My RT pulls to the right. Why is it happening and what can be done about it?

As some of you may know, I have owned both a ‘97 and a ‘98 RT. Each one was different in its tendency to drift right. I for one, never much let it bother me ř I don’t feel that it impairs the performance of the bike, and its pretty rare that I ride without my hands on the bars. If I do, its just for a few seconds to open or close the pit zips on my riding suit. I just weight the left peg a bit more and it goes straight. 

However, some bikes have demonstrated significant pull and riding requires holding a constant pressure on the left grip, which can be very fatiguing. Some riders report that its not just a problem when you're doing something you shouldn't normally be doing (riding with no hands), but that the pull can be constant and can be severe enough to cause discomfort when riding solidly.

Speaking of things you should not be doing, Peter Cleife <cleife@emirates.net.ae>   has a different reason for riding without any hands: “The only time where I notice is it, is if I take both hands of the bars, the bike will then track to the right, whereas on my Harley (Dyna Convertible), I could ride with 'hands off' and steer with my knees. This was handy when I was opening beer cans etc on the move. On the RT I have to stop if I want to open a drink. I assume this is due to the 'flat twin' v 'V in line twin'.”

All kidding aside, Mark Neblett notes “….MUCH frustration for RT owners with pulling bikes.  Lots of theories among owners and non-owners as to the source of the pull.  Add in an apparently considerable variation in the magnitude of the pull from bike to bike, and the speculation just keeps going . . . .  Nonetheless, as an engineer (former career), I've not found a credible theory, other than the wheel misalignment with the CG theory, that makes sense in view of physics/mechanics principles.”

There seems to be four main schools of thought on the reason your RT pulls right: 1) The weight of the bike is biased to the right, 2) Its caused by torque from the boxer motor, 3) The suspension is not properly set up for the rider, and 4) The front and rear wheels are out of alignment with the bike’s CG (Center of Gravity).

There is one last “school” to consider. Some people have suggested that this is an inherent design flaw with the RT and that the bike should be recalled or that BMW should be taken to task under a class-action suit. I for one could not condone this and feel that such a case would fail as it would be difficult to convince anyone that a motorcycle (or any vehicle for that matter) should be safe to operate without any hands on the controls.

Right Weight Bias

The first theory is that the bike is simply weighted with a bias to the right. Bruce Melton <brucemelton@hotmail.com>  says that he “experienced this with my '96 to some degree and the factory guys at BMW explained it this way, "if you look at the bike from the rear you will notice that all of the drivetrain weight is on the right side, hence the bike has a tendency to pull to the right." If you factor in the fact that most roads are crowned to drain water off to the right, then it is easy to see why this happens. If the tank is full it only adds to the pull.”

Some have theorized that the bike is so finely designed, it was designed to run straight with the radio installed in the left front compartment ř without the weight of the radio, it does not go straight: Calvin <no E-mail> Says “Yes, there are several theories about why the R1100RT pulls to the right, while other BMWs don't seem to have the same affliction. One that I saw posted on a K1200LT forum was from a fellow who said it was due to the bike being set up for the weight of a radio, and his didn't have the radio. Therefore, he added several pounds of buck-shot, in a bag of some sort, to the left side of his fairing. I believe he put it in the space where the radio is normally mounted. He swears it worked.”

Thomas Gerity <tcg49@earthlink.net>  has another idea:  “A cheaper solution is to drop a brick into the box on the left, and if you do that you will find that the brick works fully as well as the BMW radio in all respects.

But Mark Neblett was adamant that this weight fix was not the solution:  “Not true in my case, Tom.  Before I put the washer under the swingarm pivot head, I tried driving around with  a 13-14 lb of weight in the fairing pocket   Roughly twice the weight of the factory radio.  Hardly felt any difference.  Same with the saddlebag; unless carrying verboten amount of weight, not significant difference.  And for the folks talking tire wear or gas tanks, no joy there either -- my RT pulled from day one, so tire wear wasn't an issue for me, and I never noticed any difference in pull with a full tank vs. empty.” 

