How much weight can you tow with, say, a Mack Granite 713 when its empty? Or, maybe a better question would be what could you tow, equipment-wise? D5, small hoe, etc?
I use to haul my JD 700J, 30,000lb, behind my Pete 378 dump truck. 22,000lbs empty. was on a 25T tag trailer. It worked fine. I don't think I would want to haul much more than that. You always hear of some guy hauling a 50,000lb machine around behind a dump truck, not something i would do.
I'm the guy who hauls a 50,000lb machine, well actually my 210 is about 48,500lbs. Tow's great. I wouldn't want to do it over long highway distances, and I won't go over 60 MPH. It's not as stable as a fifth wheel at high speeds for sure, but under 60 mph it's fine. Also take corners slow, but anyone hauling something heavy with the weight up high should be. 99% of my moves are just in the city at slow speed, no issues at all. I bet there is at least 20 people around here who do the exact same thing. There is a reason they make 25 ton tags. If you're only towing 35,000lbs or less a tri-axle is a waste of money, use a tandem.