How to choose a tow vehicle (or travel trailer)
Tech > How to choose a tow vehicle (or How to choose a travel trailer)
Maybe you have a travel trailer and want to know in advance how to choose a tow vehicle. Or you have a tow vehicle, and you want to know what size of trailer you can pull. Good for you! Lots of folks don't think about these things until after they've already bought both... and many find that the two are not a good match. As an aside, most travel trailer tow vehicles are trucks, so I'll use the terms interchangeably.
PS: Similar calculations apply to fifth wheel trailers, but pin weight is 20% and you must also subtract the weight of the fifth wheel hitch from your payload. The good news is that's there's not room for much cargo in the truck bed.
Forget tow ratings and forget so-called trailer dry weight. Look at the payload of the truck you are interested in. Not the stats for the model. Not a truck next to it on the lot. Not a truck like it. The actual payload on the sticker on the door of that one particular truck. Subtract from that payload the weight of the passengers and cargo the truck will carry, and divide the resulting number by 15%. Then buy a trailer with an equivalent or lesser GVWR. For example, given a payload of 2000 lbs, 500 lbs of passengers and 500 lbs of gear:
GVWR = (2000 - (500 + 500)) / 15%
GVWR = (2000 - 1000) / 15%
GVWR = 1000 / 15%
GVWR = 1000 / 0.15
GVWR = 6667
I was always taught to show my work. Anyway... in this example, don't consider a trailer with a GVWR of higher than 6667 lbs.
In fact, if you are (a) a family with stuff, (b) want a travel trailer with GVWR of over 7000 lbs and (c) want to stay within specs, you will most likely half to look at something bigger than a half-ton.
Don't be seduced by the truck manufacturers' published tow ratings, or the so-called dry weight published by trailer manufacturers. NEVER blindly believe the popular trailer manufacturers' claim of "half-ton towable". Here's why:
I won't call into question the tow ratings claimed by the manufacturers, but almost all trucks will run out of available payload long before they approach the limits of their tow capacity.
In my opinion this is a useless number. First of all, it is almost certainly not accurate for your trailer when it leaves the dealer's lot because it may not account for such "options" as propane, propane tanks, battery, battery box, air conditioner and awnining. Secondly, you're going to load your trailer with hundreds of pounds of stuff to go camping (like food, clothing, toiletries, bedding, drinks, chairs, stove, BBQ, etc) so even if the dry weight were accurate it wouldn't be much use.
So what to do? As it happens, you can do almost of your calculations with two specs: Truck payload and trailer GVWR (Gross Vehicle Weight Rating).
Payload can be found on the driver door jamb. Here's mine. The small print above the red rectangle on the bottom sticker reads, "The combined weight of occupants and cargo should never exceed 710 kg or 1566 lbs". So payload is used up by all of the people in the truck, all the stuff they bring in the cab, all the aftermarked accessories that have been added, and the tongue weight of the trailer. A full tank of fuel is assumed and need not be deducted.
Can you find the payload online? Not accurately. For example, below is the spec for our model from the 2013 Ford F-150 Brochure. Note that a 2013 SuperCrew F-150 4x4 with a 3.5L EcoBoost, a 157" wheelbase and a 7700 lb GVWR (that's ours) has a listed maximum payload weight rating of 1840 lbs. Note the absence of trim level and options in the table - I suspect that's because F-150s in this category can be configured in any number of ways. Ours is an FX-4 with a long list of options that costs us 1840-1566=274 lbs of payload. Luxury costs.
So the only way to really know the payload of a truck is to open the door and look. Why dealers aren't posting photos of this sticker (by choice or by legislation) in their online ads is beyond me.
This spec is more readily available. Many manufacturers post GVWR with a trailer's floor plan. If not, it can be found on the outside of the trailer near the front on the road side (think driver's side). Here's mine - the GVWR is near the top left and reads 2980 kg (6570 lbs).
Why use the GVWR? Chances are your trailer's GVW (Gross Vehicle Weight), loaded for camping, will approach the GVWR. And any difference between the two is a safety margin.
We'll multiply the trailer's GVWR by 15% to determine the tongue weight. Tongue weight should be 12 to 15% of the trailer's GVW... starting at 15% is more safety margin.>
With all the numbers in hand, the calculations are fairly simple.
Find a truck
To find the payload (P) you need, Multiply the GVWR by 15% to get tongue weight (TW), then add the weight of the occupants (O), cargo (C) and accessories (A). So:
Let's say you're looking at a trailer with a GVWR of 7,500 lbs. Let's also say that the combined weight of your family is 500 lbs, you're going to bring along another 500 lbs of stuff in the truck, and any truck you buy will be equipped after the sale with a bedliner and tonneau cover with a combined weight of 100 lbs.
Easy, peasy, lemon squeezie.
You would be looking for a truck with a 2,225 lb payload. You might be looking at an HD pickup, though some newer half-tons qualify when properly optioned.
Find a trailer
To find the GVWR of the trailer you can tow, the math gets reversed. Subtract the total weight of the occupants (O), cargo (C) and accessories (A) from your truck's payload (P) and divide the result by 15%. So:
In this example you've got the same family, same stuff and those same accessories are installed on your truck, which has a payload of 2,000 lbs.
You'd be looking for a trailer with a 6000 lb GVWR... a smallish travel trailer.
In the first example we calculated a payload of 2,250 lbs for a 7500 lb GVWR trailer. If we can find a truck with at least that much payload, we can verify its towing capacity. I happened to have the 2013 Ford Brochure open and the closest I could find that met or exceeded 2,250 lbs was rated for a maximum payload of 2,310 lbs. That is a SuperCrew 4x4 with the long wheelbase, the 3.5L Ecoboost engine, and the heavy duty payload package. It would be a lower trim level, like an XL, and not overly burdened with fancy options. The same Ford brochure ranges that truck's towing capacity from 9,100 to 11,100 lbs, depending on the axle ratio and whether the truck was equipped with the max trailer tow package. In any case, well above what's needed to tow at trailer that's safe for the truck's payload.
A few more words
It's undeniable that a lot of the rigs on the road are "undertrucked" (exceeding one or more of their design specs). Maybe even most of them. Lots of people do it. It's your call.
On gas versus diesel
Ford, Dodge and Nissan offer a diesel in a half ton and Ford, Dodge and GM in their 3/4 and 1 ton trucks. Diesel trucks have more torque for towing, get better fuel economy and typically have a higher resale value. But equivalent gas powered trucks cost less and, due to their lighter weight, have a higher payload.
My friend Paul has captured the essence of this problem in Pablo's Towing Paradox:
The steeper the country you are towing in, the greater the need for a diesel. But the upgrade to a diesel motor allows you to carry less payload so you should get a smaller trailer, which you can then tow with a gasser.