Looking for a measurement Widened rear wheel

[Mayne]

Hi
   I wanted to get some measurements from anyone that has a Luftmeister/Kosman racing rear wheel. I’m hoping to be able to get a wheel widened for my k75. 
Thanks!

[Mayne]

No luck so far. Can anybody confirm the 5mm offset for the 3x17 3 spoke rear wheel?  I believe it’s the B type I know the A type 4.5x17 has a 14mm.
Thanks

[frankenduck]

Do you realize that putting a wider wheel on a K75 will make it slower and that the bike won't turn as easily?

It will be slower not only due to more weight but there will be more rotational inertia that you need to "spin up" when you accelerate.

The wider tire with a larger contact patch means that it won't turn as easily.

[Mayne]

I’m aware that that will take place. I do want to run a more modern radial set of tires. The wider wheel will help facilitate a larger selection of said tire. I could simply go with a 140 on the Y style rear wheel, but the selection, even in the confines of one tire company is pretty slim. Granted, the 150’s aren’t much better, but it’s still a bigger selection.

[frankenduck]

I've run Conti Road Attack 3s in 130/80-17 on the Y rear which is a great, highly rated tire.

Why do you need a wide selection of tires? You can only ride one rear tire at a time.

FYI: Running a 150/70-17 on the 3x17 Y-spoke only has a couple mm of swing arm clearance.

[Mayne]

It’s a matter of availability.  What’s available now tends to vanish when comes time. I’ve a line on widening the wheel. Hence looking to find the offset of the 3x17 3 spoke wheel as opposed to the Y spoke wheel.
Like beer, it’s nice to have choices.

[Laitch]

It’s a matter of availability.  What’s available now tends to vanish when comes time.

Doesn't that mean any tire you choose—no matter when you choose it—won't be available when you want to buy it? How can you overcome a fate like that? 

[Mayne]

No. Just means that your mileage may very, or in this case availability.  I like being able to get parts I need when I need them, hence the desire for a wider selection.  I guess I made too big a leap with my loose grammar. I’ve obviously dropped the ball there.
Now that we cleared that up, any help here?
Thanks again for your time.

[Laitch]

Now that we cleared that up, any help here?

We have a cadre of genuine, and ersatz, engineer-types here so help is likely just around the corner, but for my money frankenduck has concisely summed up the situation. The K75 monolever Brick is a bygone platform not in the sights of modern radial tire manufacturers so selection will continue to be limited, as you're discovering. It's hard to envision the benefit of putting a lard-ass wheel/tire combination on it now, except maybe opening the door to buy another lard-ass tire for it in the future. 

All I can offer is Chapter 46, p.79 of the BMW of the K75/K100 Service Manual downloadable from this site that offers a formula for calculating offset for front and rear rim combinations of varying widths. P.78 indicates 5mm as the maximum allowable offset for these particular classic Bricks so you might be able to extrapolate three-spoke offsets by first calculating your current Y-spoke measurements.

There's also a likelihood that raking leaves the entire afternoon has affected my perspective on this, or maybe it was coffee consumption. Anyway, good luck!

[frankenduck]

It’s a matter of availability.  What’s available now tends to vanish when comes time. I’ve a line on widening the wheel. Hence looking to find the offset of the 3x17 3 spoke wheel as opposed to the Y spoke wheel.
Like beer, it’s nice to have choices.

Like beer, I drink what's on tap now and don't worry about what tomorrow's selection will be.

Over on the K111OG forum lots of us used to ride the Avon AV46 rear radial because it came in the same size as the stock K1100LT bias ply, 140/80-17.  Then it went away. So we switched to a 150/70-17 radial that several tire companies make.

[Mayne]

Thanks. I’ll give that a look over and see if I can’t figure something out.