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Air Shock Affected By Elevation Change?

Discussion in 'The Shop' started by pedalkicker, Aug 5, 2008.

  1. pedalkicker

    pedalkicker Monkey

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    I have an older Fox Float (2005) on a Kona 'A' frame that I recently had a weird problem with. I usually run the shock at around 150 psi and after a few light XC or road rides I need to bring it back to 150 psi from about 100 psi. I recently took this bike to Colorado from Arizona (elevation change from 2000 feet to around 9500-10000 feet) for a biking vacation. Before my first ride in Colorado I setup the shock at about 100 psi for a little more plush ride. About half way through the ride I noticed the shock was packed up and wouldn't rebound unless I was off the bike. The trail was pretty smooth and I finished the ride with the shock packed up. I connected my shock pump to the shock later and it read very low, around 25 psi. So I pumped it up to 150 psi and let it sit overnight. The next day I connected the pump and it read a little under 150 psi, I figured it lost a little air during the pump connect. I rode my TOP (street bike) on the next ride of XC trails and about killed my back. So for the next ride I went back to the Kona and brought my shock pump with me. Well it lost air pressure and packed up about every 15-20 minutes and I had to keep pumping it back up to finish the trail. I figured the shock was fvcked and didn't ride it again. When I got back to Phoenix I pumped the shock up to 150 psi and it is working the same as it did before I took the trip.
    I'm thinking some seal is leaking and being at 10000 feet made the seal leak way faster. Anybody know what's going on with the shock or had a similar experience/problem?
     
    #1 -   Aug 5, 2008

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  2. Westy

    Westy the teste

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    One atmosphere of pressure is only about 14psi so the chances of elevation causing the leak are slim. Sounds like it is leaking from use. Try replacing or lubing the seal.
     
    #2 -   Aug 5, 2008
  3. HenryTheHammer

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    Was having an issue with my DHX. I just removed the valve stem and replaced it with one out of a new tube. I sprayed the valve down with triflow prior to reinstalling it. Shock has been money since.
     
    #3 -   Aug 5, 2008
  4. pedalkicker

    pedalkicker Monkey

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    Ok, I'm pretty clueless when it comes to suspension. I was going to take it to my LBS but since it has been working I haven't yet. What's the process for "lubing the seal"? If it's simple like putting on some Tri-Flow, I'll give it a shot. Thx!

    I guess I was riding it harder up in CO than I do down here in AZ, although I do ride it about 30-40 miles a week here.
     
    #4 -   Aug 5, 2008
  5. airs0ft3r

    airs0ft3r Chimp

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    Keep in mind that as you get higher in altitude the temperature decreases and along with it there should be a decrease in pressure. I'm not sure how much air the shock should lose.
     
    #5 -   Aug 7, 2008
  6. HAB

    HAB Chelsea from Seattle

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    A change in temperature from 90F to 70f would change the air pressure by ~3.6 percent. Not totally insignificant, but fairly small. At 150psi, that would mean a drop to 145psi.



    The change in external pressure on the shock at altitude isn't going to make a damn bit of difference, because the shock canister is rigid. If it were a balloon, and could stretch, the pressures would equalize, but since the volume of the shock's air chamber is rigid, that doesn't happen.