Differences between 5wt and 10wt fork oil - Speedzilla Motorcycle Message Forums
 
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post #1 of 9 (permalink) Old 04-23-2008, 05:50 PM Thread Starter
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Differences between 5wt and 10wt fork oil

I understand the technical difference between 5wt and 10wt fork oil is the viscosity, which is the ability of the fluid to flow at a defined temperature but is there much difference in the feel at the handlebar with similar damping settings dialled into the fork. Anybody got any experience of using 5wt on a standard fork ?

The reason I ask is a supension specialist has serviced my standard forks and replaced with 5wt oil instead of the standard 10wt Honda SS8 fluid.

I have found from a quick test ride the bike dives more than previous under braking although the fork still seems fairly stiff under normal riding conditions. I have the compression damping at close to max setting to limit diving under braking and the rebound seems ok at standard setting. Is the SP2 known to have little high speed compression damping and therefore dive under braking and be over damped in the low speed compression ?

Any feedback is welcome.
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post #2 of 9 (permalink) Old 04-23-2008, 07:33 PM
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I ended up putting 7w in mine and I love it so far, but I cant vouch for the 5wt personally, but I know allot of people who have switched to it...
I ended up needing about a extra turn of pre-load to set my sag.
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post #3 of 9 (permalink) Old 04-24-2008, 07:15 PM Thread Starter
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Is it better to use the lighest oil you can to get the damping effect you require, i.e if you wind a few more clicks of compression on to get the desired damping effect with a lighter oil it is better than being backed off with heavier oil.

I read some where it was as the light oil can react quicker and you are using a mechanical method to control which offers a more precise level of control and adjustment.
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post #4 of 9 (permalink) Old 04-25-2008, 11:07 PM
 
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This is a very general guideline for fork oil weights. One thing you need to remember is that, like all fluids, fork oil viscosity is reduced as the oil temperature increases... so, under racing conditions, the oil will heat up and thin out more. On the street, it will stay relatively constant. This is one reason race shocks (and superbike forks) have reservoirs to help cool the oil. They also provide a space for nitrogen to pressurize the fluid. This helps keep foaming and cavitation (air bubbles) through the valve to a minimum.

100-150lb rider with .85-.90 spring = 5 wt

150-180lb rider with .95 springs = 7.5wt

180-215lb rider with 1.0 spring = 7.5-10 wt

215-240lb rider with 1.05 spring = 10-12.5 wt

240lb and above with 1.10 spring = 12.5-15 wt

There will be some overlap in these numbers based on usage but that's about how they stack up.... BTW.. to make the half weights (I.E. 7.5 wt = 1/2 volume of 5 wt mixed with 1/2 volume of 10 wt)

Now for the disclaimer! Different fork manufacturers use different "port sizes" in their valve assemblies (requiring different viscosity) so this is not "chiseled in stone" Please verify all your oil wt questions via a manufacturer's representative!
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post #5 of 9 (permalink) Old 11-28-2009, 12:23 AM
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dammm..even more things to learn.

If temp makes a ticker fork oil thinner during prolong usage(ie race) then would it best to use the lightest oil weight as suggested above? Since again , it is a mechanical control device/valve opening?

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post #6 of 9 (permalink) Old 11-28-2009, 02:36 AM
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Also to remember is the high-velocity (bump) damping is by the compression shim stack, the low-velocity (weight transfer) damping is by the external adjuster. And of course these are all affected by oil viscosity.

So yes, you can have harsh high-velocity damping and excessive weight transfer under braking.
That's one advantage the newer bikes have with 3-way fork adjustment.
They can tweak hi and low velocity rates just like an aftermarket 3-way shock without having to re-shim the compression stack.
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post #7 of 9 (permalink) Old 11-28-2009, 12:17 PM
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My suspension workshop only uses Kayaba KYB-01 fluid (5wt) unless the fork manufacturer specifies a different grade. Until now they've had no complaints.
Switching to a thicker oil may sound like a cheap fix for the SP well known fork issues but trust me, nothing beats a good rebuild followed by a good set up followed by periodic maintenance.
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post #8 of 9 (permalink) Old 12-01-2009, 12:30 AM
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Quote:
Originally Posted by DesperateSP2 View Post
My suspension workshop only uses Kayaba KYB-01 fluid (5wt) unless the fork manufacturer specifies a different grade. Until now they've had no complaints.
Switching to a thicker oil may sound like a cheap fix for the SP well known fork issues but trust me, nothing beats a good rebuild followed by a good set up followed by periodic maintenance.
+1 on all the above.
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post #9 of 9 (permalink) Old 04-05-2016, 11:02 AM
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Switching to a thicker oil may sound like a cheap fix for the SP well known fork issues but trust me, nothing beats a good rebuild followed by a good set up followed by periodic maintenance.

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