8ball wrote:
Should I start looking for custom front forks and rear axle?
Uh, not a rear axle. The offset of the rear wheel that has been talked about is a longer spacer (sometimes called a top hat spacer because of the rim it has). The spacer is a longer version of the stock spacer and it serves to move the rear wheel to the left where the wheel splines engage with the final drive splines. There will be consequently less engagement between the splines which would be expected to increase the wear. But on a fun bike that wouldn't likely be an issue. Plus both splines can be replaced--at a cost.
The rear axle just goes along for the ride, spacer wise. At worst, the shoulder on the axle could just be trimmed back a bit.
I believe that the longer spacer is not specially made. In my experience BMW made two lengths of spacers, depending on whether they are for the front wheel or rear wheel and which side. This is a little fuzzy, but as I recall the longer spacers are used with the front wheel and perhaps the left side of the rear wheel. The short spacer is used on the right side of the rear wheel. (Interestingly, when I tried to order the shorter spacers from Bob's BMW, I kept getting the long ones. But at least I have at least one in my parts stock.)
You could custom make an even longer spacer, but it might not do you that much good in trying to fit a wider rear tire on your twin shock swingarm bike. As has been mentioned, tire width is limited by the tire rubbing against the drive tube and by your ability to force the wheel between the final drive brake shoes and the L/H swingarm. You could modify the L/H swingarm, but that would involve a lot of care to maintain the proper alignment.
Of course a monolever or paralever rear end could be grafted onto your twin shock frame, or so I believe. Then your choices for a rear tire would be considerably broadened, or rather limited by whichever rear wheel you could find. And I think that a "cross spoke" R100R or GSPD wheel could be found.
You may want to select another front fork for aesthetic reasons. I'm guessing that you wouldn't want to use the accordian rubber fork protectors. And those skinny 36mm fork tubes might look out of place with a substantially wider front tire--or not, depending on your vision.
As has also been mentioned, there is a constraint on the front tire size due to it rubbing on the fork brace/fender mount. One solution would be to simply remove the fork brace. This would compromise the fork stiffness, but on a bobber I'm thinking that handling would not be your god anyhow.
In a way it's too bad that BMW's weren't bobbed, back in the day, at least not that I've ever seen in person or pic. Back in the day only Harleys, Indians, and Brit bikes were bobbed because that's what there were to bob. Of course there had to be exceptions, but I'm thinking that a bobbed Jawa/Allstate or a pressed frame Honda would have elicited mostly giggles. If there had been a significant number of bobbed BMW's around there would be a paradigm in place for them now.
Of course, later, in the late '70's and early '80's the chopper craze went WFO, and everything was chopped without taste or mercy. But that was choppers, not the bobber look they evolved from.
Claimer: I was there, more or less, back in the day. When I was 16, my Dad and I bobbed an ex-army Harley 45. It was his vision, but I helped. Plus he had given me 50% interest in it. My emotional interest was limited though. My heart and soul were focused on those powerful sublime Brit bikes. They were bobbed too, but the paradigm (as I remember it) was not to chop them as much as it was to make it look as if the bike had just come off a scrambles, TT, or flat track. For the most part that meant no front fender or lights, and a pad on the rear fender to scoot your butt against.
Ken
