As Dennis says, "55 is the legal speed limit for towing. It doesn't matter how anyone has gotten away with anything over that speed limit while they've towed. The simple answer is, if you run over 55 while towing, you run the risk of getting either sited for it or, at the least, a warning.
There's only a few dozen variables that will or can influence whether or not an officer feels like taking action. So, again, the point is, the speed limit is 55 while towing. You can come up with ten zillion reasons as to why you were traveling over it when you get stopped, but if that officer is having a bad day, he/she has every bit of the law on his or her side in writing you a citation.
I'm not chastising you for asking the question. It's like a lot of vehicle/moving violations etc. There's lots of folks running over the 65' max length in CA and have never gotten stopped. That doesn't mean it's legal, it simply means they've not been stopped, YET!
Scott
