Warning, new guy question.

Recently bought this 91 K100RS from a friend who can't use it anymore. While cleaning it with fairing off, I noticed the 17" front, 18" rear. My wife has a modern Suzuki with 17" front and rear and this seems standard. I have an old BSA & old Honda with 19" front and 18" rear which seems standard for old bikes. But this looks weird. BMW wouldn't do anything without a very good reason. What's the philosophy behind this wheel sizing?

Because at BMW ve do it our vay.
It was at the time when the RS were using radials and LT were still using bias ply so it may be that the sizes were chosen so that there would be no need to change the front guard/fender. If you use the front guard on a LT there is very little space so going to a 18" front with a higher profile may have been too close.
My opinion and ze nutz at BMW are probably having a laugh at der aussie fruit cake.

Thanks, Rick. I was wondering if there was a driveabilty, handling, weight distribution or some other design consideration associated with the odd (my opinion) wheel size choice. But fender spacing and tire type reasons work for me too. Has anyone played with wheel sizing to beneficial/detrimental effects (understanding, of course, the difficulty with disk/caliper placement, hub widths, etc.)?

mikealso wrote:Thanks, Rick. I was wondering if there was a driveabilty, handling, weight distribution or some other design consideration associated with the odd (my opinion) wheel size choice. But fender spacing and tire type reasons work for me too. Has anyone played with wheel sizing to beneficial/detrimental effects (understanding, of course, the difficulty with disk/caliper placement, hub widths, etc.)?

I saw a pic of a K100 16v with a 1200RS front wheel and it fitted fairly easily.

RicK G wrote:
I saw a pic of a K100 16v with a 1200RS front wheel and it fitted fairly easily.

I think that the K1 done in McLaren silver has 1200RS wheels fitted:

It wasn't that one but a K1100RS in the deep red.
Oooohhhhh that does look nice but if I had one I would just have to get rid of that fugly front guard and the more I look the worse it gets. Someone said to me once that if I owned one then it would grow on me Yeah like a wart!
They might be aerodynamic and all but I just plain don't like them

RicK G wrote:It wasn't that one but a K1100RS in the deep red.

And it was a Aussie...which is a member here...search "Ausbrick".

a local up arond my place inge ....from memory

he had all sorts of goodies added ...

but nevr met him ....mores the pity

Oilhead R1100RS/RT had 17" front and 18" rear wheels too. Excepting some California Highway Patrol RTs with spoked wheels, which had an 18" wheel at the front and 17" at the rear, and narrower than cast wheels too, just to add some further confusion to the question originally asked.

BMW have always done it their own way, until recently, where they seem to have been doing the lunge into the mainstream, and in many cases (S1000RR, Waterboxer, K1600), swimming faster.

Check the various threads on wheels and tyres on this here forum for additional info about mixing, matching and swapping the variety of stock wheels between K models. There's a whole new weird and world of fun out there. See mine for an example.