Fork oil is not created equal
#1
07-12-2018 | 09:04 AM
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Tourer
Joined: Jun 2016
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From: Maple Ridge BC & Chiangmai
Fork oil is not created equal
Installed Gold Valves in my forks the other day and Racetech gave me the oil weight in SAE units - IE 19W. I am not a fan of SAE units as one manufactures oil can be very different from anothers. For example Pro PJ1 Fork Tuner 3 is over 3X the weight of Torco 5.
Hence the more scientific centiStokes scale (cSt) to measure viscosity of fluids at a given temperature
See this:
www.peterverdone.com/wiki/index.php?title=Suspension_Fluid
If your eyes glaze over with the math, go straight to the table
HD fork oil is:
http://www.spectro-oils.com/wp-conte...Data-Chart.pdf
Hence the more scientific centiStokes scale (cSt) to measure viscosity of fluids at a given temperature
See this:
www.peterverdone.com/wiki/index.php?title=Suspension_Fluid
If your eyes glaze over with the math, go straight to the table
HD fork oil is:
http://www.spectro-oils.com/wp-conte...Data-Chart.pdf
The following 2 users liked this post by 65Tiger:
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#3
07-13-2018 | 02:52 PM
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Tourer
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From: Maple Ridge BC & Chiangmai
RaceTech gives a customer tailored recommendation for fork spring rate, cartridge stack spring compression, oil level, and oil weight when you buy the Gold Valves.
I optimistically classified myself as Intermediate/Expert at a naked weight of 76 Kg
In my case they recommended SAE 19W oil x 150mm. Blue spring at 2 turns from initial contact. I chose my own spring rate of 0.95 kg/mm
They never did answer my request for an oil rating in cSt, but did say that they use Spectro oil. I assumed that their oil viscosity recommendation was based on Spectro.
According to Spectro their viscosity is 72.2 cSt at 100F and Verdun gives it as 65.00 cSt at 40C. I found 2 other sources with 65@40 that did not appear to be a Verdun cut and paste job.
I have Lucas fork oil so brewed my own oil using Lucas 20 (77.5 cSt) and 5 (25.34 cSt) to achieve what I hope is going to be the correct weight
Oil level with be a bit of trial and error, as will be the valve adjustment
I optimistically classified myself as Intermediate/Expert at a naked weight of 76 Kg
In my case they recommended SAE 19W oil x 150mm. Blue spring at 2 turns from initial contact. I chose my own spring rate of 0.95 kg/mm
They never did answer my request for an oil rating in cSt, but did say that they use Spectro oil. I assumed that their oil viscosity recommendation was based on Spectro.
According to Spectro their viscosity is 72.2 cSt at 100F and Verdun gives it as 65.00 cSt at 40C. I found 2 other sources with 65@40 that did not appear to be a Verdun cut and paste job.
I have Lucas fork oil so brewed my own oil using Lucas 20 (77.5 cSt) and 5 (25.34 cSt) to achieve what I hope is going to be the correct weight
Oil level with be a bit of trial and error, as will be the valve adjustment
#4
07-14-2018 | 08:51 AM
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Tourer
Joined: Jun 2016
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From: Maple Ridge BC & Chiangmai
Just noticed a typo in the OP and cannot edit?
What I meant to say is:
For example Pro PJ1 Fork Tuner 5 is over 3X the weight of Torco 5.
Note the SAE spec tolerance in the Spectro link in post 1
Then note that the fork oil weights given by Verdun fall far outside this tolerance. Clearly the label on a bottle of fork oil may, or not, indicate the viscosity.
No wonder suspension set up is a black art but if you understand the variables it becomes more science than art. Fork oil viscosity is one such variable.
Unfortunately there are several more variables to get a grip on, but it really is not that difficult - the other big one is air gap/fork oil level and related spring rate.
What I meant to say is:
For example Pro PJ1 Fork Tuner 5 is over 3X the weight of Torco 5.
Note the SAE spec tolerance in the Spectro link in post 1
Then note that the fork oil weights given by Verdun fall far outside this tolerance. Clearly the label on a bottle of fork oil may, or not, indicate the viscosity.
No wonder suspension set up is a black art but if you understand the variables it becomes more science than art. Fork oil viscosity is one such variable.
Unfortunately there are several more variables to get a grip on, but it really is not that difficult - the other big one is air gap/fork oil level and related spring rate.
Last edited by 65Tiger; 07-14-2018 at 09:20 AM.
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