Sidecar Design Formula - IMPORTANT!

Discussion in 'Hacks' started by Get Back, May 25, 2009.

  1. XL-erate

    XL-erate Been here awhile

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    Precisely what I have in mind! I cannot imagine any better way to do it, matter of fact. Also we have a great advantage in building it ourselves by knowing every nut & bolt and what they do! Hope the best for you in your build project!

    Say, I don't suppose you have a running commentary of that build posted up anywhere? I'd be interested to see it, thanks!
  2. ANKOF

    ANKOF Been here awhile

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    yes YOUNZ, it would be interesting to see how you made it.
  3. Old Mule

    Old Mule Been here awhile

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    I like seeing design solutions and have been wondering, what is the effect of the great height of the off road sidecars I see on this board? The long suspension travel and high seating postion makes a high and variable c of g...
    I've never ridden a modern off road sidecar, strictly a street driver. But I remember years ago I put some effort into lowering my machine. Just taking two inches out of the seat foam lowered the 175 pound rider's center of gravity. Only four inches of suspension travel on the bike and 2 inches on the sidecar wheel. A "vintage" machine, obviously.
    When a rider and passenger sit on a modern high-clearance off road sidecar outfit that's realy high to begin with, doesn't that make for a overly high c-of-g and high polar moment of inertia?
    Wouldn't handling and braking be better if the machines were much lower?
  4. DRONE

    DRONE Dog Chauffeur

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    Yes.

    But a hole in your crankcase takes all the fun out of backcountry trips. Forces me when hanging off to try to get my butt down lower than the seat height.

    What we really need is an adjustable on-the-fly air suspension that gives us 3" of clearance on pavement and 12" when off. They've got stuff like that don't they?
  5. claude

    claude Sidecar Jockey

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    Yes handling would be best on most roads with a lower CoG no doubt. However, the adventure bike crowd wants ground clearance. How much is needed? For most conditions not as much as many have. However most want the ground clearance anyhow and that is fine. Everything is a compromise to some extent between road surface requirements, road surface handling and of course 'the look; that seems so important to many even if they seldom if ever go off road. It wasn't that long ago that world touring was done on /2's and such..Face it a corvette and a Jeep are good in certain elements and awful in others if pitted against one another.

    With all of that being said the dual sport adventure type outfits can be made to scoot around pretty good on hard surfaces and still do okay off road. We have experimented with various suspension designs and feel that the anti swaybar is a great asset to any sidecar outfit but they really do shine on the adventure bike based outfits. They can be deactivated easily if one gets into th ereally harsh rocky type terrain but few ever actually unhook them.

    Body english can go to a point too as Drone mentioned. I seldom do that myself too much and can get around quite well on hard surfaces, dirt or paved. Actually all it does is transfer some weight over to the inside of the turn and, as mentioned, it can lower the weight slightly too.
  6. Old Mule

    Old Mule Been here awhile

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    The high passenger seats on the "adventure type" outfits amaze me sometimes- no one would place a 150 pound iron block two feet above the wheel spindle height of a road side car outfit, but those off road guys put their passengers way the hell up in the air.
    I guess I better bum a ride on one, maybe I will "get it" then.
    I am sure envious of their great horsepower, my 650 is good for maybe 50 HP if I keep it in perfect tune.
    Any way I have learned a lot about fabrication techniques and components on this board, that's for sure.
    Like to see more tech threads.
  7. Old Mule

    Old Mule Been here awhile

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    Looking through old books happened upon the part numbers for converting the Birmingham Norton featherbed models to sidecar use.

    These numbers are for bikes with no steering head lock on the top fork crown, 7 inches between fork tube centers.

    This replacement fork crown assembly reduces trail.

