Sidecar Design Formula - IMPORTANT!

[phyllis]

Thank you for that reference Claude. How can I begin to even start to say how much I agree with EVERYTHING Mr. Ewing says in those few pages.
I feel such a fool. I read it just now, and am feeling as though he is laughing at me for being so Big Headed. The side car world lost a giant when he left us, Jim Dodson too. I've got most of the issues of Hack'd Magazine, how could I have missed that ABSOLUTE GEM.

Mr Moderator...take down all my ravings..... and put up Mr. Ewing's thoughts!
The bit about reasoned protest "with courtesy" , will be taken to heart my me, I'm in the presence of a better man! Sadly on longer with us in the flesh.

[Nemosengineer]

Originally Posted by claude

And then there was Floyd 'POP' Dreyer who built a caster wheel for the sidecar that just kinda followed along. Bugger to roll backwqards though

Claude, I don't know why I like this idea so much, elegant in its simplicity, but as we all know, the Devil is in the details. As I "roll" the caster wheel around in my head, I can visualize really interesting weight transfer issues when turning left at speed, the pivot for caster wheel would mean that the rig would have a variable track, working in your favor as the track would be narrower turning right and wider turning left, if an inclined pivot on the vertical axis of the caster wheel (left and right rotation) was used, the wheel would have less of a tendency to tuck under when side loaded as in a left turn. I also have visions of the one spastic caster wheel on the front of a shopping cart...
Do you have any more information as to how well (or not...) this idea worked as I am fascinated by this idea.

Thanks: Mike

[RedMenace]

I am saving the gist of Phyllis' critique of the "15% solution" because it merits a closer look and I don't want to lose it if the post is nuked. I gots some thinking to do, yet.

Originally Posted by phyllis

First off I'd like to apologise for my unseemly remark, to whit "Ha Fucken Ha" I was a bit upset.
.... I have doubted the veracity of "wheel lead formula" since Hack'd Magazine published it in 1994 (fall issue)...
The problem is if you do the math, you always get, yes, ALWAYS get 15%!! HUH?? Yes... 15% of wheel base wether the wheelbase is 48" or 60" or 66". How about 3" "lineal offset'? Still 15% lead. No! No! No! Not every time? I'm afraid so!
However this doesn't mean that there isn't some good in the article, at least it made some of us think! And perhaps re-evaluate our favourite settings. The article mentions all manner of terms that I for one have never heard of, and frankly think are irrelevancies.
Who cares about static scrubbing of the sidecar tyre? It's the dynamic situation that is important to me and most other USERS of that wonderfull yet flawed device that we so love.Who cares that the headstem moves side to side or falls slightly when you turn the bars at a standstill? You don't use much steering input when you're on the move. Your biggest problem is being ABLE to turn the bars with a stock front end. (Getting older, getting weaker...sadly)
The article rabbits on about steering wobble, and it's causes, yet doesn't mention TRAIL...

[Andy-Gadget]

Originally Posted by claude

And then there was Floyd 'POP' Dreyer who built a caster wheel for the sidecar that just kinda followed along. Bugger to roll backwqards though

Talk about thinking outside the square, what a great idea.

I too have been doing the "rolling it around in my head" thought experiment as well, and as you say, going backwards has issues.
But with travel limits on the amount of caster the chair wheel is capable of moving through, so it can turn both directions with no scrubing, wow.

You could even use a spring arrangement to provide the conventional toe in vector towards the tug, hmmm, to be given much more thought.

That's what I love about this whole Hacks forum, there are as many ways of solving a problem as there are people to solve it.
It is the experiment that will prove or disprove the validity of any new approach.

[claude]

[QUOTE=Nemosengineer]Claude, I don't know why I like this idea so much, elegant in its simplicity, but as we all know, the Devil is in the details. As I "roll" the caster wheel around in my head, I can visualize really interesting weight transfer issues when turning left at speed, the pivot for caster wheel would mean that the rig would have a variable track, working in your favor as the track would be narrower turning right and wider turning left, if an inclined pivot on the vertical axis of the caster wheel (left and right rotation) was used, the wheel would have less of a tendency to tuck under when side loaded as in a left turn. I also have visions of the one spastic caster wheel on the front of a shopping cart...
Do you have any more information as to how well (or not...) this idea worked as I am fascinated by this idea.

The late Floyd
Pop' Dreyer was also well known in racing circles, both sidecar and later on auto racing. He is a member of the AMA hall of fame. Click here:
http://www.motorcyclemuseum.org/hall...page.asp?id=63
The dealership that he began is still in existance:
Dreyer Motorsports 4170 W Washington St Indianapolis IN Indiana 46241-0938 (317) 243-2203 (877) 413-8881 info@dreyercycle.com
Greg Tenbrook (sp?) from Indiana has a couple of Dreyer sidecars. I think he has one of the floppy wheel designs. This is the last email address I have for Greg. He is a great guy. If you contact him please say hello for me :-) tenbrook@hotmail.com

[The Garbone]

Ok, so my KZ has a wheelbase of 57" so my lead should be 8" or so.. Me thinks...

Good stuff..

