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Should I worry about rim failure?

Old 08-22-06, 11:39 AM
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fatsoforgotso
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Should I worry about rim failure?

I'm in the process of buying a pair of somewhat cheap 24-spoke MTB wheels. I'm gonna fit these wheels with Continental TravelContact tires (85 psi max) and/or Continental SportContact tires (70 psi max).
Normal pressure for MTB tires is 40-60 psi. The wheel manufacturer doesn't specify the max pressure that the rims will take, and the rims are double walled.
I've heard that high pressure tires could be a cause of rim failure. Is this just an urban legend or should I worry about it?
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Old 08-22-06, 11:40 AM
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Originally Posted by fatsoforgotso
I'm in the process of buying a pair of somewhat cheap 24-spoke MTB wheels. I'm gonna fit these wheels with Continental TravelContact tires (85 psi max) and/or Continental SportContact tires (70 psi max).
Normal pressure for MTB tires is 40-60 psi. The wheel manufacturer doesn't specify the max pressure that the rims will take, and the rims are double walled.
I've heard that high pressure tires could be a cause of rim failure. Is this just an urban legend or should I worry about it?
I would worry about it 3 times per day.
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Old 08-22-06, 01:04 PM
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Cheap 24-spoke mtb wheels? Hmm, usually low spoke count mtb wheels are for XC racing and are quite expensive, something like Mavic Crossmax or similar. What kind of wheels are they?...........In regard to tire pressure, the thing to remember is that a max. recommended pressure is based largely on how much air volume a tire will hold. That's why, for example, you might see a max. pressure rating of 50 psi on a 26 x 2.1 tire, and 100 psi on a 26 x 1. In other words, the smaller volume tire at higher pressure will put no more pressure on the rim than the larger volume tire at lower pressure (and it's the tire's bead that will usually give way before anything else). There is a safety cushion built in to the max reccommended pressure (by the tire manufacturer), meaning the tire has actually been tested at higher pressures than the max recommended. Run the tires at their max recommended pressure, and you should be fine-

edit: I just checked the Mavic website, and it's the Crossride's I was thinking of that are 24 spoke, and they're moderately priced I believe. The Crossmax I mentioned are 18 F, 20 R and are off-the-charts expensive-

Last edited by well biked; 08-22-06 at 01:40 PM.
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Old 08-22-06, 02:18 PM
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Originally Posted by well biked
Cheap 24-spoke mtb wheels? Hmm, usually low spoke count mtb wheels are for XC racing and are quite expensive, something like Mavic Crossmax or similar. What kind of wheels are they?...........In regard to tire pressure, the thing to remember is that a max. recommended pressure is based largely on how much air volume a tire will hold. That's why, for example, you might see a max. pressure rating of 50 psi on a 26 x 2.1 tire, and 100 psi on a 26 x 1. In other words, the smaller volume tire at higher pressure will put no more pressure on the rim than the larger volume tire at lower pressure (and it's the tire's bead that will usually give way before anything else). There is a safety cushion built in to the max reccommended pressure (by the tire manufacturer), meaning the tire has actually been tested at higher pressures than the max recommended. Run the tires at their max recommended pressure, and you should be fine-

edit: I just checked the Mavic website, and it's the Crossride's I was thinking of that are 24 spoke, and they're moderately priced I believe. The Crossmax I mentioned are 18 F, 20 R and are off-the-charts expensive-
I'm not worried about the tires or tubes themselves...
I'm just worried about rim integrity when higher (than 60psi) tires are used on a MTB wheel.
These are the wheels I'm talking about:
https://www.rodi.pt/cyclinguk/
Go to Products > Wheels > MTB Disc > Excalibur FR

Judgind by the "FR" moniker, they're freeride wheels. People I know talk highly of them, but these people pump their tires to 50psi. I ride mostly on asphalt so I need to pump them higher.
By "somewhat cheap" I mean around 55€/wheel.
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Old 08-22-06, 02:34 PM
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Like "well biked" said, the rim takes different pressures for different tire sizes. I would not dismiss this as urban legend or myth, it's a real problem - but at the same time you can be fine if you don't go nuts on the pressure.

If you are mostly riding on asphalt why not just get a 24" road rim wheelset built up? You'll most likely want to put narrow high pressure slicks on those anyways, and those range from 80-130psi around.

