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Warren Dean

Gee...I wonder why my R1100RT pulls to the right..

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Warren Dean

I did my throttle body sync today and was looking at the fuel tank and thought...maybe this is why the RT pulls right. Most of the gas tank weight is on the right. Am I seeing this wrong? ūüėúūüėú

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RogerC60

That's one theory I've heard put forward. I don't think you're wrong.

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dirtrider
9 hours ago, Warren Dean said:

I did my throttle body sync today and was looking at the fuel tank and thought...maybe this is why the RT pulls right. Most of the gas tank weight is on the right. Am I seeing this wrong? ūüėúūüėú

 

 

Morning Warren Dean

 

That is some or part of the PTTR (Pull To The Right), but isn't the one or only reason. You will also find the transmission weight offset to the right of center, rear wheel offset varies greatly on the BMW oilhead bikes (rear wheel is very seldom directly tracking behind the front wheel "tracking-wise" with the offset usually being with the rear wheel left of chassis centerline). 

 

The BMW 1100/1150 RT also came with or without a radio (OEM radio weight decreases PTTR).

 

Just run your fuel tank to empty, then ride the motorcycle (carry some extra gasoline with you, or don't go very far), you will probably  find the PTTR is still there.  

 

If you can find some of the old archives there was page after page on how we used to address the PTTR, from adding weight in the glove box bottom (non radio bikes), to removing the rear wheel shim (1100 bikes), to shimming the swingarm & final drive  to the right as far as possible, to offsetting front wheel slightly, to ????. Seldom did any one thing make a lot of difference but all things combined could significantly lower the PTTR.

 

It was mainly a new BMW 1100/1150 rider that complained as most of us seasoned riders just ignored the PTTR & rode the bike as usual adjusting body position when we had to ride hands  free for  a while. 

 

I spent hours on my first 1100RT moving the rear wheel right with swing arm pivot shims/machining, removing rear wheel shim, adding weight to the radio box (no radio), measuring rear wheel tracking off-set, moving my wallet to my L/H pocket, foot peg position re-location, etc. (you name it we tried it)

 

By my 3rd BMW 1100RT I did nothing & just rode the darn motorcycle & hardly noticed the PTTR.   

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Warren Dean

Dirtrider,

That is what I am doing. Adapt and overcome. I dont care to repeat what you and many others have done to address the PTTR issue. It just struck me as glaringly obvious that this might be part of it. ūüėä

 

Cheers!

Warren

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Jim Moore

It's pretty simple to remove that wheel spacer. You might want to give that a try. It seemed to help mine.

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Warren Dean

It doesn't pull enough to worry about or waste time on.  :)

 

Just ride, baby!!

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chrisolson
5 hours ago, dirtrider said:

removing the rear wheel shim (1100 bikes)

 

2 hours ago, Jim Moore said:

it's pretty simple to remove that wheel spacer. You might want to give that a try. It seemed to help mine.

 

Same here ... back when I had my 99 R1100RT .  The difference was noticeable ..

 

1 hour ago, Warren Dean said:

It doesn't pull enough to worry about or waste time on

 not all bikes seemed to respond the same,  still, its simple to try if it becomes a nagging issue in the future.

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Warren Dean

I think ill give the spacer a try. Simple to do. Thanks for the tip.

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dirtrider
1 hour ago, Warren Dean said:

I think ill give the spacer a try. Simple to do. Thanks for the tip.

 

Afternoon Warren 

 

Lots of 1100RT riders have done that without issue but every once in a while with  just the right stack up of final drive spool lateral  position, tire sidewall width, swing arm casting creep, & who knows what else they end up with a slight tire rub on the swing arm housing. 

 

So, after removing the spacer (if it hasn't already been removed by previous owner)  keep an eye on the swing arm for signs of a tire contact or rub. Most will have enough clearance, some will be real close, & few will actually rub a bit. 

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Warren Dean
15 hours ago, dirtrider said:

 

Afternoon Warren 

 

Lots of 1100RT riders have done that without issue but every once in a while with  just the right stack up of final drive spool lateral  position, tire sidewall width, swing arm casting creep, & who knows what else they end up with a slight tire rub on the swing arm housing. 

 

So, after removing the spacer (if it hasn't already been removed by previous owner)  keep an eye on the swing arm for signs of a tire contact or rub. Most will have enough clearance, some will be real close, & few will actually rub a bit. 

Good call, dirtrider. I'll look for clearance issues when I get around to removing the spacer. Today is yard work and house cleaning day, so maybe next weekend.

 

Cheers! 

Warren

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dirtrider
14 minutes ago, Warren Dean said:

Good call, dirtrider. I'll look for clearance issues when I get around to removing the spacer. Today is yard work and house cleaning day, so maybe next weekend.

 

Cheers! 

Warren

 

Morning Warren

 

If the PTTR isn't bothering you then why not wait until next rear tire change?

