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I was on the phone with an LBS yesterday and one of the bike mechanics mentioned that mountain bike rims can only handle about 70-80 max PSI. Something to due with a hook (I may not be getting the story right, but it's a great LBS whom I trust)?

So if I have a tire on my bike and it can handle more than 80 PSI (a slick for example), I shouldn't really go over this threshold? Or does the rim itself make a difference (I have Sun Rims...mach IV or something).

I'd like to more about this if someone has more info.
 

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featherweight clydesdale
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noonievut said:
I was on the phone with an LBS yesterday and one of the bike mechanics mentioned that mountain bike rims can only handle about 70-80 max PSI. Something to due with a hook (I may not be getting the story right, but it's a great LBS whom I trust)?

So if I have a tire on my bike and it can handle more than 80 PSI (a slick for example), I shouldn't really go over this threshold? Or does the rim itself make a difference (I have Sun Rims...mach IV or something).

I'd like to more about this if someone has more info.
I regularly run over 100 psi with a narrow slick on several Ritchey, Velocity, and Mavic mtb rims. Upper end wheels though (don't know much about cheap OEM anymore..). Have done so for years.
 

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I don't see how the rim couldn't handle it... I use to have 100+ psi all the time on my flatland bike, and never ran into a problem.
 

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its not he rim its the tire bead & casing strenght

noonievut said:
I was on the phone with an LBS yesterday and one of the bike mechanics mentioned that mountain bike rims can only handle about 70-80 max PSI. Something to due with a hook (I may not be getting the story right, but it's a great LBS whom I trust)?

So if I have a tire on my bike and it can handle more than 80 PSI (a slick for example), I shouldn't really go over this threshold? Or does the rim itself make a difference (I have Sun Rims...mach IV or something).

I'd like to more about this if someone has more info.
But tires will blow off rims if the bead of the tire and the rim arent compatible or fit loosly.
 

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I not so much the rim but the tire

It is becasue the tire casing is much wider than the rim and the force of the inflated tire will pull the side walls of the rim away from the centre. The larger the tire the lower the maximum pressure a rim can take.

The Mavic web site gives a guide line to max pressure vs tire size for their rims.

Wayne
 

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A well worn out rim sidewall from brake wear will fail due to high tire psi. Well, it's going to fail sooner or later anyway, the high psi can just make it happen sooner. It's true, I've seen it happen a few times :cool:

I've also used 26x1, 100 psi slicks with no problems...although the rims were new with no sidewall wear.
 

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noonievut said:
I was on the phone with an LBS yesterday and one of the bike mechanics mentioned that mountain bike rims can only handle about 70-80 max PSI. Something to due with a hook (I may not be getting the story right, but it's a great LBS whom I trust)?

So if I have a tire on my bike and it can handle more than 80 PSI (a slick for example), I shouldn't really go over this threshold? Or does the rim itself make a difference (I have Sun Rims...mach IV or something).

I'd like to more about this if someone has more info.
The guy is full of it.
There is a limit to the pressure a (new) rim can handle but it well beyond what most riders would even think of trying.

And as stated before, the tire is more of the limiting factor. It is good not to exceed the max stated on the sidewall of the tire. There is a large safety margin but no good reason to go higher.
 

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Yeah, it's a tire based issue. If you ever saw someone use a high power gas station air compressor you could see this in action. I saw this once- it was a riot.

sssssssssssssssssss BOOOOOOOOOOM!!

:)
 

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The pressure you can safely run depends on the volume of the tyres. Basically bigger tyres have more square inches for the pressure to act on.

So for a smaller tyre you can run higher pressure without putting more stress on the rims.

I can imagine Mavic (and other rim makers) putting a decent safety factor in their recommended pressures to deal with sidewall wear, dents and flatspots.
 
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