- Suspension forks,
are one of the parts of a mountain bike,
that can often cause a few headaches,
be that from incorrect setup in the first place,
perhaps you've not been maintaining your suspension fork or,
it could even be a problem that's happened basically,
that you could learn how to solve it.
Now today we got suspension fork here,
stripped down,
so I can tell you a little bit
about how the basics of a suspension fork works
so you can understand where those problems come from.
Now first, let's take a look at what's in front of me here.
This is a RockShox Revelation,
so this is a fairly mid range suspension fork,
fairly common to see on a lot of bikes.
This version is the R model, so it's got
the basic damper unit on it
it's a 140 millimeter travel fork,
and it's come off a 29 inch wheel bike.
Now strip this down into all the major parts
and I've got the oil in the cups here,
so I can show you that as well.
And I'm just going to take you through each component
one by one so you can understand how it works.
And basically you can use this as a process
of elimination to help figure out what goes on
with your folks and if you are suffering any issues.
So first up, let's have a look at the CSU
or the crown steerer upper.
Made of three main parts, the steerer tube,
which basically your stem clamps onto your headset
goes on to this and it goes inside the frame.
This is press fitted into the crown itself.
And then you have the to upper legs also known
as the stanchion tubes. Now these tubes vary in materials
and they vary in length depending on what wheel size
you have 26, 27.5 or 29 and also they do vary
depending on the amount of travel you have.
For example, if you have a cross country forks
that only has 80 or 100 millimeters of travel these
could be a lot shorter, which in turn will save weight.
Likewise if you have a downhill fork
with 200 millimeters travel, these are going to be longer
because you need to have a longer overlap in order
for the fork to be stiff enough to cope with the demands
of that type of riding.
Now on the top of the fork, if you look at the crown here,
you'll see that there are two threaded inserts
on the top here, now one of these is for the damper
to go inside and the other one is for the air unit
to go inside, we'll look at those in a second.
The last thing you need to know about the CSU unit,
of course, is the fact you can choose different offsets
of this and this is what manufacturers are starting
to spec differently now, in order to cope with the fact
that people are wanting decreased offset
on 29 inch wheel bikes.
That's a whole different topic and it is something
that we have covered in Ask GMBN Tech,
there's gonna be a link to that in the description below
this video so if you wanna learn more about that,
head down there.
So that is the main upper part of the fork.
Now let's just take a look at the lower part,
also known as the sliders often refer to as the lower legs.
Now, this of course is a bottom of the fork.
You see on the back here you've got a disc brake mount,
you've got the axle here, that supports the wheel in there
you also have the brake arch which has a mount
for the break hose to mount to.
Now this part of fork is equally as important
as everything else on here, and you have the seals on here
and basically the seals are made up
of a few different parts.
This part which is called the garter spring,
then you have the actual wiper seal itself.
And then there's a foam ring underneath.
Now the foam rings you impregnate these with oil,
a specific type of oil that is just there to lubricate
the lower legs and keep the bushes
on the inside, lubricated.
Now the bushes, if you look down into the forklift,
you'll see there are located just underneath
those foam rings.
The job of the bushes is to allow the upper legs,
the CSU to slide into the lower leg with no hinderance.
So we're going to start with the left leg that's rider's
left which is the air leg.
At the top of the fork, you have your air valve,
this screws into place, has thread lock around
those threads, and there's two different variations
depending on the model of fork you have
and how old it might be.
Now traditional ones use a spanner to put them into place,
and the more modern ones use a cassette tool.
Now this newer version that requires a cassette tool
to install is a much more secure fit,
you can't slip with it so,
it's actually a much better system in operation
and it means there's far less user error,
which is a problem if you're using a socket
or an open ended spanner or something like that
in order to tweak your forks.
Now if you do have the regular version that doesn't require
a cassette tool I suggest you make sure you have
a really good quality flattened socket for this.
Now, you might notice on the top of this one,
there are two gray spaces.
These are air volume spaces now they're called
different names depending on the folks that are in
whether you've got Fox, RockShox or anything else,
but essentially they are air volume spaces,
they are there to change the ride quality of the air spring.
More spaces means the fork is going to ramp up more
it will feel more progressive, you will feel very supple
on the initial part of stroke, and then it will
almost resist bottoming throughout that travel.
Less means the opposite of that means you're going to use
all that travel a lot easier.
So depending on how much travel your bike has,
how you like to ride and your preferences,
you can tune the way it feels by adding or subtracting
those from your air leg.
And next up further down is the lower part of the air tube
or the air spring so at the top here,
you have the air valve, that's where you input the air.
And currently the bottom there is nothing in there.
Now, this is what happens at the bottom end.
You have an air tube that goes in there.
Air tube has a piston it has a top out bumper,
and it has a lower part that's held in place by a circlip.
Basically, it's that simple.
Now, something important to know about this is you
have the positive air chamber and you have
the negative air chamber.
Now on older model forks,
the negative air chamber would be a coil spring,
and if you wanted to change the progression of the fork,
you wouldn't have air volume spaces
you would simply add oil into the air chamber.
And what that does is effectively take up the space
that these would do, ie. making the air space smaller
so the air volume reduces;
by reducing air volume the fork becomes more progressive.
Now with this newer system that you see
on most modern air sprung forks on the inside
of the air leg there's a small dimple.
