MTB Coil Spring Rate
Calculator.
Enter your riding weight, shock stroke, leverage ratio and target sag to get the coil spring rate you need in lb/in and N/mm, with a spring to try on each side.
Results update as you type. Coil rates are rounded to the nearest 25 lb/in, the usual step steel springs are sold in. Buy the nearest rate, then fine-tune sag with a small amount of preload.
How the calculator works
Spring rate is the force in pounds needed to compress the coil one inch. We solve for the rate that puts you at your target sag: rate = (riding weight × 0.68 × leverage ratio) ÷ (stroke in inches × sag). The 0.68 is the share of your weight the rear wheel carries when you set sag.
Treat the result as a well-aimed starting spring, not a final answer. Leverage ratio changes through the travel on most frames, and your ideal sag depends on terrain and taste, so confirm sag on the bike and adjust the damper before you judge the spring. If you are stuck between two rates, size up for support and size down for grip.
MTB spring rate FAQ
It depends on four things: your riding weight (body plus kit), your shock stroke, your frame leverage ratio and your target sag. A 175 lb rider on a bike with a 2.6 leverage ratio and a 65 mm stroke, set to 30 percent sag, lands around a 400 lb/in spring. Heavier riders, higher leverage ratios and firmer sag all push the number up. Enter your own figures above for a rate rounded to the nearest coil that is actually sold.
Leverage ratio is rear wheel travel divided by shock stroke. A bike with 160 mm of rear travel and a 65 mm stroke has a ratio of about 2.46. Most trail and enduro frames sit between 2.2 and 3.0. Manufacturers publish it, or the average is easy to work out from the travel and stroke on the geometry chart. Use the average ratio for a first spring choice, then fine-tune with sag.
Around 30 percent of shock stroke is the usual coil starting point, a touch more than most people run on air because coils are more supple off the top. Riders who want a firmer, more supportive feel run 25 to 28 percent, while riders chasing traction and plushness go up towards 32 to 33 percent. Set your target here, then confirm it on the bike with a shock stroke indicator or an o-ring.
Steel coils are typically sold in 25 lb/in steps (400, 425, 450 and so on), and some brands step in 50. The calculator rounds your exact figure to the nearest 25 and also shows the spring on each side. Buy the nearest rate, then use a small amount of preload to fine-tune sag. Preload is for trimming, not for correcting a spring that is far too soft.
Pick by riding style. If you like a supportive, poppy ride, ride bike parks or find yourself using preload to stop wallowing, size up to the firmer spring. If you chase grip on rough, technical trails or you keep failing to reach full travel, size down to the softer one. When in doubt on a fresh setup, start with the firmer spring and drop down only if you cannot use the travel.
The spring rate you need is the same whatever the coil is made of, so yes. A titanium or lightweight steel spring in the correct rate behaves like a standard steel one of that rate, it just weighs less. Match the rate the calculator gives, then choose the material and the correct spring length and bore to fit your shock body.