Gary Prickett <BeemerGary@aol.com>  commented “Per the Paul Glaves article in the December issue of BMWON, the cause is the  rightward weight bias of the transmission, driveline and final drive of the  R1100 motorcycles. Until this discussion arose on this List, I was unaware of this situation.  Even now knowing about it, I consider is a non-problem. No big deal. Ho-hum.  Just another thing that gives BMWs their unique "character".

Paul Glaves <pglaves@aol.com> is the technical editor of the BMW MOA’s monthly magazine BMW Owner’s News. Paul was kind enough to send me his take on the matter:

Another example of "they all do that, don't worry about it" is the tendency for some BMW motorcycles to wear the left side of their front tires more than the right sides of the tires, accompanied by a detectable tendency for the motorcycle to wander or pull to the right.  I have fielded questions regarding this situation since the introduction of the K series motorcycles into the United States in 1985.  The phenomena is not limited to the K series motorcycles.  It is a common occurrence with the R1100 series as well, and questions about the R1100RT are particularly common.

These BMW models are certainly not the only models effected with the tendency to wander right and wear the left sides of their tires.  One of the factors which contributes to this tendency applies to all motorcycles.  In the United States, we ride on the right side of the road.  Most roads are constructed with a "crown".  That is, in straight sections,  the road slopes from the center of the road to the edge.  This slope is typically about 1/2 vertical inch per horizontal foot.

Attempting to ride straight down a crowned road with a perfectly balanced bike in zero wind conditions would still cause that motorcycle to tend to steer to the right, toward the downhill edge of the road.  The rider corrects for this by holding slight uphill steering to the left.  This causes the front tire to wear more, left of center.  Interestingly, for many models of motorcycles this phenomenon is reversed in England, Japan, and other countries where motorists use the left side of the roadway.  But many K series and R1100 BMW's exhibit the tendency to steer right and wear the left side of the tire even in countries where riding on the left side, not right side, of the roadway is normal.  Why?

  BMW introduced the Kompact Drive Unit on the K series motorcycles.  If you look closely at the Kompact Drive Unit - engine, transmission, driveline, and final drive - it is clear that the weight is not centered left-right.  The inline engine lying on its side has the crankshaft located right of the centerline of the chassis.  The transmission is also weight biased to the right.  And, obviously the bulk of the swingarm, the driveshaft, and the final drive or rear end unit are located right of the center line of the chassis.

If you were to attempt to balance a K bike on its tires on a perfectly flat surface in a zero wind enclosure, from an absolutely vertical position it would inevitably always fall over to the right.  So, when riding the bike, more often than not the weight bias to the right will cause the motorcycle to want to lean to the right.  This again makes it necessary to hold slight left steering pressure to go straight and added wear left-of-center on the front tire.

A similar rightward weight bias exists in the transmission, driveline, and final drive on the R1100 motorcycles.  It is true to a lesser extent on the airheads too.  For K bikes and R1100's the weight bias appears to be an even stronger factor that the road crown factor.  In the United States and other countries where motorists drive/ride right of center the two factors are working together.  In countries where riders ride left of center, the two factors work opposite to each other - and for some bikes the tire wear is on the right.  But for K's and R1100's, most of the reports I am getting from overseas owners indicate that the weight bias overrides the road crown and there the tires often wear on the left side there too.

What is frustrating to owners about this situation is the question, "even if they all do it, how much is too much."  And that is a question for which there is no simple answer.  Fifteen years ago many K bike riders discovered that if they packed their saddlebags so that the heavy stuff was in the left saddlebag and light stuff was in the right saddlebag, it made a difference.

Some owners and dealers have found that omitting the flat, washer-like spacer from between the rear wheel and final drive output flange (where the wheel bolts on) lessens both pull to the right and left side front tire wear.  This has the effect of moving the rear wheel a few millimeters to the right, more under the weight so to speak, which would lessen the effect.  This is not a recommendation, and if you do it, be careful that you have maintained tire clearance from the swingarm.

