Pulling A Fifth Wheel vs. Bumper Pull

horton333 wrote:

Walaby wrote:
My friend traded his TT in for 5er. He says gas mileage IMPROVED by almost 2MPG (Ford Diesel). Towing experience, he says is better with 5er and felt more stable in windy conditions.

Mike

That extra height increases wind drag and at a 4 times rate, and drag is the main determinate of fuel efficiency at constant speed. The second is weight on hills or accelerating, and being taller the fifth wheel also tends to weigh more per unit length for most of its length. Perhaps he changed to the diesel at the same time as he bought the fifth wheel.... about the only science that could explain that huge fuel use improvement observation. I guess he could also have converted to one of those 200 mph carburetors, but those are scarse now and also difficult to retrofit on a diesel. :W
Perhaps also he had a terrible setup on his earlier trailer, there are some out there, but for equal length trailers, as under discussion, the wind on the extra height will have even more than 4 times the sideways pushing effect (not only does the wind's force go up 4 times that extra force is applied farther above the axle and so has much greater effect on stability). The higher trailer was aleady less stable sideways to begin with given the higher center of gravity, so less resistant to the push. The fifth wheels often have more robust axles which helps a bit and the length is measured differently which adds a bit of complexity to these generalizations and the "equal length" assumption, but neither is going to compensate for the huge math disadvantage to a side wind in any typical case of 35' trailers.

Well Horton, I think a couple think a couple points you miss are that as a whole fivers are heaver the the equivalent TT that helps make them more stable, most of that weight is in the frame which is relatively low. I have personally towed next to the Pacific Ocean with a very strong on shore wind 40+ mph with gust to at least 50 mph, never noticed. Never notice a passing semi either.
The biggest reason is the physical pint of attachment is right over the rear axle.
While the Hensley is a great design and works well, it has its limits, once the angle between the TV and trailer gets past a certain point the virtual pivot point starts moving back quickly. Weigh a fiver that point never moves.