Workshop: Setting up mountain bike suspension
By Ian Collins, Mountain Biking UK | Wednesday, September 30, 2009 8.00am
Setting up your suspension correctly can massively improve your speed and control. Here we show you how to get the basics right. From this base setting you can then experiment and fine tune to suit your riding style and preferences.
Time: 30 minutes
Tools: Ruler/tape measure; zip-tie; screwdriver; shock pump
16-step guide to setting up your fork and shock
1 Rider weight is very important when setting up your bike and anything you’re wearing on the bike affects that. Throw on all of your riding kit. If you use a backpack, make sure you put all the tools, tubes and food you normally take in it and if it has a reservoir, fill it with the amount of water you usually carry. If it’s your downhill bike, then put on all the body armour you would wear on an actual ride.
> The next four steps show you how to set up an air shock. If you have a coil shock, skip to step 6.
2 You need to know the stroke length of the shock. Get this from your handbook or from the manufacturer’s website. If this isn’t possible, measure the eye-to-eye length of the shock. Let all of the air out and sit on the bike to bottom-out the shock, then measure the length again. Subtract the second measurement from the first and you have the shock stroke length. Re-pressurise the shock with your shock pump.
3 If there isn’t an O-ring around the shock shaft, then put a zip-tie onto it to measure the shaft travel. If the shock has a damping platform, such as ProPedal, flick it open/off. Push the O-ring/zip-tie up to the shaft seal. Leaning against a wall, get on the bike slowly, making sure it doesn’t bounce. Sit in a central riding position. Get off very slowly and carefully, leaning forwards so you don’t compress the rear shock.
4 Grab your tape measure or ruler and measure the distance from the shock shaft to the edge of the O-ring/ ziptie – this is the sag. For a cross-country bike we would recommend 25 percent sag as a starting point, 30 percent for a trail bike and 35 percent for a downhill bike. To work out the amount of sag you need, multiply the shock stroke length by 0.25 for cross-country, 0.3 for trail bikes and 0.35 for downhill rigs.
5 To increase firmness, connect a shock pump to the valve, check the pressure and add 20psi. You lose a small amount of pressure removing the pump, so you’re only adding about 10psi. Remove the pump and go back to step 3. To make the shock softer, fit the shock pump to the valve, check the pressure on the gauge, bleed off 5psi, remove the pump and go back to step 3. Continue this until you have the desired sag.
> The next three steps show you how to set up a coil shock. If you have an air shock, skip to step 9.
6 If you have a coil shock, you again need to know the stroke length. Get this from your handbook or from the manufacturer’s website. If this isn’t possible then you can make a physical measurement of the shock. Use a screwdriver to push the bottom-out bumper up the shock shaft. Using a tape measure or ruler, measure from the end of the shock body to the upper surface of the spring-retaining collar. This gives you the shock shaft travel.
7 Wind the spring preload collar all the way off and then add one turn of pre-load onto the spring. If the shock has a damping platform, such as ProPedal, flick it open/off. Measure the eye-to-eye length of the shock. Leaning against a wall, get on to the bike slowly, making sure it doesn’t bounce. Sit in a central riding position. You’ll need a friend now to measure the eye-to-eye length of the shock again.
8 Subtract the second measurement from the first for the amount of sag. See step 4 for how to calculate the recommended sag. To increase firmness, add a single turn of preload onto the spring at a time, then go back to step 3. More than four turns, and you’ll need a heavier spring. Continue this until you have the desired sag setting. If the shock needs to be softer, then you’ll need to buy a lighter spring.
9 You can find the base setting for rebound when you compress the suspension by pushing down on the saddle, then pulling sharply up – the rear wheel should leave the ground slightly. If it lifts right off the ground then there’s too much damping, if it pushes back against you and springs back, there’s too little. Start with it on minimum and add one click at a time until the desired result is achieved.
10 Compression damping can be hard to get right. The best technique is to start with the dial right in the middle of its adjustment range. Go riding, and if the bike feels harsh and inactive then remove a click at a time until it feels compliant. If the bike is blowing through the travel easily, add a click at a time until it’s stable, yet still plush. It’s a case of trial and error and does require some patience.
11 You need to know the maximum travel of the fork. Put a thin zip-tie around the stanchion. If you have an air sprung fork, let all the air out (positive chamber if it’s dual air) and compress the fork all the way down. Re-pressurise the fork and measure the distance from the wiper seal to the zip-tie. This is the maximum travel.
12 If you have a coil fork, first put a thin zip-tie around the stanchion, then remove the top caps. To do this, back the spring preload all the way off. Using a hex socket of the relevant size, remove the top caps. Very slowly compress the fork all the way down. Extend the fork again, refit the top caps and measure the distance from the wiper seal to the zip-tie. This is the maximum travel.
13 Push the zip-tie all the way down to the wiper seal. Leaning against a wall, get onto the bike slowly, making sure it doesn’t bounce. Stand up in a central, attacking position. Get off very slowly, leaning backwards so you don’t compress the fork. Measure from the top of the wiper seal to the underside of the zip-tie. This is the amount of sag. See step 4 for how to calculate correct sag.
14 To increase firmness for coil forks, add a turn at a time to the preload dial and go back to step 13. For air sprung forks, attach your shock pump to the valve and add 10psi at a time and then refer back to step 13. For forks with independent dual air chambers, add the same amount of air to the negative air chamber each time you increase the positive. Continue this until the desired sag is reached.
15 If you have a coil fork and you need to make it softer, you’ll need softer springs. For air sprung forks, attach your shock pump to the valve and bleed off 5psi at a time and go back to step 13. For forks with independent, dual air chambers, bleed the same from the negative air chamber each time you decrease the positive. Continue this until the desired sag is reached.
16 Set compression and rebound damping in the same way as you would for rear shocks. Follow steps 9 and 10, but push down on the bars then pull up quickly to see if the wheel clears the ground.
- It’s always better to err on the side of caution when setting the rebound damping on the rear shock. Too much is better than too little.
- Virtual pivot bikes and dw-link bikes have very specific sag settings. Go to the manufacturer’s website to make sure you get this right.
Topeak make a useful Pressure-Rite connector that has a check valve to stop you losing any pressure when you remove your shock pump.
- Our sag settings are just good starting points. Experiment to see how it affects the bike’s performance.
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