There are two answers.. LEGALLY. it depends on where you live. and I can't give a better answer than that. Some states trailers 2,000 pounds or even lighter need brakes. Some 4,000 or more And yes a car in tow IS A TRAILER. [/quote]
I'll use Ca dmv law as an example.
section 29003 Every hitch, drawbar, coupler or other connection between motor vehicles towing must be securely attached to the vehicle and be strong enough to handle the weight of whatever you are towing.
section 26302 Every trailer over 1500 lbs must be equipped with brakes on at least 2 wheels.
now comes the interesting part...
section 29003-c. The raised end of any motor vehicle being transported by another motor vehicle using a tow dolly shall be secured to the tow dolly by two separate chains, cables, or equivalent devices adequate to prevent shifting or separation of the towed vehicle and the tow dolly.
Please note that Ca. separates TRAILERS from tow dollys, so in Ca. at least, a car in tow IS NOT A TRAILER