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Sidecar suspension ratings

Hi all!

I have a planned build in the near future so I'm doing lots of research and review here on tech details. One of the questions I had was about the correct spring rating for an outfit. Something sorta dawned on me last night, wanted to run it by you guys for validation.

The common formula I've heard is that the sidecar should weigh 1/3 of the total weight of the whole rig. So as an example a 600 lbs bike would ideally have a 300 lbs sidecar, right?

A motorcycle's weight is usually pretty well biased, around 50/50 front and rear. That means this 600 lbs bike has roughly 300 lbs on the rear suspension.

If so then the correct sidecar suspension should match whatever is on the back of the bike for its spring rating. This would also mean that this could stand as a general rule or formula, that it would be true of virtually any sidecar rig you find, if it is properly weight matched to bike. That is: almost any hack matched to almost any bike could use the same overall spring rating as the combined weight rating of the correct rear springs on the tug.

Sound about right?

.

One third of 600 is 200, but make sure you are allowing for your weight as well. The rule of thumb is that the bike, going down the road as normally loaded, should be around three times the weight of the laden sidecar.

SidecarMike - 11/26/2012 7:59 PM

One third of 600 is 200, but make sure you are allowing for your weight as well.  The rule of thumb is that the bike, going down the road as normally loaded, should be around three times the weight of the laden sidecar.

Thanks for reply, Mike,

My bike I'm using as a tug weighs 600 lbs. 1/2 of 600 is 300. The formula I've seen suggested and repeated many times through forums is that ideally, sidecar weight should be 1/3 of total weight.

Can't recall seeing it suggested before that chair should weigh 1/3 of bike's weight. According to others that would be too light for safe handling.

I'll go back and find some links to the sources of my info to verify it. I made a mistake in 1954, I think it was? Who knows, maybe lightning can strike twice and I actually made another mistake?!?? 🙂

.

You are way over simplifing this, 1/3 in general is to light but there is a lot more to this, how wide is the sidecar? Where does the bike carry its weight, up high or down low? How heavy is the rider on the bike? Some of this is covered in the book "Driving a sidecar outfit" by David Hough. We sell the book for $34.95
As to spring rates, all the above makes a difference but also how is the spring mounted? Is it on a motocycle type shock or some sort of torsion bar? How long is the swing arm? Where on the swing arm does the shock attach? If you are compairing it to the bike, how is the bikes spring done? mono or dual shock, how long are the linkages.
These are but a few of the variables.
Jay G
DMC sidecars
http://www.dmcsidecars.com
866-638-1793

Jay G DMC sidecars www.dmcsidecars.com 15616 Carbonado South Prairie RD Buckley WA 98321 866-638-1793 Hours Monday - Thursday 6-4:30

XLerate - 11/26/2012 8:44 PM Hi all! I have a planned build in the near future so I'm doing lots of research and review here on tech details. One of the questions I had was about the correct spring rating for an outfit. Something sorta dawned on me last night, wanted to run it by you guys for validation. The common formula I've heard is that the sidecar should weigh 1/3 of the total weight of the whole rig. .. .

I was quoting you in your opening question. Just the same, the 1/3 figure is the most common used. My Goldwing weighs 804 pounds, but goes over 1000 by the time I get on it with all my gear. My empty sidecar, which is the way I usually travel, weighs 225 pounds.

Attached files

SidecarMike - 11/27/2012 7:55 AM

XLerate - 11/26/2012 8:44 PM Hi all! I have a planned build in the near future so I'm doing lots of research and review here on tech details. One of the questions I had was about the correct spring rating for an outfit. Something sorta dawned on me last night, wanted to run it by you guys for validation. The common formula I've heard is that the sidecar should weigh 1/3 of the total weight of the whole rig. .. .

I was quoting you in your opening question.  Just the same, the 1/3 figure is the most common used.  My Goldwing weighs 804 pounds, but goes over 1000 by the time I get on it with all my gear.  My empty sidecar, which is the way I usually travel, weighs 225 pounds. 

