I used 10-40 motor oil in my forks.

[Uncle Pollo]

... lived to tell.

400 miles later and the front feels firm like I like.

Had to up the damping on my 3014 konis a notch or two.

Diffrent bike, taut as a terrier!

Thanks supershaft!

[Biebs]

I use ATF in my forks 89 R100GS.

ATF is 7 to 10 weight oil / hydaulic fluid - front forks on my bike still dive to much on braking.

10/40 motor oil andn it works tell me more????

[craydds]

Originally Posted by Biebs

front forks on my bike still dive to much on braking

Front for dive has everything to do with spring rates and preload (setting laden sag height) and nothing to do with fork oil weight.

[disston]

I once had 80/90 gear oil in the forks of a BMW. Rode it like that for awhile. Changed the oil when the PO told me about this eventually. Can't say how it worked at all it was years ago and those forks were bent anyway.

[Biebs]

Originally Posted by craydds

Front for dive has everything to do with spring rates and preload (setting laden sag height) and nothing to do with fork oil weight.

I will have to reaccess my options with this info - as stated above ATF fluid is what I use in my forks.

[craydds]

Originally Posted by Biebs

I will have to reaccess my options with this info - as stated above ATF fluid is what I use in my forks.

Shell hydraulic oil was recommended for the fork oil, equivalent to ATF. There are other (better?) options/brands for fork oils, including a variety of viscosities - 5 wt., 7.5 wt., etc. Weak fork springs are one cause of excessive fork dive, insufficient preload is a factor in this.

[Uncle Pollo]

Originally Posted by Biebs

I use ATF in my forks 89 R100GS.

ATF is 7 to 10 weight oil / hydaulic fluid - front forks on my bike still dive to much on braking.

10/40 motor oil andn it works tell me more????

I knew i was due for a fork oil service. After reading the oil threads i said "screw it".

First day i went to the sandia mountain (my test hill) and everything worked perfect on e i tighted up the rear. There is a dip on a bend right past the ski resort. Always scared me silly. After a couple passes i can tell you that it improved a lot.
It's stiffer but not jarring ... around town i can tell even more, but it is ok. On the feway the stupid front shake is gone. I am 200 pounds if that helps matters.

I'll get 5-20 or whatever and dial it in for lighter duty 50cc's at a time, but so far it works.

[R100RT Mark]

Remember that the 40 in something like 10W40 is the measure of viscosity at 210 deg F working temperature and the 10 is the measure at "cold". My guess is that the temperature of a multi-grade oil used in forks will never get to anything like 210. Instead it work more like a 10+. It seems to me to be a bad idea to have a variable damping oil viscosity. It also seems a bad idea to use oil that does not have the anti-foaming agents that ATF and fork oils use to limit performance degradation in repeated sustained use. That said, my preference is to use a "10" fork oil in my 1993 R100R and "7.5" in my 1994 R100RT and I change oils at least once a year to keep the forks and oil as clean as reasonable.

[DoktorT]

In the 80's I put all the SJ goodies on my 90/6. The anti-bottoming springs worked great to make the curb drops smooth. The nasty sticky Shell fluid was a pain. Went to ATF and worked just great.

Fast forward to my 79 RS. Same curb drop clunk with stock setup. Wilbers springs solved that pronto with no preload. Now using Bel-Ray but will go back to ATF when that runs out. Brand name MC fork oils are just fine, but at three times+ the cost, not frugal, as they simply will not last even twice as long as just ATF.

I can't image running motor oil in the forks, multi or straight grade. Makes no sence at all when ATF is better and costs no more. It certainly is much closer to spec weight than anything but perhaps 3in1 oil.

[Tosh Togo]

Originally Posted by craydds

Front for dive has everything to do with spring rates and preload (setting laden sag height) and nothing to do with fork oil weight.

You forgot oil level/height, which has the most influence when it comes to anti-dive from braking loads.


And.... if the OP likes it with 10-40, so be it. It's his ride, and he may or may not settle on something different, after the usual experimentation.

[Uncle Pollo]

the 10-40 was just sitting there ...

[Lornce]

Originally Posted by DoktorT

I can't image running motor oil in the forks, multi or straight grade. Makes no sence at all when ATF is better and costs no more. It certainly is much closer to spec weight than anything but perhaps 3in1 oil.

This.

[Uncle Pollo]

Originally Posted by Lornce

This.

Next time i am at the auto parts store i will get some.

Ill chhamge it in the spring.

[Uncle Pollo]

... or not.

Where is the data of the oil going sanctorum in the forks?

[pommie john]

Do genuine BMW forks have compression damping?

If they do, then oil viscosity will have an effect on dive.