On 19/06/2013 20:27, Chris Nicholas wrote:
GC, I know only what I read but it makes sense to me. The point is
that the spring rate is such that gravity on slopes up to some pitch
(unstated) and normal slowing down without the use of brakes does not
compress the spring and activate the trailer brake; whereas the
(greater) g developed by applying the car brakes does compress the
spring and activate the trailer brakes. Have you read the full
article Jim referred to?

Regards – Chris N

Chris - I hadn't when I wrote and was puzzled about 'braking' that
wasn't 'deceleration'. I have now and I see the point that was being made.

GC