[RedMenace]

So, going back to the original post, it appears absolutely necessary to have an accurate measurement of the lineal offset to use this formula. What I don't see is a practical way to arrive at this on a real bike, assembled, with fender,wheel and tire in place. How the hell do I do this?

[claude]

Originally Posted by RedMenace

So, going back to the original post, it appears absolutely necessary to have an accurate measurement of the lineal offset to use this formula. What I don't see is a practical way to arrive at this on a real bike, assembled, with fender,wheel and tire in place. How the hell do I do this?

Dog gone it there is more to it that just doing some math. The rigs we run are not rigid all around and supensions vary a lot. A ridgd sidecar suspension with a heavy bike like a harley may be able to do fine with less lead than a stock sprung Oil Head GS with a havy sidecar on it.
Simply put .. Suspensions move and cause things to happen. Light bikes unload the rear end with aheavy sidecar in turns away from the sidecar easier than heavy bikes.
I would love for one of the enginner types to be able to come up with an easy way to establish roll centers on each corner of a sidecar rig and from that be able to calcuslate the roll couple under various circumstances. To treat a sidecar rig as it it had no suspenaion may get one intop the basic ball park but to not be able to think things out related to how a suspension works on a given rig is a good way to put it 'out of the ballpark'.
A few years ago this deal bothered me and I spoke to some folks who were susposed to be in the know as far as suspensions go. I knew that if we could raise the roll center we coudl have decent results and create better cornering on a flatter plane. Lowering the center of gravity can only be done to a point on many rigs and off road or dual sport rigs are kinda stuck with what they have. The suspension guys basically did not really desire to get into it as far as something as weird as a sidecar goes I suppose.
So we built a k bike rig with a dual torrsion bar rear suspension on it. The torsion bars were set very high in hopes of by doing that the roll center woudl be raised. There were two bars so it coudl have a more progessive spring rate. Anyhow once the rig was done and run hard we knew we were onto something. I actually spun the thing out twice in turns toward the sidecar with no body on the sidecar frame. But, the thing was disassembled and sold before we coudl get into it more. Maybe some of the ones here like RichardNL or Phyllis would have the time to experiment with such stuff. trust me it does work but time and money are always an issue when you are walking so far out of the box.
Food for thought anyhow
Sorry for rambling and I HOPE my typing wasn't too bad

[Clancy]

Maybe I'm missing something here Claude
I just read that last bit a couple of times to make sure I had read it correctly.
With race cars, the aim is to get the roll centres as low as possible, generally speaking. There is always room for adjustment to slightly change handling, i.e. to induce more oversteer/understeer for a particular track or situation. But when building the car, much thought is put into building low down weight, and when ballast is added to bring the car up to a competition weight limit, it's always placed low in the frame.
So why, when building an outfit, would you need to raise the rollcentre.
I'm currently in the early stages of building a dual purpose rig and have been planning to put a 38 litre auxilliary tank low down, inside the triangle formed by the three wheels.
Should I be re-thinking where I put the tank?
Input from Richard, Phyllis etc welcome too

[claude]

Phyllis,
I only wish J.R. was still here. Can you imgine him chiming in on this thread...LOL. He seemed opinionated to some folks but they just didn't under stand that most of his opinions were indeed facts from a lot of trial and error.

[claude]

Originally Posted by Clancy

Maybe I'm missing something here Claude
I just read that last bit a couple of times to make sure I had read it correctly.
With race cars, the aim is to get the roll centres as low as possible, generally speaking. There is always room for adjustment to slightly change handling, i.e. to induce more oversteer/understeer for a particular track or situation. But when building the car, much thought is put into building low down weight, and when ballast is added to bring the car up to a competition weight limit, it's always placed low in the frame.
So why, when building an outfit, would you need to raise the rollcentre.
I'm currently in the early stages of building a dual purpose rig and have been planning to put a 38 litre auxilliary tank low down, inside the triangle formed by the three wheels.
Should I be re-thinking where I put the tank?
Input from Richard, Phyllis etc welcome too

Many confuse the 'roll center' with 'center of gravity' (CoG). The center of gravity to put it as simple as possible rotates around the roll center .

For example When watching a nascar race you will may hear them say " they came in and raised the track bar'. In essence they raised to roll center.

With a low roll center and a high center of gravity the weight transfer in a turn is in a large arc. This translates into body roll. In most cases it is desrable to lower the center of gravity but there are definatly limits. If we are stuck on the possiblity to lowering the CoG then raising the roll center is a means to get rid of some body roll and allow the weight transfer to be in more of a lateral motion than 'up and over' so to speak.

When we determine the roll center locations at each suspension point then from there we can establish how they work together. This, in basic terms, is called 'roll couple'.

Clancy you wote:
>>I'm currently in the early stages of building a dual purpose rig and have been planning to put a 38 litre auxilliary tank low down, inside the triangle formed by the three wheels.<<
Yes, by all means do so. You will be lowering the center of gravity which is a good thing. This is different than the roll center.


Hope that made some sense.

[Clancy]

Originally Posted by claude

Many confuse the 'roll center' with 'center of gravity' (CoG). The center of gravity to put it as simple as possible rotates around the roll center .

