Does anyone know what the key Viscometrics are that define fork oil weights?
Is it purely KV40 and KV100, or does Brookfield viscosity play a role?
Is it purely KV40 and KV100, or does Brookfield viscosity play a role?
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Key Fork Oil Viscometrics
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Does your question relate in any way to this chart?
http://mahonkin.com/~milktree/motorcycles/fork-oil.html
(btw I recently changed the fork oil in my Tiger 800 and went with Motul Expert 10W and it feels about the same as factory)
http://mahonkin.com/~milktree/motorcycles/fork-oil.html
(btw I recently changed the fork oil in my Tiger 800 and went with Motul Expert 10W and it feels about the same as factory)
I think that oil has a pretty low KV100 and VI
That's interesting, I was scratching my head over how significant VI would be in a fork oil. But since the fork oil is going to get only so hot, its effect would probably be very little.
I'm wondering about sharp, quick impacts being more dependent on VI and KV40, whereas slow movements (such as brake dive) to be more dependent on KV40.
That's interesting, I was scratching my head over how significant VI would be in a fork oil. But since the fork oil is going to get only so hot, its effect would probably be very little.
I'm wondering about sharp, quick impacts being more dependent on VI and KV40, whereas slow movements (such as brake dive) to be more dependent on KV40.
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Fork oils are marketed nominally at KV100 which as above, is a bit of a nonsense. I compare them at 40 C before choosing an oil for my bike. I know from experience that I'm look for a KV40 in the range. 20 -25 cSt
Originally Posted by bulwnkl
You select fork oil based on 40C (100F) viscosity. It won't get near 100C (212F) at any time.
That's what I was thinking. But what about VI? Does it play a role?
You select fork oil based on 40C (100F) viscosity. It won't get near 100C (212F) at any time.
That's what I was thinking. But what about VI? Does it play a role?
Hello Brian 553,
Some thoughts from my side:
if the base oil is synthetic, it does have an already high VI. I suppose too high of a VI could mean the oil could shear rapidly over use,by the shearing of the VI improvers.
Normally these oils are used also for shocks, and if they are near the exhaust they could have a significant temp. This is where VI really maters, I doubt you will see a tremendous diff for the fork, except from riding in freezing conditions or in hot weather.
Frequent changes are more important for my motorcycle than the VI diffs among brands.
Some thoughts from my side:
if the base oil is synthetic, it does have an already high VI. I suppose too high of a VI could mean the oil could shear rapidly over use,by the shearing of the VI improvers.
Normally these oils are used also for shocks, and if they are near the exhaust they could have a significant temp. This is where VI really maters, I doubt you will see a tremendous diff for the fork, except from riding in freezing conditions or in hot weather.
Frequent changes are more important for my motorcycle than the VI diffs among brands.
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Originally Posted by Brian553
Originally Posted by bulwnkl
You select fork oil based on 40C (100F) viscosity. It won't get near 100C (212F) at any time.
That's what I was thinking. But what about VI? Does it play a role?
It's not something I particularly worry about. If you're a high level desert racer and you experience fork damping shifts during a race, try an oil with a higher VI. For nearly all of us, though, it's relatively unimportant, IMO. Looks like berlyn sees it about the same way. Ask sunruh or MotoTribologist what they think, if you like.
Originally Posted by bulwnkl
You select fork oil based on 40C (100F) viscosity. It won't get near 100C (212F) at any time.
That's what I was thinking. But what about VI? Does it play a role?
It's not something I particularly worry about. If you're a high level desert racer and you experience fork damping shifts during a race, try an oil with a higher VI. For nearly all of us, though, it's relatively unimportant, IMO. Looks like berlyn sees it about the same way. Ask sunruh or MotoTribologist what they think, if you like.
A higher VI will keep the fork oil at a more consistent viscosity in the "normal" riding temps of 0 C (32 F) to ~ 40 C (100 F)-
More info on fork and suspension fluids:
http://peterverdone.com/wiki/?title=Suspension_Fluid
"On a lovely Sunday morning, the ambient temperature may be 21C (70F). Motorcycle forks will run in the 26C (78F) temp range, rear shocks will run in the 65C (150F) range and rear reservoirs will be around 43C (110F).
While motorcycle rear shocks require very high VIs (over 300) to function well over such a huge temperature range, motorcycle forks and bicycles do not. Anything over 100VI will be serviceable for them."
http://www.peterverdone.com/archive/damping.htm
Here is a graph of Harley Type E - VI ~ 160 (calculated from my VOA with viscosity at 100 F and 212 F)
Red Line Medium Wt VI ~442 (From RL site)
Red Line Heavy wt VI ~ 262 (From RL site)
a mix of 75% Red line light wt and 25% Red Line heavy WT about 375 VI
You can see the Red Line mix is about 38.5 cSt at 40 C and about 102 Cst at 0 C
the Harley Type E is about 41 Cst at 40 C and 325 cSt at 0 C
![[Linked Image]](https://www.bobistheoilguy.com/forums/attachments/usergals/2019/05/full-4497-32191-hdtypee_rlforkoil.jpg "[Linked Image]")
More info on fork and suspension fluids:
http://peterverdone.com/wiki/?title=Suspension_Fluid
"On a lovely Sunday morning, the ambient temperature may be 21C (70F). Motorcycle forks will run in the 26C (78F) temp range, rear shocks will run in the 65C (150F) range and rear reservoirs will be around 43C (110F).
While motorcycle rear shocks require very high VIs (over 300) to function well over such a huge temperature range, motorcycle forks and bicycles do not. Anything over 100VI will be serviceable for them."
http://www.peterverdone.com/archive/damping.htm
Here is a graph of Harley Type E - VI ~ 160 (calculated from my VOA with viscosity at 100 F and 212 F)
Red Line Medium Wt VI ~442 (From RL site)
Red Line Heavy wt VI ~ 262 (From RL site)
a mix of 75% Red line light wt and 25% Red Line heavy WT about 375 VI
You can see the Red Line mix is about 38.5 cSt at 40 C and about 102 Cst at 0 C
the Harley Type E is about 41 Cst at 40 C and 325 cSt at 0 C
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