Fixed my 'wobblies' with damper and bar end weight

[bjamesw]

Got my bike with 7000mi on the odometer and the owner warned me about the wobblies/shimmies/tank'slappers, etc.  There are a number of names for this phenomena.  Evidently it affects every motorcycle on the road to some degree.  Racing bikes are so highly tuned and rigid in the frame that you'd have to exceed the expected top end of the bike on uneven pavement in a sweeper curve... but eventually you'd get it to start 'tank'slappin'.

Anyway,  the R65 seems to have more than it's share of comment regarding this from owners.   Weight distribution,  geometry, whatever, make this bike pretty sensitive to minor front wheel imbalance and other misadjustments.  Even when these are perfect, it still gets pretty squirrely on those sweepers with uneven pavement or sometimes even flat out on the highway for no good reason at all.

Previous owner of my bike had the steering head bearings replaced and a beefy fork brace added up front and aftermarket Konis added out back.  I'm sure this made the dealer very happy to oblige.  I'm personally glad that he did this..  but it really only minimally helped the situation.  I just learned to live with it, and by live I mean that I had to accept that this bike must be pampered through certain riding conditions if I wanted to come out the other end in one piece.    Well, no more!

God I wish I'd done this years ago.  I started browsing through hard core racing forums and learning what I could about 'tank'slappers'.   Lots of discussion about steering damping,  mounting,  fluid weight,  etc.   Also some discussion of 'bar end weights'.    When I read about the weights I realized the physical logic to this.   Unfortunately it's not possible to put a really effective weight out there.   You're limited to about eight to ten inches of steel bar stock to insert in the ends.  This is a truly excellent form of steering damping in that it couldn't be more solidly linked to the steering, and provides a stiction free and play free and permanent added resistance to wobbling at the steering axis.  It would be really great to be able to put about five more lbs out there.

I looked into dampers and the concensus out there seems to be that the OEM BMW ones are not particulary effective.   At least in the early years we're talking about.  New Ohlins are gobstopping expensive and I wouldn't buy one if I won the lottery anyway.  Just on priciple.   Damn..  450 USD on up for a little oil filled piston?   I went to ebay and landed a two year old OEM Suzuki for 15 USD plus ship.  It arrived looking brand new and actually bolted directly onto the lower fork brace where the BMW damper was intended.  Same thread!  Yippee!  

The new damper was not adjustable and I felt it was a bit weak, especially since the rod end attachment hole provided by BMW is so close to the steering axis that it doesn't really exersize the damper optimally. So I replaced the fluid with 15w fork oil and that helped quite a bit.    I had to tig weld an 'ear' onto the frame where the horn was previously mounted.   This is where the body of the damper is now mounted.   Welding is a much preferrable method to clamping for this purpose.  Unless a steering damper is 110 percent solid (with no free play) it will be useless.   It's primary mission in life is to control those first thousands of an inch of travel in either direction since that is where the oscillations begin and quickly build upward into wobbling.  If you've got even that much play or flex in the mounting or the internals of the damper,  it's not really doing anything but getting in the way.   That was the basic problem with the original dampers that (some) of these bikes came equipped with.

Bottom line..  the difference is astonishing.   Not a hint of wobble in sweepers.  I can pick a line and glide through it where previously I always backed down at the limits of the bikes ability to keep the line before getting squirrely and shaky.   It's just rock solid on smooth fast turns and even through sweeps with uneven pavement.   There is no compromise at all either in slow in-town manuevers.   It's a well built damper and barely impedes slow movement of the bars.  It just damps jitters and sudden knocks against the front wheel at speed.   Bar end weights do the very same thing, only more elegantly as a solution.   I'm really happy with the combination.

Sorry for the novelette.   This is just one of those things that bothered me for years about this bike and I've finally solved a mystery.  Wish I'd figured this out many years ago.

[msbuck]

That's pretty interesting stuff.  I put bar end weights on my bike years ago, but that was more for the vibration I was getting.  The only wobbles I ever get is when I load it down and then it's only slow speed wobbles.  But then, I don't take it to the limit either.  

Glad you're happy with your fix.  It's always interesting to see how folks solve their issues with the bikes.  Thanks for sharing.

