Track offset

[redrider]

 Pretty sure you guys are talking about offset in terms of steering geometry , not wheel offset .

  Dusty

No, The wheel was offset to the left as I recall. There may have been different rake and trail numbers but that is steering geometry in my dictionary.

[kirby1923]

Sopwith Camel if I remember rightly.

Maurie.

Yes it had (most) Le Rhone 7 cylinder rotary engine.
Total loss oil system and was controlled during landing by a "blip" switch which cut the ignition.

I have been told by people that have flown a camel that it was VERY hard to fly but due to the performance, the pilots that could overcome the difficulties were very successful in air combat.
I have actually seen one run on a test stand....good grief. Frightening!!!

[oldbike54]

No, The wheel was offset to the left as I recall. There may have been different rake and trail numbers but that is steering geometry in my dictionary.

 Hmm , I simply can't find anything on this . Normally offset is defining the distance between the centerline of the forks and steering stem . Increasing that measurement increases trail adding stability. Any chance you might find the article , now I am curious .

 Dusty

[Mike Tashjian]

I think you are talking rake Dusty. I had a F7 Kawasaki that had a fork with three positions.  Front, center and rear. It did make a difference but I just left it in the one for trail riding.  I do have a 04 BMW 1150 RT and it does have the spacer on the rear wheel.  It does seem odd that the ABS sensor is adjusted by changing the thickness of the spacer. Changing the offset along with it.  In the BMW CLYMER manual I have, there are many other rear drives with ABS that can be adjusted with gasket like shims to get that just right clearance to the ABS ring.  I have to guess maybe there are clearance issues between different models and this what they came up with.  And as you may know with the cars, BMW never makes a mistake there either.  Mike

[oldbike54]

 Mike T , rake is unaffected by steering offset . Once again , offset in this case is simply the distance between the center line of the steering stem (or steering head , same point) and the center line of the fork tubes . Yes , rake can and does effect trail , but is a different point of reference .

 Dusty

[Mike Tashjian]

OK Dusty, I see that race bikes are using more offset(adjustable triple clamps) to have less trail and vise versa.  And yes, the rake(steering head angle) is only slightly adjusted by the fork height or rear suspension settings.   I did forget that I had to adjust the old Kawasaki fork tubes for height along with axle settings to affect rake.  Not remembering the 70's like I used to.   Mike

[oldbike54]

OK Dusty, I see that race bikes are using more offset(adjustable triple clan end a bit more mps) to have less trail and vise versa.  And yes, the rake(steering head angle) is only slightly adjusted by the fork height or rear suspension settings.   I did forget that I had to adjust the old Kawasaki fork tubes for height along with axle settings to affect rake.  Not remembering the 70's like I used to.   Mike

 "Framer" flat track bikes have employed adjustable triple trees for years as a way to tailor the bike for different tracks w/o changing everything else . The F7 was an interesting motorbike , very advanced in some regards . AND YES , raising forks or employing longer shocks doesn't alter steering geometry more than .0? degrees . The perceived change in handling is more due to weighting the front end a bit more .

 About remembering the '70.s , any true memory is better than most of us can manage 

 Dusty

[Huzo]

Kirby, your comment regarding P factor being soley due to the downgoing blade having greater angle of sttack is not true. It is a factor but not the only one. If that was the case then in straight and level flight thete would be no yaw present since both blades have the same AoA. Anoter cause is the spiralling slipstream over the fuselage striking the fin and rudder unevenly causing a yaw tendancy, but here's the reason that matters here. If you've flown a tailwheel a/c like Pawnee, Piper Cub etc. you'll notice that sn additional swing will be frlt as you are in the process of rotating onto the mains only, this is the rotating mass of the prop disc being pitched forward and gyroscopic precession taking place. Any good text book will tell you this, or Google it. The reason I touched on it was could there be a similar effect when the Guzzi or BM is pitched up or fown over a bump causing a corresponding tendancy to roll. Sorry about the dpelling errors, I csn't get the cursor to show on my little 'phone so can't go back to correct them. Huzo.

[Huzo]

Hmm , I simply can't find anything on this . Normally offset is defining the distance between the centerline of the forks and steering stem . Increasing that measurement increases trail adding stability. Any chance you might find the article , now I am curious .

 Dusty

it's in the workshop manual for the R1100S, page 48 I think

[Huzo]

Sorry, Page 18. It's not hard to look it up, really.

