Trucks are great because they have many uses. One of the purposes of a truck is towing things such as boats and trailers. You would think that having larger tires will help with the towing capacity, but it is more complicated than you would think.
Bigger tires do affect a vehicle’s towing capacity. Larger tires transmit less torque, which gives the truck less power, allowing less weight to be towed. The towing capacity is reduced by the same percentage of the increased tire diameter.
At the end of the day, you might actually want smaller tires if you want to tow a heavier load. We’ll discuss the pros and cons of larger tires below, as well as the effect that size has on towing capacity.
Having the proper tires for your truck is crucial for many reasons.
Tires help your truck move and are in contact with the road at various speeds. If they are not properly installed or strong enough for your truck, it can be very dangerous to drive on them. You could be putting yourself at risk for blowouts, suspension damage, or vehicle rolling.
Installing a set of larger tires can require maintenance to your truck, such as adjusting the speedometer and other things in the truck. If not properly taken care of, it could be dangerous to drive with this new setup.
Some people like to put bigger tires on their truck for appearances, but it all depends on what you use your truck for. Having larger tires can be great for off-roading and for aesthetics, but they may not be the best option if you are trying to tow heavy loads.
How to Read Tire Size
First, you need to find your tire size. This information will usually be available in your owner’s manual. You can also find a tire guide on the driver’s side door jamb, inside the glove box door, or on your gas tank hatch. This will tell you the typical tire size for your truck.
Of course if you know the tires are a different size than the typical size, you will have to look on the tire sidewall.
Tire sizes can be tricky to understand. They come in a code, with each letter and number combination meaning something.
The first number (275 in this example) will be the width of your tire. This number is measured in millimeters.
The next number (55 in this example) is the aspect ratio of your tire. The aspect ratio tells you how tall your tire’s profile is. They are measured in percentages, so in this example, the tire’s height is 55% of its width.
Next will be a letter. In this example, the letter is R. This is known as the construction or your tire’s stability. There are two types you will see in a tire. R, or Radial, is the most common for all tires in the United States. Radial construction basically means that the tire’s ply cords are in a radial direction. The other type of tire is D, meaning Diagonal or Bias Ply.
The last number will be the RIM diameter, which is measured in inches. The RIM diameter is the measurement of the rim that the tire can be mounted on. In the example, the tire would fit a rim with a 20-inch diameter.
Sometimes, your tire will show another number and a letter. The next number would be the Load Index, which tells how much weight (in pounds) the tire can support when fully inflated. The last letter is the speed rating. The speed rating corresponds with the speed capability. An “s” is rated up to 112 mph and “R” is up to 106 mph.
To find your truck’s towing capacity, you subtract your truck’s curb weight (which is how much the vehicle weighs when empty) from its Gross Combined Vehicle Wheel Rating (GCVWR). The GCVWR is the maximum weight of your loaded truck and the weight of the attached trailer.
Another term you will see is the Gross Vehicle Weight Rating (GVWR) which is the maximum amount of weight your truck can carry inside of it, including drivers, passengers, gas, and cargo. This measurement will be listed in your owner’s manual or on the driver’s side door.
The equation to find your truck’s towing capacity does not include the people that will be in the truck and any cargo. You will need to subtract these from the number to get a realistic number of how much you can tow.
Here is an example to see if you can carry the gear and people in a truck with a curb weight of 8,000 pounds and a GCVWER of 17,000 pounds.
- Three passengers (150 pounds each)
- Supplies weighing a total of 1,250 pounds
- Tow a 3,000-pound car
- With a 2,000-pound car trailer
Equation: GCVWR – curb weight – cargo – passengers
GCVWR (17,000 pounds) – curb weight (8,000 pounds) – cargo (1250) – passengers (3 people x 150 pounds) = 7,300 pounds towing capacity
Car + trailer = total towing weight
3,000 pounds + 2,000 pounds = 5,000 pounds total towed weight
Since the towing weight of 5,000 pounds is less than the 7,300-pound towing capacity, it is safe to tow everything in the truck while also towing the car.
Bigger Tires Effect on Towing Capacity
When you add larger tires to your truck, you are doing many things. First, your truck will be higher. You’ll have a better view of the road, as well as higher ground clearance. You will be able to go off-roading and not get stuck as easily. Another reason people get larger tires is for appearance reasons. But, if the goal is to tow with your truck, you may not want to get larger tires.
One thing that is important to know about trucks is how much torque they provide.
Torque is defined as “the force that helps vehicles start moving from a stop and pulls it up steel hills. Torque also provides power when you’re hauling items or towing something behind the vehicle” (SOURCE ).
When towing with your truck, it is important to have higher torque.
The tires that come with your truck are designed to operate well with it and help your truck perform at its best. The makers of the truck have figured out all of the necessary measurements and numbers to make sure your truck will be strong and steady. With the proper tires, the torque is perfectly proportional.
If you decide to put larger tires on your truck, it will make the overall performance of your truck weaker. A larger tire has a larger radius, which lowers the moving force (since the wheels are not turning as fast as the previous wheels) and causes a slower acceleration and less torque to pull weight.
To figure out how much you can tow based on the tire change, follow this equation:
Original tire size/ New tire size = Y
Original towing capacity x Y = New towing capacity
So, say you are driving a 2021 GMC Sierra 1500. The towing capacity is 11,800 pounds and you have 255/70R17 tires, which is a 70-inch tire, but you want 75-inch tires on your truck.
You would follow the equation to figure out how much you could tow with your new tires.
Original tire size (70) / New tire size (75) = 0.933
Original towing capacity (11,800) x X (0.933) = 11,009.4 pounds
So, with 75-inch tires, you would only be able to tow 11,009.4 pounds instead of the original towing capacity of 11,800 pounds.
These concepts might be kind of hard to visualize in a metaphorical sense. To provide some extra context and real-world examples, look at the vehicles below. Their important specifications are listed, as well as the preferred tire size and towing capacity.
2021 Honda Ridgeline
- Max Towing: 5,000 lbs
- Original Tire Size: P245/60R18 (60 inches)
- Desired Tire Size: 62 inches
- Original tire size (60) / New tire size (62) = 0.9677
- Original towing capacity (5,000) x X (0.9677) = 4,838.71 pounds
2021 Nissan Frontier (King Cab)
- Max Towing: 6,720 lbs
- Original Tire Size: P265/70R16 (70 inches)
- Desired Tire Size: 73 inches
- Original tire size (70) / New tire size (73) = 0.9589
- Original towing capacity (6,720) x X (0.9589) = 6,4433.81 pounds
2021 Ford Ranger XLT
- Max Towing: 7,500 lbs
- Original Tire Size: P255/65R17 (65 inches)
- Desired Tire Size: 75 inches
- Original tire size (65) / New tire size (75) = 0.8667
- Original towing capacity (7,500) x X (0.8667) = 6,500 pounds
While putting larger tires on your truck may look cool, it does take away from one of the functions of your truck.
Towing capacity is something to think about if you have a boat, an RV, or any other thing that you frequently tow. Before towing anything, it is important to make sure you know the towing capacity of your specific truck and that you do the math to make sure what you are towing is within that towing capacity.
If you don’t want to do the math yourself, you can always take your car to a mechanic or an auto shop to figure out what is the best option for you and your truck.
If you are not sure about your towing capacity, you can always research it or ask around. It is better to be safe than sorry before towing with your truck. If not properly installed, towing can be dangerous and can cause damage to your truck.