Like A Coiled Spring

Like A Coiled Spring

“Enduro-bro. Do you even enduro?” “Nice fanny pack”. Ever notice how just as soon as something is ‘fashionable’ it’s somehow even more fashionable to mock the thing (or, more likely, your riding buddy for adopting the latest trend)?

That doesn’t remove the thing’s original attraction or advantage though. Take coil shocks. We’ve seen a number of top enduro racers over the last year or two running coil shocks, which has seen them adopted by everyday trail riders who realise that that it’s not just elite riders that benefits from coil shocks. So, before poking fun at your mate who now has a big orange spring in the middle of their frame, if you haven’t already, let’s consider if there is something behind the coil shock hype that might be relevant to a bike’s performance. Warning: this is going to get technical so if you don’t geek out on bike-performance, the following is probably going to be worse than watching paint dry…

Back in the day

Before I start, it’s worth a bit of an anecdote about how my appreciation for coil shocks happened by accident. My first coil shock came with my 2005 Turner 5 Spot, which I bought used in 2007. The shock came with the frame and before I even rode it I concluded that ‘coils are for DH bikes’, and it would be ‘soft’ and therefore pedal poorly, especially uphill. So I bought a Fox RP3 (tuned by Push) to replace the coil before I even rode the bike. Guess what? Once I’d ridden both I found that the coil shock outperformed the Pushed Fox RP3 in every way. Because I’m a bike-nerd from way back, I even went to the extent of attaching my helmet-cam to the downtube and filmed the two shocks on the same piece of track. It confirmed what I felt riding the bike: the coil was way more active over small bumps, it used its full travel more effectively, yet it also remained more composed and wallowed less into its travel when climbing steeply. And there were fewer seals to blow up. On that bike I also had one of the original coil sprung RockShox Pikes and I still consider that to be the best piece of suspension I’ve ever owned in terms of its performance and reliability for the time. That was more than ten years ago, and I’ve been a fan of coil shocks ever since (but I’m usually riding test bikes now so I probably ride air shocks more). 

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Nerding out on springs

Of course, in the last decade air shocks have improved drastically. Claims of ‘coil-like performance’ abound with each new air shock launched to market. To an extent it’s true. Air shocks of today, with their larger, but tuneable positive chambers, larger negative chambers and slippery air seals, are more ‘coil like’ than ever, if not quite yet linear (more on that below). Also, air shocks rarely blow an air seal these days, whereas it used to be a regular occurrence, so their reliability is greatly improved too. So, what does it mean to have a coil-like feel? What you might have heard before is that a coil shock has a linear spring curve. What does that mean? It means that at the start of the stroke, if it takes 400 pounds of force to compress the spring one inch (I’m using imperial because coil springs are measured in pounds), it will take another 400 pounds (800 pounds total) to compress the second inch and so on until the shock bottoms out at, for example, three inches of shock stroke and 1200 pounds of force. Air doesn’t compress in that linear way, it gets harder to compress further through the stroke, so if the first inch takes 400 pounds, depending on the size of the air chamber, it might be closer to 1600 pounds at the end of the three-inch stroke – even more if the shock has some volume reducers inside. This is what is meant by a ‘progressive’ shock rate.  Of course, that’s not all… 

Nerding out on frames

Each frame’s suspension layout has its own linear or progressive behaviour too, independent of the shock choice. Ideally, you want the frame and the shock to be complementary. A linear frame-rate mated to a linear shock will make the whole package potentially too easy to bottom out and it won’t work very well for many riders, though it might for really lightweight riders. Having said that, a custom-tuned coil shock, like Push’s Elevensix, can take account of a linear frame-rate and produce a shock rate complementary to it. Conversely, a really progressive frame-rate mated to a progressive air shock (say one with the positive chamber stuffed full of volume reducers) will ramp up very rapidly so for many riders, they’ll never get anywhere near full travel, despite wallowing around in the mid-travel a lot. So yeah, it’s complicated. But if you have a frame well suited to coil shocks (I’d list Santa Cruz, YT, many of the Intense range, Scott Bicycles, Giant Reigns, amongst many others) what do you stand to gain from a coil shock, and what might you lose?

