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Old 08-04-17, 02:44 AM   #1
jambon
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Advertised Tyre width V Actual Tyre width and Internal Rim Width

Howdy ,

I'm experiencing a bit of confusion after trying to figure out which tire will replace my worn front .

The tire on the front at the moment is a maxxis ignitor ust 26 x 2.35 . This tyre when measured with a callipers is at its widest point on the body of the tyre just below 2.0 . measured knob to knob it is somewhat closer to 2.3.

The rims are mavic crosstrail Internal width 19mm and the tech doc recomends a max tyre width of 2.3

Id like to pop the biggest tire I can on the front and try something different .

It seems that most tires are not the width that they are advertised at or the width shown is based on the width of the outer knobs and not the tyre casing.

So from reading around various forums , for example , I see that a continental mountain king II UST 26 x 2.4 actually comes in just below 2.3 in width .


So if my thinking is correct then a mountain king II 2.4 (if it is in reality a 2.29) will work ok with my 19mm inner rim ?


Any insights appreciated ,

J
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Old 08-06-17, 09:51 AM   #2
Kapusta
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There is no set standard for measuring tire widths, so you always need to take it with a grain of salt. Asking over at a place like MTBR you might find some actual measured widths. Or just do some googling.

A tire on a narrow rim will measure narrower. 19mm internal width is considered narrow by current mtb standards.

I seriously doubt that there is going to be any real issue with running the tire you are looking at, even if they ran true to size. And since they run small, I would not think twice about it.

However, having such a narrow rim does limit some of the benefit you get from a large tire, particularly in the front. Being able to run low pressure (without getting pinch flats) is a huge benefit of a high volume tire. The issue with a narrow rim is that it does not support the tire as well and it can get "squirmy" at low pressures in corners.
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Old 08-12-17, 04:36 PM   #3
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Tire width is a sore subject for me. If you want to know the casing width, the magic number you're looking for is bead to bead width. Ignitors are notoriously undersized. Personally I don't care about how much the knobs stick out but some manufactureres use that in their width measurement. Also they measure at like 50 psi so the casing stretches a bit. At riding psi they're smaller.

For example, on a 25mm internal rim, a bead to bead of 155mm will give you a 2.35" (60mm) wide tire at 20-30psi. That is your 2.35" Hans Dampf, Nobby Nic, Bontrager XR2/3/4, Vittoria Morsa. These are all modern tires I've measured myself. Subtract 1mm of casing for every 3mm of internal rim width.

Here are some btb measurements, though some are of older tires and not relevant: Bead to Bead Mtb Tire Measurement- Mtbr.com
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