| WORDS: Myles Kelsey | IMAGES: Eric Palmer |
While incredible advances have been made with air shocks for mid and long-travel machines, the consensus is they don’t quite level up to coil shocks. High breakaway forces, poor heat management, pressure loss and other complications hinder the performance and durability of air shocks. Coil shocks on the other hand are generally more reliable and easier to set up, but they come with one issue — they do not have an adjustable spring rate. Altering the spring rate requires buying a new coil.
The main problem with coil springs is that spring rates are mostly only offered in 50-pound increments, or, in some cases, 25 lb. Inside that large increment lies a lot of fine-tuning potential (and performance advantage) that is essentially not available to coil spring riders. A second problem is both the sourcing and availability of coils – they can be very tricky to find. The result is a lot of riders end up riding a bike that is too soft or too hard. Enter the Sprindex coil spring. It’s an externally adjustable coil spring system that allows riders to fine-tune the coil rate.
How does it work?
The Sprindex coil has a glass-reinforced polymer adjuster on the coil. Operated by hand, it effectively shortens or lengths the coil, by ‘locking’ off a portion of it. When shortening the part of the coil that is free to move, the coil will become harder and the spring rate is effectively increased. Reversing the process then reduces the coil rate. It is an extremely simple yet clever solution to a problem coil shocks have had for decades.
The Sprindex coil is available in different sizes and spring rate range options that can be fitted to almost any Trail, Enduro, eMTB or DH bike. The pack includes a spring, an adjuster and performance adaptors that are specific to the model shock being used. The adaptors also prevent coil binding. High-grade tensile steel is used (so it’s pretty light) and the entire package is around R2800 or 150 USD.
Fine-tuning suspension performance is a far more complicated task on longer-travel bikes. Hence, I figured the best test of the Sprindex system would be on a 200mm downhill bike. I’m 71 kg and used a size R2 Trek Session downhill bike for this test. With the stock 450lb spring, I’m on 15% sag and am therefore a tad over-sprung meaning I’m not unlocking the bike’s full potential. The guys at Sprindex sent a 400 to 440lb spring and it took about two weeks to arrive from the USA.
Installation was really simple – it’s as easy as swapping out any coil spring and took me all of 10 minutes. With the Sprindex system fitted I headed back to Hellsend Dirt Compound — where I last rode the bike — and did some comparison testing.
With the selector at 425 lb (about 23% sag), the difference on track was immediately noticeable. I felt the breakaway force to get into the travel was way lower, the bike floated over square edge hits easier and there was a lot more grip on off-cambers and corners. All of these are performance gains one can expect when moving from an over-sprung to a correctly sprung suspension setup. Further testing also showed the difference in ride feel between each of the 5 lb indexes is subtle, but noticeable.
Another upside of the Sprindex system is the ability to accurately alter spring rates and fine-tune them specifically for the trail you are riding. For example, on a smoother flow trail or jump line, I’d run the adjuster at 435 lbs to give more ‘pop’ and handle the hits better. Conversely, on a steeper techy line, I might run the adjuster as low as 420 lbs to help the bike ‘sit in’ a little, improve small bump performance and maintain traction. This on-the-fly adjustability simply isn’t possible on standard coil setups.
What about shorter travel categories?
Right, so on a downhill bike, I’ve experienced that Sprindex does exactly what it is advertised as doing, without any perceived downsides. Looking at the eMTB, Trail and Enduro categories there’s no reason riders won’t experience the same performance gains from Sprindex. A further advantage would be on long climbs where increasing the spring rate will improve pedaling performance – especially on analog bikes.
Endless tinkering with shim stacks, LSC, HSC or preload adjustment might get you halfway there but there is no better way to unlock the full performance of a coil-shock bike than by running the correct sag — and this is what the Sprindex does. It’s a simple solution to the age-old issue of getting the right spring rate for coil shocks. What an amazing product.