Technical information for only $26
http://papers.sae.org/2008-01-1228/
Stability and Control Considerations of Vehicle-Trailer Combination.
Hac, A., Fulk, D., and Chen, H., "Stability and Control Considerations of Vehicle-Trailer Combination," SAE Int. J. Passeng. Cars - Mech. Syst. 1(1):925-937, 2009, doi:10.4271/2008-01-1228.

Or http://proceedings.asmedigitalcollec...icleid=1645010
The Effect of Longitudinal Center of Gravity Position on the Sway Stability of a Small Cargo Trailer
Michael G. Gilbert, Daniel A. Godrick and Richard H. Klein
Paper No. IMECE2008-66022, pp. 295-305; 11 pages
doi:10.1115/IMECE2008-66022

Or http://www.scientific.net/AMM.29-32.1420
Study on High-Speed Lateral Stability of Car-Trailer Combination

And many more, courtesy of scholar.Google.com (exclude patents at first)