Fork Fluid
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,157
Likes: 11,247
From: San Diego, CA
I fill them, pump the dampers slowly to release all the air pockets, then check that the level is correct... I usually have to add just a tad more after pumping....
Stellar HDF Member
Joined: May 2006
Posts: 2,809
Likes: 4,204
From: NC
Thank you. Same here. Good to know I did not err.
Road Master
Joined: Nov 2019
Posts: 966
Likes: 665
From: Rhode Island
I use Lucas, but as far as weight it's a personal preference. You have 5, 10, 15 or 20 weight and it's up to you to decide what kind of ride you want. I mix an equal amount of 10 and 15 weight
Road Master
Joined: Jul 2010
Posts: 798
Likes: 168
From: Tryon, NC Cape Vincent NY
If you are satisfied with your front end performance, stick with the same weight fork oil. If you want to change performance, you can change weights, or even mix weights, to get a performance you like. Just remember, the thicker the oil, the less compliant (stiff) and thinner the oil the more compliant (bouncy) your front end will perform.
Another thing to note, fork oils get thinner, when they heat up. Most have a basic spec and then a 100°C spec. Harley Type E is 20W, but drops to 7.95W @ 100°C. If you are a hard rider, who frequently "works" his suspension hard, you may want to start with a heavier weight fork oil..
I believe most HD bikes come OEM with their Type E fork oil (20W).
If you want a more compliant (bouncy) front end you could go with HD Type B fork oil (10W)...
If you are a canyon carver and want a stiffer front end (Ha, I said stiffer front end) you could go with the Screamin' Eagle Type heavy fork oil. It is also 20W, but fades (gets thinner) less at high temp than Type E.
HD also used to make a very heavy SE fork end oil called extra heavy, which is like 60W... I would guess for racing only, probably unsuitable for street use...
I use Bel-Ray High Performance Fork oil... They make it in 5W, 7W, 10W, 15W, 20W, and 30W. So you can pick a weight and give it try, or there are numerous weights for mixing...
The beauty of fork oil is that it's not that hard to change, and if you pick a weight that doesn't suit you, it's not too hard to change it to something more/less compliant....
Good luck with your decision...
PS- Here's a chart by Spectro Oil on fork oils. It shows the "thinning" of the oil at temp..
Another thing to note, fork oils get thinner, when they heat up. Most have a basic spec and then a 100°C spec. Harley Type E is 20W, but drops to 7.95W @ 100°C. If you are a hard rider, who frequently "works" his suspension hard, you may want to start with a heavier weight fork oil..
I believe most HD bikes come OEM with their Type E fork oil (20W).
If you want a more compliant (bouncy) front end you could go with HD Type B fork oil (10W)...
If you are a canyon carver and want a stiffer front end (Ha, I said stiffer front end) you could go with the Screamin' Eagle Type heavy fork oil. It is also 20W, but fades (gets thinner) less at high temp than Type E.
HD also used to make a very heavy SE fork end oil called extra heavy, which is like 60W... I would guess for racing only, probably unsuitable for street use...
I use Bel-Ray High Performance Fork oil... They make it in 5W, 7W, 10W, 15W, 20W, and 30W. So you can pick a weight and give it try, or there are numerous weights for mixing...
The beauty of fork oil is that it's not that hard to change, and if you pick a weight that doesn't suit you, it's not too hard to change it to something more/less compliant....
Good luck with your decision...
PS- Here's a chart by Spectro Oil on fork oils. It shows the "thinning" of the oil at temp..
This is a chart showing the min and max viscosity of a particular grade of fork oil at the test temp of 100c (212F) in centistokes.
It says that a SAE Grade 5 fork oil must have a viscosity between 3.80 and 4.09 centistokes at 100C to be labeled an SAE 5 fork oil.
Anything below 3.08 does not qualify for a 5 weight (too thin) and anything above 4.09 is a 10 weight.
This is why company A's 5 weight fork oil can offer a different feel in the the forks than company B's fork oil, one can be blended to the low end of the range and the other to the high end...they are both 5 weight but could react differently in your application
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,157
Likes: 11,247
From: San Diego, CA
This is not a chart showing the thinning of fork oil at temperture
This is a chart showing the min and max viscosity of a particular grade of fork oil at the test temp of 100c (212F) in centistokes.
