Even if you have passed the driving exam successfully, chances are that you might not know much about the difference between curb and gross weight. You might not even know what these terms mean. However, if you wish to be a safe driver, it’s more than crucial for you to understand what these terms stand for. Let’s start by briefly explaining how driver categories work, and what weight has to do with them.
The main reason why there are different driving license categories is that the weight of the vehicle can vary. Most drivers have a B category license, which means they are allowed to drive a car, but not heavier vehicles, such as buses or trucks. In order to drive a heavyweight vehicle, you need a C category license. Furthermore, if you wish to apply for C category, you need to have a B category license beforehand.
So, weight is a crucial factor when it comes to regulating driver’s licenses and vehicle categories. But there are also some less obvious differences between vehicles within the categories themselves. One of those is the difference between curb weight and gross weight. To make matters even more complicated, a vehicle can have both of these weights at the same time.
Now that I’ve got you confused enough, let’s start unwinding this discussion bit by bit. Hopefully, by the time you finish reading this article, things will be more than clear.
What Is Curb Weight of a Vehicle?
Visualize a car that you’re very familiar with — your family car, for example. Now, think about how heavy that car is (take a wild guess if you’re not sure). Here’s a hint for you: the average weight of a car today is around 4,000 pounds. But have you ever wondered what goes into this number?
When you’ve visualized your family car, you probably imagined it without passengers. But did you think of regular vehicle equipment? Even though we don’t consider equipment such as motor oil, coolant, or fuel an essential part of a vehicle, it still adds to the car’s weight, even more than you might think.
So, take a car’s weight along with all the mentioned equipment plus transmission oil and air conditioning refrigerant. What you get is the curb weight of that car. Basically, curb weight describes the estimated weight of a vehicle in operational status with all standard equipment.
However, a car can’t operate without a driver. Therefore, there needs to be a measure that takes passengers into account. You guessed it — this measure is called gross weight.
What Is Gross Weight of a Vehicle?
The easiest way to describe gross weight is to visualize your family car again, but this time with the whole family in it. On average, a car with full passenger capacity can weigh anywhere between 650 lbs and 950 lbs — sometimes even more. This extra weight makes a huge difference for a vehicle in motion.
When you calculate gross weight, you also need to include cargo in the equation. So, imagine the whole family is preparing to go on a week-long road trip together. Once you calculate the sum of all these weights, you get the gross weight of the vehicle.
The gross vehicle weight (GVW) is a variable number, but there is one constant that you should know of. It describes the maximum weight capacity of the vehicle. Gross vehicle weight rating (GVWR) tells you the maximum prescribed weight a particular vehicle can carry.
Americans use GVWR to determine which roads are safe for a vehicle to use. GVWR can also regulate insurance, emissions, and fuel economy standards.
Why Should You Know the Difference?
The most important reason for you to know the difference between curb weight, GVW, and GVWR is, of course, safety. The manufacturers test every vehicle with different loads until they establish the maximum capacity for the brakes to remain fully functional.
It wouldn’t be possible to effectively stop an overloaded vehicle since the suspension can break from all the extra pressure on the tires. That is the reason why GVW should never surpass the prescribed GVWR.
As for curb weight, it’s essential to keep in mind that the vehicle’s weight changes the moment the passengers get into it. This makes the GVW a more accurate estimate of a moving vehicle than curb weight.
There are thousands of truck drivers worldwide who are used to transporting cargo that might even weigh tons. If you are among them, remember how important it is, for both your safety and the safety of others on the road, that you abide by these regulations.
Adding a Trailer to Your Vehicle
There are also special regulations and terms regarding trailers that are attached to vehicles. They are most commonly attached to trucks, but you can also connect them to a car or bus (even a tractor).
The vehicle always carries a part of the trailer’s weight, and this extra weight depends on how big the trailer is. Thus, it would be quite absurd to attach a trailer that weighs as much as the vehicle itself.
Additionally, there is only a certain amount of weight which an attached trailer can carry. This weight is basically cargo weight, but since the vehicle pulls it, the term used to describe it is tongue weight.
It’s relatively easy to calculate the maximum tongue weight capacity once you have information of GVWR. By subtracting the GVW from GVWR, you get a number that tells you how heavy your cargo can be. If you wish to measure the trailer alone, you can do so by obtaining the gross trailer weight (GTW).
