For the engineeringly inclined, and hopefully for the rest of us.

http://www.edccorp.com/library/TechRefPdfs/EDC-1082.pdf

After reading yet another "Disco 3/4 towing" thread I went looking for information on weight-distributing hitches (WDH) and what they do. This is the only hard data I could locate.

The bottom line (on page 134 of the PDF) is that big vans (22ft, 2.7T) require either a) a weight distributing hitch set for flat ground equalisation of bumper heights {about 210kg ball load} or b) very high ball loadings {> 450kg} or c) heavy duty rear suspension, high capacity shock absorbers and moderately high ball loadings {275kg} with a weight-distributing hitch.

Altogether this suggests that trailer stability WILL be affected with towing a large van without WDH (vans were worse in the tests than other trailers) when using legal (for LR) ball loads.

All this presumes you have a tow vehicle of at least 2.5 tonne.

The heavier the tow vehicle, the lighter the ball load can be while retaining stability. A 4T vehicle with WDH only needs about 135kg ball load for trailer stability. But this would still equate to >350kg load without WDH (from earlier data).

Have I read this right?