Towing & Trailers

In February I purchased a 2003 Dodge Ram 2500 with the high output turbo diesel motor in preparation for towing my racecar this race season. At the time, I thought I was buying an unreasonable amount of truck in order to have some buffer for towing an enclosed race trailer. Everyone else does it, I’m sure I would be fine, right?

Wrong. As a newbie to the truck and trailering process, figuring out how much trailer a truck can tow was more of a black art and anecdotal quagmire that not even 33″ tires and 4×4 could wade through.

Searching the web, the message forums are littered with questions about “how much truck do I need?” with responses that all too often sound a little bit like “I tow a 44′ 18,000lb travel trailer with my Ford Minivan and I haven’t had any problems!” Let’s do this right. First, some terminology:

• GVWR – Gross Vehicle Weight – The maximum weight of vehicle with all cargo, passengers and gear
• GCWR – Gross Combined Weight Rating – The maximum combined weight of loaded truck and trailer together
• GAWR – Gross Axle Weight Rating – Each axle has a rating for how much weight it can handle
• Tongue Weight – The amount of weight the trailer puts on the truck either via a bumper hitch or a Gooseneck/Fifth-wheel hitch
• Curb/Dry Weight – The weight according to the manufacturer which is 99% guaranteed to be less than the amount it actually weighs

The following list is a carefully researched and validated method for determining what kind of truck you need and how much you can tow. No other method is valid. Although you, your cousin, your buddy or a friend of your friend might have towed for years without a problem or voiding a warranty, pay attention to #1 and judge how much your life is worth.

1. If you overload your truck or trailer and are involved in an accident with loss of life, you may be charged with manslaughter even if it is not your fault. I have only read stories online of this actually happening but legally it is clear that it could happen, probably more so if you aren’t properly licensed.
2. TAG trailers (attach to the rear bumper) want approximately 10-15% of the total trailer weight pushing down on the hitch where a Gooseneck/Fifth-wheel trailer (attaches in the back of the truck bed) wants between 15 and 25% of the total weight pushing down on the truck. Therefore, we can calculate backwards: for a TAG trailer, 1000lbs of tongue weight is equal to 1000#/10% = 10,000lbs of trailer provided we meet the rest of the requirements.
3. There is one, and only one way to accurately determine how much you can tow: you must weigh your truck loaded as you will actually use it! Curb weights mean nothing! My Dodge Ram 4×2 Turbo Diesel is listed at 6311lbs with a 150lb driver. The truck actually weighs 6630lbs. Using our above calculation, that 319lb reduction in capacity translates to a 2,126lb reduction in trailer weight (@ 15%)!

The weight of the truck empty is pretty useless. If, in my case, you’re going to use it in order to tow two or three people and gear for a weekend, you need to load it up and hit the scales in that configuration. You can estimate, but again, estimating wrong could in the most extreme case mean going to prison. You can find scales in the yellow pages and almost every landfill has one that you can use freely as you drive through. Pull halfway on the scales and weigh the front axle, then pull fully on and get the complete weight, then drive half-off and get the rear axle weight.

To clarify why weighing is important: my 40′ race trailer has a curb weight of about 7000lbs. Loaded with a generator, observation deck, countertop and diamond plate flooring, the real weight is much closer to 10,000lbs. Without weighing on scales (available at truck stops everywhere, check the yellow pages for weighmasters or call the DMV for a certified scales operator, or check this list for California), you could be off by 5,000lbs in the above setup!

Knowing that we must first weigh and secondly calculate, with the ACTUAL weight of the truck, we can now perform the following calculations to determine what we can legally tow:

1. GVWR – Actual weight of truck = Maximum allowable tongue weight (MATW)
2. Add the MATW to the Rear Axle Weight obtained at the scales. Is this number greater than the manufacturer GAWR? If so, then you must back down the MATW until you are within spec.
3. Take the MATW and divide by the appropriate percentage – for TAG trailers use 15%, for Goosenecks/Fifth-wheels use 20%. MATW / (15% or 20%) = Maximum trailer weight

These calculations all hinge on there being a specific amount of tongue weight on the truck. In order to ensure that is consistent, you must load your trailer the same every time with the same amount of gear in order to maintain that balance.

People frequently cite one of the following reasons why the above doesn’t matter:

• My [cousin/friend of friend/ole buddy/etc] has been towing (grossly oversized trailer) with (grossly undersized tow vehicle) for (probably more years than he has had a driver’s license) and has never had a problem with anything, not even the mechanicals on the truck!
• The engineers at [Ford/Chevy/Dodge/etc] build a factor of safety into these estimates making it safe to exceed them by [a little/a bit/a lot].

Both of the above statements, that somebody has done it without incident, and the engineers build a factor of safety into the vehicles, are true. To believe those mean you too will be able to exceed the limits without incident is to fail to understand how cause and effect are related.

Update (May 2006): The last bit to address is about licensing. In California, the law is relatively simple. For normal civilians who want to tow “fun stuff”, like boats, race or travel trailers, if the GVWR of the trailer is 15,000lbs or more, you will need a non-commercial Class A driver’s license. If it is 14,999 or less, you can tow without any special license although you occasionally need an RV certificate. Remember, this is the GVW RATING, not necessarily how much you’re towing. Even if you tow an empty tri-axle trailer rated at 15,000lbs, you still must have the proper license! I’ll post more about this in the future.

Update (July 2007): Thanks to TruckChamp.com for sponsoring my research on trucks. They have contributed so I can prevent further tailgate theft with an automatic tailgate locking device.

Update (November 2009): Two good resources that complement this article:

• Sherline Products Towing Guide – a comprehensive guide to towing and setup that goes beyond the simple calculations above.
• Dodge Ram weight ratings – this is specific to my 2003 Dodge diesel truck but it shows what information is available for all trucks and where you would get the information needed to plug into the above calculations.