Why not just make the wheel hub a little thicker?

Or ride a bit closer to the wheel...

At a quarter to six in the AM I'm usually picking lint from me belly button, aka, navel gazing.

Is your K-Pox in remission?

Only this weekend while moving house cross town. But already I'm imagining what to do with the added space of a full size garden shed made from timber with a sturdy floor. I could hang wheel shims over the double doorway like some upturned horseshoe good luck charm.

Are you sure that all K bikes have one?

All of mine do.  Not sure about 1200s and later models.

Interesting question. It seems reasonable that the BMW engineers would know the required offset to get good handling so they'd build that into the dimensions of the parts. A shim would be needed if they required two different offsets, but such was not the case for the classic K's. Maybe the shim helped to prevent the wheel from seizing on the final drive, in case it oxidized (i.e. ease of maintenance)? I don't have an answer to your question Duck.

Both my K1200RS and the GT version used shims, but I note the latest series (K40) do not as they mount to a splayed steel flange - which were originally alloy but were recalled.

I was never able to get a viable answer from a BMW techy when I worked for the dealership system and sat next to their gurus in classes or at mealtime. It was often one of the questions asked of them, along with K bikes smoking and Oilhead surging (early to mid-'90s). Mainly I heard it was to reduce "fretting" between the metals...but that opens up a whole new line of questions regarding the millions of other vehicles which don't require it.

Here's a link to a discussion from our friends at BMWMOA

It will likely remain a mystery like how when I wear a white t-shirt all day I still get black lint in there!

Two Wheels Better wrote:Both my K1200RS and the GT version used shims, but I note the latest series (K40) do not as they mount to a splayed steel flange - which were originally alloy but were recalled.

I was never able to get a viable answer from a BMW techy when I worked for the dealership system and sat next to their gurus in classes or at mealtime. It was often one of the questions asked of them, along with K bikes smoking and Oilhead surging (early to mid-'90s). Mainly I heard it was to reduce "fretting" between the metals...but that opens up a whole new line of questions regarding the millions of other vehicles which don't require it.

Here's a link to a discussion from our friends at BMWMOA

It will likely remain a mystery like how when I wear a white t-shirt all day I still get black lint in there!

Were the K wheels used on other models like the R? That might explain it.

The exact same spacer was user on R bikes of the era: R80, R100 and R1100.

There must be some technical reason for it.  (I'll bet Ingepedia would know. )

duck wrote:The exact same spacer was user on R bikes of the era: R80, R100 and R1100.

As well as R850/R1150, all models, and the R1200C & CL. The whole three ring circus. Step right up, we don't know what good you're doing, but we'll keep you out of comfort you might know what you're doing.

Yep to Prince, many wheels and final drives interchange 'tween K & R, although I'm not clear there's an answer there.

duck wrote:The exact same spacer was user on R bikes of the era: R80, R100 and R1100.

No, not on R80 nor R100, because they had a drum brake wheel huband it would be almost impossible to fit the spacer with no access to it.
I suppose that this spacer allows a good share of pressure on the bevel drive.
But I have some old and confused reminds of other explanations red many years ago in technical notes:
- frames were made by Verlicchi in Italy, with misalignment issues: this spacer was a way to cope with by installing, removing or doubling it.
- It was added to counter the gyroscopic effect of the engine.
No tracks; no clues...just old reminds.

Oops! My bad. I was just going by the ETK (since I know zilch about Rs) and misread.  It was the R850s and R1100s that used the same spacer.  The drum braked K75Cs and standards didn't use the spacer either.

So that wheel tracking is adjustable?

Normally only relevant during accident repairs.

I lost my shim while doing repairs at xmas time, my Great Danes decided to have a punch up in the shed and sent shit flying everywhere . I ended up putting the bike back together without it and have ridden it ever since. There seem s to be no difference. I found it buried in the dirt of the shed floor last week so I will put it back in but I feel nothing better or worse with or without.

The small difference wouldn't be noticeable, but over thousands of Kays maybe a little more tyre wear.

daveyson wrote:The small difference wouldn't be noticeable, but over thousands of Kays maybe a little more tyre wear.

I think lack of a spacer might cause the rear tire to rub on the swing arm of a K1, K100RS4V or K1100RS.  Those bikes have very little clearance for the right side of the rear tire.

Big Block has a Paralever rear end with the 5x17 K1200RS wheel & 170/60ZR17 tyre and there's about 3 or 4mm clearance without the shim. I didn't use it because there is a smidgen too much offset with it in place. It clears, that works for me.

Or time for the Burt Munro precision technique.

Two Wheels Better wrote:Both my K1200RS and the GT version used shims, but I note the latest series (K40) do not as they mount to a splayed steel flange - which were originally alloy but were recalled.

I was never able to get a viable answer from a BMW techy when I worked for the dealership system and sat next to their gurus in classes or at mealtime. It was often one of the questions asked of them, along with K bikes smoking and Oilhead surging (early to mid-'90s). Mainly I heard it was to reduce "fretting" between the metals...but that opens up a whole new line of questions regarding the millions of other vehicles which don't require it.

Here's a link to a discussion from our friends at BMWMOA

It will likely remain a mystery like how when I wear a white t-shirt all day I still get black lint in there!

Yes that's the reason why.

beachcomber550 wrote:

Two Wheels Better wrote:Both my K1200RS and the GT version used shims, but I note the latest series (K40) do not as they mount to a splayed steel flange - which were originally alloy but were recalled.

I was never able to get a viable answer from a BMW techy when I worked for the dealership system and sat next to their gurus in classes or at mealtime. It was often one of the questions asked of them, along with K bikes smoking and Oilhead surging (early to mid-'90s). Mainly I heard it was to reduce "fretting" between the metals...but that opens up a whole new line of questions regarding the millions of other vehicles which don't require it.

Here's a link to a discussion from our friends at BMWMOA

It will likely remain a mystery like how when I wear a white t-shirt all day I still get black lint in there!

Yes that's the reason why.

These are quite useful.... https://www.amazon.co.uk/Gift-House-Belly-Button-Brush/dp/B000AMJX5G

On my bikes the spacer* sits on the seat


* (Irish slang for Space cadet!!)

Possibly not just a BMW thing - My Guzzi also has a spacer.....

So I think the avoid metals fretting explanation could be the one..

Noisey wrote:Possibly not just a BMW thing - My Guzzi also has a spacer.....

Small block... Damn silly name when some of the small block engines are a bigger capacity than the big block engines! Different in the Guzzi's case - it's used to line up the disc under the caliper, IIRC. It's been a few years since I took a small block apart.