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Lightweight sidecar for 125cc bike

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(@c64club)
Posts: 200
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My bike is Romet K125, it's a Honda CG125 frame and engine exact copy with details like tank, seat etc. from Suzuki gs125. Kind of chinese "license megamix". It has also muuuuch better brakes than original Honda and produces 10HP.

I have "tested" it with 80lb 2-wheeled trailer with Sputnik sidecar (another 200lb) on the trailer and Romet pulled such rig properly, 300 miles from Sputnik's previous owner to my home. To be precise - properly for me, which means 35MPH with some RPM reserve and without torturing the engine.
But few frame mods later, when I added subframe and attached Sputnik as a sidecar (veeery temporary construction 🙂 ) it wasn't comfortable because sidecar's weight and there were no possibility to carry anything in sidecar. Unmounting Sputnik's body gave 85lb sidecar and it's acceptable weight, I could carry about 60-70lb load. Sputnik went to other guy who has Intruder 1400.

I decided to build my own sidecar with goal to not exceed 85 lb. And it should have a drum brake launched together with rear brake. Such construction would also benefit with smaller size than Sputnik and it will better fit my bike's size. There are many such constructions in Asia, they even act as taxi, so I think it's really possible to make.
My first thoughts are:
-"copy" of some bigger sidecar's frame but 70% in size
-16" alluminuim alloy wheel (there are few ones in my local junkyard)
-body made of thin plywood or 2mm fiberglass-compound boards, I have few square meters of it laying around

Some dude gave me an idea to make "semi flex" sidecar with rigid axle but with struts replaced by rear dmapers from some small motorcycle - some between flex and suspended classic. But I think it couldn't be comfortable for dog.

Do you have any suggestions for building such lightweight sidecar? Thinner-wall pipes, some lightweight patent for suspension?

Before You ask me to change my bike to some 500cc or so 😀 :
-I like it, especially due its great MPG (85 with heavy trailer/load to 105 solo)
-it's silent, cheap, has simple construction, is equipped with kickstarter and generally looks like motorbike, not like 2-wheeled USS Enterprise
-I don't drive above 45 MPH, typically about 35-40 solo
-I can afford to use it with my $600/month salary and gas prices around $7 per gallon


 
Posted : July 6, 2011 1:20 am
(@swampfox)
Posts: 1932
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Maybe you can pattern after the Enduro sidecars common to the Northwest USA region, such as found here:

http://www.dmcsidecars.com/Sidecars/dualsportsidecars.htm

Sorry, I'm do not have sufficient technical knowledge to advise as to materials and assembly.


Lee
MB5+TW200+CRF250L+GTV300+INT650
XL883R w/Texas Ranger Sidecar
Zuma 50F + Burgman w/Texas Sidecar<Mrs. SwampFox

 
Posted : July 6, 2011 2:20 am
(@c64club)
Posts: 200
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Topic starter
 

Is this suspended?
Looks gerat, simple, lightweight and should be simple to add dog-wagon(kennel?) body.


 
Posted : July 6, 2011 2:39 am
(@swampfox)
Posts: 1932
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c64club - 7/6/2011 7:39 AM

Is this suspended?
Looks great, simple, lightweight and should be simple to add dog-wagon(kennel?) body.

I've seen a photo with a fellow traveling with his dog in a kennel on a similar sidecar with the seat removed.

I defer the Lonnie, Jay and others as to the technical aspects.


Lee
MB5+TW200+CRF250L+GTV300+INT650
XL883R w/Texas Ranger Sidecar
Zuma 50F + Burgman w/Texas Sidecar<Mrs. SwampFox

 
Posted : July 6, 2011 2:59 am
(@c64club)
Posts: 200
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Thanks.

Even if this isn't suspended, I can always mount the kennel on some soft/springing/suspending "patents"


 
Posted : July 6, 2011 3:05 am
(@Hack__n)
Posts: 4720
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Here's a torsional suspension leading link chassis that is fairly easy to fabricate with .120" wall square tubing. It uses a 1" timken bearing axle that supports a disc brake if desired.

Lonnie

Attached files


 
Posted : July 6, 2011 8:01 am
(@c64club)
Posts: 200
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Topic starter
 

Thanks for photo, Lonnie.
Unfortunately i can't use disc brake nor hydraulic system because of law restrictions. Sidecar is treated as each other trailer. And a "lightweight trailer" must not have "active braking system". Otherwise it needs homologation, that costs more than my month salary. But Police and "Land Transport Supervision" officers don't treat drum brake with cable as active.

This morning i took ride to junkyard and returned home with "treasure" on my trailer:
1. a frame from old couch in warehouse condidtion. Made of 3mm wall rectangular tubing 🙂 Black powder painted 😀 Perfect base for the project. After removing backrest I will have some spare tubes.
2. some rectangular and round tubes with different walling. Freshly cut 20-40" ones thrown out to junkyard from handrail-maker.
3. struts with ball rod-ends and double twists and nuts for both twists (steering mechanism from some truck).
4. Two dampers from hatchback door.
5. Also got a front wheel fwom WSK125 motorcycle with drum brake, axle, bearings and tire in good condition, only the rim is slightly rusted. It was much cheaper and lighter than aluminium ones (they are from heavy motorcycles)

Overall "kit" weight is about 60 lb. Cost 10$. Love this junkyard. They always have what I need.
Only things they didn't have are rear swingarm and shock absorber(s). But as WSK has both wheels 18" with identical width and axle diameter, this will be easy to find. Local auction/announcement portal is loaded with WSK parts for very few bucks.

