How to Setup Suspension
Bobby Ketchum | Wednesday, 07 October 2015
Now that you have got this nice bike with a proper air fork, let's run you through how to setup your suspension.
Most modern forks use an airspring instead of using a conventional metal coil spring because they're lightweight and more adjustable. They require a little more setup, but this guide will make it easier to get your air pressure right for the best performance.
You'll need a shock pump and something to measure with to perform this.
This is the amount of travel a fork or shock uses with you sit on the bike in a neutral position. For example, if you have a 100mm travel fork, you're generally looking for around 20% sag, which would be 20mm of travel used.
Measuring And Adjusting Fork Sag
1. First, make sure the fork's compression knob is fully open, not locked out. Put the bike near a wall to make it easier to balance. Get on and get in a neutral riding position, not sitting on the saddle but not really aggressive and over the handlebars. Gently bounce up and down a little bit to let the suspension settle. Have a friend slide the rubber travel ring down to the bottom of the fork and gently dismount the bike as to not compress the fork and move the travel ring. If your fork or shock doesn't have a rubber travel ring you can fit a zip tie around the tube instead.
2. Measure how far the rubber ring was pushed up and there's your sag measurement. You can see here that we measured 17mm of travel. 17/100 comes out to 17% sag, of course.
3. 17% may be slightly firmer than you want, so in this example, we'd release some air to make the fork softer. If you had 35% sag, you'd add air to firm it up and reduce sag.
Make changes in 5psi increments when the sag is close to what you want. A general rule for Fox forks is to take the rider's total weight in KG and put that amount in PSI into the fork. For a rider/gear combo of 75kg, 75psi will probably be close to 20% sag. Rockshox often has a weight/pressure chart on the lower left leg to make it easy. They also have sag marks directly on the stanchions.
Sag amount is preference, not a hard-and-fast rule, so you could run a XC fork real firm if you're running a flatter, less technical course like Mcleans Island. Trail bikes and long travel bikes usually like 25-30% sag. Just experiment with it.
Measuring And Adjusting Rear Suspension Sag
Setting up the rear shock is very similar to the fork, but with an extra step.
1. Just like above, make sure the shock's compression lever is fully open, put the bike near a wall, get on and settle in a neutral position. Have a friend push the rubber ring all the way up and gently get off the bike.
2. For our Giant riders, here's a handy chart showing the recommended sag (last two columns).
For everyone else, you have to first know the shock's shaft length and here's how to determine that. On Rockshox, it'll have a number like 165x38 on the shaft. The 38 means the shaft is 38mm long. Fox shocks aren't labeled so you'll have to measure them. The reason for knowing the shock's shaft length is because 100mm of rear suspension travel doesn't translate to 100mm used on the shock itself, due to geometry of the suspension.
3. Measure the rubber ring. Giant riders can directly reference the chart above. Everyone else can simply divide by the shaft length, as shown below.
This Fox shock is 38mm long, so take our measured 6mm and divide by 38mm to get 16% sag. Same as the front, I'm running this XC bike a little firm, but you're generally aiming for 20% and longer travel bikes often liking 25% or even 30%.
4. Adjust your shock pressure accordingly, get back on the bike to confirm and remeasure sag. Adjust air more if necessary. Done!
Bottoming out isn't necessarily a bad thing, unless it's happening all the time and on small drops and bumps. Generally, your trail bike should be using all of it's travel if you're hitting the big trails. If you're bombing down the Flying Nun or Vic Park on a trail bike and your rubber ring isn't at the top of the stanchion tubes, you have too much air. If you're blowing through travel on easier stuff, you probably need air.
Those red knobs on your fork and shock adjust rebound, the rate at which the fork/shock returns after being compressed. Your air fork will have rebound adjustment on the bottom of the fork leg on the damper side.
We'll save the technical stuff for a more advanced suspension setup article later, but here's a basic rule of thumb to get you started. If the bike is trying to buck you over the bars on jumps and stuff, your rebound is probably too fast. If the rear rides real harsh, try speeding it up. Adjust in 1 click increments. Even though the rebound knob might have 20 positions, there will only be a 2-3 click window of useful adjustment for your given air pressure. The 20 positions is to accommodate a wide range rider weights and air pressure.