What happens to a truck if it tows more than its capacity?

If you tow often, you'll want to take steps to protect your transmission.
Ivan Cholakov/iStockPhoto

Temptation is all a­round us. That doughnut looks pretty good, doesn't it? You know you want it, even though you know you shouldn't. Go ahead and eat it anyway -- and say hello to heart disease, obesity and diabetes! Sure, you could skip out of work after lunch to bet on the ponies at the track. No one will even notice you're gone, but how do you explain to your boss where you were after you win a few bucks (not enough to justify quitting your job, unfortunately) and the local paper runs a feature on you and your windfall?

Temptation also exists with towing. You know how much your vehicle's towing capacity is; it's in your owner's manual. Unfortunately, you didn't consider your towing capacity when you bought that new boat. Now, with your boat loaded on a trailer and your truck's ball hitch just inches away from being coupled, you're having a hard time resisting the temptation to take it to the lake.


­Don't do it! There could be a world of trouble awaiting you. Let's say you're driving at a reasonable speed when a pedestrian steps off the curb in front of your truck. Because of your overweight load, you're going to have a really hard time stopping. The velocity created by the momentum of your rear-heavy trailer and boat could overcome the stopping power of your brakes, sending you sailing right into the hapless pedestrian. It could also overcome your trailer hitch coupling and send the boat careening into your back seat as well.

Even if you do make it to the lake, you'll find trouble at the boat launch. As you back down the incline, the weight of the trailer and boat could pull your truck into the water or cause the front of your truck to leave the ground -- not a good beginning for a day at the lake.

There are also a plethora of mechanical problems with towing a load that exceeds your vehicle's listed capacity. Whether you're towing a boat or a load of bricks, you're going to wear out your vehicle quickly if you exceed its towing capacity. Find out how on the next page.


Preventing Problems from Exceeding Towing Capacity

Doughnuts and exceeding towing capacity have something in common: They're both very tempting.
Dean Turner/iStockPhoto

In addition to difficulty in stopping and being dragged into the lake, exceeding your vehicle's towing capacity could also lead to swaying. This occurs when the towed load begins to move side to side, independently of the direction in which it's being towed by the coach vehicle. It's a dangerous situation, and one that can occu­r even when you're towing within your vehicle's capacity.

Even if you have a history of good luck and manage to make it from point A to point B without any catastrophes, when you exceed your towing capacity, your hubris will eventually catch up with you in the form of mechanical problems.


You place your truck's transmission in jeopardy when you exceed your vehicle's towing limit. Transmissions are designed to work hard enough to move the vehicle they power, as well as any additional weight up to the limits specified by the manufacturer. Exceeding the recommended towing capacity causes the transmission to work harder than it's meant to, which creates more heat energy. This heat breaks down the transmission fluid that lubricates the transmission's moving parts. Without proper lubrication, the transmission can seize up and cause major damage.

So how can you protect yourself from physical and mechanical problems from exceeding towing capacity?

While it might seem appropriate, upgrading to a trailer hitch won't increase your vehicle's towing capacity -- it will upgrade your trailer hitch's towing capacity. However, you can purchase a weight-distributing hitch, which will vastly increase your vehicle's ability to tow due to the weight being distributed among the coach vehicle's wheels. Vehicles have a weight distributed tow rating -- the towing weight rating -- and it shouldn't be exceeded either. You'll encounter the same problems.

One way to prevent damage to your vehicle is to install a transmission oil cooler. You can install this aftermarket product in front of your radiator to give your factory-installed cooler some extra help. In most models, transmission fluid is passed through the extra cooler before traveling along to the transmission. This extra step greatly decreases the fluid temperature and protects the transmission during towing.

The easiest method for avoiding problems is, of course, not to exceed your towing capacity. You can determine the weight of your loaded trailer (its gross trailer weight), by weighing your trailer on a scale. You should probably avoid using your bathroom scale, as it would surely be crushed under the weight. Instead, a quick Internet search will yield all sorts of public and private scale locations that will give you a precise measure of how much your trailer weighs. As long as you don't exceed your vehicle's towing capacity, you should be able to tow to your heart's content.

For more information on towing and other related topics, visit the next page.


Lots More Information

Related HowStuffWorks Articles

More Great Links

  • "Determining registered gross weights for trucks towing recreational and light duty trailers." Ontario Ministry of Transportation. July 27, 2007. http://www.mto.gov.on.ca/english/trucks/regulations/trailers.htm
  • "Frequently asked questions." Fluid Drive. Accessed November 5, 2008. http://www.fluidrive.com.au/index.php?ID=YOUR_TRANSMISSION
  • "Safety towing tips and terminology." Davis Trailer World. Accessed November 5, 2008. http://www.davistrailerworld.com/store.asp?pid=15226
  • "What an oil cooler does." Perma Cool. Accessed November 5, 2008. http://www.perma-cool.com/Catalog/Cat_page02.html