SETTING UP AIR-SPRUNG SUSPENSION
Finding the correct spring rate (ie. air pressure) for your bike, riding style and terrain is vital. A fork or shock that’s too stiff or soft can be dangerous, or at least make your bike uncomfortable or difficult to handle. Sit in the saddle wearing your riding gear and pack, and with the compression damping fully open. On a long-travel bike, tweak the air pressure until the rear shock sags 30 per cent into its travel. For a trail bike, try about 25 per cent. You can adjust these figures to suit your riding, but not by more than a few per cent, or you’ll start to upset the bike’s dynamic geometry. For suspension forks, 18 to 20 per cent sag is common.
Set the rebound first, as this is directly related to spring rate. (Higher pressures require more damping to keep the suspension controlled as it re-extends after a bump.) Starting at the rear, turn the dial until the shock only oscillates once after a good-sized compression, such as riding off a kerb. Then increase or decrease the damping one click at a time until the suspension is quick enough to actively track the ground and recover between hits (otherwise it’ll ‘pack down’ into its travel and begin feeling harsh), without bouncing you down the trail. Match the fork rebound feel to the shock.
Now the spring supports your weight, you can adjust the compression damping. Low (shaft)speed compression controls how the suspension responds to pedalling, pumping and bodyweight shifts under braking. High-speed compression limits how fast it can move to absorb impacts. Start with the manufacturer’s recommended settings (or low-speed in the middle and highspeed fully open), then turn the dial one or two clicks in each direction to find the behaviour that best suits your riding style/terrain. Compression damping reduces suspension sensitivity, so only add as much as is needed to increase support.
The next step is to set up the damping. Bear in mind that although many suspension forks and shocks offer external rebound and compression adjustment, these dials have to cover a wide range of spring rates. So, there will usually only be two or three ‘clicks’ of adjustment that you can use to fine-tune things for your particular weight, riding style and preferred trails. Lighter riders (low air pressure) will be at one end of the settings range, while heavier folk (higher air pressure) will be at the other.
If you’ve got your sag and rebound correct but find yourself using too much travel too often, you need to make the spring curve of the fork or shock more progressive, by installing volume spacers. These reduce the volume of the air spring, which increases the end-stroke ramp-up for a given pressure. If your sag is correct but you can’t reach full travel, try removing volume spacers (if you have any installed), one at a time. This will make the spring curve more linear, with less ramp-up. Remember to record your pressures before releasing air from the fork or shock to install or remove tokens.
Getting the balance right between the front and rear suspension is vital to get the most from a bike. If the fork is overly firm, supportive or fast compared to the rear end, this will shift the weight balance backwards, negatively affecting handling. The opposite is also true, and potentially more dangerous. If you bounce the front and rear suspension together in a flat car park, the fork and shock should offer similar support and shaft speeds under compression and rebound. Adjust the damping until they do.