Track offset

[atavar]

Keep in mind that there is huge difference in suspension tuning between tuning ang geometry for the 75hp suspender wearing city driving guy and the 200+hp young trained track rider.  What is good and healthy for one could be deadly for the other.

[Huzo]

Has anyone found the REAL reason yet for the track offset I'm clueless, as mentioned I'm perplexed as to why BMW would intentionally introduce it, it's not a clearance issue on modern Beemers, my mate has a slightly wider than standard rear tyre on his R1100S and it still clears easily. I'm buggered if I know.

[Rusnak_322]

Most Harleys have an offset to accommodate the weight of the big primary drive on the right side. And as you know, Harley is the winningest American motorcycle company, so they know what they are doing!

The issue is not having an offset to the wheels front to rear, it is making sure that they are parallel front to rear that will mess up handling. If both wheels are pointed straight, then when moving in a straight line they will not wear or pull. Think of a car – the front and rear wheels don’t have to be inline.

The bike has a 4.5mm offset built from the factory. That is most likely purposely put in to offset handling issues when turning brought on by the flywheel effect.

The spacer is there because there is a tolerance for offset (as would be expected of German engineers)  +/- 9mm. So having a spacer will allow adjustment by removing it, since there is no other adjustment built into the bike.

Why there is such a large tolerance is probably due to cumulative tolerances. Castings, weldments, machined parts all have tolerances to them. Sometimes all parts can be in tolerance but the tolerances conspire to throw the assembly out of tolerance. It is likely all bikes are built with the spacer and it is removed if a customer complains about handling issues.

[Huzo]

That's a good post Russy, thanx. I can honestly say that  thought it may have something to do with Torque reaction but could not understand this since that Torque reaction reverses when you shut off yet the offset is constant. Then I considered Gyroscopic precession when the bike is pitched nose up/down and sat on that for a while. Both these got rubbished on the forum to some degree, which is fair enough. Yours I think is close to the money, and I reckon like my suggestion is as far from a rough guess as I've been. Until I meet an old German engineer,with glasses on a chain around his neck,speaking broken English in a German accent at the BMW factory in Bavaria, I'm doomed to wander the dusty, abandoned halls of uncertainty looking for the definitive answer. Thank you for your valued input. Huzo.

[Testarossa]

Was it a Scandinavian country that had traditionally driven on the wrong (left) side whose gov't decided to change over to driving on the right side and simply announced the change one day .

Before the 1967 change, driving from Norway to Sweden and return involved an interesting lane-to-lane shuffle at the border. Clear customs and then line up to alternate switchover with oncoming traffic.

[Huzo]

Before the 1967 change, driving from Norway to Sweden and return involved an interesting lane-to-lane shuffle at the border. Clear customs and then line up to alternate switchover with oncoming traffic.

Oh marvellous, and every bloody second one a Volvo ?

[kirby1923]

Before the 1967 change, driving from Norway to Sweden and return involved an interesting lane-to-lane shuffle at the border. Clear customs and then line up to alternate switchover with oncoming traffic.

Ha! That is still the case going from Hong Kong to mainland China!

:-)

[Huzo]

I really hoped that the combined knowledge of thousands of readers who each know hundreds of people, would have unearthed someone who actually KNOWS why the offset is deliberately built into the Beemer and,as I understand it,some Guzzis. There have been lots of educated guesses that may or may not be somewhere near the mark. I did try to ask Kev Cameron as suggested but don't think I got through, jeez, I'd love to get a definitive explanation. As I see it, if the centre of mass is biased to the right, shimming the rear wheel to the left would only result in the centre of mass being further away from a straight line drawn between the contact patch of the front and rear tyres. Offsetting the front wheel to the right would move that theoretical line closer to crossing the centre of mass, but can you accept that BMW would do that, and then you'd have to have the front suspension arms as symmetric.

[kirby1923]

I think bmw is just setting some limits incase of damage  or suspected misalignments. The rear spacer offset for ABS sensor rings is within those limits. Most likely no other reason.

:-)

[Huzo]

I think bmw is just setting some limits incase of damage  or suspected misalignments. The rear spacer offset for ABS sensor rings is within those limits. Most likely no other reason.

:-)

That would be a slam dunk if the addition or removal of shims was to bring the wheels back INTo line, but these wheels are supposed to be OUT of line by 5 mm or so according to BMW specs.

[oldbike54]

That would be a slam dunk if the addition or removal of shims was to bring the wheels back INTo line, but these wheels are supposed to be OUT of line by 5 mm or so according to BMW specs.

 So like are you losing sleep over this ?

 Dusty

[Huzo]

No Dusty, I sleep surprisingly well, but now I'm like wondering how a definitive explanation of something so common has remained so elusive. There have been threads just as long as this over topics that are just as dis interesting to some people, there's one on this forum that's gone on for at least forty pages. For Pete's sake, how come no one knows, every explanation including mine is full of " I thinks" and " maybes". There's a mine of knowledge on this forum, every one tells me how BMW deliberately built in 5mm of offset but no one has properly explained why.

[oldbike54]

No Dusty, I sleep surprisingly well, but now I'm like wondering how a definitive explanation of something so common has remained so elusive. There have been threads just as long as this over topics that are just as dis interesting to some people, there's one on this forum that's gone on for at least forty pages. For Pete's sake, how come no one knows, every explanation including mine is full of " I thinks" and " maybes". There's a mine of knowledge on this forum, every one tells me how BMW deliberately built in 5mm of offset but no one has properly explained why.

 Well , I might suggest asking a BMW forum .

 Dusty

[Huzo]

I seem to get into enough trouble on this one Dusty !

[mtiberio]

I used to run up to 10mm offset of the rear wheel to the left on my race bike when I was running fat tires on fat rims. This could make the bike exceedingly hard to turn left, I had to lift the bike over the CG point, and I was fighting the gyro effect from the slowing crank.

Charlie Cole used to run the rear wheel offset to the RIGHT on his vintage racer. This helped to offset the slowing crank effect.

[Huzo]

I used to run up to 10mm offset of the rear wheel to the left on my race bike when I was running fat tires on fat rims. This could make the bike exceedingly hard to turn left, I had to lift the bike over the CG point, and I was fighting the gyro effect from the slowing crank.

Charlie Cole used to run the rear wheel offset to the RIGHT on his vintage racer. This helped to offset the slowing crank effect.

ok that's fine for now, but if you introduce offset to overcome one effect, you're gunna get bitten twice as hard by the opposite effect when it occurs. That's to say, offsetting one way to negate a slowing crank is fine when you're battling about 15 Newton Metres, but what are you going to do when you open the throttle and you're supplying 90 or so Newton Metres on the opposite direction of rotation, ya can't just ignore that fact and wander off. We need a Mechanical Engineer that can apply proven principles of Physics here.

[Huzo]

.

[Huzo]

Just if you feel like some revision.

[Huzo]

Well , I might suggest asking a BMW forum .

 Dusty

Oh BTW..
No bugger over there knows either...

[Kiwi_Roy]

Why aren't you out riding instead of bothering us lol
The offset is on the other side down your way the Germans just didn't bother to tell you.
To counter the coreolis effect of the earth spinning.
https://en.wikipedia.org/wiki/Coriolis_force

[guzzisteve]

Most likely offset is to counter some BS in the German engineers mind.

Mine is bout 5mm over to left cuz that's what worked to put rim in center of opening I have on swingarm, I had to cut center hub of rim. It will be awhile before I get to try it out, slow project.