On Sunday, June 15, 2014 8:01:30 AM UTC-6, GC wrote:
On 14-Jun-14 00:57, son_of_flubber wrote:

On Friday, June 13, 2014 12:23:47 AM UTC-4, Frank Whiteley wrote:

...

Bring range, horsepower, and all or 4WD.



My 2004 Volvo XC70 has all of that, highish ground clearance,

comfortable seats and a 'safety cockpit'.



No, it doesn't. Karl gave the 2 main rules and the XC70 doesn't follow

either.



It is a light truck

trapped in a station wagon body (with a low CG compared to most light

trucks/SUVs).



1. I haven't measured it but my eye tells me that there is too big a

distance from the towball to the axle - because of its station wagon

heritage.



2. It's too light. TINSFOM - there is no substitute for mass. My 4WD

is 2.2 tonnes and doesn't take crap from glider trailers.



GC

There is a test for tow vehicle suitability. Just push the rear of the tow vehicle sideways with your hands in a rhythmic manner until you find its natural resonant frequency. My old Jeep Grand Cherokee's resonant sway exactly matched my Komet trailer's - no wonder the rig would weave all over the highway above 65MPH.

My theory is every tow vehicle/trailer rig is dynamically unstable above some speed. All one can hope to do is try to raise that speed high enough it isn't a practical limitation - then never exceed that speed.