Hello and welcome to another episode of PowerDrift Simplified where we take automotive concepts,
break them down into small bite sized pieces that you can digest easily.
And every time we've done these, we've asked you what would you like us to talk about
and the last time an interesting question was, the difference between upside down forks and
right side up forks.
Now in construction, they're not very different from each other.
In both cases, you have what is called the female part, which is the outside part and
a stanchion or the male part that goes into it and there is a mechanism inside that allows
the suspension to do its job and we'll talk about that in just a minute.
Now, a right side up fork, the female part is at the bottom, the male part is in the
top, and you turn it upside down, and you get an upside down fork.
Simple.
Now, inside the fork is a whole bunch of things, the springs, there's valves, the shims, etc.,
which are all designed to do the job that the suspension is supposed to do, which is
first, the spring is supposed to allow the wheel to move up and down in response to the
imperfections in the road.
When it moves up, the damping that we use to control this motion is what we call compression damping. Right?
But once the spring has collapsed, it will also want to expand back to its original length
and it usually does this by going past the original length and then coming back again
and to control that motion, we have what is called rebound damping to stop the wheel from
going up and down if it is uncontrolled.
If you've ever sat in a really old Ola or Uber taxi, and you sort of bounced around like
this after the bumps, what you realise is the springs are working,
but, the dampers that are supposed to control the motion of the spring have failed completely,
and therefore, you hit a bump or go over a speed breaker and then the car sort of continues to bounce after that.
So that's the basic function of suspension and USD forks, upside down forks and right
side up forks, both do exactly the same task.
Now the difference in construction primarily comes from the fact that when you take an
upside down fork, you're suspending the oil up in the fork, which means that the oil seals
have to be stronger so that it doesn't leak out.
Oil seals also fail regularly on right side up forks, it's not unknown, but when they
do, the oil is still contained by gravity in the bottom of the container and minor amounts
will leak out as the stanchion goes in and out past the seal carrying a little bit of
oil with it through whatever part of the seal has been cut.
So in that sense, there is no real functional difference between an upside down fork and
a right side up fork in terms of what they do.
But, the big difference is that if you think about it, the female part of the fork
where the stanchion goes into is a much bigger structural unit than the stanchion itself.
So the reason why people started inverting forks and creating upside down units is because
structurally it's a much stronger unit than a right side up fork.
Okay, now, that doesn't automatically mean that right side up forks are worse for you,
it just means that as the performance requirement from a motorcycle gets higher and higher and
higher, you want to have more and more structural strength in the chassis, the upside down fork
becomes a better solution to create that structural strength. It's just that the triple clamp, that's
the plate on top which holds the steering head and the two fork legs and there's two
of them, so we call them the dual triple clamps,
so the upper and lower triple clamps just have more metal to clamp onto, creating a stronger structure
and that's the real reason why as performance goes up, generally, you start seeing manufacturers
move to upside down forks.
Now, you will also see fairly high performance motorcycles that still run right side up forks
and honestly, the challenge between a USD and a right side up fork is an engineer's
challenge to figure out what is the most efficient way, what is the most effective way, what
is the most cost effective way to create a structure that does what the motorcycle is
supposed to do in terms of its role.
Okay, so on a dirt bike where you're going to be landing a big jump and hitting big things
upside down forks are almost mandatory, because its structural strength requirement is much
higher because of the sudden impacts.
On a sports bike, when you go really fast, especially the 200bhp class, when you go into
a corner, you're putting a considerable amount of load into the frame,
so you do want strong forks to be able to absorb all those forces.
But, if you're riding a commuter, and even a 500cc commuter, the amount of forces that
you will generate are much lower
and therefore an engineer might say that for this cost, and role, a right side up fork does the job just as well.
So, when you see it on the specs sheet, a lot of people say, liquid cooling is better than
air cooling or right side up forks are worse than upside down forks, that's not actually true
as a thumb rule. It is a matter of what is that motorcycle supposed to do
and what is the right engineering solution for that, that determines what goes on the motorcycle.
So, upside down forks, generally seen on higher performance motorcycle, right side up forks
are cheaper, easier to maintain, and they're generally seen on less expensive motorcycles,
but the primary difference really is the structural strength, not really much else.
The only difference is, if your upside down, forks starts to leak in the middle of your
ride, you have a bigger problem than if you had right side up forks, and the solution usually
is, tie a small piece of cloth to the stanchion, to the male part that goes into the upside
down fork and allow the oil to soak into the fabric and discard the fabric as the fabric
gets completely soaked
and the only reason to do this is so that the oil can't get on crucial things like the
tyres or the brakes and hamper performance there.
The fork will continue to work, the performance will degrade, but just that little piece of
cloth will take you home so that you can get it fixed properly.
My tip for upside down forks is as soon as you buy a motorcycle with upside down forks,
go find yourself a good set of seal covers, Big Bad Bikes sells SealSavers, Kriega is
available at LazyAssBikers, both of them make seal covers that basically clamp around
the bottom of the fork and hide the junction between where the oil seal is sitting so that
any dust that falls on your stanchion cannot actually go through and damage your fork seal.
This also means that you have to be careful about upside down forks in the sense, inspect
your stanchions because if your stanchions get damaged, which are scratches or imperfections,
or there is dead bugs on it and stuff, all of these hard substances can go through the
dust seal, past the oil seal, cut the oil seal in the process and then cause damage that eventually leads to a leak.
That's all there is to it. This is PowerDrift Simplified.
Thank you so much for watching.
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