From: John De Armond
Subject: Re: Manufacturers' Tow Ratings
Date: Thu, 09 Mar 2000 13:28:39 EST
> On 3/8/00 >Alan.S.HepburnNOAlSPAM@nsc.com.invalid writes:
> >Have I misspoken anywhere above? I >thought my point was reasonably clear
> > there are many factors involved in >calculating GCWR, and tow ratings, and
> >that manufacturers are generally
> >pretty secretive about actual >specifications, probably for liability
> They are secretive of the data supporting the published GCWR ratings and how
> they are arrived at for competitive reasons. GM doesn't want Ford or
> DaimlerChrysler knowing how they do it any more than they want GM to know how
> they do it.
I suspect that setting GVW ratings is almost totally a political and
legal matter and so test data would have little to do with it.
Example: My StepVan delivery truck. According to the dealer, the
chassis is rated at around 18,000 lbs (do sue me if I missed it a
little - 10 year old memory at work here.) and yet the vehicle is
tagged at 9000 GVW. Why? probably to avoid the driver having to
have a CDL. Makes things interesting, considering the vehicle
weighs 8500 lbs empty.
One method that involves a lot of work that will get one closer to
the actual capabilities is to look at the data on the components. A
quick perusal of an SAE journal or the buyer's guide (nearest
technical library) will produce dozens of ads for axles and
transmissions and such. A call or letter to these guys asking for
data sheets will produce the necessary data. Presenting one's self
as an integrator such as a wrecker builder gives one more
credibility. Of course, you're going out on a limb once you deviate
from the mfr's rating. One COULD defend a deviation but he better
have the engineering data in hand just in case a lawyer ever wants
to look at it.