I've been entertaining the notion of a monowheel trailer for about 4 years. Camping in cold climates is just getting hard on the body and I need to bring a few more creature comforts. Aside from that the whole subject of the supension design and tradeoffs between style and space is just fascinating me.

I've decided that this year I will start the build with the frame and suspension to be able to test it before fabricating a fiberglass body.

I have identified the basic design of a swingarm and shocks that will take the least amount of internal space from the box.....


The loaded sprung weight of the trailer will be (at max) 75 kg and typically 45-50 kg. I have also found online a pit bike shock rated for 90 kg in the upright position and I am thinking that a pair of them used per the photo above might work well.

My question is; does anyone know to what extent, or what the formula for calculating the effect of the angle of mounting has on the shocks load rating?

Saw that article Dai and the table of values was interesting....Still trying to calculate my setup out but getting closer!

There are two aspects that need to be considered in the scenario above.

First, if the movement of the axle or whatever isn't directly in line with the movement of the shock/spring combination, as in 'angle of the dangle' in Dai's reference above, then the shock effectiveness and load rating are reduced by the cosine of the angle between the shock position and the movement direction of the axle.
effective load rating = shock's load rating x cosine θ  where θ is the angle between the shock and the movement direction.
This is complicated a bit by the fact that the angle will vary according to the position of the shock in its travel, but if you pick a point about in the middle of its expected travel, it'll be close enough.

Second, there is the fact that the wheel movement is pivoted to translate a vertical wheel movement to a horizontal shock movement. The effect of this is determined by the ratio of the wheel axle to pivot distance compared to the pivot to shock end distance. This can also be affected by the movement direction not being at right angles to the radius from the pivot point to the axle or the shock mount.

For Will's picture above, the shock will be pretty close to the force being directly along the shock, so the 'angle of the dangle' question won't really apply. It won't be a straight line movement, but pretty close.
Estimating from the picture, that ratio is about 5:1, so the shock will need about 5x the expected total load of the trailer and its cargo.

I'm away from home at the moment, so translating that into a diagram isn't easy, but if a picture is needed to replace lots of words, I can do that when I'm at home.  

Bill

Most shocks that are designed to work vertical will not work in a horizontal position. The spring will do the job but the hydraulics will aerate and try to compress bubbles and the oil will foam.

Thanks Bill and Rick. That all helps improve my understanding. Given the short travel I'm currently looking at Mountain bike shocks, gas would be better based on what Rick says, rated about 900lbs. (900/2.2 = 409kg x 20% efficiency = 81kg) Trailer would have a max 80 kg load.

Here's a rough drawing of what I might fabricate.....


If I mount the shock at position A it will be virtually horizontal at 10 degrees. To get it to 20 degrees I could mount it outside the swing plate and attach to the lower frame face. I presume It would be better mounted right way up too?

I don't know enough about shocks, and especially mountain bike shocks, to comment on them and mounting angle.

Re the geometry, the line from the main pivot to the 'top' shock mount should be at about right angles to the line of the shock shaft when at about typical load.
Option A would be somewhere near correct, though a small adjustment might be good.
For option B, the shock 'top' mount should be further left and/or the main pivot further right.

When you have good advice about shock suitability and mounting angle, I'm sure you'll get the rest right. 

Bill

In my limited knowledge of mountain bikes with rear suspension, especially at higher levels, there is usually a pivot arrangement so your mate's brother should be good on suitable pivot ratios too.    He'd be customising for rider weight etc.

Bill

I don't know much about shocks and their workings , but here is my 2c worth.
This is a little mono RossKKo had in mind . Very similar to the positioning you have drawn up .


Be great to see how you go with the mono style Will . 
The main benefit would be your ability to choose a wider area of road to manouvre on .



Another option is to install a Hyosung gtr250 swingarm in there . it has a relatively short shock .