We Ride Coil and Air Shocks Back-to-Back 54

Just don’t call it a comeback. Coil shocks are making their way back onto more and more non-DH bikes these days, helped by better shock design and better understanding of suspension dynamics in frame design. In other words, coil shocks are popping up on more and more bikes that were almost the exclusive domain of air shocks over the past 10 years or so. So what benefits are riders seeking that drive them to install a component can weigh almost twice as much as the one it just replaced, when just yesterday it seemed that building 27-lbs enduro bikes was all anybody ever cared about anymore? And what exactly happens to your bike’s handling when you go coil? We grabbed a couple of shocks from FOX and headed out for a little back-to-back action to find out.

The Hardware

In addition to the many different kinds of shocks we’ve ridden over the past years, one of our long-term bikes has had a FOX Float X2 on it for quite some time already, and we’ve previously reviewed both the climb switch and the non-climb switch versions of this shock with great results. Given that this particular bike sports a highly progressive rear suspension layout, it was always a prime candidate for a coil shock, which gave us the idea for this back-to-back test scenario. Somewhat unfortunately, FOX does not make a climb switch version of the DHX2 in the size we needed, so we took delivery of the standard version instead. 

Going Coil

Looking menacing with its piggy back design and an imposing orange spring, the DHX2 certainly makes a statement (not least on the scales, where this coil crusher weighed in at 776 grams compared to the air version’s 520 grams, for the same shock dimensions). The hydraulic adjustments mirror those of the Float version, while setting your sag is obviously done by figuring out the correct spring rate as opposed to just playing with the air pressure. We started out with the recommended spring rate for our weight and bike, but soon found that we needed a bit more to keep the bike from bottoming out too quickly. Going up from a 400 to a 425-lbs spring did the trick, along with approximately 3 full turns of spring preload and two extra clicks of HSC compared to our air shock baseline settings. With the adjusters properly dialed in, the bike felt close enough to the airsprung version in terms of its general behavior on the trail, although the differences between the two shock types would soon become readily apparent.

During our very first runs out with the coil bike, we literally stopped twice on the first trail to check the air pressure in our rear tire, convinced we’d find it half flat.

With the initial set-up taken care of, we gave ourselves a couple of months to ride the coil shock in order to get properly used to it and to iron out any on-trail issues. During our very first runs out with the coil bike, we literally stopped twice on the first trail to check the air pressure in our rear tire, convinced we’d find it half flat. That was all the coil shock’s doing…it certainly feels quite different in terms of how it deals with smaller bumps and the trail surface in general.

During the initial DHX2 testing period, we made sure to ride all the different types of terrain you’d expect to be able to take on with a modern enduro bike. Everything from long days out with smooth climbs and fast and flowy downhills, to more technical terrain with some airtime-inducing features thrown in for good measure. Throughout this testing, we found that our bike was still very much an excellent companion for it all. The main difference lies in how the bike reacts to rider input and to the trail. On the “plus” side, you get extra traction and a general feeling of surefootedness from the coil shock that adds another dimension of descending aptitude to your enduro bike. On the flipside, you also end up with a bike that is less poppy and playful, and that wants to stick to the ground a lot more.

In terms of pedaling efficiency, the coil shock also suffers from a lack of explosiveness. When you want to put down a few power cranks, the bike feels slightly more sluggish than its airsprung counterpart. Note that we are not talking about pedal bob here, we found both the air and the coil version fairly close in terms of how they deal with that, rather we’re referring to out-of-saddle efforts or more energetic pedaling. This has less to do with damping and more to do with spring rate curves in this case. Because the air shock has a much more progressive spring rate curve, it means that it provides a lot more support earlier in the stroke – i.e. when you are sprinting for example. This does not only have to do with the ACTUAL leverage ratio at sag, but also the SHAPE of the spring curve at that point. Because of the progressive spring rate of the air shock, the slope of the rate curve at sag and just after the sag point is also steeper, which influences how the shock is going to react to various suspension events caused by heavy pedaling, pumping, jumping, etc. Put simply, you cause a sharper change in total spring rate with less outside input on an air shock, which translates to a “platform” feeling on the trail. Note that we are taking the frame’s leverage ratio curve out of the equation for this part of the discussion since we are testing on the same bike.