It says that a SAE Grade 5 fork oil must have a viscosity between 3.80 and 4.09 centistokes at 100C to be labeled an SAE 5 fork oil.
Anything below 3.08 does not qualify for a 5 weight (too thin) and anything above 4.09 is a 10 weight.
This is why company A's 5 weight fork oil can offer a different feel in the the forks than company B's fork oil, one can be blended to the low end of the range and the other to the high end...they are both 5 weight but could react differently in your application
That's why I put the word thinning in quotations.... but I can see I was clumsy in my wording and use of that chart...
I was unaware that was the test for fork oils to qualify for their various weight ratings, I thought it was just a standard for comparison..... so thanks for the education on that point...
Thank you for clarifying...
Last edited by hattitude; May 29, 2022 at 09:16 AM.
Stellar HDF Member
Joined: Sep 2021
Posts: 2,048
Likes: 1,486
From: Black Hills of SD
Centostrokes are out of most people's "normal" discussion wording. Normal talk with all the nerdies I worked with.
Some of the chemical engineers I worked with had centi's in the brain.
But boy did some of them really know there stuff! I made a mistake about asking one about something to do with octane ratings of LL100 I used in the ATV's while we were doing some Boi-fuel testing for the Airforce......Whew, never thought he would stop talking...Still don't know the answer or even the question at that point.
"Centistokes is a decimal fraction of kinematic viscosity unit stokes. One centistoke is equal to 0.01 stokes"
Some of the chemical engineers I worked with had centi's in the brain.
But boy did some of them really know there stuff! I made a mistake about asking one about something to do with octane ratings of LL100 I used in the ATV's while we were doing some Boi-fuel testing for the Airforce......Whew, never thought he would stop talking...Still don't know the answer or even the question at that point."Centistokes is a decimal fraction of kinematic viscosity unit stokes. One centistoke is equal to 0.01 stokes"
Road Master
Joined: Jul 2010
Posts: 798
Likes: 168
From: Tryon, NC Cape Vincent NY
I knew that, but very good follow-up information...
That's why I put the word thinning in quotations.... but I can see I was clumsy in my wording and use of that chart...
I was unaware that was the test for fork oils to qualify for their various weight ratings, I thought it was just a standard for comparison..... so thanks for the education on that point...
Thank you for clarifying...
That's why I put the word thinning in quotations.... but I can see I was clumsy in my wording and use of that chart...
I was unaware that was the test for fork oils to qualify for their various weight ratings, I thought it was just a standard for comparison..... so thanks for the education on that point...
Thank you for clarifying...
It is not the min and max chart for "W" rated oils
Last edited by y22c; May 30, 2022 at 05:34 AM.
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Seasoned HDF Member
Joined: Sep 2008
Posts: 14,157
Likes: 11,247
From: San Diego, CA
OK.. now you guys are way over my head.... can't say I understand what that means...
Like I said, clumsy (inappropriate) use of that chart. I know now, that it doesn't show what I thought it did. I misunderstood it's meaning....
I shared it from a Spectro oil tech bulletin. Obviously misunderstood it, and shared it out of context from the bulletin (trying to be brief)
I THINK what I have learned here is that it shows the testing range needed, to receive a particular weight for a fork oil...
In any case, I'll just sit the rest of this discussion out in the back of the classroom shooting spit wads, and let the adults discuss fork oils...
That's something I have plenty of experience with......
Last edited by hattitude; May 30, 2022 at 08:55 AM.
Tourer
Joined: Jul 2016
Posts: 258
Likes: 175
From: Dallas, TX
Hattitude this and your original post saved me lots of research and were spot on. Thanks much.
Also, looks like the Bel Ray is on the high side of the 100 degree range for a given ‘viscosity’
http://www.belray.com/wp-content/upl...-23Nov2021.pdf
Also, looks like the Bel Ray is on the high side of the 100 degree range for a given ‘viscosity’
http://www.belray.com/wp-content/upl...-23Nov2021.pdf
Last edited by Captscotty; Jun 4, 2022 at 08:09 AM. Reason: Added link