 

Looks like that old lightning sure did whack this hackster but fortunately no lasting harm done! Found where I got my wires crossed and there's no doubt they were sizzling.

Just looked at Hal Kendall's 'Sidecar Manual' again, where he suggests that: "The sidecar should weigh between 25 to 35 percent of the motorcycle."

That gives an ideal weight for a 600 lb bike to be a 150 lbs - 200 lbs sidecar, not 300 lbs! A wealth of additional info from back in '03 on this forum, with several familiar faces including 'Sidecar Mike':

http://www.sidecar.com/mbbs22/forums/thread-view.asp?tid=294

Apparently where I got confused was with the figure of '1/3' which I'd seen in many references and that stuck in my remnants of a mind. From there I jumbled it up to 1/3 of outfit's total weight, not 1/3 of bike weight.

Glad I posted that question and even happier with your reply, Mike! Still haven't gotten to the physical build stage so I was saved from a huge pile of grief. Makes the rig a lot easier and cheaper to build too, not requiring unwanted ballast of miles of extra steel.

Back to original question: seems that a fair guess on sidecar shock absorber according to this corrected info might be that one rear shock like the tug's would be close to ideal weight if a sidecar is built to this '1/3 rule', rather than a shock equal to both rear bike shocks combined. Certainly there's many variables but my intent is to arrive at a baseline to work from and hopefully that will do.

Thanks a bunch, Mike!

<SNIP> Back to original question: seems that a fair guess on sidecar shock absorber according to this corrected info might be that one rear shock like the tug's would be close to ideal weight if a sidecar is built to this '1/3 rule', rather than a shock equal to both rear bike shocks combined. Certainly there's many variables but my intent is to arrive at a baseline to work from and hopefully that will do. Thanks a bunch, Mike!

That should work for you. You might also consider an air shock of some kind. Just put a valve on it and carry a little bicycle hand pump so you can adjust the pressure if required. That's what we did with our old HitchHiker and the Dnepr. One or two pumps was all it took to go from very soft to very hard.

Where are you? I may even have something laying around here.

jaydmc - 11/27/2012 7:46 AM

You are way over simplifing this, 1/3 in general is to light but there is a lot more to this, how wide is the sidecar? Where does the bike carry its weight, up high or down low? How heavy is the rider on the bike? Some of this is covered in the book "Driving a sidecar outfit" by David Hough. We sell the book for $34.95
As to spring rates, all the above makes a difference but also how is the spring mounted? Is it on a motocycle type shock or some sort of torsion bar? How long is the swing arm? Where on the swing arm does the shock attach? If you are compairing it to the bike, how is the bikes spring done? mono or dual shock, how long are the linkages.
These are but a few of the variables.
Jay G
DMC sidecars
http://www.dmcsidecars.com
866-638-1793

Thanks, but excuse me, Jay, I don't think I'm over-simplifying at all. Your reply no doubt provides many potential complications but no answer to the question or anything usable for a formula or even an estimation or wild guess on proper shock rating? Your intention may be to address all the parameters to prevent unhappy errors for any reader but some related data or examples would help to clarify.

For general reference I didn't just fall off the back of a turnip truck. I've built vehicle projects of all sorts since about '61. I've been around the block a few times, being familiar with applied mechanical engineering principles, basing my life and career there.

Point of inquiry here as mentioned above is to arrive at a baseline. Folks need to know whether to start with a Honda Trail 90 shock or a Vstrom rated damper so that's the point.

Doggone it, Mike, then ya gotta go and post up that pic of a great outfit and that very cool tent trailer, just feeding fuel to my latest obsession! Right square in the center of my plans: a long distance road tripper hauling a trailer which I'm also currently designing.

