Why use the spring calculator?
- Without the correct spring for your weight, bike geometry and riding style, the performance of your rear suspension (however well maintained) will suffer, as will your performance on the trails.
- This said calculating the correct spring involves some technical calculations but we have done our best to help with this.
Information required in order to successfully use our spring calculator:
You will need three pieces of information, which are listed below. If you don't have these, though, don't worry. Instructions on how to get the information are provided below the spring calculator.
- Your weight in full riding gear
- The stroke length of your shock
- The wheel travel of your bike/suspension
Spring Calculator
To be used as a guide to spring selection. The spring rates recommended give a sag of around 28 or 30%.
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, but they 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 initially. 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.
| |
Eye to eye (mm) with percentage sag |
| Eye to Eye x Stroke |
20% |
25% |
30% |
35% |
40% |
45% |
50% |
| 6.5 x 1.5" |
165 x 38mm |
157 |
155 |
153 |
151 |
149 |
147 |
145 |
| 7.5 x 2.0" |
190 x 50mm |
180 |
177.5 |
175 |
172.5 |
170 |
167.5 |
165 |
| 7.875 x 2.0" |
200 x 50mm |
190 |
187.5 |
185 |
182.5 |
180 |
177.5 |
175 |
| 7.875 x 2.25" |
200 x 57mm |
188 |
185 |
183 |
180 |
177 |
174 |
171 |
| 8.5 x 2.5" |
216 x 63mm |
203 |
200 |
197 |
194 |
191 |
187 |
184 |
| 8.75 x 2.75" |
222 x 71mm |
208 |
204 |
200 |
197 |
193 |
189 |
186 |
| 9.0 x 2.75" |
230 x 71mm |
218 |
214 |
210 |
207 |
203 |
199 |
196 |
| 9.5 x 3.0" |
241 x 76mm |
226 |
222 |
218 |
214 |
210 |
206 |
203 |
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.
Enter your details below and click 'Whats my spring?' and the results will appear in the 'Recommended Spring Rates' fields below
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 length e.g. 140 = 2.5" or 2.75" stroke, 160 = 3.0" stroke & 180 = 3.5" stroke.
How do I determine the stroke of my shock?
The stroke of a shock refers to the amount of travel available. There are 2 ways of obtaining this for yourself;
- It can easily be measured by taking the distance from the main body of the shock to the end of the shaft (see the photo above).
- You can find it on the manufacturer's website. If you do this, 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!
Failing this you can phone us on 01373 826800 – we don’t have the information for all shocks/bikes but if we do we will certainly help.
How do I determine my Wheel Travel?
Due to the multitude of different suspension linkage systems, it is very difficult to tell you how to measure your wheel travel at home. The best thing to do is to consult your manual, your manufacturer's website, or to give us a ring on 01373 826800. We don't have all the figures for every bike, but if we have the information for yours, we'll be more than happy to help!
What do spring rate figures mean?
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.
Why use 28 & 33% sag
These are 'ball park' figures as recognised sag for XC = 20-30%, Trail/Freeride = 25-35% & DH 30-40%. You therefore have to alter the recommended spring figure according to your style of riding.
What if I'm doing drops?
Generally you will need a 10-15% higher spring rate than recommended for 28% sag, if you're into hucking. This may mean you need 2 springs for your bike ... one for DH/Trail and one for Hucking
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