I was really excited to try the 90/90 V 18 from the front of my R100 (was a RT) Cafe on the K100RT.
However the wheel did not Plug N Play as I had expected.
The issue being the calipers on the K are hard pressed against the rotors on the right side (as sitting on bike)
I appears to be only a matter of a fraction of a mm difference in the spacers used on the two bikes axles.

I really do not want to alter/modify any parts.
So I put the wheels back on their respective bikes.

My question is, should these wheels have been able to be swapped without any mods?
I want to eventually get some spare wheels, possibly for wider tires, perhaps for radial tires.

TIA for any & all replies,

Troy

Swap the K disks onto the R wheel?
I know the disks are the same diameter but the carrier has a different offset.

Al

Thank you for the info about the offset.
So very slight, but enough to make it an issue.

I am leaning towards just swapping the tires and leaving the wheels as they are.
I am very curious to see how a 90/90 18 handles on the front of the K.
Knowing that the lower height will shift the COG forward.
Making the front more planted, I hope.
As it is very light up front now.

I did raise my forks up ~1.5 inches above the top triple clamp/tree on the airhead when I installed clip-ons.
And that planted the front quite nicely.
The 90/90 18 is the OEM spec for the 91 R100RT (which became the cafe bike)

I would simply buy a 90/90 18 for the K to give it a try.
But the shops here want $50 to mount a tire w wheel off bike, $100 w wheel on bike.
And only one shop here will do it if you bring your own tire.
Same shop will balance it for $20.

In Salt Lake City where I was living no shop would charge for mounting and balancing a tire you purchased from them.
And usually on $20 to mount and balance your tire w wheel off bike.

I'm surprised to read you feel the need to try to make the front feel more planted.  My 1985 K100RS never felt anything other than on rails.  I wonder if you might have other issues going on with your bike.  Have you verified all is as it should be with the bearings in the headstock?

brickrider2 wrote:I'm surprised to read you feel the need to try to make the front feel more planted.  My 1985 K100RS never felt anything other than on rails.  I wonder if you might have other issues going on with your bike.  Have you verified all is as it should be with the bearings in the headstock?

Brick, thank you for you reply.

Yes, all is as it should be on the bike.
Except I need new tires. Have some tiny age/dry rot cracks unnoticeable unless you look in the rain grooves of the tires. 
Even serviced/lubed splines, rear seals replaced, and all other items checked/serviced/repaired as required.
Every service/maintenance item has been performed
My bike is an '85 K100RT.
Is the geometry the same for the RS as it is for the RT.

I believe most of the light front and tracking is due to the Metzler M88 & 880 currently on the bike.
Experimenting with different inflation has showed some improvement. 
38lbs. front & 40lbs. rear seems best on unladen bike w all the luggage installed and full of all fluids.

You just need to swap the wheel, but keeping the discs. Offset for K is 2.2mm more than for R.

Geometry for RS and RT are the same. Final drive ratio differs, 32//1 and 31//1 but its so small you would not notice that.

But a not great front tyre would be noticeable.

jbt wrote:You just need to swap the wheel, but keeping the discs. Offset for K is 2.2mm more than for R.

Are you saying to swap the rotors on the wheels?
So that it is "keeping the discs" with the same bike as they were originally?
But the wheels are now on the other/different bike.

TIA for your reply,

Troy

You will need to undo the four bolts that hold the R series Disc Carrier to the wheel hub, then stick the K series Disc carrier on the R series wheel to fit it. Don't mix them up.

The 90/90 was used in set with a 120/90/18 rear on the R series. If you are up to a 140/80/17 you might be able to feel understeer in the wet on a 90/90 front. I will be very pleased to hear your reports on this.