01-26-2013, 12:07 AM
Joined: Jun 2007
Location: Killington, Vermont
Just trying to be helpful ...
If the 18 inch wheel you're referring to is the RT three spoke wheel, than yes, I can help.
My bikes are a 1996 R1100RT and a 1994 R1100GS. The RT has the three spoke 18 inch wheel on the back, the GS has the 17 inch.
At some point in time I had acquired a used RT 18 inch rear wheel as a spare, with pretty decent rubber on it. Considering that my GS was being ridden 20,000 miles a year, and the RT was parked most of the time, this great idea of using the RT rear wheel popped into my head. That way there could be a wheel and tire already mounted, making a quick switch quick. Plus there were a couple of spare 18 inch tires laying around.
Comparing the 18 and the 17, it was obvious that the brake rotors weren't the same, nor were they mounted the same. The RT 18 rotor is mounted to the final drive, and the 17 rotor is mounted to the wheel.
After a few months I found someone with a used RT rear rotor that would mount to the final drive (hub), and the important thing, they had the shim. You see the 18 inch rear wheel has a different offset, or some would call it dish, than the 17 inch rear.
Once having the 18 inch rotor that mounted differently and the shim, they all bolted up to the GS without an issue. There actually were two countersunk bolts that attached the rotor to the final drive. In the illustration below, they show one of those bolts going into the lug bolt hole. That's wrong, the countersunk bolts go into the two little holes that you can see. Pretty easy to mount.
Actually, I checked the 18 inch wheel on the bike, but as I recall the tire was either rubbing or extremely close to the paralever up front on the right side. There wasn't any tolerance issues without the shim, that come to mind for me, around the brakes or calipers. I could be wrong, but nothing jumps out at me.
Believe it or not, my miles per gallon improved by one or two miles. The bike sits just a hair taller, not that it's really noticeable.
As mentioned, if you're planning to use the 18 inch cast wheel from an RT than hopefully the above helped. If your plan is to have Woody or someone make a custom 18 inch spoked wheel, than please disregard all of the above!
Did all that make sense, and was it helpful?
PS: Do you have ABS? One thing that wasn't an issue for me was ABS, because the GS doesn't have ABS.
R1100GS Rear Rotor
R1100GS Rear hub 17 inch spoked wheel
R1100RT Rear Rotor - Cast three spoke 18 inch wheel
R1100RT Rear 18 inch cast rear wheel (number 2 is the shim)
MsLizVt screwed with this post 01-26-2013 at 12:33 AM