    21508 fork crown and column sidecar
    21593 top yoke sidecar
    21570 fork top cover with lamp bracket left
    21571 fork top cover with lamp bracket right
    SD1 Steering damper assembly
    159064 fork spring

    Surely some hardened old timer is now building a Norton with a sidecar and will use these numbers!
  8. ANKOF

    ANKOF Been here awhile

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    parts of this thread are really good but what about everything else on the rig that hasnt been mentioned yet. there are many different solutions on frames, suspension , atachment to the bike etc. on a 50 year old rig maby you can get away with most everyhing but on a modern dual sport or hps rig everything should be of importance. is there any intrest to talk about that? I cant contribute with much but I would be an eager listener. my build this winter have raised alot of questions
  9. Old Mule

    Old Mule Been here awhile

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    On a fifty year old bike with only 35 to 55 HP, it was much more important to build light, and emphasize handling and steering to make up for low horsepower.
    One thing I have noticed is that many builders use a bike swingarm for suspension on the side.
    If a brake is used on the side wheel, a "trailing link" side car suspension will be "pro-dive", and a "leading" arm will be "anti-dive".
    It doesn't make any diffference which way the swingarm is mounted if no brake is used, but on a braked off road sidecar with high ground clearance, a "pro-dive" suspension combined with high polar moment of inertia would cause some severe dive upon braking.
    Compare the leading link forks on a Honda 50 to the trailing link ones on an Ariel Arrow- one encourages dive upon braking.

    Sidecar tech has always fascinated me. I like to look at pictures of the URS and the other old roadrace sidecars like the Kirby BSA to see how those old builders faced the various engineering compromises.
  10. Old Mule

    Old Mule Been here awhile

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    The Wessex was a very interesting sidecar, made to aircraft design standards with a monocoque body and no frame. It was light but still offered weather protection and good aerodynamics.
    The Wessex also dispensed with heavy clamp typ connections and use small diameter chrome-moly tubes in a properly triangulated system to connect bike and sidecar.
    Interesting.
  11. Old Mule

    Old Mule Been here awhile

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    One aspect of side car design is wheel lead, and I wonder how important it really is? In the beginning rigid-frame sidecars used zero lead, but not for reasons of handling or steering. It was because almost all sidecars had doors and large diameter wheels, and there needed to be room on the side of the body for a door- therefore the wheel couldn't be moved forward.
    That was the motivating factor behind Watsonian's introduction of the small wheel in the late 50s- more room for a door on the big enclosed sedan-type sidecars sold then.
    Wheels were skinney then and "scrub" wasn't a big factor.
    The sidecars with the biggest wheel footprint now are F1 and F2 car-wheeled racers, and lead is all over the place on them.
    Ten per cent of wheelbase is a good start, and has become the usual figure now, but I don't think wheel lead dimension is very important at all.
  12. claude

    claude Sidecar Jockey

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    Wheel lead is a stabilizing factor in turns away from the sidecar. With rigid bikes it wasn't nearly as critical as it is now.
  13. Old Mule

    Old Mule Been here awhile

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    There have been sidecar outfits built where the lead was almost 50% of the wheelbase.
    What would happen ig it was zero percent? If the sidecar wheel was up front on the same plane as the bike's front wheel? I am sure someone did it before WWI in the "forecar" days, but it obviously didn't work.
    Does tire width and footprint make a big difference on what wheel lead should be?
    Claude shouldn't you be at work?
  14. claude

    claude Sidecar Jockey

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    This is weird but try to imagine it. Think of an automobile with the right rear missing and the right front non steerable.. Hard as heck to steer but very stable in left turns. Now take away the right front and have two wheels in the rear. Turning left would be awaful if not impossible. Yes, radical thoughts but maybe the point is made. Some lead is good. Too much or too little isn't. Everything is a compromise. Most outfits today do pretty well with between maybe 7 and 10 inches of lead. I think at th ebeginning of this thread Brock posted formulas that he uses. Not a bad thing but some does depend on th eoutfit and riding style too.
  15. XL-erate

    XL-erate Been here awhile

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    Yes, from a mechanical engineering perspective it's obvious there's just too many variables on any rig to lay out a chiseled-in-stone formula. Just a few examples:

    Front tire: tread ply rating, tread width, sidewall height, total height, carcass construction: glass-steel-fabric-synthetic belts and/or cords and how many layers in what combinations? Rubber formulae? Air pressure? Now multiply that for the other 2 tires, and the 3 together may all be identical, all different, or any combination. Also may be a car tire with a bike tire with a trailer tire, or 2 car tires and one sidecar tire, etc. That's just the tires and only scratches the surface.

