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Wide tire on skinny rim? How wide?

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Wide tire on skinny rim? How wide?

Old 05-13-15, 07:45 PM
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Gresp15C
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Wide tire on skinny rim? How wide?

The rear tire on my "fun" bike is nearly worn down to the cords. It's a 27 x 1-1/8, about 26 mm wide, on a rim that's labeled as 27 x 1, and is 19 mm wide. The frame could fit a wider tire, but I'm curious about how wide I could safely go. The rims are in good enough shape that they could last for many more years before I'd think about switching to metric.

And if there's an upper limit on tire width for a given rim, what's the technical rationale? Even if it's just based on experience of what could go wrong, I'm curious. I've noticed mountain bikes with big poochy tires on skinny rims.
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Old 05-13-15, 07:59 PM
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Don't think you will find much larger than 27x1 1/2" tire these days, which would fit fine on the rim. Sheldon Brown discusses this:
Tire Sizing Systems Scroll down for rim versus tire width suggestions.

The presumption is you have hook bead rims...... These would be mid to late 70s et seq.
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Old 05-13-15, 08:25 PM
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You could likely fit a much wider tire. Your problem is that you won't be able to find one. 99.9% of 27" tires are 1 1/4" wide. If you look you can find 1 1/8" and maybe some 1" floating around. I have a knobby Kenda tire that I use in the winter. It's labeled 1 3/8" (ISO 37mm) but only actually measures 32mm wide.

Good luck. You might have to switch to 700c. The bonus there is that you could run even larger tires because the rim is 4mm smaller in radius giving you a little extra room.
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Old 05-13-15, 10:15 PM
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Thanks for the comments so far. The rims are 13 mm interior, hook bead. The table at the Sheldon Brown site suggests a max tire width of 25 mm, which means that I may already be at the outer limit with my existing 27 x 1-1/8 tires. Another tire in my corral, nominally 27 x 1-1/4, is 31 mm wide.

Clearance between the chainstays is no more than about 36 mm, so this will never be a fat tire bike.

@FastJake, I'm on the fence about switching to 700c. It would not be a huge project, but I have a lot of projects on my plate right now. The brakes could accommodate the smaller radius. The dilemma is basically, when is the point of diminishing returns on trying to find 27" tires.
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Old 05-14-15, 05:48 AM
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biketiresdirect.com lists a 27 x 1 1/2 "Cross" tire, which is probably the largest you will find, of course what it actually measures is another matter and it will bump up against your
chainstay limit.
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Old 05-14-15, 09:02 AM
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Originally Posted by Gresp15C View Post
The rims are 13 mm interior, hook bead. The table at the Sheldon Brown site suggests a max tire width of 25 mm, which means that I may already be at the outer limit with my existing 27 x 1-1/8 tires.
Sheldon errs on the side of safety in his table. I currently run 60 mm wide tires on 17 mm internal rims without problems (Schwalbe Super Moto on Mavic 317).

Originally Posted by Gresp15C View Post
@FastJake, I'm on the fence about switching to 700c. It would not be a huge project, but I have a lot of projects on my plate right now. The brakes could accommodate the smaller radius. The dilemma is basically, when is the point of diminishing returns on trying to find 27" tires.
In 27", there are still some good options (Pasela, Sand Canyon), but not a very wide selection. If I were you, I'd swap the bike to 700c when you find a great deal on some 700c wheels.
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Old 05-14-15, 09:06 AM
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Mountain Bike tires on rolled down MA40 rims was done by 1 Keith Bontrager , long ago , before the rim manufacturers took up the Idea themselves.


Problem is a 27" rim not much tire choice is available any more 1.25" wide is about all You can find.
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Old 05-14-15, 09:07 AM
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I have successfully and safely used 2.2" wide tires (56mm) on 18 mm wide rims. Putting 1-1/2" wide tires (38mm - probably the widest 27" tires you will find) on your rims will be no problem at all.

But is there a need to go wider than 1-1/4" (32mm)? I rode 12 km to work this morning on a gravel road with 700 X 32 mm tires and at certainly did not feel like they needed to be wider. 32 mm wide tires can be ridden on any hard or semi-hard surface without problems.
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Old 05-14-15, 09:29 AM
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Originally Posted by Wilfred Laurier View Post
But is there a need to go wider than 1-1/4" (32mm)? I rode 12 km to work this morning on a gravel road with 700 X 32 mm tires and at certainly did not feel like they needed to be wider. 32 mm wide tires can be ridden on any hard or semi-hard surface without problems.
Depends on your weight, and how coarse the gravel is.

I'm large (#220) and the gravel around here is pretty rough (.5 - 1")

I prefer wider tires for gravel, so I'd prefer a 1 3/8" (35 mm) or 1 1/2" (38 mm) tire. In fact, I prefer my bike with 60 mm Super Motos over my bike with 38 mm Pari-motos.
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Old 05-14-15, 09:34 AM
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Originally Posted by Gresp15C View Post
Thanks for the comments so far. The rims are 13 mm interior, hook bead. The table at the Sheldon Brown site suggests a max tire width of 25 mm, which means that I may already be at the outer limit with my existing 27 x 1-1/8 tires. Another tire in my corral, nominally 27 x 1-1/4, is 31 mm wide.

Clearance between the chainstays is no more than about 36 mm, so this will never be a fat tire bike.

@FastJake, I'm on the fence about switching to 700c. It would not be a huge project, but I have a lot of projects on my plate right now. The brakes could accommodate the smaller radius. The dilemma is basically, when is the point of diminishing returns on trying to find 27" tires.
The Panaracer Paselas run pretty close to their labelled sizes these days. I'd run a 27"x1-1/8" (28-630) on those rims without any fear whatsoever.
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Old 05-14-15, 11:00 AM
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I am running 700c x35mm tires on 25mm rims with no issues, so you can run a wider tire on a skinny rim.
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Old 05-14-15, 05:23 PM
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Lots of useful info! Some learnings for me: I had always assumed that I don't need to care about metric dimensions, because my wheels use inch dimensions, but in fact it appears that the ISO sizes are a lot easier to use for figuring out rim / tire / frame compatibility. So, in the new parlance:

Existing tire: Kenda K36, ISO 28-630

Looks like this is an appropriate size for my rim, 32-630 might be pushing it, but I have one that I can try out. It might not be as urgent as I thought, there's still sufficient rubber on the tire, though the little "sipes" are gone. So I'll ride it for a bit longer.

Switching to 700c looks like a pretty good option, but it would be a winter project, so it means that I have all summer to shop for rims and spokes. We're now well into "stop wrenching and start riding" season.
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