The balance beam between positives and negatives for coil-sprung vs air-sprung MTB shocks can be frustratingly even once both lists are compiled. With all of the potential advantages on the table, air shocks often win the prize for the simple fact that their spring pressure can easily be adjusted to suit a specific rider and trail.
The folks at Sprindex have created a coil spring that eloquently addresses this issue by adding an adjustable collar at the base of the coil, allowing riders to change the spring rate without touching any tools. The glass-reinforced plastic adjuster blocks or frees a specified amount of the spring to create different spring rates. Or, as the company puts it, the adjuster is “altering the number of active coils available for deflection.” Riders no longer have to choose between a spring that’s too stiff or too soft for their bike and body weight. The springs can be purchased in all of the usual sizes and weights, with a range of 50 lb of adjustment.
Mounting the Sprindex is as simple as any stock coil. There are a series of adapters to give it a tight fit with a variety of shock bodies, so as long as you have the correct length and stroke it should be as quiet and tight as the spring that you’re replacing. Once it’s slid into place you can click the spring-rate adjuster to set sag as desired.
I have been testing a Sprindex coil with an Öhlins TTX22M shock on both a Privateer 161 and a Raaw Madonna. The Madonna has a higher leverage ratio than the 161, requiring a stiffer spring to resist that force, and with the Sprindex I am able to use the same spring for both bikes. The Privateer works well with the spring clicked down to about 455 lb, and the Madonna likes the full 500 lb. It’s notably unique to be able to take the coil shock from one bike and mount it on another without swapping springs.
Not only can you adjust the Sprindex spring rate between bikes, you can also tune the rate far closer than with any other coil for a precise rear-wheel feel. With 5 lb adjustment increments, riders can dial in their sag and desired support without purchasing piles of steel springs at €50-plus each. While the Sprindex spring is a little more expensive at €140 (available online), it’s high-quality functionality is worth the extra coin. If you’re feeling tired and want some additional give at the rear tire, reach down and click the dial with one hand. So simple. Similarly, if you are riding with a heavy pack you can add 5 lb to compensate.
Unlike a lot of coil springs, the Sprindex coil is progressive. The spring ramps up with additional pressure in the final 20% of the stroke to increase bottom-out support. The difference between this and a typical linear coil is immediately noticeable on the trail, and the advantages extend beyond bottom-out support. When you’re deep in the travel on a turbid chunk of trail that added resistance also rebounds with more force than the previous 80% of the spring, providing a sweet kick to bounce the bike out of deep holes and compressions. It doesn’t make coil shocks feel like air shocks, but it does provide some amount of the end-stroke benefits that air springs are known for.
The blocked portion of the coil wire is not the same as tuning preload. According to Sprindex, “Preloading does not change spring rate but preload does change the force to start moving the shock, and high preload dramatically reduces shock performance over smaller bumps and makes for a more harsh ride and worse traction. Spring rate is the force required to move a certain distance whereas preload adds a fixed force across the whole stroke. Heavy preloading can add over 100 lb (45 kg) of force required to start shock movement whereas optimal shock performance comes from the lowest starting force possible. Heavy preload means those smaller bumps won’t even move your suspension.” The brand unpacks this topic further on their website.
It’s hard to find anything but words of praise for this product. It’s a simple solution to a long-pondered conundrum, and the user experience has been entirely positive. The only hangup I can see is that the spring is slightly wider than some stock models, and it may not fit all bikes. If you own a frame with a shock tunnel, like a Megatower or Specialized Enduro, you may want to take a few measurements prior to purchase.
⭐️ Sprindex adjustable rate spring coils are available for purchase online.
- Quickly adjust spring rate for a more precise tune
- Tool-free tuning that’s quiet and simple
- Fits most modern coil shocks
- Weight is similar to stock springs
Pros and cons of the Sprindex adjustable coil spring.
- Somewhat expensive
- Only available in black
- Wide spring may not fit all frames