Towing Stuf and Some Math - Fiberglass RV

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Old 03-03-2009, 07:57 PM   #1
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I just posted this to another group and thought it might be interesting to some of us:

The Toyota site shows a curb weight of 4,190 lbs for the current Taco. BTW, go to that site and do a little math -- Take the GVWR (5450), subtract the 4,190 and the remainder is the Payload -- Now take the GCWR (8,100) subtract the curb weight (4,190) and get 3,910 as the maximum trailer weight -- But Toy set the tow capacity (for the standard model) at 3,500, a difference of 410. Strangely, 410/3900 is about 10.5%, so I infer that Toyota put a 10% tongue weight from the trailer in the truck as payload.

The 60 lb difference between my 410 lbs and the Toyota site's 350 lbs might be for the receiver hitch! Dunno if it comes from factory with one.

This means that every pound of extra weight that one piles into that truck lowers the trailer weight allowed, including passengers, WDH, perhaps receiver hitch, any non-standard factory or after-market options, 4WD, canopy, bike/canoe racks, etc. One must take all this into consideration when picking a tow vehicle or a trailer. Suddenly, Toyota's definition of curb weight becomes somewhat important.

Also bear in mind that these capacities are for level towing on good roads at sea level in new vehicle -- These conditions are quite obviously subject to change -- Ford, for example, says in numerous places to "reduce GCWR by 2% for every 1,000 ' of altitude -- Since the truck weight is fixed, that reduction has to come from the trailer -- At 10,000' x 2%, we have a reduction of 20% (Hmm, suspiciously like that Rule of Thumb for towing!); in this case bringing the tow capacity down to 2,800 or a total trailer weight (axle plus TW) of 3,080 (2800 x 1.10 [tongue wt]).

When up on that 10Kft pass, we are on the edge of our capacity so anything like rain, snow, crawling traffic (potentially overload tranny and cooling system), etc., puts us over the edge and extreme caution should be used (Also, turn off a/c). Now it is also clear why we want to know the real, scale, weight of the trailer and truck.

When we get back off the mountain, we once again have a margin of 'excess' capacity to account for ambient conditions and age of machinery.

Having the tow package on the current Taco almost *doubles* it ( raises it from 3,500 to 6, 500), so knowing someone who tows with the TP-equipped model doesn't at all imply that a non-TP model will be just as good. I don't know what's in the TP, but I'd venture a guess that it's more than a hitch and some wiring!! Now it's also clear why describing the truck by its engine parameters is not enough (I presume they both have the same engine).

The disparity in tow capacities between models makes it imperative that one consult the owner's manual for that truck, after determining the equipment. I know the owner's manual for my '98 Ranger shows 60!!! different combinations of options, and there are tow ratings in there ranging from 6,000 lbs all the way down to Not Recommended For Towing! That's just one model year for one manufacturer! Rather difficult to condense all that info down to the annual Trailer Life Tow Guide with the ratings tables. Generalizing from just the engine displacement or number of cylinders can be highly inaccurate, because there are so many other factors that enter into that capacity rating.

Many manfs put there OM's on-line for downloading, likely because they don't want to be placing any impediments between owners and information that might come back to bite them in a lawsuit...

Speaking of that annual Tow Guide, I believe it is in the January issue of the magazine; also a discussion of towing mirrors. The Guide has a summary of state and provincial requirements, including the general requirements for need for trailer brakes.

Personally, I also like to use the full title (in initials) when referring to the gross, because there are a number of them that affect us, primarily the Gross Vehicle Weight Restriction (GVWR) and the Gross Combined Weight Restriction (GCWR). When looking at new (to the buyer) tow vehicles or trailers, the actual scale weights are usually not available, so the Gxxx's are the next best estimating tools.

For example, take a trailer's GVWR (Usually the sum of the axle limits) and multiply by 1.15 (to adjust for tongue weight) and this will yield a max the loaded trailer should weigh, a conservatively high number, although it may not consider the weight of the axles, wheels and tires, depending on how the manf set it.

Regarding brakes on trailers, Ford now puts a note in the OM's to the effect that "Vehicle brakes were designed to stop the GVWR, not the GCWR", that means the truck, not the truck plus the trailer. I found a world of difference when I added brakes to my Scamp 13' (Nominal and fictional 900 lb trailer weighing 1,700 lbs in the real world w/o many options. One Scamper's trailer is above 2,200! Regardless, it is clear to the most clueless observer that six braked wheels on the pavement are better than four!

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Old 03-03-2009, 08:14 PM   #2
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Old 03-13-2009, 09:44 PM   #3
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I found an incorrect specification in the 2008 Trailer Life towing guide online. I'd buy a Mazda CX7 if the number they published were correct. It is a great reference, but not perfect.

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Old 03-13-2009, 11:50 PM   #4
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That's one reason why I prefer to use the Tow Guides as screening sources, but not as final info -- Besides typos, they have to boil down hundreds of specs into some generalities -- Also, they drop tow vehicles on the light end -- The magazine is aimed at Bulgemobiles, despite the Scamp and Casita ads in the back section.

Likewise, on-line numbers can be erroneous.

For final numbers, if I were shopping for new tow vehicle, I would have the door label and VIN decoded and refer to the Owner's Manual.
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Old 03-14-2009, 06:33 AM   #5
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Oh, c'mon, Pete... you know all that owner's manual stuff is like the Pirate's Code... it's more like a guideline than a law... (at least until you crash). I don't know why you'd even car about that stuff. Why, I once towed a railroad car full of coal across the country with my Austin-Healey Sprite and never had any problems... and I never needed a brake controller... and I did it with a bolt-on bumper hitch!

Well done. Good stuff and good analysis.

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