[oldbike54]

it's in the workshop manual for the R1100S, page 48 I think

 Sorry , I was referring to the Kawasaki police special needing adjustment for handling purposes . I think the BMW employing a slightly off center front wheel was explained by Kirby . It isn't a matter of handling in this instance . It was done to gain clearance for the ABS ring . Easier to machine the axle to carry the wheel slightly off center than to redesign the forks and front hub . Remember , it is only 5 MM, the front tire is still tracking inside of the footprint of the rear tire .

 Dusty

[kirby1923]

Kirby, your comment regarding P factor being soley due to the downgoing blade having greater angle of sttack is not true. It is a factor but not the only one. If that was the case then in straight and level flight thete would be no yaw present since both blades have the same AoA. Anoter cause is the spiralling slipstream over the fuselage striking the fin and rudder unevenly causing a yaw tendancy, but here's the reason that matters here. If you've flown a tailwheel a/c like Pawnee, Piper Cub etc. you'll notice that sn additional swing will be frlt as you are in the process of rotating onto the mains only, this is the rotating mass of the prop disc being pitched forward and gyroscopic precession taking place. Any good text book will tell you this, or Google it. The reason I touched on it was could there be a similar effect when the Guzzi or BM is pitched up or fown over a bump causing a corresponding tendancy to roll. Sorry about the dpelling errors, I csn't get the cursor to show on my little 'phone so can't go back to correct them. Huzo.

What I was responding too was the definition of "P" factor. Which is completely correct. No aircraft I know of has 0 AOA in level flight, and although the "P" factor is much less in level flight its still there and is trimmed out. However the "P" factor is most felt in high AOA like climbing. Almost all light piston aircraft have an off set thrust line designed in with the engine mounting. This helps with trim while cruising lessening the drag.

The effect your talking about is NOT "P" factor and the gyroscopic precession (your words) would only happen during pitch changes and "P" factor is almost continuous.

This is not an aircraft forum so I'll stop there as there is really not point in aerodynamic discussions for aircraft.
I just tried to answer a question.

:-)

BTW I own a '46 Cub.

[Huzo]

Yea Kirby, I've just got my broom out and swept out some dusty old corners of my knowledge, and not a moment too soon it seems. In my previous post I said that your comment regarding P factor being soley thrust related was not true, well I'll just select reverse while no one's watching and back away from that statement of mine. As you said P factor is the assymetric thrust produced by the different AoA of each blade when horizontal and that's not in dispute, so my apologies to you sir on that score. It's the gyroscopic precession  of the prop disc that I'd like to hear about and do you reckon it would have an effect when the bike is pitched, inducing a roll or yaw, this is where I wondered if running the bike wheels slightly offset might induce a roll in the opposite direction at the same moment. Do you have a thought ?

[Huzo]

And by the way, I'll stick to Guzzi content, thanks for the nudge to get me totally on line, I'm afraid it's been a bit too long between drinks. A little tutorial hasn't done me any harm, thanks mate.

[Chuck in Indiana]

Ahh , the original rotarys. AND , there was the Megola motorcycle with the rotary engine fixed to the FRONT wheel .
 Dusty

FTFY

Oh, and I'm not about to argue with Mike about how an airplane works because, well.. he's right. :)
He has more time on final than most pilots have total time.

[oldbike54]

FTFY

Oh, and I'm not about to argue with Mike about how an airplane works because, well.. he's right. :)
He has more time on final than most pilots have total time.

 Well , the Megola engine looks like a radial when not running 

 Yeah , never argue flying or aircraft with the Kirbster , he probably knows the guy that invented flying, or at least his grandkids 

 Dusty

[Huzo]

Yeah look when your your right, and he's damn well right.

[oldbike54]

Yeah look when your your right, and he's damn well right.

 Yeah , but you started this interesting conversation  Although it drifted a fair bit 

 Dusty

[Huzo]

Yeah Oldie it did and I'll redouble my efforts not to let it happen again, or at least as dramatically in the future. Anyway it's forced me to confront the fact that my knowledge has developed a few cracks that weren't always there, so that's gotta be good medicine although doesn't taste good going down the hatch. The good thing about chatting with people whose knowledge is current, is that you bring your own understanding back up to speed, thanx again Kirbmeister. Now as the great Homer Simpson said to Marge...." We'll never speak of this again" ( Muffled laughter)...........

[oldbike54]

 Oh hell Huzo , don't stop bringing up stuff , this was fun and educational 

 Dusty

[Huzo]

Yeah after all Oldie,fun is why we do it, isn't it ?

