I found this over in iRV2 and thought it would be a good idea to bring it here for anyone that doesn't reference that site, for one reason or another. As there, I think it should be made a sticky here too so it's readily available to those that are old and new to this. It's really a very good post.
The Physics of Towed-Vehicle Braking - iRV2 Forums
and
Tow Bar Angle and Height Difference - iRV2 Forums