I think the backing-up/jackknife problem is a ratio, not just one number. I haven't proven it, but the distance from the steering axle (front) to hitch relative to the distance from hitch to trailer axle (or center of axles) is the ratio I think that matters the most. A long vehicle like a long bed crew cab 1-ton won't work well with a short 4x8 trailer but a small jeep will. And the worst example is a towable air compressor. So short that no tow vehicle can win backing up. It all has to do with how much the towed item moves relative to the input from the tow vehicle. I'd bet you could prove it with something like the trailer fishtailing demo that is stickied at the top of the towing sub forum