My Trailex Tire Toter uses 8" wheels. When I first bought it (used), I called them to get a couple of missing parts. I asked about going to 12" wheels. The person said that he could sell me 12" wheels, but that I would get a "basketball" effect by going to a larger wheel. He said there was no need to change them. He certainly could have recommended me to spend more money with the company, but advised not to. The trailer empty weighs about 250#.
So far so good. I used it behind the 996 out to Topeka and back in '04. I have lent it to a guy with a GT3 who has used it for a few trips now and probably put 1,000 miles on it this year.
Trailex's Tire Toter: http://www.trailex.com/viewprod.cfm?id=74&mcat=88&cat_id=88
Disclaimers are that I bought parts from them, and I think it is a great tire trailer.
Matt Murray
I am perfectly capable of learning from my mistakes. I will surely learn a great deal today.