[not-so-fast-ed]

Which year bike did you put it on, James?
I have a similar problem on my "Mono".
Ed

[bjamesw]

1983 R65 (not LS).     I don't really come anywhere near pushing the limits either.  That's what was frustrating me.   I've never gotten anywhere near grazing the road with my pegs.  I've never been comfortable at reasonable highway speeds carving the cloverleaf on/off ramps, especially if the pavement was jumpy.   I've gone through three sets of tires and experimented with my weight distribution, and covered every known remedy for this to no avail.  The combo of bar end weights and damper have totally eliminated the problem.  

[trolle]

The only wobbles I've experienced are low speed wobbles when the luggagebags are unevenly loaded and then it wobbles slightly with the topcase mounted and the speed exceeds 75 mph. The last is due to the windpressure on the topcase pressing the rear downwards and lifting the front.

Without the bags and the topcase there is no wobbling at all even at speeds around the 100 mph (measured on my GPS).

Small longitudinal differences in height of the road surface gives a sort of swimmingly feeling, especially when the rear tire is loosing the rounded profil due to wear, but that does not count as wobbling.

See the article on http://wotid.com/tls/content/view/24/53/ about steering geometry and tankslapping (according to some, tankslapping is an urban myth and is more due to the rider trying to force the bike than the opposite - let go of the handlebars, and the bike will seek back to equilibrium, which is straight ahead in an upright position).

Just my 2 cents

greetings from a windy and sunny north

[Altritter]

This thread got my attention because (1) I hadn't read previously that the R65 is particularly susceptible to tank-slapping, and (2) I've had some experience with tank-slappers (a relatively minor personal episode or two and a far more serious incident that I experienced in its entirety). At the outset I'll state that I'm a believer in the existence of the phenomenon; what to me are arguable are the cause(s) of it and the appropriate remedie(s), once it occurs.

First, an R65-newbie definitional question: Is a tank-slapper the same thing as the term "boxer wobble" that I've seen referenced, but not defined, in Noemi Berry's R65 articles and those of others regarding BMWs in general? (If it is, then Berry, as I recall, doesn't think an R65 is particularly susceptible to tank-slappers.)

In high school, I rode a Yahama scooter that I had bought new by mail order (4-cycle, about 5 hp, no speedo but obviously capable of  > 55mph when in good tune and with good weather conditions). It had very modest front fork rake, and (my recollection is vague) very little trail. I had one or two occasions when I got some bar wobblies that I survived by backing off the throttle carefully, and letting the bike do what it wanted while applying just a touch of rear brake. Additionally, I've gotten high-speed bar wobble on bicycles, both of which were quick-steering to the point of being fidgety because of very little rake and trail. I found the experience more unsettling on a bicycle than on the scooter -- at least until I witnessed someone on another scooter wipe out from a wobble.

My friend had borrowed someone else's Cushman Road King scooter, and he and I were riding about double the speed limit on a very wide city street that had a downhill lefthand sweeper. No problem with either radius or crown, and no road surface hazards; should have been a piece of cake at even higher speeds than ours at the time. Coming out of the sweeper, my friend got the wobbles. I was behind him about 50 yards and observed the degenerative process close-hand. He and the scooter parted ways eventually; at that point I was totally involved in avoiding two still moving objects in the road, a sliding scooter and a tumbling rider. (I had to steer between them.) He was without a helmet (not required by law yet, and virtually no one in town used one) and wearing jeans and a t-shirt. Luckily, he had broken nothing, though he left a lot of hide on the asphalt and spent a day or two in hospital for observation.

The point of this ramble is that I remain convinced that in this case, the wobble increased so quickly that it would have required much more luck than technique to stay upright. Three factors: (1) Small wheels on the scooter (don't know what the rims were, but I doubt they were as large as 12 inches, and maybe as small as 10; (2) high center of gravity; and (3) very low-tech, low-speed, low-cost design.

I didn't even consider a small-wheel scooter when I decided to get back on two wheels a little more than a year ago. (I did toy with the notion of one of the "super scooters."

BTW, there was an extensive discussion of tank-slappers a few weeks ago in one of the BMWMOA forums (the Airhead Forum, I think). I think the sense of the discussion was that a confluence of several factors (the bike (design and mechanical condition), road-surface conditions, and speed) that can override the gyroscopic equilibrium of the front wheel and create an oscillation of the fork. It's worth checking out. (MOA permits guests to browse its forum.) Also, as bjamesw pointed out, the critical tolerance is that first 1/1000 (inch or mm, take your choice) of sloppiness or flex at a particular speed that leads to an oscillation.

