Testing for wobbles

 

1 – DISCLAIMER and SAFETY WARNING

Doing any work or testing for wobbles or instability of a motorcycle is dangerous.  A wobble often is due to a combination of factors.  Factors that may not be spelled out here, or factors that are explained here, but not understood.  Improperly adjusted assemblies, poorly torqued hardware, over-stressed parts, or any number of other factors can result in a serious wobble, loss of control of the motorcycle and possibly even an accident which can result in personal injury or death.  In this document I am merely reporting what I learned as I went through my wobble experience with BMW motorcycles of a certain era.

Wobbles, or any other instability should be examined by a fully trained expert.   If you decide to test for instability on your own motorcycle, you have been warned that it is exceedingly dangerous.  

By continuing to read this information you agree that the author is free from any liability whatsoever. If you do not take 100% responsibility for the results of reading and possibly applying what you read here, you may not read further. Reading this article and/or making use of any of the very dangerous testing procedures in this article signifies your release of the author from liability.

 

 

Tests for BMW motorcycle high-speed wobble or weave

by Duane Ausherman

This is a sure fire treatment to cure a wobble.

First please read this Wikipedia information on high-speed wobbles.

I avoided writing this article for years due to the seriousness and knowing how difficult it is to describe the testing.  Many BMW riders that knew of the reputation of my BMW franchised motorcycle business encouraged me to write this.  I write this today, still with great trepidation.  A couple of “war stories” are included, but that is in an attempt to communicate how serious this issue actually is.

I trained my four mechanics to do some basic testing for low-speed instability during all test rides.  When something new was noticed, the others would all ride it for the experience.  We needed to all be on the same page, speak the same language and vocabulary when dealing with this serious issue.

I only allowed my test riders to test to a particular level.  If the motorcycle showed tendencies that needed more dangerous testing, they would return and inform me.  Since the business was mine, I was ultimately responsible.  I did all of the more serious testing, because it would be very hard to live with myself if an employee got hurt, or worse.

I hope that I have your full attention now

This article also applies to all models of BMW that were around in that era.  I divide wobbles into two groups, high speed, and low speed.  Low speed wobbles are those that are in the range of 25-45 mph.  Once a wobble has started and the bike is slowing down, the wobble can continue down to 15 mph.  A high speed wobble is one that occurs from 55 mph and up.  The speeds between 45- 55 mph are sort of a gray area and one can ignore that range for purposes of this article.

The early models, the /3 and /2

By the time that I was in the business, few /3 models were still being ridden.  I don’t recall anything but a few low speed wobbles being found and they were easily fixed.

The /2 models made from late 1955 up through 1969 that had Earles forks were quite stable.  We often found low speed wobbles, but they were easily corrected.  The Earles forks were so stable that they tolerated a handle bar fairing quite well.  The few high speed wobbles were so rare that we easily found mechanical issues without even riding it.  Once the mechanical issues were fixed, the high speed wobbles were gone.

One common error was finding the fork swing arm in the sidecar position.  There is a reason that BMW made a solo position and a sidecar position.  Just because the rider had never had a wobble, or noticed any instability, doesn’t mean that it was stable or safe.  Many riders have no sensitivity for such things.  Riders can ride a lot of miles and never notice something that we would spot instantly.  They had just been lucky.  Skill is good, but good luck is better.

In 1968-69 BMW came out with bikes that we call “US” models.  That model was a test bed for the forks before the /5 came out.  They have the same telescopic fork as the later /5 thru /7 motorcycles.  A few ancillary parts are different, but from a construction standpoint, they are identical forks.  They too will all wobble if a handlebar fairing is mounted.  Many riders have assured me that their bike does not wobble with the handlebar fairing.  On all that I have been allowed, I have ridden it in front of the owner and demonstrated a low speed wobble.  No exceptions on any telescopic fork BMW from the first ones in 68 up through the SWB models of the /5.

My approach to a wobble is to carefully examine the motorcycle.  This included many bikes of which the owner had never reported any issue.  A visual inspection can often find the most likely causes.  Correction of these is to be done before riding it again.  A special test ride regimen was followed to reduce the chance of an accident.  First, we would find and correct the low speed wobbles and then maybe test for a high speed wobble.

