Motorcycle Trailer

[Al]

I am building a trailer to tow behind my K75 RT. I hate towing trailers but we do a lot of two up touring and camping. There just ain't no way to do this two up without a trailer. Believe me we've tried.


So I have several ruling notions about this project:


1. It must be small.
2. It must be light- ideally not more than 120 lbs loaded.
3. It must be low.
4. It must be narrow- ideally not wider than my saddlebags.
5. It must have independent suspension.


So far the bare frame weighs 19 lbs in its unfinished state.


It looks like the wheel track will be 34 inches- about 2" wider than the saddle bags. It is low.


Here is a look so far. Excuse my rat hole of a shop.

[Scott_]

My only concern/comment on what you are doing...... a K75RT-- 2-up--- pulling a trailer--   
Will it handle the load engine wise, most likely, your acceleration will be slower but it will pull it.
Will the brakes be able to stop it loaded......... that would be my concern.  Your stopping distance will definitely be affected.

I'd calculate all of the weight involved, the bike, you & your wife (in gear if you wear it), trailer + contents, and compare that number to the GVWR of the bike.
You don't want to be over it as that is the maximum of what the braking system is designed to safely stop.

[Al]

Thanks for your concerns, Scott.
I have done the calculations. Like I say the plan is for a mere 120 lbs max. 120 lbs. I don't think that is enough to lose sleep over. We already have carried most of that without the trailer just fine. But bulky stuff like sleeping bags and CPAP machines don't fit anywhere as is but they aren't heavy- just bulky. I have carried some big palooka pals who probably are close to the same all up weight.


Like any trailer towing situation you have to adjust how you ride. Obviously you can't accelerate the same. You can't stop quite as quickly ( my concern is more jack-knifing tendencies than actual braking distance). Also you can't corner as aggressively. So I won't. I will adjust my riding style.


My buddy has towed a trailer behind an R100RT for thousands of miles. It has lousy brakes and less power. The K75 brakes seem quite adequate. It would be nice to have more low end Harley-like torque but it is light and rolling resistance should be minimal.


Reynolds sold many hundreds of hitches for the K75 and I have heard no horror stories. Like anything in life one has to think through the situation, weigh the risks, manage the risks and stay alert. If I was that concerned about safety I would just stay home. Driving is risky enough. Riding is worse. But we still do it.


At the end of the day if I don't like the way it handles I don't have to keep towing it.

[BrickMW]

Mock up is looking pretty good.. Love the oil filter tail light!!


More than that, really love that 1st run Work Mate you have there, wait, is that two I see??  :yow


Probably the best product Black & Decker ever produced, especially those original ones. My dad has one like that, years later he gifted my brother and I with one of their later designs. I've had to replace the wood on mine, (later models used a much cheaper particle board for the clamping pieces) which improved it quite a bit.. definitely one of my "can't do without" tools in the garage.


Back to the trailer.. what are your thoughts for suspension? You might check out some golf cart parts. A friend of mine had good success going that route. Harbor Freight has cheap trailer frames that are set up and ready to roll. However, getting the snowflakes mounted to either of these may prove counter productive.  :dunno


Good luck! Keep us posted through your progress.. 

[Al]

Thanks,  BrickMW.
The oil filter is actually to approximate the tire since I don't have them yet.


Work Mate? They are a life saver in so many ways. When they first came out I mocked the ads on TV. Bought my first one at an auction about 30 years ago and then scored another one at a garage sale. Now I'm sold. I have a vise mounted on a rectangular tube so I can do filing and such like more easily.


The suspension is two trailing arms of 3/8" x 2" flat bar that pivot on that shaft you can see in the photo. They will pivot on UHMW bushings/ The flat bar also has 1" x1/8" aluminum angle welded so both legs are in contact with the flat bar. It runs the length of the trailing arm to provide some torsional rigidity so that the arm doesn't twist and flex.


The axles are K75 front axles that will get turned down on the lathe and threaded on one end. They in turn will go through the back of the swing arm with a nut to hold them in place.


The problem with a trailer this light is finding springs and such that are light enough. Most trailers are made for a minimum of 500 lbs so the springs may as well be solid bars.


I wanted to use a torsion bar suspension since it can be adjusted but finding 30-40 inch/lb springs of any type is a hassle. I finally found some torsion bars light enough for use in micro sprint race cars but then you need trailing arms that are splined to match the torsion bar ends and adjusters for the other end. The other problem is that the torsion bars are 20 " long so they are much too wide to put them end to end. Then they have to be stacked or one put in front of the other which plays hob with the trailing arm lengths. Then you still need some kind of shock absorber that isn't too stiff. Too much hassle even though it would be a simple (in concept) and elegant solution.


