Converting Your Mountain Bike From An Air Shock To A Coil Shock

Converting Your Mountain Bike From An Air Shock To A Coil Shock


– On modern mountain bikes, air suspension is pretty much the king. It’s really versatile. You can do a lot with it, and of course, it’s very easy to use. However, we starting to see
coil suspension being used more and more by certain Enduro races. So this has made me think. I’ve got a bike here
with Fox suspension on. We’ve come to Fox UK, and
I’m going to have a go, seeing if we can get some
coil suspension on this bike, if it makes a good difference
or not, even if it’s something that you guys should
be considering at home. Let’s go and check it out. (upbeat music) (air swooshes) Coil shocks and air shocks
are both going to have some different advantages of their own. But you’re always going to
see an air shock on bikes in your bike shop, shop
floor, quite simply because of the fact that they
almost infinitely adjustable to different ride aways. You don’t need to start
specking differing springs and things on them. And they’re very easily tunable. For this reason, the air
shock pretty much is king in mountain biking, and this adjustability is actually key for me. I’m a huge fan of air shocks. Sometimes I might ride
with a bag that weighs up to 20 pounds. And of course, I’m going to have
to put some more air pressure in the shock to compensate for that. If I had a coil shock on my bike, I’d have to be changing
the physical spring, which goes on the outside of the shock. That means having different
springs for different weights I’m going to go riding with. However, I’m well aware that
there are certain performance enhancements to be had
from running a coil shock, namely some of the grip, the traction, and that spoke feel that you
get from running a coil shock. So we’re going to have a look
at them in a bit more detail. (jazz music) Okay, first things first. Let’s take a look at
some of the differences from a coil shock to a air shock. Now the obvious one you’re going
to know is for the coil shock is it uses a coil spring. Coil spring sits on the
outside of the shock. With the air shock, your
air spring is on the inside of the shock. It’s incorporated into the shock body. One of the things this is
obviously going to mean is on a coil shock, depending
on your rider weight, how much you weigh in your
riding kit, with your bags and things, you’re going to
need to change the spring. The springs come in
different weight increments. I think it’s 25 pound increments. So you’re going to need
to get the right set-up that suits you on your bike. Whereas with an air shock,
you’ve just got a Schrader valve on here, and they’re almost
infinitely adjustable. You’re talking up to like,
2% sort of difference, all the way through. Obviously up to a maximum
limit depending on the shock and how it’s tuned and
the bike is designed for, it can be up to 350 PSI. So that’s quite a big range of adjustment, but that’s all built in. You don’t need anything else
once you’ve got a air shock. Whereas with the coil shock,
you’re going to need that. Now with coil springs, themselves, there’s various different
options available to you. There’s the stock springs,
which are fairly heavy. You get the lighter weight springs. These particular ones come in orange. They look kind of cool. They’re about half the weight. They’re insane, but they’re
also about double the cost. You can also get titanium springs. You can get progressively wound springs. And as we’ve seen on the
GMBN Tech Show recently, you can get these things
called the Sprindex springs, which can actually change the spring rate. Now that’s something we’ll
get to in another video, once we actually get to
try some of this stuff out on the trail. But they’re the basic
differences between the springs on the two options. Now probably should’ve mentioned, the only adjustment you have
to with regards to the spring, itself, when it’s on the
bike, is spring preload. That’s for using these dials
that hold the spring in place. Now the preload does not
change the spring weight. It doesn’t make it a
heavier weight spring. What the preload does,
rather than change the weight of the spring, is simply just
changes the amount of load it takes to make the spring start moving. So for example, if your bike was bobbing around a little bit, you
could put a couple of turns of preload on it, and it’s going
to basically help resist that. But it’s not the same as
changing your spring pressure in here, which is equivalent
with changing the spring for a heavier or a lighter spring. Again, there’s far more
adjustability instantly available to you with an air shock,
which is why it’s kind of key. Now there’s a few other differences. Because your swing
medium is on the outside with a coil shock, the damper
unit is just on its own. It has no additional seals. It doesn’t have to have
air seals in there. It only has the seals
to cope with the oil. And of course, you have your shim stack on the inside there for
rebound and compression and the damper rod,
basically, or the shaft, basically travels through that oil. On an air shock of course,
there’s a lot more going on. On the inside, in fact,
let’s look at this one. It’s a bit more basic so
you can understand this. On the inside, you got
your air chamber here, and you got your oil chamber. As a compressor, you can see
the internal damper shaft there moving through what
would be full of oil there. As a result though, they’re
a bit harder to compress with nothing in them
because of the fact you need a positive air spring
and negative air spring. And of course, you’ve got the oil. All of that inside a
shock body, of course, means more seals. You got seals here, you got seals here, and you got external seals here as well as on the inside there. There’s a lot to go on. Now you could arguably say,
that a coil shock could work for longer with less routine
maintenance because of the fact that it’s going to be
less stiction or friction in the system. With an air shock, of course,
you’re going to have to look after those seals a bit more and make sure everything’s
clean and lubricated in order for it to work as well as
it should do effectively. (jazz music) So at the beginning of the
video, I said there are some performance benefits to be
