Tire - Rim match
06-11-12, 08:49 AM
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Tire - Rim match
So here's a dumb quick question, but since it is safety relevant I prefer to ask:
I'm getting new wheels for my old school 27'' road bike. So far I had 27 x 1 1/4 (32-630) Conti Gatorskin tires on 27 x 1 1/8 rims. My new rims are Sun M13 II 27 x 1.
According to the wisdom of Sheldon Brown (https://sheldonbrown.com/tire-sizing.html#isoetrto), the tire width should be 1.45 - 2.00 times the inner rim width. If I have a 1 1/4 in (=32mm) tire and a 1 in (=25.4mm) rim this works out to a factor of 1.25 and it would seem I'm good. Is this correct? The Gatorskins take on a "balloony" shape (the sidewalls bulge quite a bit) when inflated and I want to be really sure that they won't pop off my rims when I'm cornering.
So: 1 in rims + 1 1/4 in tires - is it safe?
I'm getting new wheels for my old school 27'' road bike. So far I had 27 x 1 1/4 (32-630) Conti Gatorskin tires on 27 x 1 1/8 rims. My new rims are Sun M13 II 27 x 1.
According to the wisdom of Sheldon Brown (https://sheldonbrown.com/tire-sizing.html#isoetrto), the tire width should be 1.45 - 2.00 times the inner rim width. If I have a 1 1/4 in (=32mm) tire and a 1 in (=25.4mm) rim this works out to a factor of 1.25 and it would seem I'm good. Is this correct? The Gatorskins take on a "balloony" shape (the sidewalls bulge quite a bit) when inflated and I want to be really sure that they won't pop off my rims when I'm cornering.
So: 1 in rims + 1 1/4 in tires - is it safe?
06-11-12, 09:01 AM
#2
Mechanic/Tourist
You are mixing terms - 27x1 does not tell you inner width, and not necessarily even the outer. It's often the size tire it's meant to fit. Someone can correct me but I think the inner width is about 14mm. Even if it worked it is not the best combination. Narrower rims can give up strength and you are losing some of the stability and contact area of the wide tire by forcing it to adapt to a narrow rim.
Last edited by cny-bikeman; 06-11-12 at 09:09 AM.
06-11-12, 09:04 AM
#3
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So here's a dumb quick question, but since it is safety relevant I prefer to ask:
I'm getting new wheels for my old school 27'' road bike. So far I had 27 x 1 1/4 (32-630) Conti Gatorskin tires on 27 x 1 1/8 rims. My new rims are Sun M13 II 27 x 1.
According to the wisdom of Sheldon Brown (https://sheldonbrown.com/tire-sizing.html#isoetrto), the tire width should be 1.45 - 2.00 times the inner rim width. If I have a 1 1/4 in (=32mm) tire and a 1 in (=25.4mm) rim this works out to a factor of 1.25 and it would seem I'm good. Is this correct? The Gatorskins take on a "balloony" shape (the sidewalls bulge quite a bit) when inflated and I want to be really sure that they won't pop off my rims when I'm cornering.
So: 1 in rims + 1 1/4 in tires - is it safe?
I'm getting new wheels for my old school 27'' road bike. So far I had 27 x 1 1/4 (32-630) Conti Gatorskin tires on 27 x 1 1/8 rims. My new rims are Sun M13 II 27 x 1.
According to the wisdom of Sheldon Brown (https://sheldonbrown.com/tire-sizing.html#isoetrto), the tire width should be 1.45 - 2.00 times the inner rim width. If I have a 1 1/4 in (=32mm) tire and a 1 in (=25.4mm) rim this works out to a factor of 1.25 and it would seem I'm good. Is this correct? The Gatorskins take on a "balloony" shape (the sidewalls bulge quite a bit) when inflated and I want to be really sure that they won't pop off my rims when I'm cornering.
So: 1 in rims + 1 1/4 in tires - is it safe?
Personally, I think the chart that Sheldon Brown presented is rather conservative. Coming from a mountain bike background, I regularly run 2" wide tires on 17mm (inside) width rims. I'm not pumping them much more than 60 psi (usually more like 45 psi) but I've never rolled a tire off a bead. I have had some tires blow off the rim in the past but I blame that on the tires...Continentals, by the way...and not on the rim or tire width.
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Stuart Black
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Days of Wineless Roads. Bed and Breakfasting along the KATY
Twisting Down the Alley. Misadventures in tornado alley.
06-11-12, 09:14 AM
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I measured the rims myself: the inside width is exactly 1 in. The dimensions of the tires I've taken from the Conti website. I run my tires at around 100psi though.
06-11-12, 09:18 AM
#5
Mechanic/Tourist