Tire selection and tire pressures can also effect both handling and tire wear.  Handling effects are hard to predict, but tire wear is less so.  A sport touring tire with a soft tread compound will wear more quickly and the uneven wear will be more noticeable.  Low tire pressures will permit more tread squirm and abnormal wear will occur faster.

And, of course, a mechanical defect, either from manufacturing, adjustment, or wear can exaggerate the problem.  This is insidious because dealers often simply dismiss the complaints without a thorough check of the bike because "they all do it."

The best way to determine if one bike is abnormal is to comparison ride it with a like bike of the same model.  Don't just do it on the way to a rally.  Do it with both bikes unloaded so weight distribution of the load doesn't skew what you feel.  Ride one bike then the other.  If at the same place, at the same time, under controlled conditions you feel a significant difference in the pull to the right - then investigate further.

If not, well then, "they all do that, don't worry about it."

Good Wrenching

Paul Glaves

Tech Editor

BMW Owners News

ă Paul Glaves. Reprinted with permission.

 

 Engine Torque

Another major school of thought on the matter is that the pull is caused by the torque of the boxer motor:  <johnsonjohns@hotmail.com> says ”The reason your BMW pulls to the right is because of the torque reaction of the motor. At a stop, roll the throttle on and off and you can fell the bike try to lift up and roll right. There is nothing that can be done to change this because the motor and bike is responding to the inertia generated by the in-line motor configuration.”  <jwing@iserv.net>  agrees completely: “Am I missing something here? A BMW pulls to the right because of engine torque. The torque from the flywheel spinning pulls the bike in that direction. Don't think it can be avoided. I've come to just accept it as part of the BMW experience.

Mark Neblett addresses the torque issue as so: ”With due respect, the torque reaction theory is not correct with  R11RT's. I have a '99 RT and a couple airheads -- all with torque reaction. The airheads go straight, not withstanding any torque reaction; the R11RT pulled right *strongly*…” I don't put much stock in the engine rotation/torque-causing-the-pull theory, in large part because my R75/6 goes straight down the road when driven under the same conditions as the RT.  My /6 has a Vetter SS and Krausers (similar aerodynamic drag as the RT), so the /6's torque output to maintain highway speeds must be in the same ballpark as the R11RT's.” 

Joshua J. Fielek <jfielek@home.com> asked “Are you letting go of the bars and getting a drift? If so, are you using a throttle lock to keep steady throttle? If not, you'll drift because the engine is braking, providing a torque reaction to draw the bike to the side. My RT tracks straight with the throttle lock on, and goes to the right  under engine braking.

Eckhard Grohe <egrohe@dsuper.net> thinks it’s a weight issue and not a torque issue; ”I have an RS that pulls straight. I can ride it hands off no problem. My RT is another matter. Let go of the bars and it goes right. I don't think it is the torque reaction but I have no good argument against it. It would be very difficult to eliminate torque reaction as a cause unless on coasted down hill in neutral. Then it would only be the friction of the bearings in the drive shaft and tranny as well, as the oil drag that acted on the bike. As the driver automatically compensates for any lean when letting go of the bars one would not notice any subtle changes in the position of the driver's body to compensate.”

“I believe that it is a center of gravity problem as the gas tank is mostly on the right and the drive shaft is also all on the right. By removing the shim the line joining the wheel centers would be moved to the right closer the center of gravity. It is probably some of both but I think it is more of a center of gravity problem. The question is as I said above IS IT WRONG or is that the way they meant it to be? Either way a nice ride.”

