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Help setting up shocks PLEASE

flyerflyer Posts: 608
edited June 2011 in MTB beginners
Having just upgraded my bike from a Hardrock I know nothing about air pressure in front shocks.

I have tried some reaserch am I on the right lines?

1. Put zip tie on shock
2. Sit on bike
3. Measure sag (this should be around 20-30% ?
4. So a 100mm shock should have about 20-30mm of sag?


Also not sure where the riders weight comes into it etc etc..

Any help much appreciated

Flyer

Posts

  • nicklousenicklouse Posts: 81,520 Lives Here
    set sag in normal riding position, so the attack (riding out of the seat).

    weight has nothing to do with anything. just add air to give the sag required.

    as to how to set up the fork depends on what it is.

    ( disregard most of the above if the fork is a coil fork with air assist).
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • AnonymousAnonymous Posts: 79,692
    flyer wrote:
    Also not sure where the riders weight comes into it etc etc..
    Riders weight will dictate the amount of air pressure needed to get the 25-30% sag.
  • TuckerUKTuckerUK Posts: 398
    It it's an air only fork, and your weight is at the upper spectrum of what is allowable for the fork, you may not be able to achieve full travel (I have this on my forks - coil conversion required).
    "Coming through..."
  • nicklousenicklouse Posts: 81,520 Lives Here
    TuckerUK wrote:
    It it's an air only fork, and your weight is at the upper spectrum of what is allowable for the fork, you may not be able to achieve full travel (I have this on my forks - coil conversion required).

    does not make sense.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • apreadingapreading Posts: 4,532
    nicklouse wrote:
    TuckerUK wrote:
    It it's an air only fork, and your weight is at the upper spectrum of what is allowable for the fork, you may not be able to achieve full travel (I have this on my forks - coil conversion required).

    does not make sense.

    I think what they are trying to say is that if you weigh 18 stone and set sag for 25%, the forks will be so solid because the air inside is already under alot of compression to resist your weight, that it takes alot more force to make the forks compress and full travel will be very hard to achieve without the internal pressure being too high for the forks to take it. I think at the extreme you therefore have to set for more sag to start with.

    Does that make sense?
  • supersonicsupersonic Posts: 82,708 Lives Here
    The sag compensates for this though. If it is already moving 25% with your weight, it will behave similarly to a lighter rider with the same sag. It takes more force, but you have more force ie your weight.

    This is why going on sag levels the playing feel. Forks and shocks can happily handle the max quoted pressures. Set your sag, note the pressure.

    But look at the dasmpers too.
  • RansakaRansaka Posts: 474
    supersonic wrote:
    The sag compensates for this though. If it is already moving 25% with your weight, it will behave similarly to a lighter rider with the same sag. It takes more force, but you have more force ie your weight.

    This is why going on sag levels the playing feel. Forks and shocks can happily handle the max quoted pressures. Set your sag, note the pressure.

    But look at the dasmpers too.

    This. I had air forks when I was 18st. Set them up as per the guide on here and they were buttery smooth over everything. Wish I had the air version of the Pikes on my current bike.
  • TuckerUKTuckerUK Posts: 398
    does not make sense to me.

    Fixed it for you.

    It does make sense to me, apreading, anyone it has happened to, and the two fork tuning companies I spoke to about it.

    There is no way I can bottom my forks with the 54psi preload I required to set my sag where I like it. I reduce preload and I can bottom the forks easily.
    "Coming through..."
  • TuckerUKTuckerUK Posts: 398
    Nicklouse, you've been very active in my post about the issues with my forks, so I'm sure it makes perfect sense to you!
    "Coming through..."
  • nicklousenicklouse Posts: 81,520 Lives Here
    TuckerUK wrote:
    does not make sense to me.

    Fixed it for you.

    It does make sense to me, apreading, anyone it has happened to, and the two fork tuning companies I spoke to about it.

    There is no way I can bottom my forks with the 54psi preload I required to set my sag where I like it. I reduce preload and I can bottom the forks easily.

    I would suggest that you have too much oil in the fork then.

    as it is ramping up too much.

    I now remember what you are playing with.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • supersonicsupersonic Posts: 82,708 Lives Here
    You do adjust sag though to your preference. Add more if you need it.

    Basically you can not equate pressures fork to fork ie 100psi in a Magura will behave totally different to 100psi in a Rockshox fork for the same travel.

    25% is just an average starting point. DH riders with more travel may want to up it to 30% or oven 40%. XC riders may like just 15%.

    In the end set it to what works best. Rider weight is rarely an issue unless you need more pressure than the maximum pressure.

    The only other issue is that some shocks with small volume chambers ramp up more quickly. But this is factored into safe working limits.
  • supersonicsupersonic Posts: 82,708 Lives Here
    ANd as nick says, too much oil reduces the air volume in some forks.
  • supersonicsupersonic Posts: 82,708 Lives Here
    Also worth adding that the negative spring can be used to tune ride height and feel too.
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