Fork Oil Weight Experience

jeiner · Nov 14, 2018

I was planning on putting thicker oil into the forks to help with dampening (I have the airpro and it works great for ride height, but it needs help with dampening as it feels like a Christmas gifted pogo stick).I'm riding a 2017 YZ450F and the owner's manual says to use Yamaha Suspension Oil S1 (does that mean it is weight 1?). In looking on Rocky Mountain's website, the Bel-Ray High Performance fork oil goes all the way up to a 30w.

My question's are as follows:

How thick of oil can you run (I'm not sure if oil that thick will ruin it)?

How much does it help to change weights (if I go from 5w to 10w, what is the difference)?

Is there any advantage/difference of running a different weight on the outside then on the inside (I was planning on changing both out, but I'm curious)?

In commenting, if it is an opinion please make sure to clarify it as such. If it is by experience, please indicate the bike and year. Thank you!

mk818 · Nov 14, 2018

I am curious as well. I have the same feeling on a 15' husky with 4CS and airpro kit. I would assume running a higher viscosity and more oil would help. Its worth a shot at least.

CATSLEDMAN1 · Nov 14, 2018

oil the thing

experience: more oil in the forks will help bottoming out
KTM forks on my 13 exc 500 do better with 5wt oil,I run air and
the heavier oil helps

for the Yamaha guy. try more heavier oil, experience says it won't hurt the forks. My opinion is you just experiment with it.

jeiner · Nov 14, 2018

I have no problem experimenting, I just want to be certain that the forks will work with 30w oil (and it won't destroy them!). Can anyone verify that?

byeatts · Nov 14, 2018

jeiner said:
I was planning on putting thicker oil into the forks to help with dampening (I have the airpro and it works great for ride height, but it needs help with dampening as it feels like a Christmas gifted pogo stick).I'm riding a 2017 YZ450F and the owner's manual says to use Yamaha Suspension Oil S1 (does that mean it is weight 1?). In looking on Rocky Mountain's website, the Bel-Ray High Performance fork oil goes all the way up to a 30w.

My question's are as follows:

How thick of oil can you run (I'm not sure if oil that thick will ruin it)?

How much does it help to change weights (if I go from 5w to 10w, what is the difference)?

Is there any advantage/difference of running a different weight on the outside then on the inside (I was planning on changing both out, but I'm curious)?

In commenting, if it is an opinion please make sure to clarify it as such. If it is by experience, please indicate the bike and year. Thank you!

Run 15 wt oil and most important is the oil height , raising oil level increases the pressure as forks compress which can prevent bottoming, start by raising level 30 cc.

Norma Stitz · Nov 14, 2018

I don’t think you can hurt them with thick oil.

tek9tim · Nov 15, 2018

I wasn't brave enough to jump too high in oil weight when setting up my FC450, but I also have experience with 4CS forks and I didn't want to bring out any of their demons. I did go to 10wt, but I haven't had the bike out yet.

Here's my hesitancy: rebound. It took me a while to appreciate a quicker rebound. Repeated bumps can pack the fork further into its stroke, and hitting a bump mid turn with a slow rebound can keep the ski from recontacting the ground.

eric82930 · Nov 15, 2018

There is a very small chance the really heavy oil might warp the shims on the mid valve. I have had it happen on some dirt only forks in cold weather but was probably a fubar from the tuner who did the revalved didn't put in enough float not really the oil fault.... If you are running air pro and don't want to re valve for it the heavy oil should help the pogo rebound.
But be be sure to try running lots of oil with less air, its the best thing you can do.

Leterip · Nov 15, 2018

I run 15 wt oil, with .64 springs and my own air pro type setup. Since you have an air pro, i wouldn't worry about adding more oil yet, try the thicker oil first then add if you feel the need. But remember doing this is just like pumping up the air pressure in the fork, and by adding more oil it can cause a "harsh" hit per say at the end of the stroke, since it essentially limits the distance the fork can travel. And the colder it is out the slower the forks will respond with the thicker oil, once they get moving it helps but just something to be aware of.

byeatts · Nov 15, 2018

Leterip said:
I run 15 wt oil, with .64 springs and my own air pro type setup. Since you have an air pro, i wouldn't worry about adding more oil yet, try the thicker oil first then add if you feel the need. But remember doing this is just like pumping up the air pressure in the fork, and by adding more oil it can cause a "harsh" hit per say at the end of the stroke, since it essentially limits the distance the fork can travel. And the colder it is out the slower the forks will respond with the thicker oil, once they get moving it helps but just something to be aware of.

