RV Accident US 131 in Michigan

Ron Gratz wrote:

myredracer wrote:
The rule of thumb below to minimize sway has been around for a number of years (from David's RV Tips). I've seen it elsewhere too. Doesn't seem to come up much. If the Armada wheelbase is 123", the max. TT would be 23', well under what the TT appears to be.

The First Guideline
(This guideline was first used by the RV Consumers Group rv.org)

For the first 110" of wheelbase, this allows you 20' of trailer.

For each additional 4" of wheelbase, this gets you 1' more of trailer.

Wheelbase / Trailer length
110" = 20'
114" = 21'
118" = 22'
and so on

According to this ROT (rule of thumb), Suburbans (including 3/4 ton Suburbans) should not be used to tow trailers which are longer than 25'.

No one seems to be able to provide any information about how the numbers were derived. And, IMO, no one has presented any convincing arguments as to how increased TT length should make a TV/TT combination less stable assuming that the TT length is the only thing that changes.

IMO, we have no clear understanding as to how TT length affects TV/TT yaw stability. However, IMO, it is pretty clear that there are four primary factors which do affect stability. These are:

• Tow Vehicle Weight
• Tow VehicleWheelbase
• Hitch Overhang (distance from TV rear axle to ball coupler)
• TT Weight
• Tongue Weight Percentage

The "guideline" attributed to RV.ORG ignores four of these five factors. My guess is that the "data" which were used to formulate the "guideline" might have contained some correlation between TV weight (which might be correlated to TV wheelbase) and TT weight (which might be correlated to TT length).

One could then take an "average" wheelbase for a range of TV weights and take an "average" length for a range of TT weights and come up with a wheelbase-length relationship for "safe" and "unsafe" TV/TT combinations. However, correlations that might have been appropriate for TV/TT combinations which existed in the 1950/60s (or whenever the unknown data were collected) might not be appropriate for combinations in use today.

IMO, staying within all the TV manufacturer's weight ratings is the primary consideration. If you do that, then the TT length probably will be acceptable also.
Perhaps someday we'll have a "guideline" which properly accounts for all of the primary factors.

Ron