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AviP

The weight is definitely part of the problem but the difference is really noticeable when accelerating. Grip the handle bars loosely and accelerate hard from any speed always creates the torque causing PTTR. PTTR is different from tire wear. Some tire wear can be attributed to the weight mismatch but most of it is the effect of PTTR.

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dirtrider
1 hour ago, AviP said:

The weight is definitely part of the problem but the difference is really noticeable when accelerating. Grip the handle bars loosely and accelerate hard from any speed always creates the torque causing PTTR. PTTR is different from tire wear. Some tire wear can be attributed to the weight mismatch but most of it is the effect of PTTR.

 

Afternoon AviP

 

What am I  missing? A motorcycle is  a single track vehicle so all the driving torque is applied in same direction as the rear tire travels.  (tire to road surface is where the torque reaction is, not the engine, or engine & chassis, to the surrounding air)

 

There is some lateral rotational twisting due to engine accelerating mass, or even negative twisting due to decelerating engine mass  but that goes away as soon as the  engine stabilizes at a constant RPM. 

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AviP

I was referring to the torque at the longitudinally mounted crankshaft that IMHO causes the PTTR effect. It is obviously noticeable under acceleration by that strong rotational effect to the right and under deceleration by righting itself up. PTTR effect is even more noticeable when the handlebars are held lightly.

 

At a constant RPM, PTTR seems minimal but it is still there as there are no opposing forces to counter the rotation of the crankshaft. This is not a problem in V-bikes or Japanese 4 bangers as the crankshaft rotates perpendicular to the longitudinal axis.

 

I always thought that the PTTR effect was primarily due to the longitudinal crankshaft and less due to the weight. Is that wrong? I only stay on the Oilheads forum but have the newer R-bikes stopped suffering from PTTR? 

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dirtrider
34 minutes ago, AviP said:

I was referring to the torque at the longitudinally mounted crankshaft that IMHO causes the PTTR effect. It is obviously noticeable under acceleration by that strong rotational effect to the right and under deceleration by righting itself up. PTTR effect is even more noticeable when the handlebars are held lightly.

 

At a constant RPM, PTTR seems minimal but it is still there as there are no opposing forces to counter the rotation of the crankshaft. This is not a problem in V-bikes or Japanese 4 bangers as the crankshaft rotates perpendicular to the longitudinal axis.

 

I always thought that the PTTR effect was primarily due to the longitudinal crankshaft and less due to the weight. Is that wrong? I only stay on the Oilheads forum but have the newer R-bikes stopped suffering from PTTR? 

 

Evening AviP

 

A lot of people think the same way you are now. It seems so simple & straight forward. (but, think about it some more & even research it if you need to) 

 

Unfortunately the spinning crankshaft/ flywheel, clutch & even the transmission output can have no PTTR influencing torque (at a steady RPM) as there needs to be a reaction point. 

Now if the engine is mounted to the frame with rubber mounts then there will be some "constant RPM" engine to frame reaction between the two   but even that is local to the mounting point only  & not to the outside world. 

 

The only twisting (assuming content crankshaft  RPM) on the BMW boxer bike is the rear wheel to the road as that is where the ACTUAL torque reaction to the outside world  takes place & that is in the wheel driving direction. 

 

Think about it: the engine is mounted solidly to the frame, the transmission is mounted solidly to the engine, the swing arm is mounted solidly to transmission (in the rotation direction), the final drive is mounted solidly to the swing arm (in the engine output twisting direction).

 

Now find a way to prevent the rear wheel from  turning (more than just a rear brake apply) but not to the outside world (like bolt a bar on the rear  wheel studs then lock to the frame).

 

Now start the engine & bring up to a constant RPM,  now engage the clutch with trans in gear. What do you think will happen? Will the engine crankshaft torque flip the motorcycle over on it's side?  If you say no then you now get it, if you say yes then think about it some more until you can  explain to yourself how the torque from  the fore/aft  spinning crankshaft  is reacting against WHAT to push the motorcycle over on it's side. 

 

 

 

 

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Warren Dean
22 hours ago, dirtrider said:

 

Morning Warren

 

If the PTTR isn't bothering you then why not wait until next rear tire change?

Ah, hell...I couldn't stand it. :4322:

So I took 15 minutes and removed the spacer. I am completely amazed. The PTTR is now a slight drift but if I get on the centerline, i.e. off the crowned side, it tracks straight.  :14:

So thanks again for the tips. Looks like I have the bike tuned and tweaked for me. Now I'm going to just ride it. 

 

Cheers!

Warren

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AviP

That's interesting Dirtrider. I'll definitely think about it.

 

Also, just curious about whether the PTTR effect is still present on the R1200 and R1250 series bikes.

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dirtrider
17 minutes ago, AviP said:

That's interesting Dirtrider. I'll definitely think about it.

