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Pulling to the side


Ian

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Firstly I got bored trying to find the previous threads on boxers pulling to the side. Either our search engine sucks or I'm getting senile. So I'm just starting another post.

 

I'm in Scotland so I ride on the left. I cannot feel any pull in normal riding but when on a deserted straight country road I sometimes try a brief hands off style just to see if anythings changed. I can just keep it straight but I have to lean WAY to the left otherwise I'll be on the right side of the road. Is this the same pull direction that you get in the US? I'm thought perhaps it was the road camber but if I try it on the centre of the road it still has a big pull. The effect is the same even if the bike is in neutral gear. Anyone know if Moto Guzzi has the same "problem"?

 

Ian

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This is the same behaviour I experienced with my '98 R1100RT and my '92 R100RT before that. But it was only a problem if I took my hands off the bars and normally was unnoticeable. I have heard where people have been constantly fighting the pull but I never knew it to be that bad on these two bikes.

The R1200RT is completely different - take the hands of the bars and it goes straight.

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Hi Ian,

 

This is commonly known as PTTR (pull to the right) and falls under the category of TADT (they all do that). I hear tell that there are some that don't or do to a lesser degree but most everyone has noticed it. There seem to be many theories as to why--torque reaction from the final drive, assymetry of the gas tank, crown of the road (likely not since it happens in left and right driving countries), alignment of the rear wheel relative to the rest of the bike, etc., etc.

 

There's actually a bit of info on this in the MC/FAQ. Do note though, that when you get to the bit about removing the rear wheel spacer, that DOES NOT apply to the 1150s.

 

I've just gotten in the habit of making sure my left bag is loaded more heavily that the right. It seems to help. Some simply adjust their seating position a tad.

 

I can't help you with the Guzzi question.

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Hi Ian,

 

How utterly timely was your question, because I chanced open the same phenomena this past weekend. I know from my flying days that aircraft, such as the Cessna 172, will roll noticeably to the left under certain power settings and situations, and must be counter-steered with opposite rudder. I attributed the same tendency of my 03' 1150 to some hidden forces in the drive train which exert a right twist to the motorcycle in a "hands-off" mode. Part of the charm, don't you think?

 

Regards

Howie

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Hi Ian,

 

I know from my flying days that aircraft, such as the Cessna 172, will roll noticeably to the left under certain power settings and situations, and must be counter-steered with opposite rudder.

 

Controling roll with the rudder in straight and level....hummmmm....sounds like you're talking about yaw, not roll. As for the motor, yes mine tends to yaw to the right as well, but as Leslie stated, barely noticeable. Maybe yaw dampers for the RT, now there's an idea... lmao.gif

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Wellllll ....okay - I'll give you that as long you can explain how a bike yaws, it seemed more like a "roll" issue. I wasn't thinking of straight and level when I made the comment - more like mostly straight up with my right foot on the floor to control the roll to the left induced by the propeller thrust .... Yaw under power is a problem mostly on the ground where I did very little flying.

 

Cheers - Have a good one!

Howie

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I can't believe that there's any mystery to the 'PTTR' characteristic, at least not to anyone who's ever washed their RT on the center stand.

Put the bike on the center stand and watch what happens. The front wheel comes up (put a helmet in the top box if it doesn't) and turns to the side. Every time. It's because of pressure from the brake line.

Now, push your finger on the front edge of the tire to straighten it out. It doesn't take much. Remember this pressure.

Now go riding. Take one hand off the bar, and put the same amount of pressure as it took to straighten the wheel onto the right handlebar (pressure forward, not down or back in case countersteering is a new concept).

The bike straightens out. Magic. No shims, hi tech, whatever. A simple cause, a simple solution. A change to the brake line or an offsetting spring would likely make it disappear.

I can't believe it's been discussed for years. Maybe I'm missing something here.

 

Brock

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The only thing I'd point out here is that this seems to be unique to the RT. I've ridden R1100GS's and R1100RS's and both bikes ride dead on straight when you let go of the handlebars, so I don't quite buy the "drive train" theory.

 

In any case, my RT does this same thing. Oh well.

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My RT front wheel stays straight ahead while on the center stand. I cannot notice any difference in the force required to move the bar left or right. I just tried this again after reading your post. In fact it takes almost no force to move the bars while the bike is on the center stand. And my Rt pulls to the right.

