I do the lowers servicing on my Rebas – the manual says 5ml of 15wt in each leg.

Would altering this make any difference to how the fork performs, or is it simply for lubrication?

What alternatives are there to the overpriced RS branded stuff?

Not much as that oil is for lubrication, plenty of oil around and some charts as it even the same weight oil has the same resistance.

I’ve used catrol gtx 5w30 in the lowers of my RS forks for years with no issues or difference in performance IMO

I sometimes use a squirt of engine oil (usually 10w40 cos that’s what my OH uses in his bike) to help things along. Most of the damping’s done in the cartridge, isn’t it?

Yep, I’m not talking about the damper, just the lowers. I’m wondering if the ‘nicer’ feel my forks have after a lower leg service is just some kind of delusion on my part, or is just due to a bit of grease on the seals.

They will feel ‘nicer’ though, won’t they? They’ll have fresh oil in them! RS branded (or any other ‘badge’ version of a generic product) is a rip-off. You can buy litre bottles of motorcycle fork oil for less than a tenner which should last ages at 5ml per service 😀

It’s just for lube, the wrong weight could lead to things not being lubed as well, however you’re not deluded, it’ll get full of crap/empty out past the seals over time, so it will feel nicer after a service when everything is clean and well lubed.

You could argue that you should service more often if you can feel the difference, but IMHO life’s too short.

Oil volume in the lowers is more important than viscosity? Too much oil and forks can have travel restricted. Higher viscosity (thicker) lube oil may be more effective or may not be as mobile to reach all operating surfaces during normal use!

I’ve as always found correct volume of 15-20wt motorbike fork oil and generous smear of slick honey or similar fork seal grease is very effective 😉