Wheel sizes

[leswaller]

When I got my R60/5 it came with a box of bits, one of which was a spare wheel complete with half decent tyre. The puzzle is that this is an 18"" wheel whilst those on the bike are 19".
So here are the questions - sorry if they are stupid.
I know the wheels are interchangeable but why would you use a single 18" wheel, is it desirable, what effect would it have, is it any use to me or shall I put in on flea bay
Les

[tvrla]

The /5 uses an 18" rear and a 19" front. The hubs are identical, except for the drive splines riveted to the rear.

Are you sure the rear is a 19"? That would take some doing to accomplish, and I don't know why anyone would? I'm not even sure a 19" tire would fit. Perhaps a front was installed on the back just to roll the bike around?

[nhmaf]

It is *possible* that you've got a custom-laced wheel, but not likely.   The R60/5 front wheel had a drum brake, so the brake housing might look sorta like the rear wheel, but they are definitely not the same, and the front, of course, is a 19" stock wheel, while the rear is an 18".

[tvrla]

...they are definitely not the same.

Are you certain of that?

I had a /6 front drum brake wheel and used the drum for the rear on my 76 R90, after attaching the splined drive. Worked just fine.

I can't imagine the /5 having a unique drum for the front. The /2 had interchangeable wheels - they'd work on the rear or front.

Just checked the parts fiche and it lists separate numbers for the rear or front, but the difference in price is roughly what the spline plus labor would be. So that doesn't necessarily tell you the parts are different.

[leswaller]

Have looked at things again and am now a little clearer following your comments. In my ignorance I assumed that both back and front wheels were the same size, and had previously only measured the front wheel.  The back wheel measures 19" from the outside edges of the rim.The front wheel measures 20" from outside edge to outside edge. So I assume these are 18" and 19" wheels respectively
The "spare" wheel measures 19" from rim edge to rim edge  and appears to be a front wheel as it has no splines but I dont know what machine it came off, it is a spoked wheel on an alloy rim and the hub appears identical to the one on the bike. So I assume that someone had thought of putting the smaller wheel on the front. Would putting this wheel on the bike have any effect on steering or handling etc, would it lower the leg height noticeably.
My apologies for confusing people with my previous statements.
Les

[nhmaf]

...they are definitely not the same.

Are you certain of that?

I had a /6 front drum brake wheel and used the drum for the rear on my 76 R90, after attaching the splined drive. Worked just fine.

I can't imagine the /5 having a unique drum for the front. The /2 had interchangeable wheels - they'd work on the rear or front.

Just checked the parts fiche and it lists separate numbers for the rear or front, but the difference in price is roughly what the spline plus labor would be. So that doesn't necessarily tell you the parts are different.

Well,  no, I am not certain, and I don't have a /5 to look at.  I had assumed that they were different because
1) The front and rear tire widths on the /5 (at least the R75/5 that I've seen more of) were different - so I am led to believe that the wheel rim widths are different.
2) The front wheel doesn't have a receiver with drive splines of course - I had assumed that the central part of the hub onthe rear wheel had been built up/bolstered to handle the torque transmission and add more meat for the bolts/rivets that hold the receiver
3) The front hoop diameter was 19" on all the /5 bikes, as far as I know, but again, I don't have one.

Are the front and rear wheels actually laced the same way (same cross pattern and center offset/ "dish")?

[tvrla]

The rear wheel is an 18" and is 2.15" wide. Those measurements are taken at the bead - the edge where the tire seats. The front is narrower at 1.85", but is 19".

I'm assuming the sizes are different to compensate for the different tire sizes. Previously (on the /2) front and rear wheels and tires were the same. I'm thinking the engineers decided that the rear needed more rubber to handle the increased torque, while the front didn't need to be as large. But they wanted them to remain the same over-all diameter. So that's how it wound up being a 19 in the front.

The /5 hubs are all the same except for the drive spline - whether it's installed or not. It's all machined and just requires placing the spline in there and inserting rivets. It's exactly the same!

[leswaller]

here is a link to some photos if anyone can help

http://tinyurl.com/crdtxx9

Les

[montmil]

Les,

I've followed your "wheel" question posted here and on the Airlist- and the multiple and varied responses you have received from some serious BMW gurus. Definitely a mystery. Good luck with finding a definitive answer.

Perhaps the PO is just messing with your head. Would make a nice bit of wall art in your shop.

[tvrla]

So what's the problem? I'm not on the airlist...

The pictured wheel appears to have a rim from a 1977 RS, and even though I'm unable to read the size, it looks like a rear tire.

Since the hub is obviously a front, I'd say the wrong rim was laced to that hub.

Is this the spare wheel? What size is the tire - 110x90 18??

I'd say this rim should be laced to your current rear hub. Unless it's a custom 19" rim on there now, and is the normal front - it'll be too narrow. It's possible the PO did that to gear the bike up to get better mileage. That's the only reason I can see for it, though I don't think the total circumference of a front tire is greater than the rear.

Whatever... I'd just make it right and not worry about it.

[leswaller]

Ok, I dont think I am going to get to the bottom of this. The tyre is a 100/90-18. Which is a front wheel width, but a rear tyre type tread which matches the one on the back wheel.
Would I have any problems using this 18" setup as a front wheel to replace the 19" wheel currently on the bike
Les

[tvrla]

Les - I really don't have enough data to know precisely what you've got. But what I'm guessing is this: your current front wheel is correct and should remain. The rear is wrong.

The rear should be an 18", with a width of 2.15". The /5 had a narrower rear in the early years I believe, but don't worry about that.

The way to correct it is by taking apart your current rear wheel and the spare. Then lace the 18" rim to your rear hub.

The 100x90 tire is a little small, but will work until it wears out, then replace with a 110x90.

Or, just find a good used /5 rear wheel and be done with it.