Mine's to be a cargo rig, vaguely similar in body lines to your pic. If you shaved off all the accoutrements on top like windshield and aero mount, and lopped off the raised headrest etc. and eliminate passenger accomodations that's real close to my plan. To simplify things I'm going with flat aluminum sheet top, sides and bottom in an aero wedge-nosed design that also has some taper end effects in the rear, stretched over a 1-1/2" x .1250" angle-iron subframe, on top of a 1-1/2" x .1250" DOM tube chassis. Tug is my '96 Kawasaki KZ1000P-15, all original.

Hope it will look okay but function is way ahead of form here. First is aerodynamics, then good size for ample cargo, separate compartment for 6 gallon poly fuel cell, deep cycle battery, small compressor etc. and as inexpensive as possible to build.

Thanks for the generous offer! I'm way out on the left coast and in my stash I think I have some good dampers to use, along with a lot of the materials as leftovers from a scratched 2F/1R build. Sure like the idea of air shocks though, as I'll have an onboard mini-compressor. I might be interested in purchasing such an air shock if that's what you meant was laying around your place?

There are no simple formula's. For many of our sidecars we run a progressive shock with a spring rate of 250-350 however if we were to change how long the swing arm is or where the shock attaches to it we would want a different rate. If the sidecar is going on a light bike to be ran empty most of the time we would want a lighter spring rate which is why we stock different springs. Some people want a real firm sidecar suspension as they like the way it corners better then a soft suspension other like it softer. How wide the sidecar is mounted also makes a difference as in essence the sidecar wheel is at the end of a lever arm so if the sidecar is wide it will not need as heavy a spring as a narrow sidecar would on the same bike as less of a load this also speaks to the question of how high up the bike carries its load. And then of course, how heavy is the load in the sidecar?
No simple answers.
Jay G
DMC sidecars
http://www.dmcsidecars.com
866-638-1793

Jay G DMC sidecars www.dmcsidecars.com 15616 Carbonado South Prairie RD Buckley WA 98321 866-638-1793 Hours Monday - Thursday 6-4:30

XLerate, I just started with a shock that I had on hand as I wasn't sure how much the cad would weigh as I was building with what was available for free or dam near. The skin on my car is all .120 aluminium but with a full size van battery and tools in the car it is not lite but it handles very well and the shock is still on the lowest preset. I figured I could always go up or down with the spring weigh after testing.

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Seems that one should be able to make a reasonable estimate per the actual weight that's bearing on sidecar wheel with a bathroom scale; this measurement made with rider and gear aboard. This allows for any leverage forces, which would be seen in the weight measurement.

To my thinking a torsion bar system is a whole different animal from a common coilover shock sprung swingarm suspension. Obviously the torsion bar is acting as the primary load bearing suspension with a shock added only for damping of undulation and rebound. So is a leaf spring suspension different, only requiring a damper shock to control frequencies beyond the spring support.

Most rigs I see use a simple swingarm with coilover spring damper and that seems to be what most home builders do as well because it's simple and it works. There the spring on shock is the suspension and the damper inside takes care of rebound and jounce. For this last and most common it seems that using a coil sprung shock matched to the static weight, as if it was a motorcycle's rear wheel bearing same weight, must be fairly close to what's needed. That is, with car loaded with gear or persons as for most normal use and with rider on bike: that scale weight is what needs measuring to estimate sprung shock needs.

Seems best to run 2 shocks, possibly one on each side of swingarm if it's a yoke type arm. I'll call one a primary, the other secondary. Primary matched to unloaded weight. A quick disconnect on secondary coilover shock for unloaded running, and hook up that secondary coilover for full load, road tripping and hauling. Primary may be at much lighter spring rate for empty car, secondary more heavy duty for max load. Any where, any time a person could adjust for load.

Additionally, if both were quick disconnect it gives 4 spring weight options, by the ability to swap primary for secondary and run with either one disconnected or connected. That is 1] lightweight primary - 2] lightweight primary plus heavy weight secondary - 3] only secondary - 4] hook up the primary with secondary again for max load. 4 separate quickchange load ratings depending on load circumstances. Also the shocks may be installed with a choice of mounting holes to vary the spring/shock effect, easily having a dozen or more different choices with dual quickchange coilover shocks!