Maybe someone with mtb wheel experience can chime in.
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Old 08-22-06, 03:32 PM
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Originally Posted by fatsoforgotso
I'm not worried about the tires or tubes themselves...
I'm just worried about rim integrity when higher (than 60psi) tires are used on a MTB wheel.
These are the wheels I'm talking about:
https://www.rodi.pt/cyclinguk/
Go to Products > Wheels > MTB Disc > Excalibur FR

Judgind by the "FR" moniker, they're freeride wheels. People I know talk highly of them, but these people pump their tires to 50psi. I ride mostly on asphalt so I need to pump them higher.
By "somewhat cheap" I mean around 55€/wheel.
If you're saying you're going to run your tires at much higher than recommended pressures, you might have a concern (and again, it will probably be the tire's bead that will go first, and/or the tube). But in your original post you mentioned two tires, and their recommended max pressures. As I said, it's the tire's volume that mostly determines the max recommended pressure. Hence: skinny tires, high pressure; fat tires, lower pressures. The stresses on the rim are more or less the same ( whether fat tire or skinny tire) if you stay at the max recommended pressure for an individual tire, which will mean lower pressures for fat tires, higher pressures for skinny tires. Stay at the recommended pressures, and rim failure due to air pressure should be no concern at all-
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Old 08-22-06, 03:58 PM
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If you are using caliper or V brakes they will eventually weaken the rim through wear. However the failure would not be catastrophic like a carbon fork. The side wall would bulge out, causing unwanted breaking, and wobble of the front wheel. Dont worry.
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Old 08-22-06, 07:43 PM
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I used to concern about htis also. I emailed Sun rims asking, they said their rims are stronger than whatever tire you put on. You can pump any tire to the max with your rims as long as they fit.
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Old 08-22-06, 08:07 PM
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Originally Posted by phantomcow2
I used to concern about htis also. I emailed Sun rims asking, they said their rims are stronger than whatever tire you put on. You can pump any tire to the max with your rims as long as they fit.
Yeah we'll see about that.
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Old 08-22-06, 08:15 PM
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Originally Posted by operator
Yeah we'll see about that.
? Just curious, what don't you agree with?
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Old 08-22-06, 08:29 PM
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I've been running 90 psi MTB slicks on two sets of cheap rims for about 4 years now. Never gave it a second thought. Thousands of miles riding a time bomb....

Naw. It's just fine.
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Old 08-23-06, 12:57 AM
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Thanks for the replies. I'll order the gear today.
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Old 08-23-06, 04:54 AM
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Originally Posted by well biked
If you're saying you're going to run your tires at much higher than recommended pressures, you might have a concern (and again, it will probably be the tire's bead that will go first, and/or the tube). But in your original post you mentioned two tires, and their recommended max pressures. As I said, it's the tire's volume that mostly determines the max recommended pressure. Hence: skinny tires, high pressure; fat tires, lower pressures. The stresses on the rim are more or less the same ( whether fat tire or skinny tire) if you stay at the max recommended pressure for an individual tire, which will mean lower pressures for fat tires, higher pressures for skinny tires. Stay at the recommended pressures, and rim failure due to air pressure should be no concern at all-
Okay, so if you go from a 2.125" tire at 65PSI to a 1.5" tire what would the equivilent pressure be, as far as the rim is concerned? The reason I ask, is that I am planning the same kind of thing, currently have 2.125" knobbies on my bike (Alex Ace-18 rims), and would like to switch to a slick, and run a little higher pressure there too, just what is reasonable?

Sheldon got a chart for this somewhere**********
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Old 08-23-06, 05:42 AM
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Originally Posted by operator
Yeah we'll see about that.
Would you like to see the email?
You will be the first I let know when my rims fail due to what I believe is tire pressure.
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Old 08-23-06, 06:01 AM
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Originally Posted by Wogsterca
Okay, so if you go from a 2.125" tire at 65PSI to a 1.5" tire what would the equivilent pressure be, as far as the rim is concerned? The reason I ask, is that I am planning the same kind of thing, currently have 2.125" knobbies on my bike (Alex Ace-18 rims), and would like to switch to a slick, and run a little higher pressure there too, just what is reasonable?

Sheldon got a chart for this somewhere**********
According to info on the Mavic website (taken from the max. recommended pressures for a given tire size to be used on one of their 26" rims), the max pressure for a 1.5" tire is 88psi, and for a 2.1" tire it's 59psi, so presumably the pressure on the rims would be equivalent with these two sizes at these two pressures. But I don't believe there's any need to over-think this, just stay at or below the max recommended pressure that's on the tire itself, and you should be fine. In fact, you could go higher than the recommended max pressure, but I'm not gonna recommend you do that, that's up to you-

Last edited by well biked; 08-23-06 at 06:10 AM.
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Old 08-23-06, 06:10 AM
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Originally Posted by supcom
I've been running 90 psi MTB slicks on two sets of cheap rims for about 4 years now. Never gave it a second thought. Thousands of miles riding a time bomb....

Naw. It's just fine.
Same here. I'd be much more worried about rim damage from potholes and getting run off the road
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Old 08-28-06, 07:04 PM
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mountain bike rims can take a bigger beating than a road wheel, they will hold just fine, the guys are right, it depends on the specific volume in the tire, pressure alone isnt a factor. if the tire is designed for a generic mountain bike wheel , then it will be able to take it , no bother.
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