Forum home Mountain biking forum MTB workshop & tech

Help With Setting Sag - RockShox Monarch R

DonLykeBDonLykeB Posts: 34
edited March 2018 in MTB workshop & tech
Hi Guys -

Recently bought a Boardman Team FS and although it’s been a great bike I’m having some newbie trouble with the rear shock.

Without any weight on the bike, the rear shock stays at around 30-40% sag, and when I try to return it to the original starting point is just pings back to 30-40%.

I’ve lost the schrader valve since purchase and that may be the issue. Could this cause air leakage?
It’s been quite cold in my area - heavy snow and temperatures of around -5 (Could this affect air pressure?)
I am quite a heavy rider, 115kg or around 250lb. I had the pressure set to 150psi when I bought it and I’m not sure whether there has been a leakage since I don’t have a shock pump yet.

If this means anything the rear shock felt sorta bouncy even with high rebound on, could it just be a matter of too low of a PSI? Would a higher PSI extend it back to it’s original position?

Many Thanks Everyone!

Posts

  • JBAJBA Posts: 2,708
    Not sure what you mean by "I've lost the schraeder valve". The valve is part of the shock.

    Anyhow, you need to get a shock pump and check the air pressure. Without checking the pressure you won't know if any has been lost.

    How long have you had the bike?

    As a rough guide the shock pressure should be the same as your weight in pounds. 150psi was therefore too low anyway.
    Get a shock pump and pump the shock up to 250psi and check the sag. Then increase or reduce the pressure to get the sag you want.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Bird Zero Mk1 ¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • JBA wrote:
    Not sure what you mean by "I've lost the schraeder valve". The valve is part of the shock.

    Anyhow, you need to get a shock pump and check the air pressure. Without checking the pressure you won't know if any has been lost.

    How long have you had the bike?

    As a rough guide the shock pressure should be the same as your weight in pounds. 150psi was therefore too low anyway.
    Get a shock pump and pump the shock up to 250psi and check the sag. Then increase or reduce the pressure to get the sag you want.


    Really sorry, told you I was a newbie haha - I meant the valve cap.

    250psi sounds like a lot but I’ll give it a try tonight, the max PSI of the shock says 275 so I hope I don’t damage anything.

    Other than that thanks for the reply, I’ll update whenever I get the shock pump tonight.
  • JBAJBA Posts: 2,708
    As long as you don't exceed the maximum psi it will be fine. Even at 250psi you are only at 90% max.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Bird Zero Mk1 ¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • JBA wrote:
    As long as you don't exceed the maximum psi it will be fine. Even at 250psi you are only at 90% max.

    I’ve posted this same question on Reddit and someone suggested it could be a broken internal seal as the suspension ‘resists’ when I try to pull it back into 0% sag.
  • JBAJBA Posts: 2,708
    They are surprisingly hard to pull fully extended.

    If you now have a shock pump the best thing to do is release all the air from the shock and then pump it up to 100psi. Compress the shock several times to allow the air to enter the negative chamber. Then pump up to the required pressure, stopping after every 50psi increase to cycle the shock a few times to ensure the negative chamber gets air in to it.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Bird Zero Mk1 ¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • The RookieThe Rookie Posts: 27,748
    The rule of thumb for shock pressures is pretty useless as the linkage ratio can vary from 2:1 to 3:1, obviously a 3:1 ratio will need about 50% more air pressure than a 2:1 with the same shock.
  • The Rookie wrote:
    The rule of thumb for shock pressures is pretty useless as the linkage ratio can vary from 2:1 to 3:1, obviously a 3:1 ratio will need about 50% more air pressure than a 2:1 with the same shock.

    Okay - Could I have a bit of advice here - I got the bike back today and it worked for a while and then went back to the same issue as I had before. I've left it with the LBS and they said they'd have their head mechanic look at it tomorrow.

    Could it be my weight? I weight 250lb exact - If this is the case could I please have some buying advice on an appropriate rear shock? I do really like the feel of a full suspension (When it worked atleast).

    About the ratios, I am not 100% sure where to find that information but here is the bike: http://www.halfords.com/cycling/bikes/m ... -20-frames

    I'd just like some overall clarification because I splashed a lot of cash (atleast relative to me :lol: )

    Many Thanks!
  • 02GF7402GF74 Posts: 1,294
    Was it bought new?
    I don't believe your weight is the issue. Fully dressed with backpack I probably don't weigh much less.

    Re. Without any weight on the bike, the rear shock stays at around 30-40% sag

    With no weight on it, it should be fully extended, else it is bollocksed.
  • 02GF74 wrote:
    Was it bought new?
    I don't believe your weight is the issue. Fully dressed with backpack I probably don't weigh much less.

    Re. Without any weight on the bike, the rear shock stays at around 30-40% sag

    With no weight on it, it should be fully extended, else it is bollocksed.

    I mean, the LBS said they replaced it (to be fair) with a new one (same model). But it was not bought new - however it is months old and the seller had said it was hardly used and never taken on a trail and I mean to my basic knowledge I can confirm this because cosmetically it didn’t have a hairline scratch.

    I might be running the PSI too high to be fair, as both times it had been set to 250 PSI - the seller had asked my weight and set it and when I got the second shock I did the same (against my better judgement, boy am I bad at this stuff haha)
  • The RookieThe Rookie Posts: 27,748
    Just randomly sticking pressure in a shock is a bad idea.

    I’m about 190lb ready to ride, I have the right sag (30% bike manufacturer recommended) at 90psi in the shock.

    Sounds like it’s blowing through into the negative.
  • DonLykeBDonLykeB Posts: 34
    The Rookie wrote:
    Just randomly sticking pressure in a shock is a bad idea.

    I’m about 190lb ready to ride, I have the right sag (30% bike manufacturer recommended) at 90psi in the shock.

    Sounds like it’s blowing through into the negative.

    Spot On - It’s blowing into the negative and the LBS confirmed this. Could it be too high a PSI? My weight (250lb, 115kg, 18st). I doubt it was bottoming out too hard as I never felt it bottom out and the sag band thing was always at around 60-70% tops. Hmm. Maybe the PSI was way too high...
  • 02GF7402GF74 Posts: 1,294
    As the selekter said, too much pressure.
Sign In or Register to comment.