Now what happens is
when you're putting it into the air valve at the top,
you're, depending on the model of fork,
the brand to fork you have to press the fork a few times
to allow the air to swap from the positive chamber
into negative, which is this space here.
Now, if that does it correctly, the fork feel very supple
because you have that negative spring that is charged
and then of course you have the positive
to support your weight.
That is how you should be working.
And of course when this is in place in the leg, in fact,
I will just demonstrate just by roughly sliding it in
that air tube then has threads in the end that are met
with the foot nut on the bottom, obviously,
this goes into the lower leg part of the fork first
and the foot nut will screw into the base of this.
Now when you're doing a lower leg service,
or you're taking the lowers of the fork in any case,
this is why you need to shock these sometimes
because these can stick both of these rods can stick
to the inside of the fork.
Now what the shocking simply does is
you would undo the bolt a certain amount of weight
and then tap firmly with a soft ended mallet.
This could be a wooden mallet it could be plastic
or rubber mallet, and the idea of that is just to shock
this away from the inside of the fork,
then you can remove this,
and then basically slide the upper legs
out cleanly with this in place.
Now the air tube itself depending on how long it is,
that equates to how much travel the fork can have.
Now on older designed forks, these would be notched
and it would have a space system and different amounts
would protrude, but that doesn't work now
with a negative air system.
So you get different length ones, this is for a 140 mil fork
and this one is for a 130.
As you can see they're slightly different lengths,
but other than that, visually they are identical.
So if you want to change the travel of your fork,
this quite often is the piece that you need to change.
It don't cost a lot and their fairly easy
to change yourselves.
And we'll make a video on changing exactly that on a fork.
In fact, I'll do on this fork to show you
the entire process,
we'll do that in another video on GMBN Tech soon.
Now for the riders right leg, so obviously the right leg
as you're looking down on the bike, when you're on it.
You have the compression damper.
Now on your bike you might be familiar
with seeing a dial like this.
And on this you have a three position open, mid and locked.
Locked means the fork resists moving on to your body weight,
open means is fully active.
Now this is controlled by oil flowing through a series
of ports and shims inside this complete unit.
Now that is that simple, this is basically just
an RL damper, but there are other options available
depending on what you have.
Now this version is very, very simple to do full service on
because there's no additional parts.
You just have this which sits in fluid,
that goes inside the leg and you have the rebound,
damping rod that is a bottom part
which we'll get to in a minute.
I'm just going to show you the difference between
this compression damper and the other type
that you often see.
Now the other type has the rebound as part of it
and this is compression part and it's a bladder format.
Now it's a self contained damper it's all in one.
You don't need the oil on the external the damper
only for lubrication.
The oil is on the inside here and this bladder expands
as it compresses you can actually see
some of the workings on inside there.
Now I also have one of these without the bladder on
just so you can see what goes on on the inside.
But as a more complex item that's found on
much more expensive forks just for example like
the RockShox Lyrik RC2.
Now this is the rebound damper rod, so this sits
in the bottom part of the leg there and on here
you see a series of shims and ports that as the road extends
basically as the fork compresses and extends
it is pulled through the fluid and it controls the rate
of which the fluid goes through those ports and holes.
Now on the bottom of the leg much like the air leg
you have a foot nut except this one is actually hollow.
Now it screws in place just the same.
And you have a cap on the bottom which has an allen key
on it, that actually goes through that foot nut
and into the adjuster itself.
Now that is for controlling how many clicks of rebound
(clicking)
as you can hear there that you would like your fork to have.
It's that simple they are the parts
of most modern suspension forks.
Now as you'd imagine, amongst different brands,
they do vary but this is the basic layout
of all suspension forks on the market.
Some are a bit more refined,
some have a more advanced damper that's a whole damper
that sits within the leg as a cartridge unit,
and some have air legs on them that allow you to change
the travel of the fork without changing the actual air leg,
we saw that on the Cane Creek fork.
The only other two things you need to know about them
are there's oil inside and how much you need.
Now there's different types of oil
and has a different purpose.
Now in this one, I have the lower leg oil.
Now the job of this is literally just to lubricate
those lower legs to make sure the bushes slide over these
stanchion tubes and make sure everything
stays operating smoothly.
Now it's very different from the damper oil
that goes inside the damping leg.
Now dependent on the model of fork you have
and the damper it has in it, you have different viscosity's
known as oil weights, and you will also have
a different amount you will need it's a very precise amount
for different models of fork.
So if you're unsure about that, you will have
to actually check the manufacturer website
for your particular fork and the model year number.
RockShox do this by part numbers,
Fox do a very similar thing, so it's very easy to identify
your particular one against a chart.
So there we go that is the basics
of your average suspension fork.
Hopefully, it's going to make you understand a little bit
about what goes on on the inside.
If you've got any questions about this one or this video,
let us know in the comments below.
In the meantime, I'm going to get scripting and write some
detailed fork analysis videos to break some more stuff down
to help you understand and maintain
these yourselves at home.
If you want to know a little bit more about suspension forks
and what they do, click up here for our
Essentials Setup Series, tells you about how to use
those adjusters how to set up your sag
how to set up your rebound all that sort of stuff,
and click up here if you want to see the effects
doing all this sort of stuff does out on the trail
and that's for some video stuff of me riding
with different setups you can actually see
visibly what's going on.
As always, if you love GMBN Tech give us a huge thumbs up
and please don't forget to share and subscribe.