It is often related to the differential gear ratio as much as anything else.
But, since the advent of unibody construction, too much force on a hitch can twist the body enough to affect traction.
If it were me, I wouldn't risk going that much over the rating.
I simply wonder if the rating is always a bit conservative. I've heard that the X5 rated in US for 6000 lbs is rated for 7700 in the EU... So I was just wondering about the physical ability of the car vs politics and over-protective rating process. I take the point about illegality of it, but still wanted to get a sense for the true capacity of all the components that matter when towing. The trailer has its own brakes.
A properly set up boat and trailer should not have more than 10% of its mass on the trailer tongue.
MDX max tongue = 450lbs
max boat trailer = 4500lbs
It is a local tow to the ramp or taking a trip?
I would lock it in D4 for the highway and leave extra room for braking.
Consider the AirLift 1000 helper bag kit to prevent rear sag and tire eating camber.
It is not the safest thing to do and if you do decide to proceed, make all steering brake and gas inputs gentle and gradual.
It would be a 3-hr trip. I always tow in D4 (used to have a smaller Bayliner 175).
I also have Airlift 1000 installed and could not be happier with it. Braking should be ok as the trailer has its own.
What kind of boat? What is the dry weight?
I towed a 5000lb 22ft wakeboard boat a short distance. The rear suspension sagged and caused unsafe steering. First Gear in the MDX is not low enough to pull it up the boat ramp. A V6 VW Touareg with 6speed trans tows this boat with no problems. (7700lb factory tow rating)
Was your boat 5000 or boat with the trailer?
Chaparral Sunesta 244, dry weight 4400 lbs, probably 5400 with trailer.
No sag due to Airlift 1000. Are you saying the MDX would have a hard time pulling it out of the water? It would be about 6000 lbs with some fuel remaining on board. Is that a major concern?