You can also determine the extra weight the trailer adds to a loaded vehicle. The GVW changes depending on how much weight the vehicle takes over from the trailer. So, you need to calculate the difference in GVW with and without the trailer. This number should be similar to, but not the same as GTW. Remember that tongue weight also goes into the GVW.
How to Redistribute Cargo Weight
In case the current estimate states that the vehicle is over its GVWR and you need to transport heavy cargo, there are ways to solve this problem. The vehicle mostly carries the part of the load closest to the hitch. If you try re-distributing the cargo around, you can get some weight off the vehicle back to the trailer.
However, there is no magical way to carry too much cargo without causing a safety risk. If you situate all of the load at the end of the trailer, the vehicle will be less stable. Try to picture taking sharp turns with an unstable trailer. You don’t need to know much physics to realize that accidents in such conditions are very likely to happen.
If I still haven’t assured you, you can watch the videos on Youtube to see what the consequences of bad cargo distribution can be.
Additional Info for Truck Drivers
Things only get more complicated when trucks get involved since there are several different types of truck trailers and cargo regulations. It’s of the utmost importance for trucks to abide by the GVWR, which provides a safe basis for a loaded moving vehicle.
It’s advised not to overload the trailer because the truck shouldn’t bear more than 20% of the GTW. This percentage can be bigger if the GVW with the trailer isn’t that close to the GVWR. But keep in mind that the heavier the trailer, the bigger the risk.
There are also different types of hitches that one must use to attach a trailer to a truck. Hitch class depends on what the GVWR standards for the particular vehicle are. There are five classes of hitches based on max GTW:
- Class I – 2,000 lbs maximum tongue weight
- Class II – 3,500 lbs maximum tongue weight
- Class III – 5,000 lbs maximum tongue weight
- Class IV – 10,000 lbs maximum tongue weight
- Class V – 10,000+ lbs maximum tongue weight
It sounds like common knowledge that you need a stronger hitch for a greater GTW, but why not simply use a Class V hitch for all trailers? Well, for one, you don’t need it. The hitches alone are heavier when designed to pull more weight, so you don’t want that extra weight on a smaller truck.
Class IV and V hitches are made to pull massive weight, but not all of them are designed to distribute weight well. For such reasons, weight distributing hitches were invented. Today, most of the 10k+ trucks have weight distributing hitches, which enable the pulling force to distribute further around a truck’s frame.
Other Weights You Should Know About
Aside from the previously mentioned weights, there are some other terms you should know about to get the full picture:
- Manufacturer’s curb weight — the weight of the car listed in the official specifications of automakers
- Maximum load — GVWR minus the curb weight
- Maximum authorized mass (MAM) — the same as GVW, but in the U.K.
- Dry weight (also called unladen weight) — the vehicle with an empty tank, no oil or fluids
- Shipping weight — a standardized weight automakers publish officially for the purpose of vehicle transport
- Down-planting — a vehicle that is adjusted so that it can’t use its full weight capacity
The difference between curb weight and gross weight is just the tip of the iceberg when it comes to categorizing vehicles by weight. In this article, I tried to cover as many weight categories as possible and introduce some terms that drivers are not that familiar with.
All drivers need to understand why there are so many vehicle categories based on weight. When it comes to speed and weight, the laws of physics are reasonably simple. The heavier the vehicle, the faster it accelerates, and consequently, it becomes harder to stop. Brakes can only do as much, but if the vehicle’s weight is too much for them to handle, they will undoubtedly fail.
All of these regulations and standards are here to ensure safety on the road. However, accidents can happen (and they often do) even when we abide by the rules. What every driver should do is try to avoid unnecessary risks, and the chances of an accident happening would be far smaller.
Inexperienced drivers need to think about the vehicle’s weight, because more weight always equals less control. There’s no need for a newbie C category driver to tackle a 10k+ tuck before gaining experience on smaller trucks. Moreover, there’s no need to load the truck to its fullest capacity.
Safety should be your number one concern on the road. So, if you’re just a couple of pounds under the proscribed GVWR, that’s a good enough reason to think about getting rid of some weight before setting off.