26 Apr 2016


Mountain bike full suspension setup can seem daunting, and the more adjusters there are to twiddle, the more like black magic setting it up can seem. Approach it methodically, however, and you’ll have your bike flying in no time.

We’ve looked at hardtails and covered how to set up a suspension fork  before, and the principles don’t change just because there’s a rear shock involved. Combine the above fork guide with this for the perfect setup – but start here with the shock.

You need:
• A shock pump
• A ruler (steel is best, and short for getting into tight spaces)
• A calculator. Alternatively, a good head for percentages!
• All your riding gear
• A wall or post to lean the bike against
• An assistant (ideally)

Sort your sag – use the rubber O-ring on your shock as an indicator

Sort your spring
The first thing to do is set the sag. By doing this you’re setting the basic spring rate, making it appropriate to your weight. All other adjustments follow. The sag is how much the suspension compresses with you aboard, stationary. It’s typically between 20 to 30 percent, with XC at the tighter end and trail or downhill needing more.

How to calculate sag
It’s trickier to measure on the rear than the front, because here the stroke is not the same as the travel. You may have 100mm rear travel, for instance, but it’s the shock’s stroke length – say, 38mm – that you must work with.

Either measure the shock shaft or look up its dimensions on your bike manufacturer’s website. If the shaft doesn’t slide all the way in (some don’t), deflate the shock, fully compress it and use the telltale (O-ring or ziptie) to find out where to measure from.

Next, calculate what your desired sag is in millimeters. For instance, if you want 25 percent, divide the shock travel by 100 and multiply the answer by 25. So if your shock travel is 38mm:
38mm ÷ 100 = 0.38mm
0.38 × 25 = 9.5mm
Here, 25 percent sag is 9.5mm. Either round it up or down!

How to get it
Wearing all your normal riding gear (so your weight is right), position the bike against a wall and bounce a few times to let the suspension settle. Don’t hold the brakes, and don’t lean any weight on the wall – use just an elbow to keep yourself upright.

While sitting, get an assistant (if one is available) to carefully push the rubber O-ring (or ziptie) up against the seal, then gently slide off the bike without pushing down. It can help to drop the saddle first.

Lift the rear wheel to make sure the shock is fully extended. Afterwards, measure carefully between the telltale and the shock seal. Adjust air pressure in 5 or 10psi increments until the measurement is correct.

Once you’ve set the fork sag, it’s time to move on to rebound and perhaps compression settings – again, revisit our suspension fork guide for how.