 

Also, just curious about whether the PTTR effect is still present on the R1200 and R1250 series bikes.

 

Morning  AviP

 

It doesn't seem to be an issue. Most of the BMW 1200/1250 bikes track pretty straight with few complaints (that I have heard of anyhow). This alone kind of nixes the spinning crankshaft theory.

 

With the majority of the 1200 bikes having cruise control you would think that IF tracking (PTTR or PTTL) were an issue we would be hearing plenty of complaints as some of us ride (on cruise control) for miles & miles & miles with hands off the bars including lane changes, curves, & side winds.  

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MontanaMark
1 hour ago, dirtrider said:

 

Morning  AviP

 

It doesn't seem to be an issue. Most of the BMW 1200/1250 bikes track pretty straight with few complaints (that I have heard of anyhow). This alone kind of nixes the spinning crankshaft theory.

 

With the majority of the 1200 bikes having cruise control you would think that IF tracking (PTTR or PTTL) were an issue we would be hearing plenty of complaints as some of us ride (on cruise control) for miles & miles & miles with hands off the bars including lane changes, curves, & side winds.  

 

Having both a 1999 RT and a 2013 RT, I can confirm that PTTR on the 13 is non-existent.  I can ride with cruise on and no hands on the bars, tracks straight.  It's a different story on the 99.  While I don't notice it much with the Atlas lock on and hands on the bars, if I remove my hands I have to leans far to the left to counteract the PTTR.  Front tire wear is also an issue.  

 

Ultimately it doesn't matter much to me.  I've been riding R1100RT's for 10 years and have grown used to the phenomenon.  

 

Cheers,

Mark

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Skywagon

Mark...that's interesting no PTTR on 13.  I have it on my 14RT.  Its not nearly as bad as it was on my 1150RT - 2005. the 14 has different degrees based on speed.  Below 50 it is pretty straight, but not completely.  Above 50 it begins to increase.  At 70 and above it's pretty pronounced.  I actually like riding hands free for a minute or two every so often, but that isn't very easy to do on my 14RT unless you weight shift.  I even have considerably more weight in the left bag.  Like others I am so used to it I haven't tried to do anything about it.  On my old airhead I would just tighten the steering knob.  That generally worked.

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AviP

Well, thanks all. I definitely stand corrected. :4607:

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Lowndes

Does gyroscopic precession of the drive train or wheels have anything to do with PTTR??

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dirtrider
1 hour ago, Lowndes said:

Does gyroscopic precession of the drive train or wheels have anything to do with PTTR??

 

Afternoon  Lowndes

 

Good question & one that is difficult to define. I don't deal with this much in my automotive job so I am FAR from an expert on the subject.  

 

To (hopefully)  answer your question: it probably does at times but not with enough force to make a notable difference. 

 

Just riding along in a straight line it should have little effect as the spinning plane of both  wheels is fairly constant except for minor line corrections (so it probably has little effect on straight line PTTR).

 

As you put in handlebar movement to change direction (counter steer) that would drive some gyroscopic precession tendencies as the gyroscopic effect on the front  wheel changes.  How much I can't say but you can definitely feel it in the motorcycle's reaction to a quick bar input. 

 

Added: If you (or anybody else) would like to play with this just find an old bicycle front wheel (the larger diameter the better). The wheel needs to have the axle & bearings still in it so it can be spun up.

 

Next, find an old broom (or anything with round wooden handles).  Then cut off two pieces of round broom handle about 8"-10" long,  then drill holes in the end of each cut-off broom handle pieces. Drill the holes just slightly smaller than the bicycle axles.

 

Next, drive the wooden handles on the bicycle axles to act as axle extension handles.

 

Next, hold that bicycle wheel out in front of you with a hand on each broom stick handle.

 

Now have someone spin that wheel as fast as they can get it going.

 

You should find that as long as you hold that spinning wheel steady (like riding straight down the road) that wheel will just sit there spinning it's little heart out with no fight-back & no tendency to PTTR or PTTL.

 

You should also find that as soon as you try to put any force into handles of that the spinning wheel to change it's spinning plane that  it then starts fighting back  trying twist on your hands at angles to the input force.     

 

 

 

 

 

 

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Lowndes

Thanks, DR,

I'm NOT an expert there either.  I did take physics twice in college, but it wasn't because I liked it. 

 

I googled the precession thing and found a very good demo and discussion of it: https://www.youtube.com/watch?v=XPUuF_dECVI  starting at 14:02.

 

It doesn't seem to take much in the way of mass or rpm to have a "strong" effect on effort to turn the handlebars or the direction of the bike, judging from the demo with the bicycle wheel above.  As he says , it is definitely NOT intuitive.

