Max rim pressure

flester
flester Posts: 464
edited May 2009 in MTB workshop & tech
In this post, http://www.bikeradar.com/forums/viewtop ... t=12618836, a max pressure of 45psi is quoted for some specific mountainbike rim and one of the responders reckons this is high. For road use on my 2004 Hardrock XC rigid I use Michelin Rock tyres, recommended pressure 50-80psi. Also many high pressure tyres are available for mountainbike rims. Am I risking an explosion at 80? I think my rims are Alexis something but not sure after that.
'I do not believe in the three-speed gear at all', the sergeant was saying. 'It is a newfangled instrument, it crucificies the legs, the half of the accidents are due to it.' (From 'The Third Policeman')

Comments

  • nicklouse
    nicklouse Posts: 50,673
    what rims?

    i dont see a problem.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Chaz.Harding
    Chaz.Harding Posts: 3,144
    I read something on this a while ago. Well, not specifically this, but it was wheelbuilding. The more pressure you inflate your tyres to, the more that it 'squeezes' the rim, and the spokes become more loose. Hence your wheel strength drops, so you are more prone to getting a pringle-shaped rim.

    It's more of a problem should you have rim brakes, especially hydraulic rim brakes. Obviously as you brake, the pads will wear away, and with it, the rim too. This is accelerated if you ride in gritty / muddy conditions, as it acts like a grinding paste. Nice...

    If you don't have rim brakes, however, there isn't that much to worry about. Eventually, the rim will expire through metal fatigue (IF it lasts that long, but it's doubtfull)

    Hope this helps!

    Chaz.
    Boo-yah mofo
    Sick to the power of rad
    Fix it 'till it's broke
  • flester
    flester Posts: 464
    Oh I see, I imagined something like a blowout due to the bead popping out from the rim etc. Offroad I wouldn't use anything like 80psi anyway so I should be OK.
    'I do not believe in the three-speed gear at all', the sergeant was saying. 'It is a newfangled instrument, it crucificies the legs, the half of the accidents are due to it.' (From 'The Third Policeman')
  • nicklouse
    nicklouse Posts: 50,673
    bigchazrocks
    but you take that into consideration when building the wheel.

    Some rim makers do suggest a max pressure. but like i said dont worry.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • captainfly
    captainfly Posts: 1,001
    Yeah it's the reduction in spoke ptension that is the worry with high pressures, so it is how the wheel is put together, I don't know anything about wheelbuilding but would guess there things like intended use and expected tyre pressures are factors in the build.
    But 45psi or more is quite high when the going rough esepicialy for front end grip. On the road grip isn't such an issue where rolling resistance it, it's all a compromise.
    -_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
    Mongoose Teocali
    Giant STP0

    Why are MTB economics; spend twice as much as you intended, but only half as much as you wish you could afford? :roll:
  • Chaz.Harding
    Chaz.Harding Posts: 3,144
    nicklouse

    Yup, I know. But it maybe handy info for flester, if he didn't already know. Was just saying that it does what it does. Not really a concern on a MTB anyway.

    :lol:
    Boo-yah mofo
    Sick to the power of rad
    Fix it 'till it's broke
  • flester
    flester Posts: 464
    Thanks all, that IS useful info for me. Manufacturer site says my rims are 'Alex DM-20, 26"x1.5", double wall, machined side wall, black', for what it's worth. I believe black is the strongest colour of all ;-)
    'I do not believe in the three-speed gear at all', the sergeant was saying. 'It is a newfangled instrument, it crucificies the legs, the half of the accidents are due to it.' (From 'The Third Policeman')

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