Fork Oil

[A.B.]

I must be using the forum search wrong because I can't find the thread that talks about changing the fork oil.

I know how to do it (from the SP2 forks on my VFR) but not the oil weight and amount oil/size of air gap...

Shirly someone has done this already!

Cheers
AB

p.s. I'll need the torque settings for the fork clamp bolts too if anyone has them!

[DrIoannis]

I think the oil height is 90mm and 7.5w oil.I would go for 10w oil and more oil than original(it will make it stiffer in the end of the suspension travel).

More info
BMW S1000RR Service Manual on FILESERVE

[ChrisMag]

If the stock oil height is 90mm, I would not recommend increasing it. 90mm is really high already. Stock on the RSV4 Sachs was 110mm, and it made the lower stroke damping really poor. Better to fix the valving problem than to band-aid it with excessively high oil level.

In general, the higher the oil level, the less effective suspension travel you will have. 2 things will happen if the oil level is too high - you will hydraulically bottom early, perhaps 2 inches off the lower casting, and you you will have massively progressive spring rate which will create wildly inconsistent rebound response in the lower portion of the stroke. If you hit hydraulic bottom at 2" and you have 40mm front sag, you only leave yourself about 30mm of stroke from your static ride sag position. Any additional bump energy will transfer to the tire carcass, which will accelerate wear and could cause a loss of traction. If you wind in a bunch of preload to force the front to sit higher in the stroke, the bike may top-out hard under acceleration, and if the bike hits a bump mid corner on the gas, it can cause deflection (tank slap).

If you're blowing through the stroke on square-edged bumps, it's a high-speed valving problem generally. If you're bottoming on the brakes, more likely it's a low-speed damping/spring rate issue. Changing oil viscosity might help, but it can cause secondary damping response problems if the shim stack is not modified to match, or if the pistons are restrictive.

Talk to someone who has extensive experience tuning the OEM forks. A good tuner can modify the shim stack for either problem, and then set oil level and spring rate to give you consistent overall response while allowing for the maximum stroke w/o hydraulic bottoming.

Amauri posted the following on the Apriliaforum re: the Sachs fork on the RSV4-R APRC. I would not be surprised if the same shim size is used on the BMW fork.

Sachs uses 7mm ID shims, compared to Showa's 6mm and Ohlins 8mm. That makes it a bit more difficult to source the shims locally, time to start searching for a source of 7mm shims.