The towing capacity of a vehicle is an often misunderstood subject and as much as people don't want to believe it, it really is not just about horsepower.
Most vehicles have enough power to tow a trailer. A small car or even a motorcycle has the capability to pull a trailer. It’s not always recommended, but it can be done. An average sedan can tow about 1,000 lbs while larger cars and minivans can tow around 3,500 lbs. Go up a step and light trucks and SUVs can tow close to 5,000 lbs with the heavy duty trucks being able to tow much more.
The difference isn’t just the horsepower or the torque of the engine. There are many factors that determine towing capacity. Some of those are:
- Overhead camshafts versus overhead valves
- Engine configuration
- Axle ratio
- Rear wheel drive versus front wheel drive
- Frame design
- Hitch-to-car mounting
- Wheel load ratings
- Tire load ratings
- Suspension load ratings
- Transmission and oil cooling equipment
- Brake size
- Electrical systems
Towing capacity is built into the vehicle during manufacturing based on what the company thinks the vehicle will be used for, by whom and where these people live. The towing capacity is based on a vehicle’s ability to tow a specific load up a steep incline as any driver might come across when driving in mountainous terrain with steep hills.
This really means that it isn’t horsepower as the main requirement but low RPM torque. Major highways in the US normally have only a seven percent grade at the most. The easier a vehicle can make it up this grade will determine the towing capacity of that particular vehicle.
Generally, automatic transmissions with torque converters are more capable of towing a heavy load than the same vehicle with a standard transmission.
There are several ways to change RPM torque for hauling. Some of these are:
- Increasing tire size will reduce torque and the reverse is true as well
- Installing a 4.10:1 axle ratio instead of the 3.7:1 will increase torque by about 10 percent to the wheels.
Instead of changing axle gear ratios or tire sized, most drivers change the gear they are driving in. It’s usually better to drive in a lower gear for towing. Both manual and automatic transmissions are built with overdrive gear ratios. An overdrive gear does reduce engine rpm, make the vehicle more fuel efficient, with less wear and a quieter ride, however it also lowers torque to the wheels.
If you are driving a five- or six-speed, either automatic or manual, then driving in fourth gear is often recommended for towing heavy trailers. If you are driving a four-speed automatic then it’s better to drive in third gear. The lower gear decreases the load on the engine while increasing the torque to the wheels. When the engine isn’t overworked, the driver doesn’t need as much throttle and therefore it will still use less fuel than by driving the other way.
Once the various elements have been worked out for a new vehicle, the engineers can then determine the towing capacity. With this information they then, match wheel bearings, braking capability, axle strength, and even the frame design to the towing capacity to create the best combination to suit the consumer’s towing needs.
Acronyms for Towing Capacity
Like any industry, it helps to understand the language commonly used to explain the science. There are a few acronyms for towing that need to be understood.
GVWR – the stands for Gross Vehicle Weight Rating. The GVWR of a vehicle is the maximum allowable weight of a vehicle including the vehicle, driver, passengers, cargo and the fuel the vehicle carries.
GVW – Gross Vehicle Weight. This is the total weight of the driver, passengers, cargo, car components and any accessories.
GTWR – Gross Trailer Weight Rating. This the maximum weight recommended for the trailer and its contents.
GTW – Gross Trailer Weight. This is the total weight of the trailer including all cargo.
GCWR – Gross Combined Vehicle Weight Rating. This is the maximum recommended gross weight of the trailer and the vehicle plus the driver, passengers, cargo and contents of both vehicles.
GCW– Gross Combination Weight (also called GCVW). This is the total weight of the vehicle and trailer plus driver, passenger, cargo, and contents of both vehicles.
GAWR – Gross Axle Weight Rating. This is the maximum allowable weight for a single axle to safely tow.