For example When watching a nascar race you will may hear them say " they came in and raised the track bar'. In essence they raised to roll center.

With a low roll center and a high center of gravity the weight transfer in a turn is in a large arc. This translates into body roll. In most cases it is desrable to lower the center of gravity but there are definatly limits. If we are stuck on the possiblity to lowering the CoG then raising the roll center is a means to get rid of some body roll and allow the weight transfer to be in more of a lateral motion than 'up and over' so to speak.

When we determine the roll center locations at each suspension point then from there we can establish how they work together. This, in basic terms, is called 'roll couple'.

Hope that made some sense.

I have to admit I DO confuse the two myself sometimes
But in the NASCAR situation, when the track bar is raised or lowered, it only moves the roll centre miniscule amounts in order to slightly change a handling situation. In the'build' of the car, the aim is always to get the roll centre (and CoG) low in the frame.
But I think I've got my head around what you're saying about roll couples.

[claude]

Originally Posted by Clancy

I have to admit I DO confuse the two myself sometimes
But in the NASCAR situation, when the track bar is raised or lowered, it only moves the roll centre miniscule amounts in order to slightly change a handling situation. In the'build' of the car, the aim is always to get the roll centre (and CoG) low in the frame.
But I think I've got my head around what you're saying about roll couples.

Most will use the term 'ceneter of gravity' and 'center of mass' as being the same. Pretty much true.....but both are different than the 'roll center'.

If the roll center and the center of gravity were on the same plane laterally the weight transfer woudl be in a lateral motion(little body roll).

When the roll center is low (the location of the roll center is determined by suspension geomtry and can be many times below ground level) we get more body roll. The higher the cog is above the roll center the more body roll is induced in a turn.
Again, the center of mass or center of gravity if we want to use the terms together rotate around the roll center. They are not one and the same. :-)

Keepin weigth inside the wheels of the vehicle is usually a good step toward be able to manuver well. weigth bias front to rear and side to side is important and can be a good or bad thing depending upon the situation. This is really getting into a whole different thing though.

[Andy-Gadget]

I have been doing some research into the whole “roll centre” – “centre of gravity” thing, and have come up with the following thoughts, which I now share with you for discussion/character assassination:

All the information I can find about roll centres has to do with cars, which have suspensions completely different to the suspensions seen on almost all sidecars.

http://www.neohio-scca.org/comp_clin...namics2007.pdf

By different suspensions, I refer to the arc that the suspension allows the wheel to travel through.
On cars, the movement is up and inwards, necessary to ensure that the flat car tyre tread remains flat to the road.
Even very simple car suspension, the model T type solid front axle, does this.

Motorcycle suspension works on a different plane, as it needs to, being after all a single-track vehicle, combined with rounded profile motorcycle tyres it isn’t needed to move in any other plane.
That plane is purely vertical with no lateral movement relative to the chassis at all, or at least this is what the designer had in mind, the “hinge in the middle” Japanese chassis of the 70’s being an example of result not matching design intention.

I am forced to interpret this major difference to mean that the volumes of work done on car suspensions is of little use when applied to sidecars, made even less relevant if flat treaded sidecar tyres are used, as the contact patch area is influenced by the angle of the wheel to the road surface.

Some of the points made with regard to car suspensions hold true, such as the use of “roll bars” to ensure the correct tyre contact patch relative to the road surface, but is done for different reasons.

On a typical car system, the virtual centre of pivot of the essentially side acting suspension system ensures that the tyres remain correctly oriented to the road surface, and so the “roll bar” is just that, it controls body roll, which at small lateral force situations is a comfort driven system.

The typical motorcycle system, being longitudinally based, means that the body roll of a sidecar also causes the tyre contact patch to roll relative to the road surface, less of a problem with sidecars still fitted with motorcycle tyres.
But reducing the contact patch area, and hence its ability to resist the side forces being applied to them, on sidecars fitted with flat treaded tyres.
In this situation, the “roll bar” is essential from a road holding point of view, not just comfort.





If you take my point that there is no “roll centre” with sidecars, due to the suspension orientation, then the argument that it is the “roll centre” to “Centre of Gravity” distance that is driving the cornering dynamics of a sidecar is no longer valid.
It is driven more by the distance from the road surface contact with the tyres at the three extremes to the “centre of Gravity” that is important.



Roll bars are useful to maximise the tyre contact and so resistance to lateral forces.

Off road sidecars have a higher “centre of gravity” than road sidecars due to the greater under body clearances required and will be more susceptible to “tipping” than a low slung road outfit, and there is little that can be done to help the situation other than clever loading to move the C of G to its most advantageous position between the three tyre contact patches.

EDIT, just found this site here, http://www.cyclesidecar.com/Guides/A...ing/index.html

[Nemosengineer]

Originally Posted by claude

The late Floyd Pop' Dreyer was also well known in racing circles, both sidecar and later on auto racing. He is a member of the AMA hall of fame.

Claude,
Thank you for taking the time to write this wonderful response, I found it informative and helpful.

: Mike