I am keeping my eyes open for another BMW airhead to add to my garage, this one is intended to get matched up with a sidecar (my first). I may have a good opportunity with acquiring a late 80s R80 (monoshock frame) to use - I am planning to use a subframe and get help on setting it all help regardless of whether I end up getting a mono or older dual shock airhead, but is one easier/better to use for this duty than the other ? I assume that the subframes would have to be different for the 2 bikes anyhow, but is the mono frame any more/less stiff or handle the side loading of the hack any better/worse ?
Thank you for any pointers/advice !
If it is a back swing with parralell guide (the one that got BMW out of the "rubber cow" image) I ask myself if that thing is resistent enough for the extra force a rig demands...remember those are designed for solo bike.
I have seen once a broken Honda cardan plate (pinion/wheel base casting) that made me think. Nowerdays most engineers not even think about sidecar use when they design a bike.
There are for sure more knowledgeble gentlemen here in the forum who can answer that question.
Regards
Sven Peter
The twin shock models are the prefered platform for sidecar duty for several reasons.
The MAIN reason is the wheels/bearings.
The later monolever and paralever bikes use straight ball bearings in the front wheel, and the rely upon a similar large ball bearing inside of the final drive unit to support the rear wheel.
The twin shock models, by contrast, use automotive style tapered roller bearings in both the front and rear wheels. These bearings are designed to handle the kind of side loading that is seen in sidecar duty. The rear wheel, being held on both sides is also MUCH more solidly braces against the side forces, so that there is less flex in the rear swingarm/wheel when cornering.
One other advantage is the WIDE range of different final drive gear ratios that have been available for the twin-shock rear ends over the years. It allows you to source the correct ratio to tune the bike's performance to the extra weight of the sidecar. There just were not that many different ratios made for the monolever drives, and there were fewer of them produced over the years, so they are more scarce.
Sourcing heavier shocks/springs for a twin-shock model should also be less expensive.
The tradeoff in selecting which model year to look for basically comes down to brakes/ignition system versus power and shifting ease.
The 1981-1984 R100 models have the FAR supperior Brembo dual-piston calipers up front and the virtually maintenance free and foolproof electronic ingnition system. However, they share the lower horsepower and lighter flywheel with the later monolever models. (although the R100 monolever bikes use 32mm carbs rather than the earlier 40mm units, so they suffer from ever worse performance, another reason to avoid the monolevers)
The earlier models with the heavier flywheels are much nicer shifting bikes, especially with the extra load of a sidecar, but suffer from the inferior ATE brake calipers, and still have points based ingition which do require regular maintentance/adjustment. However, they also have higher compression/horsepower motors, which aid in pulling a sidecar.
For myself, I prefer to have the better brakes and lower maintenance ignition system. You can always dual plug and ad high compression pistons to bring up the horsepower on one of these units. Look for a 1982-1984 model to avoid the early model "teething pains" that always happened. Some 1981 models were probematic, and all the 1981's had a one-year-only frame that was changed for 1982 and beyond.
Hope that I have helped...
Thanks for your insight !
The wheel bearing differences are significant - I have an '82 R65LS but have not wanted to turn that little pseudo-cafe bike into a tug, though it has the lowest geared (highest numerically) final drive BMW made. The 81-84 bikes all have the exhaust valve seat issues to deal with though, and I used to own an 88 R100RT that I foolishly sold many years ago. It didn't have the top end power of the "old" R100 bikes, but it seemed to run a little smoother and seemed slightly more torquey, at the expense of peak HP. While the monolever swingarm was supposedly much stiffer than the old dual-shock setup, it just didn't appear to be better for sidecar duty from a purely visual perspective. Perhaps ultimately I'll have to buy an older twin-shock frame and eventually mate it with a late-80's era powerplant for the ultimate combination. hmmm. decisions, decisions...
Of course, you could go look in the want ads section and see the nicely set up rig that I just posted for sale... 😉
(Yes, it will need valves soon, and probably a timing chain; but then it will be good for another 90+ thousand miles...) 🙂
That is a very nice rig - unfortunately I've gotta look for things closer to home at this time. Best of luck with the sale - I am sure that you can get a good price for it, particularly with that transmission. Can I ask who built/modified the transmission for you ?
Hey, I would be willing to deliver for the cost of fuel and hotels... 😉
The transmission was built by an Airhead specialty shop in Germany called Motoren Israel. They do nothing but Airhead BMW work. From mild to wild...
http://www.motoren-israel.com/
I have fun just browsing their offerings... 🙂
