BMW R75/5 vs 87 R80

Being somewhat biased toward the /5, as I have had one for 34 years now, I would go with the /5.
I'm not much of an expert on the 87 R80, but the small difference in HP will not matter. My /5 has the 32/10 rear end and has plenty of grunt.
the front brake on the 87 is a disk, and if it is a single, is not much of an improvement over the /5 drums, when they are properly set up.
the /5 front forks are very strong, and you can add a triple tree to it for easier steering, or an Earles LL, as I did.
I had a Velorex, then a Vetter Terraplane mounted to my /5 bike and it pulled them great along with a cargo trailer.. I ran into problems later. when I mounted a bigger Motorvation FII SC, and pulled the trailer and passenger. then I had a '77 R100RS engine put in it. problem solved.
but, If you are NOT contemplating a bigger sidecar than the Terraplane , the /5 will be fine. You will be very happy. keep the '87 R80 for 2 wheel cruising.

First let me say either bike should work well with your sidecar as long as you add some subframes to mount the sidecar. I'd avoid using the sidecar's universal mount kit on the BMW frame, as neither the bike frame or universal mounts are that rugged and in combination will probably be very hard to keep aligned.

That said I'd advise the reverse of Bob. The /5 is much more of a classic and is increasing in value, where as the r80, a very nice bike in its own right, is not as collectable as the /5. The r80 frame and front forks from the k75 that were used in 86 should be slightly stiffer then the /5 front end and the 37/11 rear drive will be slightly better for sidecar use then the 32/10 on a 750 or 800. I agree with Bob that the /5 front drum, when properly adjusted is comparable to a single disk front brake. It would be realativly easier to upgrade the r80 front brakes to a dual disk compared to upgrading the /5 front brakes.

The end result with either bike will be very similar and the costs to convert either will also be very close. My main reason to suggest the r80 is I like to see /5's preserved because I think they make a nicer "classic" solo bike, and sidecar use will devalue the bike as a collectable.

Thanks for your thoughts.
I'm a relative newbie to /5's. I've only had my R75/5 for 25 years.
I think I'll try to mount the chair on the 87 R80 for many of the reasons that Tod stated in his post. My R80 has the dual front disk brakes and that should help slow the extra weight better than well adjusted drum on the /5.
Thanks for your advice.
Lindsey

Hello Lindsey,
Personally, I am not much of a fan of putting a sidecar on the monoshock BMW bikes.

The Dual-Shock BMW twins all have tapered roller bearings in the wheels which are designed to be able to resist side loading as well as radial loads. The later wheels only use standard radial ball bearings.

In fact, for the rear wheel, the bearings are built into the final drive unit, and if you wear those out you are looking at some major repair cost... Assuming you haven't torn up the gears in the process from the increasing play in the worn bearings. Then you are better off shopping for a new final drive unit.

On the twin-shock models the rear wheel runs on its' own bearings on the axle, which is held pretty solidly in alignment on both ends, which I feel is stronger overall. The tapered roller bearings virtually never wear out if kept properly lubed and adjusted.

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1982-1984 R100 models are excellent tugs. They still have the tapered wheel bearings and rigid rear axle. They also have the later electronic ignition systems for hotter sparks with little maintenance. (no point adjustments, etc...) Most of the R100's also have the dual Brembo front disk setup, which work excellent for stopping a rig. The 1981 models were a transitional year, and had some quirks which were addressed later in the model year, but not all of them. The 1982-1984 units had all of those addressed. And, they came with circlips on the transmission output shafts... Your '87 might have it missing and be a potential tranny failure in the future.
Check this link for information about the circlip issue:
http://pweb.jps.net/~snowbum/transmission.htm

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I had a lightweight HitchHiker sidecar mounted to both an R75/6 and an R75/7 The /6 had the 32/10 final drive, and yes, I feel it was geared a little bit too tall. The /7 had a 3.56 ratio final drive (not sure about the gearset 32/9?). The 3.56 was a nice ratio for the sidecar with the R75.

I currently have a 32/10 final drive in my 1982 R100RT and it was a hoot with the lightweight HitchHiker. (even more so when I run it solo!) I now have a slightly larger/heavier Champion Escort on it right now, and I sometimes feel like I might like to try a 37/11 (3.36) ratio with the new chair. I know of others who run this ratio with heavier hacks.

SO... In my humble opinion. Find a nicely maintained 1982-1984 R100 for your sidecar.

Here is a link to a nicely sorted out unit with lots of information about how he set it up.
http://pweb.jps.net/~snowbum/RigSale.htm

Lindsey, If Whitmore Lake is near Ann Arbor than you must no Kevin L. The bestBMW mechanic you could ask for that lives in Celine. MI. He loves side cars and can put you in touch with Marshall who does not have a computer in Beford, MI. He has a small shop and is retired but is very generous guy with a fountain of knowledge about every thing BMW. HE designed and built his own reverse for a BMW trans. I will provide you with the phone numbers if you need them. Tom

Tom,
I've met Kevin Linski (spelling?) a few times over the years but don't claim to know him. We have some mutual friends and acquantances. I've often heard that he is a good m/c mechanic. I didn't know that he was a sidecar guy.
I've never met Owen Marshall but have heard his name over the years as a source of knowledge and obscure BMW parts.
I would appreciate contact information.
Thanks

Lindsey