For another recently published feature, we had the opportunity to ride an air and a coil shock from RockShox back-to-back on a 2018 Devinci Spartan in Whistler. The Spartan is also quite a progressive bike, and our findings match the FOX results in the present feature very closely. In our discussions with Duncan Riffle and Chris Mandell of SRAM/RockShox, the “adiabatic” nature of the air shock compression characteristics were referred to as a possible cause of the extra pop of air shocks. Whilst it could be taken at face value to mean “air springs are more progressive,” the simple fact remains: even DH-oriented air shocks behave quite differently to their coil-sprung counterparts.

Because of their aggressive looks and proliferation on DH bikes, people tend to equate coil shocks with more aggressive riding. This is however only partially true. On the right bike, the coil shock will be more confidence inspiring at speed over rough terrain, but when it comes to jumping and airtime, it’s hard to beat the bottomless feeling of a good air shock. With the coil shock on our test bike, we were able to confidently hit everything we usually do even with just a moderately stiff spring rate, testament to this particular frame’s progressiveness, but there is no doubt that the air shock provides a lot more margin for error and a much more controlled bottom-out experience.

In addition to the inherently more progressive nature of the air shock making it easier to live with on many frames, the ability to tune the spring rate curve with both volume spacers and air pressure is another advantage. Once properly set up for your frame, it is indeed possible to get pretty close to that "coil-like" behavior - in everything but small bump compliance. Whilst the air shocks featured in this article are far from sticky, the way a coil shock takes the edge of even the smallest bumps remains un-matched. We are really talking about high-frequency chatter and similar here, as the air shock does an admirable job on mid-sized rocks and such. The difference is more tactile than anything else.

Back To Back

At the end of the test period, we headed out for a day of back-to-back testing on a local loop we ride a lot. Featuring a good mix of speed, rough terrain, and some drops, this track would quickly help us really pinpoint the differences in behavior between the two shocks. For your viewing pleasure, we documented the day on video:

For this day of back-to-back testing, we ran each shock at our preferred settings, which involved a bit more HSC on the coil shock (two to three clicks). We were impressed at how effective this adjustment was in terms of dialing in the extra bottom-out resistance we needed on the coil shock, which is a fancy way of saying "the knobs do what it says on the box." Riding the two shocks back-to-back like this didn’t reveal anything we hadn’t already figured out, but it served to further underline how different the two types of shocks are on the trail. Note that we did not specifically set out to try to measure things like heat build-up on long runs, compression and rebound “fade” etc, nor did we attempt any timed measurements of any kind. Once again, our goal here was to hone in on how the different shocks “feel,” and not which one is “best.” A subjecto-objective measurement, if you will.

What’s The Bottom Line?

It’s a good time to be a mountain biker! With advances in knowledge of suspension design and the evolution of damping technology, we have more good options than ever when it comes to building our dream bikes. And while coil shocks are not for everybody, we are now at a point where they are a 100% valid choice for your enduro or trail bike – provided you have a frame with a suspension design that is progressive enough. If you want a bike that is super supple off the top and that leaves you feeling glued to the ground even through the roughest sections of trail, coil is for you. If you’re after maximum playfulness and more pop, you need to plop for air. In either case, a quality shock with multiple adjustments and a climb switch will help you get the most out of your bike.

About The Reviewer  

Johan Hjord loves bikes, which strangely doesn’t make him any better at riding them. After many years spent practicing falling off cliffs with his snowboard, he took up mountain biking in 2005. Ever since, he’s mostly been riding bikes with too much suspension travel to cover up his many flaws as a rider. His 200-pound body weight coupled with unique skill for poor line choice and clumsy landings make him an expert on durability - if parts survive Johan, they’re pretty much okay for anybody. Johan rides flat pedals with a riding style that he describes as "none" (when in actuality he rips!). Having found most trail features to be not to his liking, Johan uses much of his spare time building his own. Johan’s other accomplishments include surviving this far and helping keep the Vital Media Machine’s stoke dial firmly on 11.

Photos by Tal Rozow, Nils Hjord, and Johan Hjord