Results 1 to 7 of 7
  1. #1
    mtbr member
    Join Date
    Jun 2010

    Air Pressure to get 30% sag

    I called Pivot about the right way to measure sag. He told me to have someone told the bike straight, sit on the bike, stand on the pedals, plop on the seat, stay put, have the helper slide the washer up, get off and measure it.

    I tried this 5-10 times and never had two exact measurements, but all somewhere around the recommended 0.74" for a medium Mach 5. A couple were more sag, but most were less. I though the stroke on this bike is 2.25" and so 30% of that is 0.675" and not 0.74", so who knows??

    I'm 170 lbs and maybe 175 lbs with all my gear. I found an old post from 2009 where the guys around my weight were running much less air - maybe around 90 psi. I have mine set at 150 psi.

    Am I running too much air for my weight?

  2. #2
    mtbr member
    Reputation: bauhaus's Avatar
    Join Date
    Feb 2007
    I weight 165 and run about 120 to 125 lbs. I am getting between 30 and 35% sag.

  3. #3
    dog is offline
    sit! stay!
    Reputation: dog's Avatar
    Join Date
    Aug 2006
    yeah, it's a pain... it can depend on everything from the leverage ratio to where you are on the saddle... if you think it's close, try runninging it on a road or parking
    lot... position yourself like you normally ride and rock in the saddle, pedal hard and/or bounce little in the saddle. you'll probably feel the bike pass through the sweet spot of resistance... then you can get an idea if the sag in a normal seated position is ahead or behind the sweet spot... assuming all that made sense... but it's one way to tell if you need a little more or less air...
    i need to develop my crashing skills...

  4. #4
    Jamin, Applesause, No?
    Reputation: Senor StrongBad's Avatar
    Join Date
    May 2009
    150 psi seems hi to me. I am 210 or so and run mine between 160 and 170. I find it works best for me to set it in the parking lot before my ride them about 1 mile in, I stop and check it and pressure it up from there. I use the stop and hold onto a tree method in a flat section of the trail. There is also a nice rock next to the tree that alows me to easily dismount without compressing the shock anymore.

  5. #5
    c'est la vie
    Reputation: Maluco's Avatar
    Join Date
    Sep 2005
    My suggestion comes from my motorcycle days -if the suspension is not warmed up it tends to have more stiction and never gives consistence sag readings. Also, very low temperatures cause more stiction and false sag readings.

    This assumes you have a few miles on the bike, a new shock and fork that are not bedded in yet will NOT give correct sag measurements.

    Also, make sure your pro-pedal lever is set to off.

    First off, turn the bike upside down for say 10 or more minutes. This allows the internal lubricant to leak down into the fork and the top of the shock seals. A good idea to do before any ride.

    Second, get on the bike and ride say 10 to 15 minutes depending how cold it is. In hot weather this step is needed for say 2 or 3 minutes.

    Third, stop at a flat location you can get off the bike without upsetting the suspension. Before gently getting off the bike (a little tricky) make sure you have pushed the rubber rings to the shock and fork seals. Take sag measurements and make adjustments to PSI. The sag measurements should be repeatable at this point with the shock. With the fork a 2mm deviation in sag readings is normally acceptable.

    The trick is to focus on sag and not PSI.

    Hope this helps.
    "Who are you?"
    "That's a long story." -Christopher Walken, The Prophecy

  6. #6
    mtbr member
    Reputation: scoutcat's Avatar
    Join Date
    Mar 2008
    if you have the boost valve shock and are really 170 then your pressure should be around 120.

  7. #7
    mtbr member
    Join Date
    Jun 2010
    Ok I set it at around 120-125 psi and will check it again after a ride. It's funny - either my scale is off or I can't set sag for the life of me. At 125 psi I get around an inch, so I'm assuming I'm leaning too far back and will leave it as is.

    Looking at the Pivot website:

    It says to set the sag at 30%, so for a medium Mach 5 it should be 0.675". The math does add up since the website above has 0.74" for that frame. 0.74" of a 2.25" stroke is about 33%. I called Pivot and the sales rep wasn't sure either. He said he'll look into it and get back to me.

    I'll post what he tells me, but in the meantime thanks all for the help!

Members who have read this thread: 1

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts



VISIT US AT and the ConsumerReview Network are business units of Invenda Corporation

(C) Copyright 1996-2018. All Rights Reserved.