So I am using two mountain bike air shocks. The problem with mountain bike air shocks is that they are very heavy rated. Some as high as 700 lbs. So two would mean 1400 lbs of springs on a 120 lb trailer. These ones are straight air and the damping rate is adjustable so here's hoping. I looked at mini bike springs, go kart springs, medical scooter springs- pretty much everything I could find and they are all too heavy. They have to support the weigh of the machine, plus a potentially porcine rider (much like myself) and any shock loads from dips and bumps.


My shocks will be horizontally mounted since the sides of the car top carrier flare out too much to mount them vertically. The manufacturer says they can mount in any orientation. They will operate through a bell crank system off the trailing arms.


My buddy's trailer has no suspension at all- just a solid axle and two trailer tires at 5 PSI. He says it works great but I don't like the idea.


Once I get the trailing arms back from the welder I'll post t some pix. Here is a picture of the pinch blocks and frame bushing that mount the pivot shaft.

[Al]

A couple more pictures. The tacked together trailing arm with one UHMW bushing in place. One showing how the pivot bushing was fabricated. Some warping is evident just from tacking so I will have to back bend the arm for welding.

[F14CRAZY]

Are you positive a trailer is needed? My wife and I have been camping...

[Al]

We've tried and we've tried and we've tried. But we can't get no satisfaction.


So it seems a trailer is necessary.

[aces59]

Hi - a couple of thoughts
Do you guys have Indespension units over there? Sorts out all the suspension and wheel fitting in one part
The mountain bike units look a bit over the top. Cheap standard sprung bike units should be ok - or at least the springs out of them and if you are operating them off bellcranks you can tailor the movement ratio to the spring rate. Could just use the springs and Polyurethane or rubber doughnuts to act as bump stops they will provide the damping. In fact they would probably work without springs - That's effectively how the indespension units work. Look at the rubber bits usually fitted on shocker tubes inside the springs.
Also.... You could use tension springs - or rubber bands. Or back to compression springs - Valve springs?
Steve

[aces59]

By the way - you're shop looks like my shed after I've cleared it up
:-)

[Al]

Thanks, Aces.
The problem with any spring units I have come across is that the spring rates are way too high. Mountain bikes use 700 lb springs. So a pair of them is going to be 1400 lbs. Way to stiff on a trailer that will be 150 lbs loaded. Believe me I have looked into all and sundry.


By" indespension" are you meaning the rubber mounted units? We have them here but again they are designed for 1000 lb minimum.


I saw in a 1961 Popular Science that a guy built a trailer that used a spare tire under the deck as the spring. Too bad I already got under way with this unit. Kind of cumbersome and ugly and probably heavy but it is food for thought.


Unfortunately my shop is cleaned up. Usually  its even worse. Too many interests (trains, planes automobiles, guns, motorcycles, steam engines, fishing, etc) leads to too many unfinished  projects.


All the best across the pond.


Al

[aces59]

Most old brit bikes used about 100 lb springs in the rear shocks so  those mountain bike springs must be running on a huge mechanical advantage.
I'm thinking Tension springs would be a good option. easier to tune and multiply up than compression.
With a rubber bump stop to damp it.
Some old speedway bikes used rubber bands on the front forks Also an old hillclimb and circuit racer did it - Can't think of the name atm but it will come to me
Might be worth looking at whats used on Pushbike trailers - the ones for carrying kids about in?
Steve

[aces59]

Gottit!!
Allan Staniforth - Terrapin hillclimb and sprint cars
He's written several books on suspension etc like 'The Race and Rally car source book'

[Al]

Sounds like a good read but I'm well into this now. If it doesn't work out I may have to do some redesign over the winter. If I get it finished before winter.


Mountain bike shocks are heavy because they are only one shock for a rather big lout on rough trails. So if I (at 230 lbs) ride off a small embankment or jump it off a log, a 12" drop is going to put the load on the back wheel through the stratosphere. You are right they have a significant mechanical advantage which is why the travel is usually fairly short- on the order of 2" for most of them. Thats why I'm hoping this air shock will lighten up the spring rate significantly.

[The Mighty Gryphon]

I had a couple of friends back in the early 80's who were building and selling trailers for Gold Wings using X-Cargo rooftop carriers. 

They used leaf springs from snowmobiles without dampers, and they worked pretty well.  It's been a long time, but I think they took one of the leaves out to lower the rate.  They had over 100,000 miles on each of their personal trailers.