Possible gains

Thanks to fewer seals, coil shocks have very little stiction and so are better at taking out the little chattery bumps, providing better traction and comfort.  Some riders liken it to feeling like riding with a slightly flat tyre (but without the sidewall folding) because what should be chattery bumps just seem to disappear. Better traction helps your bike stay on line around rough corners and helps you slow down by letting the tyres grip rather than slide under braking. Comfort might not sound that important, but it can play a big part in how enjoyable a ride is, or how successful a race is. If you feel your hands and feet are rattled to pieces ? of the way through a ride or a race, your ride will start to suck and you’ll either be slower or risk crashing. As well as more traction and comfort, a coil spring also falls into its middle-travel less readily (also called ‘mid-stroke support’) and can therefore provide better climbing, especially up steep climbs, and delivers better support when pushing the bike into corners. This is the part that I think a lot of riders misunderstand (I know I did until I rode a coil shock): if you’ve got the right weight coil, coil shocks provide more mid-stroke support, not less. It’s common for riders looking for more mid-stroke support to add volume reducers to their air shocks. But once you’ve lowered air pressure to still allow for full travel, what you’re likely to find is that mid-stroke support is lessened, not increased. If you don’t drop air pressure, you’ll simply not be able to access all the travel your bike has to offer. In case you’re thinking “this guy has it backwards!”, I recommend Dougal at Shockcraft’s explanation: shockcraft.co.nz/technical-support/volume-spacers.

A coil shock (with the right spring for your weight) will make their full travel more available, as opposed to air shocks which will ramp up harder at the end of the stroke (because, progressive), though this could also be a con, depending on how you ride and what frame the shock is fitted to. Coil springs don’t get hot, and aren’t affected by changes in altitude. Warm air is harder to compress, and make your shock feel more harsh at the bottom of a run compared to the top.

Possible losses

Coil springs are heavier. You’re likely to add in the order of 400 grams (the weight of the metal coil) switching to a coil shock, all else being equal.  Is that weight something you can notice riding? No, it’s not, it’s a non-issue (our own testing with a power meter, published back in 2014, which mirrored what the physics would tell you, showed I needed an extra 0.25% (as in ? of a percent) increase in my power output to carry an additional 450 grams and go the same speed uphill). Adjustability. If you put on or lose more than 5kg or so, you might need a different coil spring. They only cost around $50 though if you ever did need another. Bottom out resistance. Depending on your frame, you could find that the linear nature of a coil spring means you bottom out the shock too much. Having said that, some of the most linear frame rates (like Specialized) have been run by very aggressive and fast riders on the EWS circuit with coil springs, so depending on the shock, you might find sophisticated high-speed compression damping can counteract this. There is one other cost though, which is the hardest to describe and probably the most important for certain riders; that is ‘pop’, for want of a better description. It’s easier to get an air shock to bounce the bike off the ground when you want it to, which is down to its progressive nature(when the bike doesn’t bounce of the ground when we don’t want it to, we’d call this ‘traction’ or the bike being ‘planted’). This is not as easy to remedy as just running lighter rebound damping, it’s something else that’s oddly subtle yet also obviously felt. Ride a coil sprung shock, even on a bike you’re not overly familiar with, and you’ll probably feel it. Really active riders who like to jump off every trail feature (like ex-BMXers) are probably going to miss the pop the most.

Wrap up

Is a coil shock worth considering? That depends. If you value traction and comfort, you prefer a firm middle supportive feel over a ‘forgiving’ or ‘soft centre’, you’d like to get to that last bit of travel a bit more easily, and you don’t mind losing a bit of pop, a coil spring is probably going to make your bike ride more like you want it to. That’s especially true if you I know you know you’re going to be riding rugged tracks or tracks where traction is needed. If, on the other hand, you regularly bottom out your air spring (assuming you’re not running the air-can with no reducers), or you love to bounce from one trail-double and root-kicker to the next, then a coil might detract from parts of your riding experience.  

Forks

What about coil forks? This piece has centred around coil shocks, not forks. Forks are the same in some ways in that coil forks provide a more supple initial travel and a more supportive mid-stroke. This can be even more keenly felt than the rear shock due to the front end’s tendency to dive into the middle travel under front braking (which tends to feel awful!). On the other hand, forks are a bit different because unlike a frame’s suspension linkage, there is no opportunity for telescopic forks to build progression into the chassis. A fork chassis is linear by nature. This means that a linear coil spring can work well for lots of riders but can also bottom out too readily under really aggressive riders. There are a number of manufacturers coming out with ways to add bottom out resistance to coil sprung forks. I’m hoping to have one on review within the next couple of issues, so look out for it and bit of a summary of coil forks then.


Images & Words: Digby Shaw &  Carl Patton

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