Suspension Fork Maintenance
Recommended weights of oil and air pressures should be verified by reading your owner’s manual – those provided below are for the Fox Float 140, which is a popular, good quality air/oil shock.
Most shocks are initially tuned for an average weight rider (140 to 180 lbs) doing average riding (primarily all mountain or cross-country). For those of you who don’t fit into this “average” category, adjustments can be made to improve (sometimes, significantly) on your shock’s performance.
Oil thickness (viscosity) will determine the compression and rebound speed of your shock. The thicker the oil – the more resistant the shock is to compression and the slower the rebound. Typical oil weight is SAE 7.5. For light riders SAE 5 should be used, for very heavy and hard riders, as high as SAE 10 could be used. To improve the rebound speed lost by using the thicker oil, the air pressure can be increased.
The amount of oil (or oil height) in the shock can be varied to also provide additional tuning. By using more oil, the volume of air is reduced, which will make the shock stiffer at the bottom of its travel and make it less likely to “bottom out”. Light riders, who are less likely to be bottoming out the shock, can therefore ride with less oil and get a more consistent compression through the whole travel, while heavier riders should ride with more oil to reduce the chance of bottoming out.
Air/oil shocks often have Alan key or knob adjustments which allow you to set the threshold pressure required to open the oil valve ports in the shock. For a softer, cushier ride you would set it to a lower threshold by loosening off the adjustment. For a heavier, harder rider the threshold would be set higher so that the shock doesn’t start compressing on every little bump.
So, pick up your owner’s manual and read up on your shock – you may be surprised how much you’ll be able to fine tune the performance of the shock to suit your riding style.