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I think that CaptKcorb is on to something.

And yes to maintain balanced flight the rudder would be trimmed to counter the roll caused by engine torque in a single engine aircraft.

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Howie,

If you are referring to a power on (departure) stall, it is generally referred to as P-Factor which is a combo of engine torque PLUS prop blade thrust and a spiralling vortex around the body/onto the side of the empennage.

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Phil,

 

Thanks for that. Mention of "roll" issues in aircraft was meant to open up discussion as to whether the PTTS characteristic in some RT's might be related to torque forces acting somewhere in the drivetrain. On another unrelated note - Someone much more mechanically inclined than I might test whether there is a balance issue at stake here - ie: is there enough of a left-right weight distribution difference to cause this problem? I did a "hands off" test at various speeds and noted the pull everywhere, but has anyone thought of a way to see if RT's are heavier to one side, or whether the swingarm unbalances the RT enough to cause the roll? Seems unlikely.

Maybe a static test might provoke a few more answers.

 

Cheers

Howie

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Check out Brock's earlier post....interesting theories abound grin.gifgrin.gif

 

Mine actually just slightly PTTR and is hardly noticeable at speed. This was with Metzler ME880's at 40/42 and just me and the topbox. Perhaps the next time I go out, I should remove the Top Box and see if it has any aerodynamic effect(s) on the bike cool.gif

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Joe Frickin' Friday

It may be difficult for folks not schooled in statics/dynamics/physics to visualize all of the forces in play, but I can confirm (with a high degree of confidence) that PTTR is not related to any sort of torque reaction in the driveline, or the longitudinal boxer crankshaft. Kill the engine and coast in neutral (hands off bars), and you'll see the same PTTR. If you think it's the driveshaft or gearbox output shaft, then pull your driveshaft (duct-tape it to the outside of the swingarm so the lateral weight distribution remains unchanged!), coast down a hill, and you'll still see the same PTTR. If you do the driveshaft experiment and I'm wrong, I'll pay you big money for your trouble. crazy.gif

 

Maybe a static test might provoke a few more answers.

 

OK. thumbsup.gif

 

On vacation right now. I'll buy an inclinometer when I get home.

 

Proposed procedure:

 

1. measure garage floor to confirm it's level.

 

2. Assume RT's centerstand has even-length legs, so bike is vertical when on centerstand.

 

3. Place RT on centerstand, place inclinometer on tank filler; measure angle (should be darn close to level).

 

4. Put RT on wheels, steering pointed straight forward. With inclinometer on tank filler, tip bike left/right/center until it's just barely balanced on wheels, prevented from tipping by the effort of maybe a finger. Note angle on inclinometer. I expect this will show that the bike is leaning to left under this circumstance. Angle may vary with full or empty tank; will check both.

 

We shall see... cool.gif

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  • 1 month later...

Well, believe it because my front wheel does not pull to the right, it pulls to the left when the bike is on the center stand. Has absolutely nothing to do with the brake lines. Gross oversimplification IMO.

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Take the back wheel off, remove the small disk that serves as a spacer, then rebolt and torque the back wheel back on the bike.

 

The disk is ~1/8" thick, and removing it will significantly help with PTTR, but not completely eliminate it.

 

One of the RS guys did this with ~20K+ trouble-free miles thereafter.

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Take the back wheel off, remove the small disk that serves as a spacer, then rebolt and torque the back wheel back on the bike.

 

The disk is ~1/8" thick, and removing it will significantly help with PTTR, but not completely eliminate it.

 

One of the RS guys did this with ~20K+ trouble-free miles thereafter.

Warning--double check this! I think this is for the R1100 series that have the rotor fixed to the Final Drive and NOT to the rear wheel. I believe someone with an 1150 tried this and ended up wearing one of his rear brake pads through prematurely as the caliper didn't center properly.
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I can't believe that there's any mystery to the 'PTTR' characteristic, at least not to anyone who's ever washed their RT on the center stand.

Put the bike on the center stand and watch what happens. The front wheel comes up (put a helmet in the top box if it doesn't) and turns to the side. Every time. It's because of pressure from the brake line.

Now, push your finger on the front edge of the tire to straighten it out. It doesn't take much. Remember this pressure.

