In case anyone else tries to make a trailer with suspension. In this case it's for ferrying photographic equipment - and the inevitable groceries. My #1 trailer has proved to be slightly too small and I fancied making my final effort a relatively ambitious one.

After several weeks of gurning and much headscratching I put a prototype together. The wheel sections are hinged at the back. The spring is roughly 6" long rated at about 40lbs/inch. Apparently the damper is called a 'belt tensioner damper' and belongs inside a BMW's engine. It seems suitable, perhaps a little too well damped. The result is approximately 2" of useful travel with no bouncing (a criticism of the Bob Ibex, I believe). The spring can be preloaded with tension by adjusting the U-bolt thing at the bottom end of the spring. A decent grocery trip should cause no more than 0.5inch of static sag, the remaining 1.5" reserved for potholes.

As for tips, I recommend building one side of the trailer and using the pieces as templates to make the other side e.g. clamping a finished and unfinished piece together and drilling through the pre-existing holes into the unfinished piece. The result should be a mirror-image. I've always found this to produce highly symmetrical chassis and nicely aligned wheels.

As for springs, twice I underestimated how stiff the spring would need to be. The final choice was basically the stiffest my hardware store had. Design around the available stock springs because they often don't come nicely organised by rating, and custom jobs are expensive.

wheel-wheel =20"
Trailer bed is 5.5" off ground. This produces a very stable trailer. Althgough not yet attached the hitch will be a universal coupling (as in trailer #1, somewhere on this website). The upgrade from 12.5" to 16" wheels seems to have been a good move.

The weak point of this trailer would be the lateral rigidity of the wheel sections. Also the chassis probably need reinforcement at the mid-section.

Does anyone know how to paint aluminium properly? My previous efforts have not lasted, the paint comes off very easily. I sandpapered, cleaned, rinsed, primed and painted them, but might've been using the wrong products.

Cheers.
AR.