyre Company and the Coke Tyre Company had tires of equal quality and technology, but the Pepsi 700-25 was actually a 700-24 marked as a 25, the Pepsi tyre would be lighter than the accurately-marked Coke 700-25. This would put them at a competitive advantage. In self defense, Coke would retaliate by marketing an even lighter 700-23 labeled as a 700-25.

This scenario prevailed throughout the '70's and '80's. The situation got so out-of-hand that cooler heads have prevailed, and there is a strong (but not universal) trend toward accurate width measurements."

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Zaskar [133 posts] 5 years ago
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Is there a international set standard on how to measure the tyre?

(I would like to know as I'm guessing every manufacturer uses different methods)

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dave atkinson [6201 posts] 5 years ago
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In theory there is, but so far as i know the ETRTO specs for measuring tyres only stipulate that it's the width of the tyre at the widest point, it doesn't have to be on a set size rim although that shouldn't make *all* that much difference...