Suspension Settings

Walt Klimek  of Tonawanda, NY  <WKlimek46@aol.com>  pointed out an additional resource on this issue: “I don't own an RT, but I did read about correct rear suspension adjustment on the R1100RT to eliminate the pull to the right. Refer to the Jan. 2000 issue  of "Rider" magazine in Andrew Macdonald's Tech Q&A column on page 61. Except for the contributor who just shared his wisdom with us this column is the only time that I've ever heard of this solution for the "pulls to the right" problem”

Bruce Anderson <BAnder6125@aol.com> also saw the MacDonald’s column: “The tech editor, Andrew MacDonald, fields a question about right pulling RTs  in the Jan. Rider magazine. He says that all instances of this he's encountered were with short  inseam  riders who had totally backed off the rear suspension preload to lower ride  height, which in turn lightens the load on the front suspension. He also said  that all bikes were restored to straight tracking by putting some preload in  the rear. He suggested that front tire cupping may exacerbate the problem.”

Tom Brown <tbrown@inil.com>  sums it up “The Tracking "problem" is pretty much caused when people set the rear spring pre-load too low.  This is usually done in an attempt to lower the ride height to make it easier to reach the street for the small of inseam. Another reason is to make the bike ride "softer". It's best to set the pre-load so that it sags about  1.25 - 1.5 inches or so with rider and normal load.  This keeps the bike in the range it was designed to work in and will provide the most comfortable ride. Adjust compression damping (that screwdriver adjustment on the left side of the bike at the base of the shock through the side fairing, for softer ride. Set it soft, ride around.  Set it a little harder, ride around.  Repeat until the bike starts to get harsh on the roads you normally ride, then back  off a little.  That's the setting you want.

If compression damping is too set to high, the bike will be very uncomfortable. Preload makes less of a difference unless it is bottoming.  If it is hitting the top of the stroke when rebounding from bumps, the bike will handle strange, but will not be as harsh as the wrong compression setting.”

Mark Neblett found no success in this area: “ I did try a variety of suspension set ups, with no difference noted anywhere within the adjustment range of either the spring preload or damping.  I actually prefer, even though I'm, ah, "altitude challenged," to ride with the suspension on the higher/firmer side.  (for info, I was an engineer in a prior career and have been tweaking suspension setups on my bikes since the late '70, so I like to think of myself as reasonably well qualified to speak on this subject)  So, even though not logical, I did try suspension adjustment before I resorted to removing the swingarm pivot bolt.  Suspension adjustment simply had no effect.  Moreover, while a number of folks have repeated this theory, I've yet to hear one person say it helped fix their pulling problem.

Don't get me wrong -- I'm perfectly willing to accept as real a result without understanding the theory behind it, and just as willing to accept a rational theory without requiring results to confirm it (I was trained that way -- a lot of theoretical particle physics in undergrad days).  Here we have no results and no theory -- just an unsupported suggestion that ride height changes tracking.”

“How does soft suspension effect the direction the bike wants to go in?  If the wheels are properly aligned, then the suspension adjustment should only affect what is going on in the vertical plane of the bike ř in other words, changing ride height shouldn't change the wheel alignment to cause the bike to track to the right or left.  I'm open to suggestions, but I've yet to hear anyone with a mechanics- or physics-based explanation for how suspension height can make, or cure, a tendency to pull to one side.  My RT had a pronounced pull to the right, and I had the spring and damper set at mid-level. 

What I'm suggesting is that unless folks are aware of an actual positive result, or have a reasonable explanation as to how suspension height could alter tracking, we should let this well-intentioned but apparently baseless theory fade away.

Tom Brown <tbrown@capseal.com>  How does lowering cause a pull to the right?  I don't know.  I've never experienced a pull to the right.   If your suspension is static sagging to half of the travel, the pre-load is set too low.   Just crank it up and see if it helps the tracking.   Just because I don't know the logic doesn't mean it can't be so.  Try it.  You risk nothing.” “I'm not promising that it will work.  I'm saying it might work and save you a lot of grief.” Tom also pointed out that “”softening” and setting pre-load lower aren't always the same thing. If pre-load is too low, the shock and spring do their work near the bottom of the stroke and this can make things much harsher, especially on the big bumps. I cranked pre-load up and got a much better ride...too much is too much, of course, but too little can be very bad too....especially with the "sitting up straight" riding position on the RT.” 