    Trailing swingarm, leading swingarm, no swingarm on hack? Springs on hack - leaf-eliptic, semi-eliptic, quarter-eliptic, coils? Torsion bar? Swaybar? Air over oil, or all hydraulic, or all air, or no shock and just a torsion bar, or no torsion bar and just a shock? Wheel lead numbers in combination with length numbers, width numbers, track/wheelbase numbers, ground clearance, frames flex, wall thickness, frame materials, no frame? Center of gravity?

    Solo on bike, or two up, or 2 up plus a herd of pygmy goats in sidecar? Towing a trailer, plus a Shetland pony in the trailer? Freeways, country roads, city streets, gravel, dirt, snow, rutted or smooth, crown, road surfacing material, condition, weather characteristics? And that's still only a very small part of the whole equation.

    If you can say any one thing about all sidecars: they're ALL UNIQUE!
  16. claude

    claude Sidecar Jockey

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    Some stuff:
    If it dips the nose of the sidecar in left handers more wheel lead may help. More lead will make steering a little harder and can increase tire wear. Less lead will make steering easier. Wider track width will improve stability in both directions but can make steering harder and will increase th e'pendulum effect' in acceleration and braking. . More lead may allow sidecar to lift easier in right handers.
    Suspension variations can play into all of th eabove in abig way.
    Balance of sidecar weight to bike weight ?(loaded an dunloaded) can play into the above also.
    Sizes of tires can play into the big picture in various ways depending on the outfit.
    Toe in on most outfits does basically nothing but load the bearings and curtail wandering when underway.
    Mounting systme sshoudl nto move when underway. The bike and sidecar should be one unit.
    Toe in can be far too great and all it will do on most outfits is increase tire wear. Toe out, however, will creat a pull toward the sidecar.
    To get good tracking the adjustment to use if lean out or sometimes lean in.
    Leaning the bike in or out can affect toe in settings. This is due to lower moutn positioning. Toe shoudl be checked after lean adjustments are made.
    Softly sprung rigs are harder to keep consistant when loaded or unloaded than stiffly sprung outfits.
    Loading the sidecar and/or bike will / can affect setup and handling. A stiffer sidecar supension than bike supension can work to one's advatage in thsi area in some cases.
    Electric tilt adjusting devices and anti-swaybars are good devices to deal with this easily. On and on it goes but these are the bare basics.
    Suspension and steering geometry changes do come into play. Most dicussions talk to sidecars as if suspensions do not exist. This is a mistake. There is much more surface to be scratched as far as sidecar and bike suspension relations go.
    All in all sidecar outfits are probably one of the most unique vehiclles on the planet. From the fore car that seated a human airbag to the pull behind traillers with seats in them that seated a dirt and debris eating passenger to the sidecar of today we have come along way.
    Yadda yadda.....are we having fun yet?
  17. Old Mule

    Old Mule Been here awhile

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    Yes we are. It took me a few tries and some trial-and-error to get my outfit just right. Before the net was invented we learned from English books and magazines, and from copying what older riders had always done.
    Bikes back then had much smaller suspension travel, that took one big unknown out of sidecar setup.
    "Everthing has been tried at least once", a sidecar builder in Oz once wrote, that is one of the fascinating things about sidecar bikes.
  18. claude

    claude Sidecar Jockey

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    Built a chassis once with a sliding mechnisim for very easily adjustable wheel lead. Learned a lot for than thing. You could make it do some wild things but once outside the practical use triangle it surpassed the compromises than we need for common use.
    Suspensions are , I feel, a necessity on the road going outfits today..... But then we look at the sidecar road racing outfits that have no suspension on the sidecar for safety reasons and ...... hmmm.
  19. Kyler

    Kyler Confused Hack Nut

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    I did not realize that safety was the reason for the suspension rules. Learn something new every day here!
  20. Old Mule

    Old Mule Been here awhile

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    I wonder what the suspension travel of an old Earles for BMW was? I know the Steib suspension travel is just 3 inches or so, at the most.
    If you google "Zundapp gelandesport gespanne" or "ISDT sidecar" you get a lot of pictures of off road sidecar outfits with interesting mods for ground clearance and suspension travel. One of my favorites was the Velocette OHC KTT 600cc single built for the 1938 or 39 ISDT.