Air vs. coil shocks. It's a well-worn debate, especially when it comes to downhill bikes, although coil shocks continue to be the more popular choice on the World Cup circuit. But what about on trail bikes? If your bike had suspension kinematics that worked well with a coil shock would you run one? Or are you satisfied with the performance delivered by a modern air shock?
There are a few reasons why the vast majority of full suspension trail bikes (I'm using that term in the generic sense, to refer to anything that's not a DH bike) come with air shocks. The most obvious is the ease of setup – air shocks don't require shops to keep a selection of springs in stock; all that's needed is a shock pump and you can get set exactly the right amount of sag. It's also relatively simple to add volume spacers in order to adjust the amount of end stroke ramp up, something that's not possible with a coil shock. There's more trial and error when setting up a coil sprung shock, and in some cases riders may find themselves forced to choose between a setup that's a little too firm or a little too soft due to being in between spring weights.
Speaking of weight, that's another reason why air shocks are so prevalent. Installing a coil sprung shock typically incurs a .5 pound weight penalty vs. air. That's not an astronomical amount, but it's certainly something to keep in mind.
If air shocks are easier to set up, and weigh less, what are the benefits of a coil shock? Well, traction is the biggest one. Modern air shocks have excellent small bump sensitivity, but it's still really hard to beat the supple, ground-hugging feel of a coil. That extra grip is particularly useful in wet or loose conditions, situations where you want your rear wheel firmly planted on the ground. They also tend to maintain a more consistent feel on long, rough downhill runs, although that difference has diminished a bit as air shock technology has progressed. On the flip side, coil shocks tend to have less a less 'poppy' feel to them compared to air, due to their more linear spring rate. If you're the type of rider that tends to boost off of every little bonus feature you can find a coil shock might not deliver the ride characteristics you're looking for.
The extra-plush, supple feeling delivered by a coil shock is one of the reasons we've been seeing them appear on more and more shorter travel machines. There's also the fact that there are more shorter stroke options than ever; for a time it was difficult to find coil shocks that would fit anything other than a freeride or DH bike. And don't forget about that climb switch, the little lever found on shocks from all the major brands that can be used to firm things up for the uphill, and then opened up when it's time to go down. It's small detail, but it's another reason why coil shocks have become more appealing in recent years.
What do you think? Given the choice, would you pick a coil or air shock?