Gary Prickett <BeemerGary@aol.com> suggests that you consider the analysis of Paul Glaves and Andrew MacDonald within the context of their experience: “Although the explanations by both of these knowledgeable Tech Editors seem plausible, I tend to lean more towards that of Paul Glaves. Although Andrew  MacDonald certainly seems to have a broad base of knowledge about just about  every brand of motorcycle out there, it appears to me that Paul's knowledge  about BMW motorcycles is more focused on this single brand and therefore  somewhat more detailed. It boils down to the difference between a generalist  and a specialist.”

Alignment

Mark Neblett, “I believe the problem is a basic alignment issue, as  evidenced by reports that the only fix that seems to improve the condition is shifting the rear wheel to the right.”  “Those reporting improvement have all moved the rear wheel to the right, i.e., removed the 2mm rear wheel shim, and if that's not enough, moved the swingarm to the right with shim(s).”   “I fixed the problem myself with the help of my very cooperative dealer…”.

“The short answer is it was cured by moving the rear tire to the right a total of 4mm.  I pulled out the spacer between the rear wheel and the final drive output flange (2mm) and placing a washer/shim (another 2mm) under the head of the right-hand swingarm pivot bolt.  Four mm doesn't sound like much, but my back-of-the-envelope calculations say that the 4mm shift eliminated a moment in ft-lbs that was equivalent to driving the bike while holding a bag of sugar out to the side at arm's-length.”

“All done empirically; removing the rear wheel shim took care of about 1/2 the pull, so I figured that another 2mm to the right would take care of the rest. Since it worked, I haven't bothered to check alignment (especially since I didn't know whether the wheels leave the factory in line or deliberately offset in the first place).“

The first fix is easy  The first 2mm is simple ř just remove the spacer between the rear wheel and the final drive output flange. The second 2mm comes at a higher price: Mark Neblett again: “Insert a 2mm washer/shim under the head of the right-hand swing-arm pivot bolt (if you can break the pivot bolt loose without destroying the threads in the tranny case!), then move the left-hand pivot pin in (toward the right) a corresponding amount.”

“…beneath this short explanation is more than seven hours of @#$%^#@ work removing/replacing the pivot bolt at my BMW dealers shop *with* the constant help of the Service Manager and at least one (and often more) of his techs. This ought-to-be simple piece of work (removing the swingarm pivot bolts), but it won't necessarily be so. Mark was unable to even loosen the swingarm pivot bolt, so his dealer said he would help out.  “What was to be a 20 min courtesy assist from my dealer to break the right swingarm pivot loose turned into a *seven* hour extravaganza, starring up to four professional mechanics and a shade-treer (me).  Getting the pivot bolt out/replaced was a !#$*&@!#^$# (God bless the guys at Morton's - Charlie, Rich, Zarin and Bill -- they even kept their sense of humor through this!).”

“Suffice it to say the OE Locktite used by Hans during installation was *far* stronger that the alloy used for the pivot bolt, and the threads that stripped from the middle section of the pivot bolt were glued so hard to the tranny case threads that the remaining *good*  threads at the back of the bolt couldn't pass. I was pretty lucky with the threads in the tranny case.  It turned out that the right hand swingarm pivot bolt material is a surprisingly soft Aluminum alloy, and thus was much softer than the tranny case.  Apparently, the engineers had enough sense to make the pivot bolt the sacrificial part of the system.  That said, you have to think long and hard about whether you want to do this -- I can easily envision something being "different" with you bike, such that the tranny case threads strip out (the old "$300 TV blows to protect the $.10 fuse" theory).  At some point, though, you'll need to lube the clutch and tranny output shaft splines, so the pivot bolt will have to come out anyway.  My $0.02 worth (with the usual disclaimers!): Your best bet may be to take the bike in to your dealer (and pay them an arm and a leg) to have them perform the spline service, so that if the pivot bolt strips out it will be theirs to fix -- though check with them first to make sure that they won't charge you for fixing the pivot or, worst case, replacing the tranny.  If your service folks agree that you won't be charged if your pivot bites the dust, then hand them an appropriately sized washer/shim and ask them to kindly install it under the head of the pivot bolt when they are reassembling the bike.