had from running a coil shock. What exactly are those? Okay. Well first up is that
small bump of sensitivity that everyone talks about
with coil versus air. Now you got to think that on a air shock, you have to overcome the
force of the air spring in order for the shaft to start moving. And quite simply, the coil
shock unit, basically, it takes less effort to
get that shaft moving. So it’s kind of famous for having
that small bump sensitivity that you’re going to get by
the combination of the lack of, sort of friction, it has to
overcome here at the shaft, and of course, with the actual
movement of that coil spring. And finally is the consistency of damping. So if for example, we’ve just
removed the piggyback for this and compared this directly
to this air shock, you’d think that there is
technically more space here for the oil on the inside, basically, than there is on the air and oil system. So this can heat up more
rapidly than this version can. And of course, hotter oil can get thinner and become less consistent in its behavior when going through the shim stack system. Essentially what that means
for you is more consistent damping on those really
long, sort of, alpine, rowdy sort of descents. Of course, this isn’t
always the case because some of the more modern shocks
like this huge X2 here are incredibly consistent. (jazz music) Okay, so what about some of
the limitations of coil shocks? Well simply put, they’re heavier. First up, so if you put
an X2 on the scales here, you’re talking 420 grams. Of course, this has cutaways. It’s got no oil in it. We’re well aware of that. If you take coil version
of the same shock here with no spring on it, it weighs 336 grams. Plus, you need to then add in
the equation of the springs. So the standard spring, steel spring, that is a 516 grams. That’s a whopping weight. Of course, you can have the
lighter options available on there. So it’s the super light
steel springs, much lighter. So they’re 274 grams. So that’s quite insane actually. Obviously, there’s a price
tag that goes with that and the same with titanium springs. So you are limited on what
you can do with those. Now something very
important to say with one of the limitations of the
coil shock, as a stock shock, as you’re buying off the shelf,
coil shocks are quite linear by action whereas an air shock, of course, is quite progressive by action. And a simple reason for that
is you’re compressing air in a compressed space. And what does that mean? It’s going to get firmer the
further into travel you get. Why it ramps up more. So you’re going to get
three, kind of, bike designs as far as suspension goes. You’re going to get falling rate. You’re going to get linear rate, and you’re going to get a rising rate. If you were to put a
coil shock, for example, on a falling rate bike, the
linear action of it means you’re going to go through
that travel quite easily. And you’re actually going to bottom out on the bike quite a lot. It’s going to feel quite wallowy. Ideally, you want a coil shock bike to be a rising rate by design. Whereas a linear rate bike, in combination with an air
shock, very different thing. And you can also tune the
air spring very easily by adding volume spaces. So they change the size of
the air chamber internally to get it to ramp up even more. You could say off the shelf,
an air shock really is better because of those factors. Very easily tunable, it’s
stuff you can do at home. Now your spring rate is the
next thing that’s not ideal, I guess you can say on a coil shock. The coil springs, themselves,
come in different weights. And what I mean by weights
is the fact that you buy them in different weights to
suit your body weight. Now with the longer ones
you see on downhill bikes, you can get them in 25 pound increments. Whereas the ones you start
seeing on trail bikes, tends to be 50 pound increments. So you might not get the sag
to be a complete optimum. Now the last thing to take
into account, of course, is not all coil shocks have any kind of, sort of low speed compression
or a climb switch. Now a climb switch is something
that we’ve basically come to love on air shocks
because of the fact you can, never enough lock out our rear
suspension if you want to sort of wind up a far road
or even pedal it to work on some tarmac, whatever your fancy. You don’t tend to get that on
quite a lot of coil shocks. On the very more expensive
ones, you can but even then, you don’t get it on all of them. It’s a retro fitable thing
so that means having to get a shock customized to have that. Now on a coil shock arguably,
on a trail or Enduro bike, you’re going to want
that feature even more than you would than on an air shock because it’s so much more active. Just think pedaling a six inch travel bike that weighs 32 pounds uphill all day long, and the thing is bobbing
up and down, basically, just because it’s just
such an active shock. Take that into account with
different riding styles, and of course, the bike styles. If you’ve got a bike that
perhaps got loads of anti-squat, it might be okay because
the body’s naturally going to stand up. If yours hasn’t, you’re going
to be pedaling the thing. It’s going to be like pedaling
the rugby ball, not ideal. (hip-hop music) Okay, so we’ve already
looked at some of the basic differences between air
shocks and coil shocks. But what I want to know, Tim,
is can I actually put one on the bike first up? – Short answer, yes. Majority of bikes out there, you’ll be able to fit a coil shock in. No problem at all. ‘Cause generally dimensionally,
they’re very similar to the air shocks that are
usually already on the bike you’re replacing it with. There are some limitations. Certain brands have very
specific mounts at different ends of the shock. Not always a version that was available. So it’s worth checking
out with your dealer or by giving the shop
manufacturer a call first. The, in terms of clearance,
generally, no problems. However, we’d always encourage
someone fit in a shop to a bike that’s slightly different to what they already have on there, to run the shock through
the travel first before with normally with no coil spring on. Just to check all the linkages are clear. There’s nothing fouling so
you’re not going to have a nasty surprise when you take
it off the first jump. – Of course, yeah.