[oldbike54]

Yeah after all Oldie,fun is why we do it, isn't it ?

 Well mostly , and maybe to learn something .

 Dusty

[kirby1923]

And by the way, I'll stick to Guzzi content, thanks for the nudge to get me totally on line, I'm afraid it's been a bit too long between drinks. A little tutorial hasn't done me any harm, thanks mate.

I guess I came down a bit strong. They let me rant about aviation stuff here sometimes! Its been my life.
Absolutely no apologies' needed as allot of topics get touched on here.

Flying and riding have a many common elements and attract folks of the same metal!

Cheers mate!

:-)

BTW, just in from a great dinner with a wonderful Bordeaux and Cognac!

[Huzo]

Ab so bloody lutely not Kirbster. I've got 2,000 hrs gliding, 10 years instructor rating and unrestricted PPL with CSU Retract and still lumped P factor in with the other effects, better you belt it back into me than I spruke it wrongly in front of people who know, or worse people who are looking for correct info. No way would I want someone to go on saying that, fact is Kirbo, I actually remembered all that when you put me straight but would not have fixed the mistake myself, I'm better off for it and thanks for being patient enough to persevere. Like I said to Oldie, a bit of a clip under the ear from someone who knows is good for ya. That's why we do a BFR (Biennial Flight Review)isn't it ? So you don't build new ideas on top of flawed knowledge. Now for ME, that's it on this topic. Now old bean, how's your bike ?

[Huzo]

I found one mention of the K model BMW rear wheel being offset 5 mm to the right to offset it's weight bias to the right.  Would make more sense than they set the welding jigs up wrong.  Not seeing any way to adjust the rear of shaft drive bikes in any manual I have.  I am a bit confused about the brake comments since Calipers and or Pistons must move the pads to contact the rotors. They are designed to do that compensating for where the rotors end up on a wheel and pad wear.  If you don't move a wheel too much most brakes should be able function fine.  But why would you want to move something from where it is designed to be in the first place?    Mike

But it's just not the BMW way of doing things is it ? I mean you'd think that they'd machine a recess for the ring to sit into or something rather than expect the pads to take up the slack, I don't buy it for a manufacturer like BMW.

[Huzo]

Having said that, has anyone come up with a plausible answer based on some sound design principles ?

[John A]

I don't know about the design principals behind it but I've found that the Cal series has a track offset of about ten to twenty mm. When I first discovered it, I thought it was damage or a defect on my bike but I could not adjust it out. I then found it on others but I don't know the reason for it.

[Huzo]

I don't know about the design principals behind it but I've found that the Cal series has a track offset of about ten to twenty mm. When I first discovered it, I thought it was damage or a defect on my bike but I could not adjust it out. I then found it on others but I don't know the reason for it.

Neither does anyone else yet by the looks of things

[oldbike54]

Having said that, has anyone come up with a plausible answer based on some sound design principles ?

 Occam's razor Huzo , Occam's razor .  Simpler than redesigning the hub .

 Dusty

[RANDM]

I've bin reading this waiting for the definitive - but I think
maybe the Dusty one has it, though I'm still a puzzled
Puggle.

I've a friend on the "hill" who is a Classic race guy,
Spannerman, Fabricator .........  He's got a lot of hats!
I don't remember how many times I've watch him carefully
Straightline the wheels while preparing a bike for the track.
I guess that's the ideal to be aimed for for best handling -
there may be some leeway where a few mm "offset" or out
line staightline wise can be accommodated but Shirley not
much - either would make the bike crab and affect
cornering?
I find it hard to think a designer would deliberately put offset
into a bike and much easier to believe a beancounter had
petulantly stamped his foot down demanding lower costs.

Strange things happen though - while back he was showing
me the asymmetric rear subframe on a rigid Triumph when
We were discussing the stupid shit done to get around
whatever manufacturing fo pah they happened to be faced
with.
If I've got it right there are two offsets on the front end -
The Wheel could be offset side to side affecting tracking,
and the offset of the fork and steering stem holes in the
tripleclamp affecting Trail.

I don't know about the design principals behind it but I've found that the Cal series has a track offset of about ten to twenty mm. When I first discovered it, I thought it was damage or a defect on my bike but I could not adjust it out. I then found it on others but I don't know the reason for it.

If I remember rightly the Tonti's had an adjustment side to
side on the swing arm to help align the driveshaft - that may
be where it's coming from?

Maurie.