     On to my thread story!  Once we stripped enough threads off the pivot bolt to loosen/pry it out (it only took 300-400 ft-lb of torque (before the 12mm Allen socket stripped out the socket in the pivot bolt), drilling out the center of the pivot bolt with progressively larger bits, then Dremelling out the inside of the bolt to near paper thinness!), we found the tranny case threads in pretty good shape, considering all that had transpired. The case threads are 1/2 - 5/8 inch deep.  The @#$)@&^ Locktite had effectively welded a ring of pivot bolt threads {about three threads' width) to the case threads about 1/4 inch in from the outer edge of the tranny case.  After we picked out glued-in pivot bolt thread chips for half and hour and thread-filed the remaining glued-on threads out (a b*tch operation itself), we found we could run the new pivot bolt in from the outside about 2 threads before it hung up on bunged-up threads and unseen pivot bolt debris, and from the back (after removing the swingarm) we could go in more than half way into the case.  We cleaned the case threads up a little more, and then, because we didn't have a thread chaser that big on hand, we threaded the pivot bolt from the inside of the case to the outside. Apparently we had cleaned the threads sufficiently, because the new soft alloy pivot bolt survived and threaded into the case from the outside on final assembly without further excitement.  Unfortunately, I only have one datapoint -- mine, so I can't predict the same will be the case with your pivot.  The experienced folks in my dealer's shop had never seen anything like this in six years of R11 wrenching. 

But, it was all worth it (well, maybe not to Charlie and crew!).  Maybe it's just the afterglow from getting the job done, but to me the RT feels completely different -- as neutral as any /5, /6 or /7 I've ever ridden. Finally feels "right.""

One reader wanted to try this himself at home, but was concerned about getting the bolt out and asked Mark “….if when, you were loosening the pivot bolts, did you attempt to soften the locktite with a heat gun?  Also was the locktite blue or green or something else?   I am getting ready to proceed on this and would like to minimize the things that can go wrong.”

Mark replied that one “Definitely needs heat to break down the OE locktite (it's definitely not the "blue" formula -- it was stronger than the pivot bolt itself), but we couldn't get the pivot hot enough to break the locktite down. -- in fact, we were aware that the BMW locktite requires higher temperature than other compositions to break down, and applied heat accordingly.  Two professional's heat guns, used simultaneously, consistently got temps up into 120-130 degrees C range (250-260 F) at the surface, as measured by a pin-point infrared pyrometer.  SOB pivot bolt just laughed at us.  Only reason we didn't use a torch was BMW's warning that application of open flame can result in sudden sagging/melting of the tranny case without warning!”

“We used plain blue locktite on reassembly. This may be an operation you want to have your dealer perform -- they have access to tools/replacement pivot bolt, and can handle a warranty claim, if needed.”

D. Guy Harris <dguy@cts.com> of San Diego, CA performed the pivot bolt shift and had positive results. Guy rides a 99 RT and for some reason, the whole procedure went a little smoother than Mark's: Guy installed "a shim under the swingarm right-hand pivot bolt. This along with removing the shim between the wheel and final drive has, apparently, removed all traces of pulling." 

"I installed a .098", ss, washer that I cut down to match the bolt head. I had no problems with removing the right-hand pivot bolt -- heat must be used for it's removal! And the threads need to be CLEAN before re-assembly. The only thing that isn't ideal is the left-hand pivotbolt could be a little longer. I used loctite 242 on reassembly--the blue stuff."