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General Category >> Rubber Side Down! >> Fork oil viscosity
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Message started by diamond jim on 06/21/09 at 07:47:04

Title: Fork oil viscosity
Post by diamond jim on 06/21/09 at 07:47:04

So I'm looking to change my fork oil maybe on Tuesday. In researching fork oils I found this awesome chart- http://www.mediaturbo.com/clients/marzocchi/forkoilviscosity.html

Clymers says to use 15wt fork oil. For those who have changed either to 10wt or 20wt, what are the benefits you are experiencing? What are the drawbacks?

Title: Re: Fork oil viscosity
Post by thumperclone on 06/21/09 at 08:32:37

one thing ive noticed no one has mentioned the fork spring service limit.
SSM:"measure the fork spring free length. if it is shorter than the service limit,replace it."
S.L. 15.45 in (392.5mm)

id guess if your suspension was "soft" and the spring(s) were under the service limit higher vis oil would help stiffen it up some..
but higher vis may have an adverse effect on the seals imo..

Title: Re: Fork oil viscosity
Post by SV og LS on 06/21/09 at 09:07:54

3538303C3E3F353B383C510 wrote:

I've noticed much larger difference between old and fresh fluid than between 10W and 15W. I've used several viscosities and there's an initial difference but the viscosity goes off quite quickly. 20W might feel initially slightly harsh but after 30000 kms any fork oil I've used is like water, maybe not exactly but there's very little damping left. If the original 15W wasn't too harsh to begin with, you could try 20W because it might last just a bit longer before thinning out.

Title: Re: Fork oil viscosity
Post by mikestrikes on 06/21/09 at 10:21:26

I just use auto trans fluid.............. ::)

I've got 4 qts of it here just for this if you want to try it for free ! Ride it for a week and if you dont like it then buy what ever you want...

Title: Re: Fork oil viscosity
Post by BouleTard on 06/21/09 at 11:31:40

Amsoil advertises a synthetic fork oil (http://www.amsoil.com/storefront/stm.aspx) that is supposed to keep its viscosity over time, and has antifoam agents to reduce shock fade when things get all bumpy and sloshy. Sure it's over $10/quart, but any good stuff like Belray will run you almost that much anyway.

Another solution is to run 5W oil (so the viscosity pretty much has nothing to lose) and use cartridge emulators to dial up the compression damping to your liking. I'm not sure if emulators are available for the Savage, but that's what I did on my dirt bike.. works great.

Title: Re: Fork oil viscosity
Post by SV og LS on 06/21/09 at 11:42:47

717C667F7667726177130 wrote:

Another solution is to run 5W oil (so the viscosity pretty much has nothing to lose) and use cartridge emulators to dial up the compression damping to your liking. I'm not sure if emulators are available for the Savage, but that's what I did on my dirt bike.. works great.

I understand Gold Valve emulators go by the tube diameter. There were emulators for 38 mm forks last time I checked.