Hi there… John Talley with Partzilla.com. Today I want to take a couple minutes to talk to you about
fork oils… and specifically how your choice of fork oils will affect your motorcycle’s
handling and performance. Now, what do you need to look for? Well, first you need to have a basic
understanding of what happens inside your fork and how the different oils will impact what’s going on
inside… so if you’re ready… let’s go… [MUSIC INTRO]
Okay… so what’s going on inside the fork? Well… basically there’s a spring that
compresses as you go over bumps and then rebounds once you get on the other side…
now there’s also a dampening system that controls the rate of compression
and the rate of rebound… and that’s where the fork oil actually comes into play. The dampening
system will have a dampening rod… some number of valves… which are basically just holes… and
the fork oil… which flows through those valves. When the spring compresses… that pushes against
the dampening rods… and the rods force the fork oil through those valves… or holes.
So the rate of the oil flowing through those holes controls the rate of compression and hence,
the rate of rebound… Now you can control that rate by the viscosity… or thickness… of the fork oil.
So what happens if the oil is just a little too thin? Well, your compression and rebound rates
will be quicker… you might feel the fork bottom out and the motorcycle might feel like it’s…
well the front end is bouncing around… and that means it’s going to be unpredictable.
Now on the other hand… if the oil is too thick… it can’t pass through those little
holes as efficiently. And that’s gonna mean the compression and rebound are gonna be slow…
and that can make for a really harsh, bumpy ride since the oil is holding up
the springs from allowing travel inside the fork.
Now the other thing that fork oil does is provide lubrication for the fork tubes themselves…
now this helps to slow down wear and corrosion… and also helps with heat… since the constant
movement of the tubes generates a lot of friction… So the thickness of fork oil is measured in
viscosity… and that’s just a measurement of how resistant a fluid is to flow.
Got me so far? A higher viscosity… slower it flows… like syrup versus water. So the higher
the viscosity… the more dampening you get since it takes more force to get the fork oil through
the holes in the valves in the fork. Now with a lower viscosity… you get the exact opposite…
Simple, right? Well… the trick is finding out what’s what… because viscosity and
weight? They don’t always line up. You can end up with lots of different viscosities
that are all the same weight… and even end up with higher viscosities at lower weights…
so a 5- or a 7-weight fork oil might end up being thicker than a 10 or 15W fork oil… and that just
makes it even more confusing… so what you need to look at is the *viscosity index* or V-I for short.
What that does is gives you a measure of how consistent the viscosity of your oil is across
a temperature range… and the higher the number… the more consistent the oil is. Now it also
means that you’ll have less fall-off in dampening capabilities as the oil heats up since it’s going
to be more consistent… and a lower number fork oil will thin out and offer less dampening properties.
So… how do you pick an oil? You get on the internet… the VI indexes are
all over the place… I mean, how do you get to the right fork oil to go in your fork?
Well… think about how much weight you’re gonna be putting on the suspension… you… maybe a passenger…
maybe some luggage… and realize the more weight you carry… generally the thicker the oil needs
to be. Then… you need to think about the surface you’re riding on. Are you just on public roads…
do you get off on the trails sometimes on a dual sport… maybe you’re racing on really
smooth asphalt… so you won’t need anything nearly as thick there. And finally… some of
it goes down to personal preference… how do you want the motorcycle to ride? A big cruiser needs
something thicker to handle the additional weight… and a dirt bike… where you’re going
to be in nothing but bumps… might do better with something thinner and more reactive.
So here’s the thing… your manufacturer is going to offer some recommendations
as to what kind of oil your fork should take… and it’s a good idea not to stray far away from that…
maybe you want to move a little bit one way or the other… but you don’t want to go crazy… if
the manufacturer says use a 5-weight oil… maybe go to a 5-weight oil with a higher or lower V-I
index… or maybe get an oil a little bit heavier… but don’t switch say… from a 5 to a 15 weight…
that’s going to drastically change what happens in your fork and how your motorcycle
rides. So just remember… moving around that viscosity index is going to allow you to
fine tune the ride as opposed to jumping to a way heavier oil and just hoping for the best.
Well… that’ll about do it guys… just remember… think small changes to fine tune your ride as
opposed to big swings into the unknown… and if you want to see us change the fork
oil on a motorcycle… we’ve got a couple videos taking you through that process.
Well listen… if you need parts for your machine… come see us at Partzilla.com and we can get you
taken care of. If you have any questions or comments…, leave them in the section
below and I’ll do my best to answer them. We just want to say thank you for shopping
here with us at Partzilla… and we will see you in the next video.