Spring Calculator

The stroke of a shock refers to the amount of travel available, and can easily be measured by taking the distance from the main body of the shock to the end of the shaft or damper body, depending on whether you have a coil or air shock. If you decide not to measure your shock stroke, you can find it on the manufacturer's website, or by phoning us. If you refer to the manufacturer's website, you will probably be given a figure like '8.75x2.75”', where 8.75” refers to the overall length of the shock, and 2.75” refers to the shock stroke. The figure you measure should be between 1.25 and 3.00 inches. If you get another figure, you're probably measuring the wrong part of the shock.

NB. Fox mark springs by quoting the maximum travel the spring will go to before it becomes coil-bound. e.g. 1.65 = 1.5" stroke, 2.35 or 2.38 = 2.0" or 2.25" stroke, 2.8 = 2.5" or 2.75" stroke & 3.25 = 3.00" stroke. All other brands mark the spring with either the stroke of the shock it is designed to fit eg 2.5" x poundage, or the range of shock strokes it is designed for eg 57.5-65mm (metric RockShox)

The term “wheel travel”  refers to the distance a wheel would move from the shock being fully extended, to being fully compressed. The easiest way to obtain this figure is probably to refer to your manufacturer's website or to give us a ring. If you're feeling ambitious, though, you can try to measure it yourself. To do this, you'll need to measure the distance as shown in the photo below.

The spring rate is the amount of force required to compress the spring one inch, and is measured in pounds. To determine which spring you need, you'll need to know which spring rate you need, and what your shock stroke is. A spring with a spring rate of 350 is easier to compress than one with a rate of 450, and is therefore softer. Springs are usually marked with their rate, and then the stroke of shock they're designed for, e.g. "350x2.75" 

NB. Fox mark springs by quoting the maximum travel the spring will go to before it becomes coil-bound. eg 1.65 = 1.5" stroke, 2.35 or 2.38 = 2.0" or 2.25" stroke, 2.8 = 2.5" or 2.75" stroke & 3.25 = 3.00" stroke. BOS mark their springs by quoting the free lenght e.g. 140 = 2.5" or 2.75" stroke, 160 = 3.0" stroke & 180 = 3.5" stroke

Sag is the compression of the front or rear suspension caused by the rider's weight & is the most important suspension setting (especially on the rear). Correct sag allows the wheels to follow the contour of the terrain as you ride and has the biggest effect on how the bike feels.

By having the correct amount of sag the wheels will not only be able to rise up over any obstacle it will also allow the wheel to fall into most holes. In this way the rider should not feel much variation in bike movement as you track across rough ground. Sag is expressed as a percentage of maximum travel.

Sag is very difficult to measure on front forks as it is difficult to know where to centre your weight on the bike. Some people ride with their weight way back over the rear wheel whilst others attack the trail & have their weight over the front. It is therefore difficult to make specific recommendations on spring selection or air pressures for forks apart from to go with the manufactures guidelines in your owners manual intially. If you find on the trail that things are too soft/hard adjust the air pressure or take another spring.

On Rear shocks sag is expressed as a percentage of maximum stroke and is best set at 20-30% for XC (firm), 25-35% for Enduro and 25-45% Downhill. The better damped a shock the more sag you can usually run because the compression damping will prevent the shock from blowing through it's travel. This allows you to run deeper in the stroke without blowing through the travel giving better control over braking bumps & cornering stability (due to lower centre of gravity).

The table below can be used to determine/set the correct sag on your bike. To set/check your sag you are going to need the help of a friend. Wearing your normal riding gear sit on your bike with your feet on the pedals (do this next to a wall so you can prop yourself up with your elbow). Push up & down allowing the the shock spring/air pressure to push your weight back up until it settles. Now get your friend to measure the eye to eye of the shock (distance between the shock mounting bolt centres). Check this distance with the table below to see if you have the correct sag.

Coil Rear Shocks: Spring preload fine-tunes the amount of sag & is done with the spring preload adjuster collar. Adjust the spring preload adjuster up or down to achieve the desired amount of sag. If you reach the manufactures maximum spring preload & the sag is too much, then go to the next harder spring. Turning the spring preload collar to compress the spring will decrease the amount of sag & vice versa.

If you need a new spring or advice on the selection of the correct one see spring calculator or call with details of your bike, style of riding & your weight.

Air Rear Shocks: To increase your sag reduce the main air spring pressure. To reduce sag increase the main air spring pressure.