– And you snap something. So it’s always a good practice to do that when swapping a shock and even
with air shocks actually so. – And in terms of ride feel, how different is this going to feel? So as far as I know, this is standard. So I might have like a small spacer, air volume spacer in there. So how much of a difference
in feel do you think on that I’d expect? – With the coil shock, it
depends first and foremost, how the frame has been designed. If it’s been designed purely
with an air shock in mind, there is a chance when
you put the coil shock on, that you don’t have enough
progression in the frame design to give you support deeper in the travel. So a trait of that would
be that the bike’s feeling like it’s riding too low in the travel. Dead would be a description
some people might use. You lose that kind of
springiness and poppyness if there’s not enough progression. If however the frame has been
designed with a coil shock potentially in mind, then
you will, you will still have an element of that there, hopefully a good part of that there. And the feel, theoretically,
with the coil shock is it will be suppler at
the early part of the travel because you haven’t got
the air seals to overcome when you’re going into, into the travel. – So that’s why I might
feel a bit more grip maybe– – Potentially yeah. A bit more grip and traction
on that, on that sort of, the early part of the travel. – Okay, so and then the final question. Now I have done this years back,
but it’s honestly I’ve been on air shocks for so long
I’ve quite forgotten. Setting up your sag on a,
on an air shock is easy. You pretty much get your shock pump, and you dial in what you want. What is the calculation
or how do I find out what sort of spring rate I
need with the coil shock? ‘Cause that’s a whole
different realm I’m trying to figure it out.
– Sure, yeah. There’s a number of spring
rate calculators available, readily available online now. I mean to the shock
manufacturers would have one. A lot of the bike brands
provide them as well if their bikes come with a
version with the coil shocks. – [Doddy] So I guess it’s
going to be different to each bike design kind of as well. – Yes, exactly ’cause the leverage ratios on different designs so it’s to all, dependent on the stroke of the
shock then the rider weight, and put all those numbers
into the calculators, and they’ll get you in the
ball park of what spring to start with. That’s a guideline. So what we do then is
fit the shock on the bike and the spring to the shock
on the bike, get the rider on, measure the sag. You can fine tune that particular spring by altering the preload,
but you are limited on how much you can do that. So then, in sort of the range
of adjusting a particular spring rate so what you would
need to do then potentially is go up a spring rate
or down a spring rate until you get the right amount of sag. So it can be a little bit more
challenging to achieve that than on a shock or else you
just screw a pump on and– – And get going pretty much.
– And alter the air pressure. Yeah, absolutely, yeah. – Well in that case then,
let’s get one on the bike, and let’s see if it works. I’m dead keen to have a little try. – Yeah, no problem. (jazz music) Yes, we fitted the shocks to the bike and calculated the spring in advance. So assuming your weight, you’re being honest about your weight. – Yeah. – Didn’t eat too much over
Christmas and all that? Then we should be, it
should be in the ball park. So we’ll give it a go,
get you on the bike, measure the sag, and take it from there. So what we recommend doing is sometimes, well most of the times,
it’s easier to have someone helping you with this. Measure the eye-to-eye of
the shock before you sit on the bike and then measure
it again once you sat on the bike. The difference is the
amount of sag you have. So it’s a little bit more
complicated than the air shock, where you can do it all on there. – There’s a calculation but yeah. – Ah, yeah, so this shock is
210 millimeter eye-to-eye. Fox recommends 30% sag. So that would be 15 millimeters
on this particular size and stroke of shock. – [Doddy] Okay. – So what we’re looking for is 210. So we’re looking at a measurement,
eye-to-eye measurement of 195 once you’ve sat on the bike. – Okay. (jazz music) – So yeah, bang on 195. So that shows us 15 millimeter sag, which is what we were aiming for. So I’m going to go for about
seven clicks out, seven to eight. – So you have, a kind of, of a
rough gauge you’d start with? – Yeah, if you check the
owner’s manual for Fox products, there’s a table that’ll give
you the shock eye-to-eye, stroke, the spring rate,
which is obviously determined by the rider weight,
and then it’ll give you a recommended starting point. They are just suggestions. You, obviously, riders
have different preference to what sort of feel they’re
looking for, but it gets you in the ballpark and then
you can deviate from that. (springs squeak) – Feels as good as any
place to start, yeah. – Yup, excellent. – Well hopefully that
clears up a few things about coil shocks and air shocks and this whole compatibility
things you need to factor in on your bikes. I’m actually going to do
some back-to-back testing. I’ve got this one set up with
the bearing mount on here. Going to ride it back to
back against that coil and see how things feel,
see what my feelings are. We’re going to make another video on that. But actually to make it a bit fairer because it’s obviously got
an air fork on the front, I’m actually going to
be fitting one of these. So this is a Marzocci Zevran fork, and it’s actually coil sprung. So we’re going to run
the coil front and rear versus the air front and rear. And look out for our video
coming soon on GMBN Tech. Thanks for hanging around. Hit that subscribe button if
you already haven’t done so. Cheers guys!