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Getting Ready to Tow? Here’s What You Need to Know

Towing – We Americans love to do it. Boat, RV, off-road toy haulers…basically any industry that’ll sell you something to go behind your vehicle is experiencing record sales, to say nothing of sales of trucks themselves.

Before you hitch up to a trailer, you need to know one thing: Numbers are king.

Now I’m not talking about horsepower or torque. I’m talking about GVWR, GAWR, GCWR, payload, tongue weight, TWR, etc. If this alphabet soup is familiar to you, this will be a refresher course. If not, then strap in.

First and foremost, it’s critically important to stay within the limits of your vehicle’s weight ratings. Ignoring these is not only dangerous, it’s also illegal and you could even be denied an insurance claim if you are found at fault in an accident. IOW, these ratings matter. How do you find these numbers? They’re usually found on a special sticker on the driver's door jamb as well as on your manufacturer’s website or owner's manual.

My land cruiser door jamb sticker with GVWR listed.

  • Curb weight – Your vehicle’s empty weight.
  • GVWR – Gross vehicle weight rating – The max weight your vehicle is rated to. Remember that this number includes everything you add to an empty vehicle, including tongue weight. Never exceed the GVWR.
  • Payload – The maximum additional weight over your vehicle is rated to carry, typically the GVWR minus the curb weight, but not always. Never exceed this number.
  • GCWR – Gross combined weight rating – The maximum your vehicle and trailer combination can weigh in total including all passengers and cargo. This number doesn’t take into account your tongue weight. This number accounts for the weight of 1 150 lb driver.
  • TWR – Trailer weight rating – The amount your vehicle is rated to tow. If your vehicle was made in the last 5 years or so this number is validated through a method (SAE -J2807) that confirms that your vehicle can actually do what it says on the tin including braking, cooling and accelerate up a grade in the heat. NOTE: the numbers listed on the hitch are for the hitch capacity and do not reflect the actual TWR of the vehicle. Never exceed the vehicle TWR or the hitch rating capacity listed, whichever is lower. If purchasing a receiver hitch aftermarket, make sure it’s rated at or higher than your TWR.

Let’s use my 2008 Lexus GX470 as an example, which has the following numbers:

  • Curb weight – 4871
  • GVWR – 6200 lbs
  • GCWR – 12,850 lbs
  • TWR – 6500 lbs
  • Payload – 1200 lbs.

GX470 towing my portly boat. What more comical the size difference or the trailer wheels?

This 6000 lb boat (with trailer) is well within the TWR. No problems there. Boat weight (6000) + curb weight (4871) = 10,871. GCWR (12,850) – 10,425 = 1979 lbs. Plenty of safety margin in the GCWR.

Weigh safe trailer hitch

Now factor in the weight the boat is adding to the back of the truck. This weight is called tongue weight and it’s probably the single most important factor for tow safety. Too little tongue weight causes a dangerous exponential oscillation, commonly known as trailer sway. It’s the point at which the tail starts wagging the dog, so to speak, and where most accidents happen.

I’ll say this again, getting tongue weight right is critical for tow safety!

There are devices that can take the guesswork out of taking this measurement and are well worth checking out.

The ideal tongue weight is 10-15% for a standard hitch and no less than 15% for a 5th wheel or gooseneck hitch. Toyota recommends 9-11% for standard hitches or 15% for weight distributing.

Let’s assume a tongue weight of 10%, or 10% of the TWR, as boats typically have most of their weight in the rear. That’s 600 lbs pressing onto the rear of the vehicle as if you’ve added 600 lbs of cargo in the bed, given that tongue weight counts against payload. Payload (1200) – tongue weight (600) = 600 lbs of remaining payload. Remember, unlike GCWR, the payload rating doesn’t include you, the driver. All the math checks out so long as I keep any additional weight (passengers and cargo) under 600 lbs.

Let’s add a driver, 3 passengers, and 150 lbs of gear. 600 – driver (150) – passengers (450) – gear (100) = -100. No go. Even though I’m within the tow rating and the GCWR, I would be overloaded on payload. In this case I didn’t have any cargo with me and only light passengers (kids).

With regards to payload it’s also important to note that even if you have load-leveling suspension as my GX470 has in the back, it doesn’t mean you’ve added capacity. You’ve just leveled the load.

While it is critical to have enough tongue weight, too much can also cause problems. Let’s say instead of a boat you had a cargo trailer that weighs 6000 lbs but had 20% tongue weight. Even though the trailer would be dynamically safe, the tongue weight alone would put you over your payload rating before you even got in.

NOTE: trailers above a certain weight need to have their own brakes. Most manufacturers have a number at which point you should have trailer brakes and most states have laws requiring trailer brakes above certain weights. Check with your state and manufacturer on this before heading out, but in most cases you can assume anything over 2000 lbs should have trailer brakes. Some trailers have built-in brakes that don’t require a vehicle connection and rely on hydraulic pressure on the trailer coupling, called “surge” brakes. Other trailers have electric brakes that connect to your tow vehicle and require a brake controller, either built-in from the factory or bought separately.

I mentioned earlier that newer trucks comply with a rigorous standard for rating the TWR, but on older vehicles the best you can do is to take the manufacturer's word for it. In most cases it’s not the weight ratings that will be the issue, but braking performance and engine and transmission cooling as these factors weren’t given standardized rigor.

In this case it might be wise to consider upgrades to these components if you plan on getting close to your towing limits. Brake upgrades, transmission coolers, and auxiliary radiator fans are all popular upgrades for towing vehicles and can increase the life of your tow vehicle, even a brand new one. Heat kills transmissions, and even a difference of 30 degrees Fahrenheit can decrease the life of your transmission fluid by half. Electronics that monitor vehicle data like transmission temperature can be purchased if your vehicle doesn’t have one built-in.

In some cases, performance modifications might be beneficial as well but always keep in mind heat when looking at power upgrades.

When you are on the road there are a few safety tips to consider. Check the speed rating of your trailer tires. It may be lower than your freeway limit. Check tire pressures on your vehicle and trailer. Many manufacturers have a loaded tire pressure and an unloaded one. Always secure your cargo. It’s dangerous and illegal to have unsecured cargo. Make sure to attach safety chains and check that the emergency breakaway cable is securely attached to your vehicle if your trailer is equipped with electric brakes. Find a hitch that will allow your trailer to be level when hooked up. There are many good adjustable models available.

If you are driving and you experience trailer sway, hold the steering wheel firm and straight. Let off the accelerator, but don’t hit the brakes. Allow the vehicle to slow naturally. If you have a trailer brake controller, use it to manually actuate the trailer brakes. When the trailer sway has stopped, look for a safe place to pull over and check the trailer balance again, add more weight to the tongue if you suspect you might be light. Some trailers like popup camp trailers with single axles can be delicately balanced and only allow so much tongue weight before you exceed the trailer's rating. In this case, consider an alternative method of sway control like a friction sway bar. I have this one on my popup trailer and it’s very effective.

There is a lot to proper towing, but hopefully now you can consider yourself sufficiently armed to take on your next towing challenge safely and securely.