Any physicists in the group who can explore the theoretical possibility of the interaction of two gyroscopes (three, counting the flywheel) spinning in different planes, and possible interactions if one or more of them is spinning erratically on its axis?

Anyway, congratulations on your fix. Now, if I can just find an OEM Suzuki and a good welder . . ..

John

[montmil]

...First, an R65-newbie definitional question: Is a tank-slapper the same thing as the term "boxer wobble" that I've seen referenced, but not defined, in Noemi Berry's R65 articles and those of others regarding BMWs in general? ...

The Boxer Wobble is usually associated with frame flex and suspension inadequacies. A tank slapper, from my KTM X-country racing times, is just as it sounds... and shortly after it begins, I would do some up close and personal agricultural inspections. Face plant!

I've watched road racing 'stocker' BMWs wobble through fast sweepers and been amazed that the rider stayed aboard.

Monte

[bjamesw]

I'm not an expert rider.  Never raced (have raced bicycles).   Not an engineer.  Never stayed in a Holiday Inn Express.....   but I've done quite a share of reading up on this subject while seeking a remedy to my "boxer wobbles".    My tentative opinion, until someone can convincingly argue otherwise, is that all of these wobbles, tank slappers, shakes, shimmies, and whatnots, are the same animal rearing up in different riding situations.  

We don't talk much about tank slappers with regard to the stock boxers because, frankly, few of us are attempting to follow professionals into a sweeper at 215 mph.   Ride your stock R65 at Laguna Seca into a turn at 150mph and I will guaranty you tank slappers (and your last meal looking for daylight).  What is referred to as "boxer wobble" is, as a life saving gesture, backed away from by most riders well before it builds up to a "tank slapper", but it would get there eventually.   With the professionals on the track,  this instability has been tuned so far "upward" with exotic metal box frames, steering damping, super critical weight distribution,  ultra tuned forks,  race engineered linked rear suspensions and more, that when it does commence oscillating, it comes on suddenly and builds more quickly sometimes that the rider can back away from.  

We just don't push our machines into that territory.  Nothing near it.   What we experience are shakes, "wobbles" that are the result of idential physical forces, and are subject to the same remedies that racers avail themselves of.   They are oscillations that build out of control.  I've had the crap scared out of me on cloverleaf entries and exits on my R65 under certain circumstances.   No broken welds.  No bad or maladjusted bearings.  No tire/wheel imbalance.  Everything gone over in minute detail.  Previous owner had it.   I had it.  I've had the very same fright on racing bicycles (riding no handed any ultra lightweight bike will exhibit this oscillation in certain circumstances), various skateboards at high downhill speeds (especially short boards with the trucks we had back in the 70's), and even econobox automobiles with shitty suspension to begin with, worn shocks, and bad pavement (and stupid speeds ....   the seventies again).  

Some of that is simply the result of shameful engineering.. not much to be done.  Some is the result of mishandling the equipment..  the designers of racing bicycles really didn't anticipate your dumb ass riding no handed on bad pavement at speed.  Some, like the R65 are a different category. Great engineering, and a majority of riders that use them quite responsibly.   Mine was just crying out for a little help in managing "boxer wobbles".    I think I solved it finally.   I didn't really anticipate any argument.    Noemi Berry is one of those, of quite a few on the net actually, whose mention of this with regard to the R65 suggested to me that I was not alone with it.      

[steve hawkins]

And here is me contemplating reducing the trail of my R100.....Having said that my R65 Cafe Racer is hardly standard - 19 inch front wheel, clip-ons and rear sets.  More weight over the front wheel, progressive springs in the front, plus thicker fork oil and spacers, then Koni's at the back.

Handles great now though, even with its bog standard Continental tyres.

Although, I vaguely recall in days of old, the R65 used to wag its head a bit on the roundabouts when cranked over - I thought it was quite fun - never scarey though.  Perhaps I should try and let go of my handlebars one in a while....

Glad you've managed to get the bike how you like it.

Cheers

[Semper Gumby]

Torqing the rear swing arm to the top torque setting of its range greatly inproved my handling.  As for barend weights I used these on the BSA to help get rid of the BSA "Buzz".  I have the 17oz universals on the Firebird.  Come to think of it, it wobbles less too....  

http://www.hvmp.com/

[suecanada]

Way back in probably 1985 or 86 I had a minor tank slapper that I got out of before disaster. I wasn't going all that fast at all and I never did figure out why the bike did it, but it was exactly as they describe...a true tank slapper with the bars going one side to the other without me doing it! I think I slowed down grabbed the bars and it stopped thank goodness. It was my first 1982 R65LS and it was pretty new at the time. Never happened again and I always take a look at the road surface where it happened and wonder what did cause it. No luggage load either.  I'll never forget it.

