Spring Rate – Printed vs. Measured Ratings

This isn’t meant to be an article detailing who has the most accurate springs, but more to bring light to the fact that the spring rate that is printed on the side of your coil spring sometimes isn’t as accurate as you might think.

The value on the side of the spring can fluctuate a bit from spring to spring. Certainly there is an accuracy percentage range that all manufacturers aim for. The reality is that most springs do not measure the same as their printed value, so this is more of an educational tip for those who are looking to get the right spring. The measured value can easily be higher or lower than the value printed on your spring.

For example, if the tolerance is set at say 10% for a steel spring from Manufacturer A, then a 350lb spring could measure between 315lb and 385lb. Similarly, a 400lb spring could measure between 360lb and 440lb within these same guidelines. So a 350lb spring could give you the same real spring rate and sag as a 400lb spring! The heavier the spring, the greater the chance for the spring to measure higher or lower given the same percentage tolerances.

We have gathered a small sample batch of springs that we had tested. This sample batch was examined just to illustrate the point that the measured value on the side of the spring isn’t always what you think it might be. If you get a few springs (even from the same manufacturer) that all have the same printed value on them, it might be worth your while to check the values of the springs you have verified (or try another spring that has the same value) if you’re not getting the sag you’re after.

Sample Batch (all steel springs except where noted)

* check the gallery for large images

, Spring Rate – Printed vs. Measured Ratings

FOX Racing Shox 600lb spring = 607lb actual

, Spring Rate – Printed vs. Measured Ratings

FOX Racing Shox 450lb spring = 440lb actual

, Spring Rate – Printed vs. Measured Ratings

FOX Racing Shox 350lb spring = 361 actual

, Spring Rate – Printed vs. Measured Ratings

Manitou 600lb spring = 609lb actual

, Spring Rate – Printed vs. Measured Ratings

BOS 225lb spring = 232lb actual

, Spring Rate – Printed vs. Measured Ratings

Rock Shox 500lb spring = 490lb actual

, Spring Rate – Printed vs. Measured Ratings

Rock Shox 350lb spring = 334lb actual

, Spring Rate – Printed vs. Measured Ratings

Cane Creek 550lb spring = 542lb actual

, Spring Rate – Printed vs. Measured Ratings

Cane Creek 350lb spring = 342lb actual

, Spring Rate – Printed vs. Measured Ratings

Cane Creek 300lb spring = 293lb actual

, Spring Rate – Printed vs. Measured Ratings

Nuke Proof titanium 350lb spring = 362lb actual

, Spring Rate – Printed vs. Measured Ratings

DSP titanium 200lb spring = 201lb actual

, Spring Rate – Printed vs. Measured Ratings

Elka 200lb spring = 205lb actual

, Spring Rate – Printed vs. Measured Ratings

Elka 250lb spring = 262lb actual

, Spring Rate – Printed vs. Measured Ratings

Elka 450lb spring = 472lb actual

So how were these springs tested?

Fadi at DSP tested these for us awhile back. We asked about his method of measuring the springs. The method he used on their Intercomp spring tester is below:

All springs were preloaded

3.5 springs were preloaded 1.25″
3.0 springs were preloaded 1″
2.75 springs were preloaded .75″
2.5 springs were preloaded .75″
<2.25 springs were preloaded .5″

1/2 stroke of shock -.5″ is starting point of test.
1/2 stroke of shock = .5″ is ending point of test.

This test gives a good indication of the spring rate in the middle of its stroke (neglecting the 1mm -4mm of preload).

When the spring is not flat and gets preloaded, it straightens again just like on a shock during its application. This does not affect its rate. When springs are not very straight, its spring rate goes down not up.

Our (DSP) spring rate came out very good, but you must remember that all springs have a range of error as a percentage. The higher the rate of the spring, the percentage of error is the same, but the spring rate value is increased.

EXAMPLE:

200 lb spring (assuming 2% error range): 196 – 204 allowed (8lb range difference)
500 lb spring (assuming 2% error range): 490 – 510 allowed (20lb range difference)

There are a variety of people who offer to check springs for you. If you know a tuning shop chances are they have a way to measure the spring rate. PUSH Industries and DSP for example can do this for their customers as well. Check with your favorite tuner to see if they can measure your springs for you if you’re curious.

Certainly this isn’t something you have to do when you buy a coil spring, but it can help you narrow down issues if you are having problems with getting the right sag with a coil spring that is recommended for you. Sometimes riders crank down the preload ring too much on a spring which is not what you want to do. Ideally you don’t want to turn it more than the recommended turns stated by your shock manufacturer in your manual. Learn more about the basics of how to measure a shock.