 

Just a guess,  but the effects of the crankshaft and clutch on a boxer or K at 60 mph would be many times the effects of the bicycle wheel in the demos.  I'd like to see him do the same demo with a BMW R1100RT front wheel with the discs.  He might need a seatbelt on the stool.  

 

With a seeming lack of other obvious culprits for PTTR, it might be a good excuse.

 

 

 

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dirtrider
36 minutes ago, Lowndes said:

Thanks, DR,

I'm NOT an expert there either.  I did take physics twice in college, but it wasn't because I liked it. 

 

I googled the precession thing and found a very good demo and discussion of it: https://www.youtube.com/watch?v=XPUuF_dECVI  starting at 14:02.

 

It doesn't seem to take much in the way of mass or rpm to have a "strong" effect on effort to turn the handlebars or the direction of the bike, judging from the demo with the bicycle wheel above.  As he says , it is definitely NOT intuitive.

 

Just a guess,  but the effects of the crankshaft and clutch on a boxer or K at 60 mph would be many times the effects of the bicycle wheel in the demos.  I'd like to see him do the same demo with a BMW R1100RT front wheel with the discs.  He might need a seatbelt on the stool.  

 

With a seeming lack of other obvious culprits for PTTR, it might be a good excuse.

 

 

 

 

Afternoon  Lowndes

 

It looks like you found a nice video showing what I posted above (I was typing my "added comment" about the same time you were posting the video).

 

That definitely isn't the reason for the PTTR  as it only effects the bike lean & reaction when the spinning front wheel is turned side to side or quickly leaned over. As long as it is upright, spinning, & rolling straight down the road  then it really has  no effect on PTTR. 

 

If the straight line  gyroscopic precession  was the reason then every motorcycle out there would have PTTR, & it would get MUCH / MUCH more severe the faster that you travel (faster the wheel spins) .  I'm pretty  sure that you have owned other motorcycles that didn't have PTTR. 

 

But back to the BMW boxer bikes, back in the day (Day Of The PTTR) we could get them to track with no PTTR by getting the front & rear  wheels in line & getting the bike's weight balanced on the wheel's  center line. If it was gyroscopically induced then  we wouldn't have effected it with subtle weight shifting to be evenly balanced.    

 

 

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Lowndes

DR,

 

I've never had a bike with an inline crankshaft (before the BMW's) either.  I did have a '77 Honda CB750F2 SS with a bent frame.  The PO put it in a ditch 6 mo after buying it, bent the forks and sold it back to the shop where my brother repaired it (we found out later).  Several years after I bought it, I was aligning the rear tire after tightening the chain when I noticed the front wheel was angled/tilted about 3-5 degrees to the right, as in the steering head was slightly bent/torqued to the right.  I tried to find any "bad effects" it had on the handling, pulling one way or another, tire wear, etc, but couldn't.  Maybe it just handled so badly to begin with it wasn't obvious.  My takeaway was that "tire alignment" wasn't that critical.  

 

I have noticed that I do not normally sit perfectly vertical or in line with the bike, I'm leaning 3-5 deg to the right, too.  No PTTR, no lopsided tire wear.  Has anyone looked at wheather rider posture or "handedness" has any bearing on PTTR??

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dirtrider
3 minutes ago, Lowndes said:

 

I have noticed that I do not normally sit perfectly vertical or in line with the bike, I'm leaning 3-5 deg to the right, too.  No PTTR, no lopsided tire wear.  Has anyone looked at wheather rider posture or "handedness" has any bearing on PTTR??

 

Evening   Lowndes

 

It doesn't seem to be discussed much lately as PTTR isn't much of a problem on the new (post 1100/1150) BMW's with the same  inline crankshafts.

 

Back in the 1100/1150 days  when PTTR was a big issue  on the BMW boxer bikes we discussed, tested, tried, brandished about, & guessed at just about any & all possibilities & influences. 

 

Rider position was usually included in the conversation at some point as well as some testing while riding. We determined that rider position had an effect  & it could effect PTTR but a rider had to REALLY get his/her weight off the center line (very odd riding position) to get the motorcycle to ride with no PTTR. Again, if random rider position was the cause then why did all the  1100/1150 bikes have PTTR?  None (that I know of anyhow) had PTTL. 

 

But even more important, why did some of us get the 1100/1150  bikes to ride with no PTTR with just common sense weight centering back to tire centerline. 

 

 

 

 

 

 

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Lowndes

DR,

 

THANK YOU for beating this dead horse with me. 

 

It sounds like maybe "the factory" figured it out but didn't  let it be known, possibly because of liability and/or competitive reasons.

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Warren Dean

Wow!!! This thread is growing faster than the Woohoo virus....:4323:

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wbw6cos

....similar to an oil thread?

  • Haha 1

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Warren Dean
On 3/23/2020 at 5:39 PM, wbw6cos said:

....similar to an oil thread?

 

Precisely...or a tire thread...  :4322:

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