If a tire is 24x3.0 then I believe the diameter of the tire is 24 inches but what’s the 3.0? I thought it was the the width of the tire, but my neighbor tells me it’s a measurement from of the sidewall from the rim to the tread. Is that correct?

Actually, the 3.0 is the estimate of the width. tire companies usually label the tire bigger than it truely is. for example, a nokian gazzaloddi is actually 2.8 (about?) inches wide.

> If a tire is 24x3.0 then I believe the diameter of the tire is 24 inches
> but what’s the 3.0? I thought it was the the width of the tire, but my
> neighbor tells me it’s a measurement from of the sidewall from the rim
> to the tread. Is that correct?

The traditional tyre dimensions are not any actual measurement (in
that if you measure a 24x3.0, nothing actually measures 24 and nothing
actually measures 3.0. This leads to all sorts of oddities. For
example, a 26x1.25 tyre doesn’t fit on a rim that takes a 26x1 1/4.

In theory the first number is based upon the final rolling diameter of
the tyre when installed and inflated, and the second number is the
tyre height (ie, the difference between the first number and the rim
diameter). I think that’s what your neighbour was saying.

In practice, it’s all fudged because tyres that fit on the same rim
all have the same first number (although as noted the converse is not
true).

Also, the height of the tyre is pretty near the same as the width of a
tyre (in general), so since neither is precisly 3, it doesn’t really
matter which you regard the 3 as applying to.

The ISO dimensions are more sensible. These are the xx-yyy numbers on
tyres. Xx is the height (as measured) and yyy is the diameter of the
bead seat (ie, almost the diameter of the rim). Tyres with matching
yyy numbers should fit he same rim, though they might not be suitable
(eg a really narrow tyre on a double-width rim). The final diameter
ought to be pretty close to yyy + 2*xx.