Every snowbike needs the oil raised, When ewe clamp the spindle to the fork leg ewer total travel is about 1 inch less therefore the oil dampening quality s as fork compresses is altered, The oil level adds a rising pressure rate as fork compresses.

needpowder · Nov 15, 2018

Even with airpro?

byeatts said:
Every snowbike needs the oil raised, When ewe clamp the spindle to the fork leg ewer total travel is about 1 inch less therefore the oil dampening quality s as fork compresses is altered, The oil level adds a rising pressure rate as fork compresses.

Do you think this is true even with the air pro? I have .62 fork springs in mine and with the air pro it seems pretty good. I really only run a couple pounds in the air pro usually unless I am going to send it. I only go big when it’s deep.

jeiner · Nov 15, 2018

tek9tim, you'll have to let us know how it turns out after the first ride.

Leterip, are you running the 15w in both chambers?

I called a Pro Action suspension dealer today and he has never seen a mx bike with more than 5w in the inner chamber (he's only set up a couple of snow applications and had never heard of airpro or putting air in the top of the forks (he thought the airpro was a gimmick and a bad idea). Haha, I'm not about to stop running the airpro as it is golden for ride height!).

I'm going to call around to a few more suspension dealers to see what they have to say about it (specifically will it damage my forks).

Sheetmetalfab · Nov 15, 2018

jeiner said:
tek9tim, you'll have to let us know how it turns out after the first ride.

Leterip, are you running the 15w in both chambers?

I called a Pro Action suspension dealer today and he has never seen a mx bike with more than 5w in the inner chamber (he's only set up a couple of snow applications and had never heard of airpro or putting air in the top of the forks (he thought the airpro was a gimmick and a bad idea). Haha, I'm not about to stop running the airpro as it is golden for ride height!).

I'm going to call around to a few more suspension dealers to see what they have to say about it (specifically will it damage my forks).

Call brockstar racing.
He’s done more snowbike forks than most people have seen pictures of.

http://www.brockstarperformance.com/mobile/

Leterip · Nov 16, 2018

Yes I do. Things to remember. The thicker oil is not the cure all, the valving in the forks regulate pressure, and by adding thicker oil the valving sees the pressure and will only try to open further to accommodate the thicker oil. Guys that setup forks in the summer will not condone this in the slightest. And with adding oil to the outer Byeatts is right it helps with bottoming when you lose some travel with the ski clamp on the forks, but in my opinion unless your very aggressive in jumping the air pro will do everything you need.

tek9tim · Dec 15, 2018

jeiner said:
tek9tim, you'll have to let us know how it turns out after the first ride.

Got the bike out yesterday. Damping was great with the 10wt. I started with the compression maxed out and the rebound backed out and never changed it. As far as the damping goes, there isn't anything more I could ask for. Got it in the air a little bit, didn't come close to bottoming, super smooth action out of the forks. I do need to step up in springs though, and that would allow me to take out some compression damping, add rebound, gain a little ride height and reduce diving when letting off the throttle. But for the 4CS with motocross valving, I was really impressed.

needpowder · Dec 16, 2018

I know this isn’t the point of this thread, but i rode a 2018 YZ with a trio yesterday and sent it pretty big off a cornice a few times. Really impressed. Not only did it not bottom but it felt super smooth. I know it is a spendy upgrade, but it might be worth it if you don’t want to mess around with your forks changing back-and-forth.

snobikr · Dec 16, 2018

Ran straight pig semen with stock cc height in my forks last ride plus 50 pounds in my air pro, it was a pretty rough ride, hope I didn't damage my forks. Oh and I was riding a 2016 YZ450:eyebrows:

Answ3r · Dec 17, 2018

snobikr said:
Ran straight pig semen with stock cc height in my forks last ride plus 50 pounds in my air pro, it was a pretty rough ride, hope I didn't damage my forks. Oh and I was riding a 2016 YZ450:eyebrows:

What a usefull post !

Ben 500RR-S · Dec 17, 2018

I had just fully stiffened my the compression and totally speeded up the rebound on my front forks and left both the 2.5W and oil level alone and I also plan on doing the same thing this upcoming winter.

It would be nice to have the front a bit stiffer but for the most part, as we are not jumping anything as we don't have much, or many places to get air in our part of the world, there has been no need for springs or air pressure increase or increased oil weight or viscosity.

chumbilly1 · Dec 17, 2018

I have done the 10wt at max volume and .54 springs. Worked well. Then i added the airpro. Typically ran around 10-15psi. Works great for ride height bottoming resistance etc. Then last year I sent a set to Brockstar Performance. Brock set them up for my weight and riding style. They are amazing! For what he charges, I recommend everyone gets a second set of forks off of ebay and sends them to Brockstar. You will not be dissapointed, nor will you ruin your good dirt forks, or be without a spare set when the inevitable happens!

Fork Oil Weight Experience

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