Final Drive Unsprung Weight

[macx]

Just an observation -

I'm swapping final drives this winter to change gear ratio and have my replacement
FD ready to go in.

I noticed when I first picked it up that it's quite heavy - of course with the ring & pinion etc
one should expect that.

I know performance vehicle reviews obsess over excess unsprung weight, including high
performance street cars. That's why they go to exotic lightweight materials for suspension
components, differential housings, etc etc.

Considering that some models, especially, seem to get a lot of attention for FD failures,
one has to wonder how much of an advantage that setup really is - especially considering
the cost it adds to the bike to start with and to repair or replace it.

Makes one think more about clean, simple, lightweight, easy and inexpensive to repair, belt drives.
When I bought this bike (first beemer, first shaft drive) one thing I anticipated was no longer
having chain lube slung all over the rear of the bike, or frequently replacing and adjusting chains.
Now, after learning more about shaft drives and the final drives, those belt drives are looking
better all the time! Also, so much easier and cheaper to change ratios, which is what really
started me looking at all the aspects of the shaft drive & final drive on my BMW to start with.

[NoRRmad]

I like belt drives. Never riden one, but the maintenance requirements and performance figures look good. I do wonder, however how much that big, wide rear sprocket weighs.

[macx]

I would have to believe they're an aluminum alloy being they don't have to resist wear
and abrasion from a metal chain, so probly not near as much as a FD.

I've read they're actually not that much cheaper to produce, if any, than a shaft drive
with a rear gearset, but if a belt brakes on the road, which has got to be the main
potential breakdown, sure seems it would be easier and cheaper to fix than a FD
bearing going out.

And no driveshaft joints or splines or pivot bearings to worry about, or the seals
in the drive either by the gear or at the front pivot.

I'm sure they don't give the sprockets away, but compared to the price of a new
or rebuilt final drive, or a new set of gears with dealer setup? Whew!! And more
ratios likely available to choose from to suit your individual type of riding. For our
r1150r's, there's I believe only one other final drive with a different ratio that will
bolt on. And good used final drives are probly at least as much as a new sprocket.

Oh, well. The bike owns me now, so it's a little late. I'm in too deep.

[boxermania]

Belt drives have been around for awhile and have improved at every turn. The belt was the main setback, as they streched and broke. With the advent of hi-strength fibers and the weave indicated for the belts the prior problems have been corrected.

Simple, clean, reasonably easy to change amd fairly inexpensive.

[macx]

I'm fairly familiar with industrial belt drives on assembly lines that run 24x7 and carry some
significant loads and have very low downtime as a category.

Just for curiosity sake, I looked at a listing of bike reviews on a big bike magazine and was
kind of taken aback by the relatively low number of major brands made - noticeable when
seen in a list - which really narrows the choices.

Buell made a fairly decent looking sport tourer with upright seating, tall windshield and detachable cases, and a friend of mine has a Buell that he really likes - oil/fan/air cooled V twin with a broad torque range, 103 hp or so and 85 torque on a 465 lb dry bike, not a Harley motor but a Rotax which surprised me. Interesting - hollow aluminum frame, swingarm is the dry sump oil reservoir, and interestingly they advertise "low unsprung weight" But Harley shut down Buell so there would be the issue of service and esp parts. Right now mostnew 09 & 10 Buell's are going in the $7k range at the dealers - Harley chopped the price to
get rid of them. Shot the heck out of the used market, too.

I'm just not into Honda's, and don't think I'd care to constantly be subject to the "rump rump"
and the vibration of a Harley, let alone the size and weight.

Not that I was looking to change to something else particularly, but curious. After that little
foray into what's "out there", it looks like i'll be "putting up" with the shaft drive for awhile.

I did find a different used FD with the ratio that I was looking for to match up to my RTP
trans, but it isn't a simple FD swap, either, necessitating a rear wheel from that bike (just
lucky it happens to look exactly like my R wheels and is the same size etc), and also lucky
that the ABS and rear brake system mates up to my R system also, but it all has to be
swapped which took a lot of research for one thing. Lucky I found very good used low
miles parts relatively quite inexpensively. But all that considered, a belt drive would have
been so much easier and cheaper for a simple ratio swap!

I still like the idea of a belt drive.

[ruddy]

My wife's '06 Suzuki Boulevard S40 (Savage) has a belt drive, and I definitely like it. So long as you keep it clean, tensioned and aligned, a belt is great. They squeal if the alignment is off, but that's pretty minor.

I was interested when I saw a write-up in this month's Cycle World about BMW's new F800R Roadster model, but I was disappointed when I learned that they went with the GS model's chain drive.

I tolerate chains on dirt bikes, but not for the street and touring.

[boxermania]

The BMW F800ST has a belt dive. CycleRob went from his R1150R to the F880ST and for the most pat it's a better package on all fronts, or so it appears. Weight, acceleration, vibration, consumption, let long all the nuances of the R, time will tell.

