I think there is a point. Anytime you are using a trailer, truck or anything at its maximum capacity will increase the chance of failure. I see LCOs all around that have two ztrs, a walk behind, two push mowers, and various other equipment on them without tandem axles; it looks like a jigsaw puzzle. Even with the idea that 3500 lb. axles are strong, they are still 3500 lb. axles and when you put that much equipment on it you are over the limit. Have fun with DOT or even better when you get into an accident and your insurance company denies coverage and you get sued, the fun will begin. With some of the bigger ztr's just two will put you over the limit when you add a push mower and equipment, fuel, etc.. The minimal cost will be well worth it in hindsight.