I changed my Cobra wheels from the factory original 13s to 17 inch
wheels and tires. I made the change because of the lousy experiences I
had while towing. (with various tow vehicles) It was obviously a issue
with the weak sidewalls of the factory supplied tires. I also wanted to
increase the ground clearance at the aft end of the trailer. Initially,
going to a trailer tire with a stiffer higher sidewall using the same 13
inch wheels was my plan. That however seemed counter intuitive to my
initial desire to improve lateral stability. In my research, the bolt
pattern of 4 X 100 was found to be that commonly used on a Honda Civic
among others. It was apparent that the path of least resistance was to
find a 15 inch takeoff wheel from a Honda. That proved to be a fairly
expensive proposition and led me to a Japanese aftermarket shop located
here in Phoenix. The best Value turned out to be a closeout 17 inch
wheel and low profile tire. With that combo, the lateral contact patch
doubled, the sidewall height was halved and it is the most solid trailer
I have ever towed. Total cost out the door with tax, mounting and
balancing was $295.

Photos can be found @

http://www.asa-soaring.org/aco/pc.asp