I may do that if I don't go with the air shock option from Mike's suggestion which sounds very good. I prefer oil damping, but air can work very well with its adjustability.

cleatusj - 11/27/2012 5:06 PM

XLerate, I just started with a shock that I had on hand as I wasn't sure how much the cad would weigh as I was building with what was available for free or dam near. The skin on my car is all .120 aluminium but with a full size van battery and tools in the car it is not lite but it handles very well and the shock is still on the lowest preset. I figured I could always go up or down with the spring weigh after testing.

Photobucket

Thanks for the info there, Cleatus! VERY slick rig and yes, I followed your detailed build thread with great interest, THANKS again for that!

Roger that on the 'damn near free' ha!

I've scrounged around here and counted up the blessings: so far found my 80' of 1-1/2" x .125" DOM tubing, plus 40' of 1-1/2" x 1/8" steel angle, 20' of 3/4" angle, leftovers from a 1F/2R project that went back burner. Also have my GS550 swingarm with 18" cast rear wheel, good tire, brakes & sprocket. Then there's the cool 6 gallon poly fuel cell donated from a buddy's race car build, plus a brand new Carter P4070 electric fuel pump. Two nifty little 12V compressors [vintage high quality stuff], a small tank for air storage plus 30' of 1/4" poly line, 4 lovely Per Lux stainless offroad lights from a truck build, several cycle tail/stop lights with license frames to choose from, various clearance lights, plus a stash of 100's of stainless Allen head screws in several sizes! Today I found 4' x 8' x .125" sheets of aluminum at $145 each for plain, or $170 per sheet in diamond plate, one of few things I need to actually pay for!

If that wasn't enough, a very dear but recently departed long time friend gave me the '96 Kawasaki KZ1000P-15 Police Bike tug as a gift before his passing, God bless his soul! 48K on it so quite a bit of life left, probably more than me!

Did I forget anything? Pretty near got it I think and the trusty old Millermatic 35 stands waiting with a fresh spool of wire!

.

When I built my Greevorex I followed the lift rule.
Standing beside the bike, one foot on the streetside peg and both hands on the bars, you should be able to lift the sidecar off the ground with reasonable effort.
Not easily but with effort. The rear shocks were the trick for me. The stock trials shocks (1960 Armstrongs) were way too soft, I used a set of BSA B50 MX shocks set at the highest setting.
That eliminated the wallowing I initially experienced and allowed me to set up a proper preload so the bike assumed the correct leanout with me aboard.
The Greeves only weighs 215 or so as a solo, and I pared the 560 Velorex down to 130 lbs. Seems to be a good rig and has proved to be very capable.

Don in Nipomo

Attached files

MOV09196.MPG (13.1 MB) 

Attachments didn't behave the way I wanted...

Here's a link to a recent slideshow..

http://s25.photobucket.com/albums/c58/dbeezer/Carrizo%202012%20November/?albumview=slideshow

Don in Nipomo

Thanks, Don,

Another mighty fine looking rig and I'll wager it performs as good as it looks. Plus it's a Greeves, enough said. Great ground clearance and the second headlight on the fender is really cool. I'll only have about 6" ground clearance if that but can't do extremes of offroad anyway because of health issues so no loss there. I'll bet that thing is loads of fun!

Fortunately I can weigh this thing piece by piece while assembling and even before. There's also sites on the net that post materials weights for metal tube & plate etc. so I can see where I'm going before I get there. Bath scale will tell me about components. Found out tons of info here and elsewhere but one of the murkiest areas has been: what spring/shock rating?

One of the problems with establishing proper spring/shock rates is 'trial and error' is rather impractical on a severely limited, to almost non-existent, income.

X, have you thought of going with an air shock? It will give you some adjustability. You'd only need to get it "close 'nuf" then air up or down depending on load.

Yes, thanks, first mentioned by Don in Nippomo in a post above. Good idea!