If all of the standard mechanical possibilities have been checked, it’s time for the low speed test.  Testing for low-speed wobbles isn’t very dangerous.  I have not had any scary experiences with them.  I look for them first, as they can show the likelihood of a high speed problem.  Our usual test ride was much more inclusive than I will describe.  Here we are only investigating wobbles.  First, I test for straight tracking.  If the bike doesn’t track straight, I want to find out what’s crooked.  My test is to get up to about 20-25 mph and let go of the bars to see if it goes straight.  The amount of lean I must use to keep it straight is my measure.  I will lean my body however much it takes to go straight.  I estimate how far off center my head is with the bike.  If it takes 6″ of lean, that’s too much.  I want to find out why.  We often found a 2″ or less lean on brand new bikes.  Some weren’t perfect when new.  Some lean isn’t going to ensure a wobble, but it needs investigating.  I have seen a 6″ to 8″ lean that handles very well and safely at all speeds.  I actually think that a bike with a “lean” is less likely to wobble.  However, after several hours of riding with a lean, the rider’s shoulders and back will get sore from holding it up.

We weren’t even concerned with a lean related to wobbles.  The discovery of the lean just meant that something was amiss that we hadn’t discovered during our working on the motorcycle.  What else had we missed?

Yamaha motorcycle wobble story

My cousin’s wife rode a Yamaha 350 and had felt a bit of a twitch, but nothing really scary.  My cousin had ridden it and he had found nothing.  They were both experienced riders, but different riders, especially amateurs, find different results.  At 65 mph the bike went into such a wobble that the bars were immediately wrenched out of her hands.  The speed and force of the bars were such that the knuckles on both hands were broken by the bars swinging back and forth.  She had no time to get her hands out of the way, it was instant.  Then the bike flipped over.  When someone tells you that you should speed up or slow down, remember, there may be no time.  Her injuries were not limited to broken fingers.

BMW motorcycle wobble story

I asked Jim for his permission to use his story and here is his answer copied directly, but slightly edited for grammar and punctuation.

Duane, after all the help I have received from your site, you are welcome to anything you need from me.  As I said, I’m no brain child when it comes to the fine details you guys get into on that forum, but I have had an Earles fork under me since around 1972.  I went down twice over the years for the same reason.  It can be passed off as some anomaly, bearings, etc.  It comes down to proper maintenance on the rider’s part.  A false sence of security because I have this “tank” under me, just doesnt cut it.  This is my first ground up restore and I have not much to go on except a parts catalog, a Clymer manual, Slabon’s book and the most helpful so far, you guys.  I ask some dumb questions at times but I do learn from the answers.  Thanks again for all the help.  Jim

His story

Not being the engineer type I can only say you beat the grim reaper, this time.  I agree with Duane, you never want to experience the excitement of flight twice.  Last year a high speed wobble broke my bike and my bones.  I have since replaced every bearing, wheel, spoke and tire on the bike.  It is still not done but getting back on it will be a slow process.  Not being able to determine the cause of these events is the scariest part of the deal.  I have also changed out my US bars for lower Euro bars.  They are the longer sidecar bars.  I have no idea how this will affect handling but I guess we will see.  I regularly rode my bike at 70 to 75 mph.  All I remember was an uneven bit of road between lanes.  As I crossed that ridge, all hell broke loose.  Things happen so fast that you only have time to realize you are a goner.   The bike spent an eternity in the air, hitting all four corners before coming to rest right behind me.  The brunt of the damage to the bike was sustained by the crash bars, handle bars, front fender and headlight bucket, rear solo seat and hard bags.  I have also installed new shocks, the rears being nitrogen filled replacements by works performance in California.  I figured I had to start at the beginning anyway so why not replace everything that could have gone wrong.  Keeping everything in proper adjustment is next.  You can get to a point where you feel these old Beemers are indestructible and snicker at hog riders who have to wrench their bikes daily to keep all of their parts aboard.  I have spent nearly 12,000 bucks to repair the bike.  the hospital bills were much higher.  Consider yourself ahead of the game if no doctors were involved.

