Originally Posted by Green_Mtn_Boy
Don't know the exact ratios but here's something to consider regarding hitch loads.
The forces involved in a carried weight are considerably greater than the forces imposed by a trailered load. In other words, a bike rack with 100 pounds of load will impact the hitch and it's attachment in a fashion similar to a 1000 pound trailer. Not in all respects, engine and tranny load of course doesn't care how the load is attached. The hitch and the frame it attaches too does. I've seen a 1000 pound motorcycle destroy a 10,000 pound motorhome hitch when it was carried off the ground.
All this is to suggest that using the focus to tow a small trailer is probably no more troublesome than a 3 bike rack carried 18 inches past the hitch.
The force you're referring to is about the torque put on the hitch. Not the forces put on the car's drive train.
A loaded hitch bike rack can put as much destructive force (torque) on a hitch as a 1000 pound trailer, but is a small fraction of the load (tension) to the drive train.
I believe a very modest amount of trailer pulling will cause no harm to the Focus. I would install modular wiring that is easily removed before taking my car in for service concerning a drive train issue. At least until the warranty expires.