What weight of fork oil to use?

[Scoots]

I'll be doing a total service of my R100RS monolever this winter ....... I have lots of time on my hands due to an encounter with Black Ice 2 weeks ago.

What weight of fork oil do you fellows recommend 7.5w or 10w?

Probably many more questions to come in the coming months.

Thanks

[dougie]

I am using 7.5 wt.
I found 10 wt. to be a bit much, but that's just me.

[ontic]

I've got progressive springs in the front of my R90.
I changed the fork oil that came in the bike when I bought it, because it was leaking and there was not much left in there- not sure what grade it was- to 15W (on the recommendation of a local beemer dealing bike shop/wreckers, and a friend who had followed the advice and was happy with it in his R75/7).
Way too hard. Great and confident for smooth road cornering, but hard and tough on the wrists for real world riding and ended up cracking my GPS mount!
Then just before my last big ride I changed to 5W. With a lot of gear on the bike it was very soft and comfortable on the road, if a little too soft, but on the dirt it was positively disconcerting if not dangerous. With too much weight on the back end it felt like my front end was made not just of rubber, but JELLY. It was really weird- it felt like the whole front forks were flopping around, twisting, bending, wobbling... I don't really understand the dynamics, but I felt I needed heavier oil pronto.
So, then, halfway through the trip I had to try to find some more fork oil. Options were slim where we were (Jindabyne).
My memory is failing me of what I exactly got this last time, and whether some mixing of the 5W in the forks with the new oil occurred (Charlie, do you remember?). What it left me with IIRC was 7.5W or 10W.
Either way, with a loaded bike, this was an improvement, especially on the dirt with too much weight on the rear.
On the road and with no gear (currently) it is a little too stiff, but I can deal with it, and so can the replacement GPS mount!
Not much help, I am sorry, but the moral of my story is that you will probably have to fiddle around with a couple of different weights to figure out what works and feels right for you, your bike, its load and load balance, and the roads you ride.
IIRC Charlie (Airbear) uses 5W on his same model same year bike as mine (without the progressives) and is happy with it (loaded and unloaded)(step in to correct me Charlie), and my friend John on his 75/7 (unloaded) uses 15W and is happy with that...
Next time I feel like covering my boots in fork oil I will start at 7.5W and then have a bottle of 15W on hand (same brand I suppose would be a good idea) to try gently upping the weight a little by little till it feels 'just right'.

(*thread degradation*)
For me, through my fork oil trials, what stood out was the importance of load distribution. Too much on the back is not good. I want a bigger tank bag and some tank saddle bag type things to stash heavy stuff and bring the weight more forward. Front 'jelly forks', on an rear-overloaded R90, with 'road' tyres, on the dirt... not much fun!

[Motorhead]

I use 7 Weight with BMW heavy springs

recenty to Progressive springs and so far the 7 weight works

[ME 109]

I find 10 wt in my RS to be a good average for dirt and loaded for touring. Ok for blasting through the mountains too.

[Airbear]

G'day Scoots. Sorry to read of your black ice experience. I hope you weren't damaged beyond repair.
Just to help out Ontic with his dodgy memory I'll add what I can from my dodgy memory - I'm pretty certain that it was 10wt he added to the 5wt, making it roughly 7.5wt, give or take. I like 5wt with my stock springs, and I weigh 70Kg (155 pounds). It suits me well enough under all conditions. My bike seems to handle better with a bit of extra load.

If your forks haven't been looked at for a while you may want to pull them apart and check that all is clean and complete in there. The fork tubes on mine each contained a handful of rubbery pellets in the bottom - apparently the remains of the rubber bumper.

[CVA-42]

7.5 wt with '82 and BMW heavy duty springs and '76 with Progressive springs seems about right to me. 10 wt with the HD springs was too hard for my liking. On the other hand, 10 wt with '71 and stock springs works well.

[daz]

You really want to hear from someone with a monolever RS. With the same stock springs as you. Or take a guess and be prepared to change if it doesn't work out. Once you have the inside of the forks clean, changing the fluid is easy enough.

[Scoots]

Thanks for your replies - much appreciated.

I went thru the RealOEM.com web site and for my R100RS, made 10/1988, they have listed a 10w fork oil.
http://www.realoem.com/bmw/showparts.do ... g=31&fg=05

I have no idea what weight is actually in the forks, but I thought the ride was very good, so I'll try the 10w first. It's easy enough to change to 7.5w if I think the ride's a little stiff. With my riding gear on I weigh about 215lbs., add the Krauser saddlebags, tank bag, and camping gear, the 10w may be right on target ..... I'll let you know.

[Duane Ausherman]

How is your fork alignment? That is a must no matter what oil you use. Simply changing the oil can mess up a good alignment. One must do it carefully.