astro - I actually added a drive side support (it's there in the second pic) as there was a tiny bit of flex that wasn't problematic but something I thought might lead to some fatigue issues.

I am presently re-working by bike's hitch and fabricating a new mount by using stainless rod which will be stiffer and more elegant and then I can use a single arm mounted to the non drive side.

I like the larger wheels as with bicycles, a larger wheel might tale a little more to get it up to speed but once they are rolling they are more efficient and ride far better.

I will be towing this bike through the winter and not having the trailer turn into a snowplow was also a consideration in my design.