Lou Schneider said:
Tow ratings have been used as marketing one-upmanship for so long, they've reached the point where the maximum ratings have only a passing relationship with reality when towing a conventional or 5th wheel RV trailer, IMO.
I believe that Lou's comment is insightful.
When tow ratings were first introduced, they were, in most cases, artificially low and used by truck makers as a tool for selling powertrain upgrades. (Want to tow a trailer? You'll need the big engine to be safe.)
Recent years has seen the ratings used as a point of competition between manufacturers, at least for pickups.
I personally will not be seen towing an 8,000 pound trailer through the mountains with a 1/2 ton truck, even if the manufacturer claims it will tow 11,000 pounds because it has the V10 or the diesel or the 4.10 gears. That's lunacy. But by the same token I think it's safe to tow the same 8,000 pound trailer through the mountains with a 3/4 ton truck that (like my 1997 Chevy) is rated for less than that, because of the entry level power train.
You can't just take 10%, 15%, 20% or whatever off the capacity and expect that to provide a more meaningful guide.
Tow ratings are usually set using a small frontal area trailer that largely slipstreams behind the tow vehicle. Think horse trailer, utility trailer, etc. Not high and wide RV trailers with vastly more wind resistance.
Right, and one of the nuances that gets lost in these discussions is that it is safer to tow a 34' airstream, which sits low to the ground, than it is to tow a 34' 5er that will barely clear a 13'6" bridge.
When you're towing at the vehicle's maximum rating, by definition you'll have performance that's barely acceptable in one or more areas. If the limiting factor is available power or drive train stresses, adding the extra wind resistance of a high, wide trailer can push you into unacceptable stress or performance areas.
Limiting the towing weight to less than the published maximum gives better performance, so when you run into an unexpected situation (strong headwind, long upgrade, extra cargo in the tow vehicle) you have some performance in reserve to handle it.
By that logic a Ford Mustang is safer than a Ford Escort because it has more performance reserve, but the statistics bear out the opposite. That aside, there is nothing to indicate that 10%, 15%, 20%, or any other particular figure is the right amount. In absolute terms we're safer if we stay in a hotel.