Jim


Testing for wobbles

Some caution first.  I am describing these tests to acquaint the reader with our methods.   I can’t over emphasize the danger.  A wobble can kill or maim.

The most likely condition for a wobble is in slowing down, while in a downhill gentle curve with hands off of the handlebars with no weight on the seat, sort of posting while riding a horse.

This testing is progressive, in that I perform a test under unlikely conditions for a wobble.  If that passes, then I make it a bit more likely to wobble.  From experience, I know when to stop increasing the risk and quit.  This is not for your average owner/rider.

I take it up to 30 mph and slow down gently and feel for any sign of instability.  Then up to 40 mph and slow down.  Then I take it up to 35-40 mph and shut the throttle off and let go of the bars.  I actually try to induce a wobble by hitting the bars.  This one will get a lot of failures, maybe 25 % will wobble on this one.  Then up to 40 mph and let go of the bars and bang them quite hard and see if the shake dampens out quickly, or slowly, or not at all.   At any time, the wobble can be controlled by grabbing the bars.  The last test and the strictest is to “post” or stand up a bit and take the weight off the seat and put it on the pegs.  My legs aren’t gripping the tank, but sort of bowlegged to clear the tank.  I want to reduce the biomass dampening to the bike.  All the while I am slowing down from 40 mph with hands off the bars and then I give the bars a “hit” with my hand.  This position shifts my body forwards as I must balance on my feet.  It is very hard to shift the weight forwards with a fairing, but easy with low bars.  No telescopic fork BMW I have ever tested, with a handle bar fairing, will pass this last test.  I have had many owners tell me that “My BMW doesn’t wobble.”  If allowed, I have gotten on the “stable bike,”

I have had many owners tell me that “My BMW doesn’t wobble.”  If allowed, I have gotten on the “stable bike,” ridden down the street, turned around and come back at 35 mph with the bike in a wobble.  I have probably done this 100 times.  Point made.

Possible causes of the low speed wobble.  A low speed wobble has few aerodynamic factors.  Some of the factors are hard, or impossible, to isolate to only one thing.  It is usually a combination of several things.  Often one can get a false sense of security.  The owner will remove or correct something and the bike now shows no wobble.  Is the bike fixed?  Maybe not.  What if the wobble goes away with some other aspect removed?  What if the wobble will go away with any of several things changed?  I contend that just removing one of the factors is usually only a start.

A good example is the handle bar fairing or windshield.  Is the problem one of raising the center of gravity or of the pivoting front end?  Is the greater weight on the forks compressing the fork enough to change the trail?  A handle bar fairing will always alter results, remove it for the tests.  Here are some things to check.

1.  Correct tires and air pressure.  Twenty-five years ago this meant Conti or Metzler at about 30-34 lbs.  Today it may be higher.

2.  Tires balanced correctly.  Are you sure you have really balanced them? Can your repair shop really do it?  Read about balancing a BMW motorcycle wheel.

3.  Tires in very good condition, especially the front?  We found that when the tread is down to 1/2, replace it, balance it and many wobbles will disappear.

4.  Tight wheel, swing arm, and steering bearings?

5.  Good shocks and mounting bushings?

6.  Saddle bags?  Remove them for testing.

7.  A top box is just about the worst thing on a bike.  The problem is both aerodynamic and weight.  Even empty it can cause a wobble.  Remove it for the tests.

8.  A /5 BMW (and others too) must be neutral steering.  To test this I prefer to go through a 50-60 mile sweeping curve.  Let go of the bars and it should stay in the same curve.  If it wants to turn tighter (fall down) it is too low in front or too high in the rear.  Is the bike high enough?  Does it have sagged out springs or a front tire with a low profile?  It can also have forks bent straight back towards the engine.  It may track straight but not turn properly.  If it wants to stand up and go straight in the curve, maybe the front tire is too big, the rear too small or the rake too great.  When the dealer got the BMW it was neutral steering.  You may not care about neutral steering, but you better be concerned to find out what has changed.