[bjamesw]

I hate to sound like a fanatic here, but I took the bike out again today for about four hours on some of the most twisting demanding roads around here and am still amazed at the improvement from these two modifications.   Even if you never noticed any instability before,  it is probably there.   The most dramatic improvement is on those 60+mph sweeping turns through hilly country roads when the pavement is less than perfect.  Before, I'd just set my teeth and hold the bars through the line that I'd picked.  Now I just choose a line and settle into it.  The bike just sails through without so much work on my end.  There are primarily four things at work here.  The gyroscopic effect of the wheel, the slight friction of well adjusted head bearings,  steering dampening from the damper, and dampening from the end weights (along with your hands and forearms).   All other things being accounted for such as swingarm adjustment and other bearing adjustments, the motorcycle seems to benefit significantly with a little damping assitance applied to movement along the steering axis.   My bars still settle to the left/right when up on the center stand, so nothing has been restricted to the point of affecting slow maneuverablity or steering respose from my own input.   All these mods do is stabilize the front against wind buffets, off camber bumps at speed, and incipient 'wobblies'.  

I promise I'll post a pic of the damper assembly/weldment tomorrow.  

[bjamesw]

Thumbnail photos.   Click on one for full screen version.











 
Thumbnail photos.   Click on one for full screen version.

Not too good with my camera or making thumbnails.   This stuff is always frustrating for me. Photobucket is horrible with directions.  As usual, I had to go to Google to learn how to make them.

Second pic shows the axle spacer I made on the lathe one day.  I always hated the look look of that flimsy looking length of axle sticking out of the left side of the wheel.  The spacer is purely cosmetic.  Just a piece of alum billet turned into a cone and bored for the axle a couple of thousandths small.  It is cut through on the underside and to remove/replace it I just tap a wedge/chisel into the cut and it slide on/off the axle.  remove the chisel and it clamps very tightly onto the axle.  Been there for ten years without a problem.  Shortly after installing it I had the wheels powder coated so I just threw it into the batch.  

Third pic shows  shrink tube applied to the fuel line ends and as strain relief on the choke/throttle cables at the carb.

Fourth pic.  I removed and trimmed a lot of fat off the rear fender.  I fabbed a brace to support the fender on the swingarm.  I then incorporated the rear light and license plate assembly into the tool box.   I never liked the way the bulk of all this hung out of the back end of the bike. It made the rear wheel look too far forward and gave the silhouette of the bike a really ungainly aspect (to my taste anyway).  I like this much better.

Fifth and sixth.  More pics of the fender treatment.  The muffler heat shields were a really lucky find at my favorite scrap metal dealer down the road.  A whole bin of scratch and dent harley davidson mufflers was just tossed on a pile.  The heat shields were just SS worm clamped on and in perfect condtion.  I got four of them for just a couple of bucks.  Never again will a passenger get a leg roasted on these mufflers.  It was one more of those design oversights on this bike.  Just in front of the rear shock you can see a small gas strut that holds the seat open when it's swung up on it's hinges.  Used to just irritate the crap out of me whenever it slammed down on my fingers before.

Seven and eight.  The damper. Tight fit, but plenty of clearance all around.  Took some planning.  The 'ear' that the main body is bolted to is TIG welded to that cross-brace.  The rod end screwed right into the connection already supplied by BMW in the lower fork clamp.  Damper is bolted to the ear through a
3/8in spacer through a 3/8inch rubber bushing that I cut to fit.  This connects the internal bronze bearing of the damper to the frame and isolates the body of the damper from movement.

Nine shows the narrower handlebars. I didn't want to go 'clipon' narrow, but I did want to get a little narrower and tuck into the wind a bit.  I really don't want a fairing on this.  These were off the rack at a Yamaha dealer and stamped with the Yam tuning forks. Have no idea what bike they were for, but they were perfect for mine.  Bar end weights were simply hammered inside of them.  The speedo and tach lenses are convex glass from a clock repair shop.

[Justin B.]

Some nice mods, I particularly like the muffler shields...

[Rob Valdez 79 R65]

Real nice!  I like the rear-end treatment.  I even found the steering damper appealing.

Your pictures are a very good first try!  Next lesson - learning to rotate pics.