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Rules fitting specific width of tires on rims

Posted: Sat Apr 27, 2019 4:24 am
by nrsnow
Lets get to the point ... would a 25mm tubular tire width be to big to fit on a rim width of 20.5mm? Whats the rule on fitting tire rim width fitting?

Re: Rules fitting specific width of tires on rims

Posted: Sat Apr 27, 2019 6:44 am
by Etienne
nrsnow wrote:
Sat Apr 27, 2019 4:24 am
Lets get to the point ... would a 25mm tubular tire width be to big to fit on a rim width of 20.5mm? Whats the rule on fitting tire rim width fitting?
Hi, remember the tubular's shape won't be affected by the rim's width ... so the criteria for rim/tire adequation are :

> rim wide enough for a correct gluing surface ... 25mm tub on 20mm rim is then totally OK, I have that setup on several wheels, no problem.

> aerodynamic : there, you probably loose a little bit of aero ... depends on what you do with the wheels :idea:

You can even glue 27-28mm tires on 20mm wide rims without having the clincher's syndrome, I mean excessive deformation of the tire under lateral forces ... you'll just have a sub-ideal gluing surface but if the job is well done, no problem either.

Re: Rules fitting specific width of tires on rims

Posted: Sat Apr 27, 2019 6:44 am
by Weenie

Re: Rules fitting specific width of tires on rims

Posted: Sat Apr 27, 2019 4:31 pm
by JerryLook
I’m in the same boat as you OP. I just bought some 20.5mm wide Oval Concepts 932t wheels. I glued on some Vittoria 23mm tubs (22-22.5mm actual width).

I’m not sure how much basetape is supposed to show on the sides of the tub after being mounted, but my 23mm tires show about 2mm of basetape on each side.

Looking at a Veloflex Arenberg (25mm) for the rear, and a Carbon (23mm) for the front for my next set of tires.

Pls post some pics when you get your tubs mounted up.

Re: Rules fitting specific width of tires on rims

Posted: Sat Apr 27, 2019 5:33 pm
by Calnago
There are no “rules” per se but ideally the radius of the tire should match the radius of the rim bed as closely as possible. If the tire’s radius is larger, the center of the tire will have a tough time pressing against the middle of the rim bed when inflated, as it will tend to push up a bit with the majority of the pressure ending up at the edges. That’s ok, since that’s the most important area you want a good bond. With a narrower tire you get the opposite scenario and may end up with the edges wanting to pull up from the rim. Not ideal.
A 25mm tubular on a standard rim will work ok, but if you’re running rim brakes you may have an issue with removing the wheel easily, since the pads will likely be set close enough to the rim that the 25mm tire may get “stuck” on removal, even with the calipers released. I think the ideal size is a 24mm tubular on “standard” tubular rims these days. That’s what I run on my older Boras and it’s perfect. They don’t make the 24mm Roubaixs anymore but the newer Specialized S-Works Turbo seem like a fantastic option as they come in 24mm and 26mm sizes.
Forget about the whole aero interface between the clincher rim bead and the tire, since a tubular doesn’t have a bead. And in order for that kind of effect to be achieved with a tubular, the sides would have to come up much further and thin out at the tire/rim interface, which would go a good ways towards negating the handling and ride characteristics of the tubular in the first place. If you want to keep things narrow up front, then for sure a Veloflex Carbon (23mm) would be a nice option for those wheels too.

Re: Rules fitting specific width of tires on rims

Posted: Sat Apr 27, 2019 11:07 pm
by nrsnow
Thanks for all the information... colnago made a great point about the issue w rim brakes, def have to keep that in mind...