9.  The US forks and the /5 and later have a reputation for wobbling.  It is only partly true.  If the forks are properly aligned they won’t have stiction.  This can be a very important factor in wobbles, especially high speed wobbles.  The forks may need to go through the alignment procedure to work correctly.

Testing for high speed wobbles

This requires a lot of experience, paid up life insurance and a bit of insanity….  maybe more than a bit.  I will describe my worst experience.

Chris Blum, my parts man at BMW of Marin bought a new 1972 R75/5 in Curry color.  The only modification was mounting European low bars.  By 2000 miles he complained about a wobble and was afraid to take it up in speed.  Everything mechanical was perfect and we could find no error in our inspection.  The tires were in balance and only took the minimal weight.  The rims were quite true.  All bearings were tight.  After all, the bike was new.

I was sort of doubting that it had a problem worth mentioning.  Maybe Chris was super sensitive and was complaining about a quiver, not a full wobble.  As the owner of the shop, I had the most experience with wobbles.  I put my riding stuff on and prepared to take it out for a ride.  Chris’ last words were, “Watch it, this thing is dangerous.”

I took it out on a seldom traveled road to perform the tests.  It had a minor low speed wobble, but it dampened out easily by putting my hands on the bars.  Many bikes had worse low speed wobbles and no high speed instability.

I started the high speed tests at 50-55 mph and it showed no instability at all.  Of course I was posting during each test in order to increase the chance for a wobble.  I repeated it at 60 and it was as solid as a rock.  I did the same at 65 mph and the forks went into a full wobble instantly.  There was no time to do anything.  Had my hands been on the bars, my fingers would have been crushed by the wildly swinging bars from fork stop to fork stop.  The front tire was skipping and airborne.  It would come down at the end of the travel and make a huge squeal.  The front wheel would become airborne again and head for the other stop.  This happened about 10-12 times in maybe one or two seconds.  I wasn’t paying close attention to my watch.  My only reaction was to try to sit down again.  Due to the added biomass, or some unknown factor, the bike snapped out of the wobble.  It dampened out as fast as it started.

I immediately stopped and got off.  I was so scared and weak kneed that I could barely put it on the center stand.  I just fell to the ground and was in complete shock.  Finally, I recovered enough to get up and ride the bike back to the shop.  My employees and I had a new aspect to think about.

We got into the truck and drove back to the scene.  This was an hour later and I was sort of OK by this time.  We examined the tire tracks.  Every 15-20 feet there was a long black mark and each was about 90 degrees from the previous one.  The marks weren’t straight but oddly shaped.  You could see where the tire smashed back down on the pavement with a wide part and then the traction and trail forced the wheel to correct.  This correction was with enough force to whip the bike back into the air with the tire again off of the ground.  If one drew a line through all of the “left” part of tracks and another through the “right” tracks, those lines were about 3-4 feet apart.

The only thing that we found wrong with this new motorcycle was that the forks were not in alignment.  It showed very little stiction.  The forks were .006″ out of alignment in both planes.  The BMW spec was .004″ and so it was very close.  We had been aligning forks for about a year to .002″, but we had never suspected that such a small error could cause such a wild wobble.  We reduced our previous spec to .001″ or better.  After all, what is wrong with perfect? The alignment procedure fixed the bike and it never gave a problem again.

Earles forks on the /2

BMW introduced the Earles forks in 1956 to appeal to the sidecar driver.  They have the characteristic of being very soft and comfortable.  This is for the sidecar to allow braking while maintaining a constant wheel base length, a good thing for sidecars.  Earles forks are heavy and swing slowly.  The unsprung weight is, however, very light.  For solo sports riding, the Earles forks are a poor choice.

This configuration has unfairly been criticized for being susceptible to wobbles.  That is simply untrue.  Any motorcycle can wobble, it is the nature of the beast.  There is nothing wrong with the design of the Earles fork or /2 frame to make it wobble.  At this point, only a bare bike as delivered by the factory is being discussed.  If one decides that a wobble is dangerous, therefore undesirable, then it follows that it is a fault that should be corrected.  Since they didn’t wobble when new, the ones that do must have something different about them.  It is logical to say that that particular bike has a problem that is very dangerous.  We should find that “difference” and correct it.  To alter the design is not the solution, finding and correcting the fault is.