Now go riding. Take one hand off the bar, and put the same amount of pressure as it took to straighten the wheel onto the right handlebar (pressure forward, not down or back in case countersteering is a new concept).

The bike straightens out. Magic. No shims, hi tech, whatever. A simple cause, a simple solution. A change to the brake line or an offsetting spring would likely make it disappear.

I can't believe it's been discussed for years. Maybe I'm missing something here.

 

Brock

 

One problem with this; if your bike is already pulling to the right and you push on the right handle bar you will go even more quickly to the right. That's why it's called "counter steering." In addition to that hole in the theory, the front wheel on my '98 sits dead straight when on the cneter stand. Well, actually it will stay where-ever I leave it. I personally believe it (PTTR) to be a wheel alignment problem and completely eliminated it on my bike by removing the 2mm shim between the rear wheel and final drive. Now, as stated by others; this will cause problems on the 1150s but has work for me for over 60K on the '98 R1100 with absolutely no ill effects of any kind. PTTR is a problem that BMW writes off with the "they all do that" statement but that still does not explain why they do it nor does it make it an acceptable condition to me. Most of the beemers (old and new) track straight, why can't BMW just admit that some were manufactured a little off kelter and correct the problem instead of making up flimsy a$$ excuses or pretending it doesn't exist at all? A few other models have been reported to experience PTTR as well (R1200CLC, R1100RS and K1200GT) I helped a friend with a CLC remove the shim from his bike and his PTTR was almost totally eliminated just as happend with my RT but others have tried it and reported no noticeable difference. I will stick with my fix and I'm sure other will stick with theirs. The next thing that usually comes up in this tired old discussion is, "why would you want to ride with your hands off the bars in the first place?" A couple of points to make and I'm done. 1. there are times when I like to (or need to) adjust something on my helmet, jacket, etc), that requires two hands but only for a few seconds. It's nice to be able to do that without worrying about running off the right side of the road or leaning out over the left side like a professional racer; just to makethe bike track straight. 2. this is the biggie: when I drove my RT home the day I purchased it 450 miles from home, the ride home caused my left elbow to hurt so badly from pushing on the left bar that I knew something had to be done. Since removing the shim, I have no problem with PTTR nor a sore left elbow. clap.gif

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Take the back wheel off, remove the small disk that serves as a spacer, then rebolt and torque the back wheel back on the bike.

 

The disk is ~1/8" thick, and removing it will significantly help with PTTR, but not completely eliminate it.

 

One of the RS guys did this with ~20K+ trouble-free miles thereafter.

Warning--double check this! I think this is for the R1100 series that have the rotor fixed to the Final Drive and NOT to the rear wheel. I believe someone with an 1150 tried this and ended up wearing one of his rear brake pads through prematurely as the caliper didn't center properly.

 

The original poster has a 2000 R100RTse, so should be OK.

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i believe cruisin's on the right track.it's an alignment issue.i also believe "pull to the right",is incorrect.it should be a push to the right.like the back wheel is pointing slightly to the left or that it is off center to the left side(shim)kindof dogtracking so to speak,thus making you countersteer to the left.this i believe also explains the cupping on the left side of the front tire.

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ShovelStrokeEd

Theories abound on this topic and most of them are outright silly.

 

Wheel offset will not effect this even a little tiny bit. So long as both wheels are vertical. More about that later.

 

Road crown can, and probably does effect this a bit. Doesn't matter which side of the road you ride on the road still falls off to your right even in jolly old England. Even with that, the tire will tend to want to climb the crown giving PTTL not PTTR.

 

Static balance of the bike can have a slight effect as well but the old paving stone in the left bag will solve that issue.

 

Given that the motor drivetrain and chassis are bolted together there may be some issues there and it could explain a good deal of this. If the motor is at a slight angle in the chassis the centerline of the rear wheel could be aimed in a different direction than the steering axis and that could cause it.

 

Another possibility is that the rear wheel is not perfectly vertical when the front is pointed straight ahead. It wouldn't take much to induce a little steer that way.

 

Measuring all this stuff requires some pretty sophisticated equipment and, at minimum, the removal of the tires from the bike. You could start by making some precision measurements with the bike located on a level pad such as is available at a good many race tracks. Getting and holding the chassis straight and level shouldn't be too much of a problem. You could then check that the front and rear wheels are vertical via some form of jig and a precision level.