[WorkinMan]

I had a Buell M2 for 5 and a half years. Bought it new in 2001, and REALLY liked the bike. I had, I think, 13 or 14 K on the bike when I sold it and I never once had to adjust the belt. It was very quiet, very clean, and had less "slack" in it than the FD on my 1150r. I wouldn't hesitate to have another belt drive.
However...
The big thing you always have to be wary of with a belt is a rock. I've heard stories of guys just pulling over on the shoulder of the road and getting a rock between the belt and the pulley. There goes your belt, Dude. (Or Dudette.) Riding down a dirt road was a REALLY scary proposition. You just KNEW you were gonna get a rock in there. I never did get a rock, even though I did venture down a few dirt roads.
Replacing the belt called for FIVE hours of labor. That's still better than a FD, I'm sure, but it's no picnic. You have to remove the swingarm and that's not a day at the park. Also, there was ONE set of pulleys for the Buell and that's it. I don't remember ever seeing a different ratio being offered for the bike. They may have some alternatives offered for the newer Buell's, but the tube frame Buells had the one the bike came with and that was your only option. Some of the guys who did more serious riding converted over to chain drive so that they could switch sprockets. If you'll notice, all the Buell race bikes have chains just for that reason.
I did like the belt, and wouldn't mind having another one, but they do have their drawbacks. As for the BMW and the final drive. This is my first Beemer and I'm a bit disappointed in the slack that is in the FD. Even compared to the shaft drive on a Honda, there seems to be alot of slop. I might think it was high milage, but my 1150R had less than 3500 miles on it when I bought it, and only has 5400 on it now. I have yet to find the "Perfect" bike, but this BMW is as close as I've gotten, so I'll get used to the FD. Just my thoughts.

[macx]

I agree on the drivetrain slop.

I've read somewhere a bit about the transmissions and their development
and design, and if I recall a lot of that slop is attributable to the transmission.
For a name like Getrag that builds transmissions for some of the world's most
expensive and exclusive cars, they must have let their apprentice engineers
work on the BMW bike transmissions or something. Nothing to be proud of -
not only the slop but the sometimes sticky shifting etc. Surprising - or maybe
just disappointing - that BMW would accept something like that. After all,
they like to think they're near the top of the heap in exclusivity. My son in
law drives a Ducati 1000 Monster and I've had a couple Suzuki's a way back
in the 80's and those trans were light years ahead in shifting smoothness and
"tightness" for lack of a better term. For the transmission in an inexpensive
Japanese bike of 81 vintage to be so much better engineered and smoother
to operate than a current BMW is downright shameful! Maybe there's just a
bit of brand haughtiness blinding their eyes to reality? To tell the truth, if I
had a few more long green rectangles to spare, I'd be real serious about taking
a good hard look at one of those Buell sport touring bikes going for in the $7k range.
That friend of mine said when he test rode a Buell, he was immediately impressed
and convinced and bought one on the spot. And has nothing negative at all to
say about it after riding it for nearly 2 years. That tells you something! I wish
I could say that about my R1150.

Anyway, there's alway some slop in a differential type gear arrangement too, of course.

[ruddy]

The BMW F800ST has a belt dive. CycleRob went from his R1150R to the F880ST and for the most pat it's a better package on all fronts, or so it appears. Weight, acceleration, vibration, consumption, let long all the nuances of the R, time will tell.

That's true, but the new for this year F800R has a chain.

[Arbreacames]

The backlash in the drivetrain and the notchiness of the boxer gearboxes is related to configuration choices rather than poor design. Here, the gearbox is driven directly by the engine, without stepping up.

The advantages of getting a gearbox to operate at higher speeds are:
-at a given hp, torque through the box is reduced, so smaller gears are required
-less backlash
-reduced rotational inertia, so easier meshing of dogs
-no tipping toque from unbalanced rotary inertia.

Our configuration is almost a direct requirement of having a flat twin facing the air. If you like that layout, you have to live with the drivetrain layout. However, there are some advantages to our configuration
-fewer components
-specialized gear oil
-direct drive
-dry clutch, use any automotive oil.

Now, I don't dislike the gearbox one bit - I just find it difficult to use smoothly. I have spent the past year in Italy and when I came back it took me a full 3-4 weeks to re-learn how to shift properly. Interestingly, even my old BMW 323i also took me a while to re-learn. And it's not lack of driving practice, since I was driving a manual car and riding an old XT600 every day.

Proper timing is essential on these boxes. The gears are heavy and only exact timing and pedal preload can make them shift smoothly. Timing is particularly important from neutral to first: hold the clutch too long and the gears will stop and first gear will not engage. Wait too little and the spinning of the secondary shaft will make the dogs grind. Lengthen the delay as the gearbox oil warms up! When you do it right, its all so satisfying!

[MattPie]

The backlash in the drivetrain and the notchiness of the boxer gearboxes is related to configuration choices rather than poor design. Here, the gearbox is driven directly by the engine, without stepping up.

Good post! I kinda figured there was more to the story than 'BMW stinks'.

I've found that using two fingers on the clutch and pulling the lever back to touch the remaining fingers smooths things out quite a bit. I'm not sure what implications that has for clutch or synchro life, however.