It is possible for Earles forks to be bent backward and cause a wobble.  It will certainly increase its tendency to wobble.  Can you see black paint on the front engine cover?  If not, the cover might have been replaced.  The older frames didn’t have strengthening gussets at the head stock and bent easily.  There is no “proper” distance between the engine and front cover.  It is never less than 3/4″ and usually more.  Two types of covers and three types of cross braces were used so it takes lots of experience to know if it is correct.  I used to be able to judge it by sticking so many fingers in that space as my measure.

Do not ever put the Earles forks swing arm in the sidecar position for solo use.

The manufacturing tolerances of the /2 were not very close in some respects.  One can easily find small variations in the forks and frame.  I know of one case where a frame was out of spec and it didn’t track straight.  It was a European delivery and was taken back to the factory to get the frame straightened.  It was returned tracking perfectly.  That is an unusual case but serves to show that these bikes were made by humans.

The few that wobbled were usually fixed by standard repair practices.  My sample wasn’t large enough to see real problems.  In 1966 I cut up a perfectly good 1962 R60/2 and installed a VW engine.  It required cutting the frame in half and lengthening it by about 2.”  Knowing nothing about frame geometry, I just welded it up in alignment.  It was stable, it should be, as it was now longer.  It also had neutral steering, but that was an accident.

I opened up a BMW motorcycle repair shop in 1967, in San Francisco, and started learning just how little I knew about them.  Wobbles fascinated me and I did all I could to learn more about them.  Here are a few factors and how to check them.

Front wheel, swing arm, and steering bearings

Testing the front wheel and swing arm bearings.  Grab the front wheel in one hand and the fender brace in the other.  Shake the wheel sideways.  If any “play” is felt it must be in the wheel or swing arm bearings.  By looking at the gap at the wheel or the swing arm pivot, one can see which is loose.  Grab the front fender with one hand and pick it up till the wheel is off of the ground.  Spin the wheel, with your other hand, and “feel” any vibration through your fender hand.  It should feel completely smooth.  If you feel a vibration, it is from a failed wheel bearing.  Replace them.  Read my page about BMW wheel bearings

If the swing arm has some play, it must be adjusted to fix it.  It is more likely that the bearings need to be replaced.  If no play is felt in the swing arm, that doesn’t mean that the bearings are good, only that they haven’t yet been proven to be bad.  To make the next check: block up the front end and remove the wheel and shocks.  The swing arm is now loose and will swing up and down freely.  If it is more than a few years old or hasn’t been lubricated regularly, or both, it probably has notched bearings.  Do you feel it swing smoothly or with some “tight spots?”  Replace them.  Before 1965 the front swing arm couldn’t be lubricated.  It is easy to add a grease zerk for lubing the bearings.  Read about adjusting the /2 front swing arm.

With the front wheel in the air, the steering damper off, gently and very slowly swing the forks back and forth through the straight ahead position.  Does it swing completely smoothly, or with a notch in the dead ahead position?  A notch can be felt while riding at low speeds by the rider noticing that the bike won’t go straight.  It wants to constantly curve.  Notched bearings must be replaced.  Loose bearings can be checked in a few ways.

1.  When applying the front brakes lightly, at low speeds, did you ever feel uneven braking or a kind of resistance that was related to wheel speed? This could be an out of round brake drum or loose steering bearings.

2.  With the engine off, push the bike and apply a bit of front brake.  Do you feel a “click” or movement in the front end?

3.  With the front wheel off of the ground, grab the front end by the lower shock legs, just above the swing arm, and pull gently.  Don’t pull if off of the center stand.  A bit of “play” or a “click” can be felt if the bearings are loose.  Tighten the steering bearings, as needed, and retest it for a notch or proper tightness.  It is common for one to tighten up the steering bearings and only then be able to feel a notch in the bearings.