Rearshocks: Coil vs Air

The coil-factor. For AM bikes its somewhat to the favor for the air shock when looking at factory assembled bikes from various bike brands. But its quite common to see riders swap out their air shock to an coil shock - and then absolutely rave about it. I want to know whats that all about. And more importantly answer the ever present All Mountain question: "Should I go coil?"

So I did just that, swapped my Specialized AFR shock, and installed a well known coil shock - the FOX DHX 4.0. Now im not new to air-shocks, ive ridden the FOX RP2, the more heavy duty Manitou ISX-6, and been on a Specialized AFR 2008 and 2009. Coil shocks however is a new game for me, so I wanted to test this thouroghly. Ive been testing this shock for 4 months, ive taken it to 3 very different bikeparks, ive ridden some DH, done some considerable drops, some good sized jumps and everything in-between. And I really mean in-between, because ive also taken the coil shock to xc trips, AM trips, trail, street and what not. So here are my thoughts and learnings, categorized to give a better overview. First the basics:

Coil & Air characteristics:

Air characteristics:
Air shocks by nature have a non-linear spring rate, meaning the spring rate ramps up exponentially towards the end of the stroke. In plain English: The air shock will have a tendency to bottom out faster and harder. Air shocks are usually light, and have a good beginning-stroke support, air shocks are likewise more steady in the beginning-stroke - making it desirable for xc and trail riders.

Coil characteristics:
Coil shocks have a linear spring rate, meaning the shock will ramp up in the end stroke in a linear fashion. In plain English: The coil shock performs very good right untill the very end of travel. Coils are however more heavy and are more lively - and that can be a disadvantage for some.

This is a simplified grapfh I did, showing a coil (blue) and an air shock (red). The coil is very liniear all the way through its travel. Air shocks takes a bit more to "activate", and has a weaker midstroke support, by going faster through its travel. The airshock also bottoms out faster than the coil.

(Click to enlarge)

So thats the (simplified) basics, how does all this reflect on the trails and riding types? Well lets take a look:

XC: Forget about coil. Install a good air-rearshock like the FOX RP23 or the newer Rockshox Monarch, and enjoy a bob-free ride, where youll feel no efficiency lost when hammering the pedals. The coil will drag you down, and wont contribute to anything positive.

Trail: Go air, air shock are very much capable for all manners of trail riding, you will most likely be slower on a coil, compared to a good air-shock.

FR: If big hits and aggressive riding is your thing, then youll most likely get most out of it via a coil. The very liniear end-stroke makes jumps or drops feel more controlled, and way more smooth. You can still pedal, but youll work a bit harder to do so. Air shock comes short at FR due to its poor midstroke/endstroke support (compared to a coil). This is generally speaking.

DH: Want the best ground tracking, and the best rockgarden swallowing capabilities, then go for a coil. The coil will pretty much ease up everything when going downhill, and make you a faster rider. Sag it all you can, and watch the coil do its buisiness. Air shocks will eat the travel way faster when sagged deep, and wont ramp up in the end stroke, to give you a smoother ride, and leaving you with less control.

AM: Ok, the tricky one for last, and its tricky because it really depends on your trail - and what your priority is. But let me put it this way:

If your trail mostly consists of:

Technical climbs - Technical descends : Go air.

Technical climbs - Easy descends : Go air.

Easy climbs - Technical descends : Go coil.

Easy climbs - Easy descends : are you riding AM?

Summary

You might have noticed that I haven't mentioned the Fox DHX AIR, or the new Monarch Plus, or the Manitou ISX-6. Heres why; from what I have experienced, and from what ive been reading and hearing from AM users, air shocks like the Fox RP23 (2010+) and the Rockshox Monarch (2010+) are very much capable to tackle very demanding terrain, and have over the years been fine tuned to suit the AM market, some of the improvements have been done to the midstroke and endstroke feel. This has resulted in some very good air shocks, that continue to impress end users. Fox even declared its RP23 to be FR compatible in 2010, thats how much they believe in their RP23 performance. These are good times for All Mountain riders.

My AFR shock is good for XC, trail, and light AM. But it ignores the end stroke, and eats the mid stroke way too fast. Classic airshock downfalls.

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Im using the coil for bikeparks. It lets me sit deep into my sag, without blowing through the rest of the travel. Great for aggressive riding. It also smooths out the hits, and that really adds to the control. It gives a very good ground tracking.

(Click to enlarge)

The ISX-6 is an airshock that tries to mimic some of the features we see on a coil. It has good midstroke performance, but ends up a bit too fast in the end stroke. Initial stroke is a bit too lively as well. Overall, it feels like a shock that wants to do alot of things, but fails to properly succeed.

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So that pretty much sums it up. Its really a daunting task to elaborate why one should go coil or air with a few more words than just "its way batter man!". Ive done my best here, with what ive learned on the trails.

Heres is what I personally do; When going to a bikepark, a DH session, or something gravity oriented, I put on a coil (it takes me less than 10 minutes to switch, so its no biggie). If im up to technical riding, where climbs are tough, I stick to my air shock - thats how I roll, so to say. Thanks for reading.