What is the widest tire that I can safely fit on a rim that measures 700x19.6 (outside)x14 (inside). It's got 25's on it now. I'd like to go up to 28.
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Generally if the tyre fits in the frame without rubbing on the brakes, brake bridge, or chainstay then you're generally OK.– Criggie ♦Jan 20, 2017 at 22:09
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You can generally run wider-than-spec tires on a (narrow) rim with relatively little difficulty. There is a point at which it gets ridiculous, and the tire can roll off the rim, but usually you'll run into trouble with the tire rubbing first. Going the other way around -- narrow tire on a wide rim -- is more apt to cause problems.– Daniel R HicksJan 20, 2017 at 22:27
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2 Answers
Assuming you're measuring accurately, you can use this table from Sheldon Brown or this table from Schwalbe.
The (inner) rim width is measured this way:
(Source: Schwalbe)
and for a 13 mm width, 18-25 mm tires and for 15 mm width, 23-32 mm tires. So, So, a 14 mm width (assuming you're measuring properly) should be fine with 28 mm tires; you can exceed the recomendations by a bit usually without adverse effects.
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Just a minor point: the illustrated measurement is the rim's internal width. It's common practice today to differentiate a rim's external and internal width. For example, the other answer by @Moz likely refers to a rim with 24mm external diameter; if it were really 24mm internal, that is considered wide for drop bar bikes even today. I believe the Aeroheat is a 26 inch MTB rim; one source I found specified an 18.6mm internal width. Jul 9, 2020 at 17:54
I habitually run much wider tyres than that on narrow rims. My shopping bike has a 559 rear wheel with an Aeroheat rim that's 24mm wide. I run a "Fat Frank" 55mm tyre on it. That is, however, a low pressure tyre (4bar/60psi).
On 406 wheels it's much more dramatic. I run high pressure flatland tyres 55mm or so wide at 6bar or more (100psi+) on my load bikes, and the rims range from 28mm on the back of my touring bike to some generic Taiwanese aero rims that are about 22mm wide.
The answer is that once the tyre is Ʊ shaped at all it doesn't seem to matter. If you're running a 25mm tyre on a 19mm rim, you're already putting all the outward force on the rim that you're going to put, regardless of tyre width.