So I can't wait for all parts. Cut, drill, grind, weld, paint, GO! Yummy!
Going to do something similar to http://advrider.com/forums/showthread.php?t=680239
Interesting construction. Only one lower mounting. Whole rig is rigid tkanks to four struts. Looks perfect for my bike, as Romet doesn't have full tubing below motor.


 
Posted : July 6, 2011 11:38 pm
(@swampfox)
Posts: 1932
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c64club - 7/7/2011 4:38 AM

... I can't wait for all parts. Cut, drill, grind, weld, paint, GO!....

Please keep us up-to-date. And post pics if you can.


Lee
MB5+TW200+CRF250L+GTV300+INT650
XL883R w/Texas Ranger Sidecar
Zuma 50F + Burgman w/Texas Sidecar<Mrs. SwampFox

 
Posted : July 7, 2011 3:23 am
(@c64club)
Posts: 200
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Topic starter
 

I will post pics and descriptions on my site - both polish and english version, and give a link (and maybe some hotlinked pics) here.
Now the wheel is cleaned off rust and coated with mineral rust-protecting paint. I'm searching for cheap swingarm and absorbers somewhere close to my home.


 
Posted : July 7, 2011 4:02 am
(@c64club)
Posts: 200
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Topic starter
 

I spent last weekend on making additional roof for my workshop (over the parkplace) - parking my rig will be safer and more comfortable.

Wheel is completely painted, brake pads and brake drum matched, tire is weight-balanced.
I've bought swingarm and two shock absorbers in good condition, swingarm is waiting for paint. Cost 10$.
Also bought used upper-arm bolts from some veteran bikes. Cost 4$

Overall cost at this moment - 26$ (incl. painting). There is big chance that it will not exceed 50$ incl. body, lights etc, cause I own many old parts and materials.

Next weekend should be spent in workshop, making my sidecar.


 
Posted : July 13, 2011 1:53 am
(@peter-pan)
Posts: 2042
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Masseltov Igor,
good luck, that MZ did reminded mi to my MZ with superelastic s/c from 86 to 89.
Excellent in winter, but a pain in electrics, thirty like a swedish sailor and every few thousand km you had to bend the frame into shape again.
My 350 Jawa back home in Germany or Poland would be a good rig for back roads, (here its hopeless too weak)
125ccm sounds very week to me, and for a rig allways watercooled is preferable. - think about it

Just stay safe with your construction, Its Your life you risk if you start to build flimsy.
Remind that the Jawa uses excellent tough materials and industrial tubingor chineese bikes are not at all comparable.
May I suggest that before paint you present fotos here and to somebody with experience. Isch, Dneprs and Ural are very heavy, but can serve as reference for where to reenforce.
Best wishes
"Piotr"
Sven Peter


 
Posted : July 13, 2011 3:52 pm
(@c64club)
Posts: 200
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Topic starter
 

I have consulted some things with two guys who ride their rigs frequently. There is one conclusion, also from your post. Bike must be reinforced in few places and the SC frame must be done with redundant thickness in some elements. I can afford to do some parts heavier becaise i don't care about v-max.
I know that 10HP high-rpm 125cc OHV isn't the best motor for pulling a rig, but that's i have. There are two 18HP 250cc OHC motors available for my bike. The same mounting points etc, bigger bore and heavier crankshaft. But their cost can kill. About 600$ for aircooled and about 900$ for liquid cooled. But even if i could afford both them, I will prefer aircooled. Less parts that can be dmaged.
Generally I will try to "copy" that MZ three-points mounted rig.


 
Posted : July 13, 2011 10:42 pm
(@c64club)
Posts: 200
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Topic starter
 

Did almost whole sidecar. But now i have problem with bike's frame. It's too elastic. This could bear some test rides but if I'd like to do a rig for regular use i must make my frame way more rigid, especially its rear part.

What idea is better:
1. mount some pipes along with existing ones, or
2. make a sub-frame that combines trhee functions:
-adds rigidity to whole frame
-acts as crashbars (in solo)
-acts as frame for trunks.


 
Posted : July 25, 2011 12:19 pm
(@peter-pan)
Posts: 2042
Noble Member
 

Helo Igor,
Subframe, and perhaps a self made heavy duty back swing.
You should have seen my MZ how often I had to bend everything back into position. (Erich was using the softest boiler plate iron you can imagine)
Sven


 
Posted : July 27, 2011 6:23 am
(@peter-pan)
Posts: 2042
Noble Member
 

Igor, how is the summer,
bussy swimming or welding?
I was bussy planting trees these days with the help of my Jawa rig.
I look forward for the coming weekend close to the beach (sadly in 4 wheels.)
Sven


 
Posted : August 9, 2011 4:54 pm
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