 

There are also a couple of shops scattered around the country that do laser chassis and wheel alignment on motorcycles. One in Sacremento as I recall. They could quickly tell you if things are in line and where any problems might be.

 

The older K series motorcycles actually had shims at the motor mounts for correcting this kind of stuff.

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so could it be that maybe the transmission was machined wrong and causing this AND the dreaded spline issue???if your bike has pttr then your gonna have spline issues!!just a thought.(pttr,spline issues,cupping on left side of front tire.i bet they are all related.

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Theories abound on this topic and most of them are outright silly.

 

Wheel offset will not effect this even a little tiny bit.

 

then explain why removing the shim corrected my PTTR 100%

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Theories abound on this topic and most of them are outright silly.

 

Wheel offset will not effect this even a little tiny bit.

 

then explain why removing the shim corrected my PTTR 100%

 

While you're at it, in addtion to explaining why removal of the shim helped eliminate my own PTTR, also explain why it still does PTTR on uncrowned roads. I've even driven on the wrong side of the road to see the effects: Especially with the shim installed, it more or less does PTTR regardless of road crown or which side of the road. Obviously, pronounced road crown (or lack thereof) can exacerbate or attenuate PTTR, but as long as the bike has the shim, PTTR will be noticeably worse.

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Joe Frickin' Friday
Anxiously awaiting results of proposed test!

 

Bought a nicer inclinometer and did a very casual test shortly after we got back from that vacation. Found that the bike's center of gravity leaned one degree to the right (i.e. the bike was leaning one degree to the left when zero lateral force was needed to balance it on the two wheels), which is consistent with a tendency to pull to the right. Sometime in the not-too-distant future I'll repeat the test and provide better documentation of what I did.

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cruisin, and others who have successfully corrected PTTR with shim removal,

 

Did this also give you even wear on the front tire? My 98 RT always wears a flat spot left of center.

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ShovelStrokeEd

OK, in regards the shim thing. Remember, I said so long as the wheels are vertical when reading the rest of this. If the bike is not undergoing acceleration and within limits far greater than the 1/8" thickness of the shim, the bike will track straight and true with the wheel offset. In fact, the wheel is not centered on your bike right now. Neither is it on all the K100, K1100 series of motorcycles. It is offset a good 1/4" to the left of center for tire cleareance at the front of the swingarm. My old turbo K100 had a custom wheel done by Kosman specialties and we offset the rim band another 1/4" to accomodate a larger section rear tire from a 160-18 to a 170-18. That bike would go straight and true at speeds well in excess of 180 mph. I could also take my hands off the bars at any speed and it would go straight down the road. Now, we did spend considerable time with plumb bobs and the like to get that wheel vertical and it did require changing the shims that mounted the drive train to the frame.

 

Did the same with the two drag chassis I have helped design and build. A great deal of attention paid to keeping the steering head at exactly 90 degrees to the rear axle. A great deal easier to do and measure than the single sided swing arm setup. Both of those bikes ran dead straight down the track on each and every pass but one with the new chassis when I broke an axle adjuster 1/2 way through first gear while pulling over 2g's of acceleration.

 

I will still maintain that PTTR is caused be either or both of the following.

Rear tire not tracking the front (fork lift steering) or rear tire tilted with respect to the steering head.

 

Mitch may be on to something as well if the bike does, indeed, achieve vertical balance while tilted one degree to the side.

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Mitch is onto something, alright.

 

Here are three cheap tricks:

 

1. Do the aforementioned removal of the goofy shim* from the rear hub and ride the bike to see about PTTR before and after the following:

 

2. Tape a spirit level to the front rim, in vertical position, then sit centered on the bike with handlebars centered and balance the bike vertically, so it does not tip to either side. See if the spirit level indictes the plane of the wheel rim is vertical. Whatdya figure the odds will be that the wheel is vertical when the bike is balanced?

 

3. Get some yellow sewing thread, and run it around the outside of the front and back tires as close to their equators as possible without fouling on the frame or fairing, etc. See if there is bias to the front/rear wheel alignment. Wazzat tell you?

 

* I've read they put that goofy shim on the bike because they screwed up in design phase, such that the swing-arm geometry would not allow wider tires without shimming. When you remove the shim, you'll see it is a cheap POS, unlike the otherwise well laid out hardware on the rest of the bike. It was an afterthought.

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