Do Bigger Tires Affect MPG? [Fully Tested!]
When you put bigger tires on your car or truck, you’ll end up using more gas. This happens because bigger tires weigh more. More weight on your wheels means more work for your engine when moving your vehicle. Like carrying a heavy backpack, it takes more effort. Wider treads and larger diameters also increase friction between your tires and the road. Due to this reason, the engine has work harder to push and turn those tires, burning more fuel. So if you want better fuel economy, stick with the manufacturer’s recommended tire size. But if you don’t mind filling up more often, upgrading to larger tires can be worth it for the looks and performance
Do you love the way bigger tires look on trucks and SUVs? Many folks install them because they improve traction off-road or just make their ride look cooler. But what about gas mileage? Let’s dig into how tire size affects MPG.
Some Importance Dimensions Of a Tire
Before proceeding further, you need to familiarize yourself with the following important dimensions of a tire:
- Tire width
- Section Height
- Diameter
In the image above, I have labeled the important tire dimensions that contribute to its size, and have an effect on your vehicle’s performance and fuel economy. Section height is also called a ‘Sidewall‘.
Whenever you buy the tire, it is marked as 250/60/16. In that example, 250 is the tire width, 60 is the aspect ratio and 16 is the tire diameter to fit the rim. Aspect ratio of a tire is calculated by dividing section height by tire width.
If tire width is increased, the section height of a tire should also increase to maintain the same aspect ratio.
You can use this tool to play with the different dimensions of the tire and their effect on the tire revolutions.
The combination of all those dimensions will affect the mass of a tire. If the tire diameter is larger and sidewall height is lesser, the rim (wheel), which is made of metal, will have a larger size. So, the overall weight of a combination of tire and wheel will also change.
Off Reading Of Speedometer and Odometer
Before proceeding further on how tire size affects MPG, you also need to consider that after changing the tire size, the speedometer shows the reading a bit off.
This is because the speedometer of your vehicle is calibrated based on the factory tire size. When you change the tire, the speedometer also needs to be calibrated.
The smaller tire will rotate faster than the larger tire. So, a larger tire will cover fewer revolutions. This is just like a gear train in the transmission system in which the upshifting engages the smaller gears due to which your vehicle can travel at higher speeds.
Now, the speedometer calculates the miles by counting the number of revolutions of a tire instead of measuring the distance covered.
But bigger tires have a larger circumference, due to which they naturally cover more distance per revolution. This is the same as a person taking larger steps and covering a larger distance.
The MPG readings of the odometer after using a larger tire (assuming that the width is the same as the stock tire) are a bit off because the odometer is using revolutions of the new larger tire and the size of the small stock tire to calculate the distance covered. As a result, this would give lesser MPG.
Your speedometer will show you are going slower than you actually are and your odometer won’t track your mileage accurately.
That’s why the odometer needs to be recalibrated after installing a tire of a different size so that it could use the diameter of a new tire to calculate the distance covered.
I found this forum on tire diameter and mpg calculation quite helpful. You should surely check that out. This blog is also good.
How Do Bigger Tires Affect MPG?
Having bigger tires or wheels will increase your fuel consumption because of the extra weight and added energy needed to move the vehicle.
Larger tires have a greater contact patch which increases the contact area between your tire and the road. Due to an increase in the contact area, the engine needs more power to move the vehicle and hence more fuel is consumed.
So, here are the following factors, due to which the bigger tires affect the MPG:
1. High Inertia or Weight
Inertia might seem a technical term for you. Being a mechanical engineer, let me simplify this concept. Inertia is simply a resistance offered by an object to move it from its resting position. Inertia increases with the weight of an object.
Since large tires have higher weight, they will have higher inertia. So, they will offer more resistance to the engine to accelerate the vehicle.
Now, keep in mind that the weight of the tire does not entirely depend on its size i.e. diameter and width. The material and sidewall height of the tire also comes into play.
Since a tire is like a thick-walled cylinder tube rotating on its own axis, the moment of inertia of a cylinder on its axis of rotation is:
I = 0.5m(r12+ r22)
In the above equation, the letter ‘m’ stands for mass, or how heavy something is. ‘r1’ is a shorter distance – from the middle of the tire to the inside edge. ‘r2’ is a longer distance – from the middle all the way to the outer edge.
A tire that weighs more has something called inertia. Inertia is resistance to movement. So a really heavy tire takes more engine power to get rolling down the street.
That heavier tire also pushes down hard on the road. More push means more friction trying to slow it down. Again, the engine has to overcome all that friction to keep it moving.
So when picking new tires, weight and size are important. Bigger, bulkier tires might look awesome, but they make it harder for your car to drive fast and use more gas.
2. Contact Patch and Rolling Resistance
Rolling resistance of a tire also affects fuel economy. A wide tire has higher rolling resistance because the contact patch between the tire and the surface on which it is rolling is also greater.
Here is what a user says:
“I put slightly wider wheels and tires on my car and noticed about a 2 mpg drop in highway driving.”
Tires with larger width increase the contact patch between the tire and the ground. The larger the contact area, the more energy is dissipated when the tire rolls.
In addition, the larger the tire, the greater the stress on the tire itself. The tire’s durability decreases as it is subjected to increased stress, which also affects the MPG.
To understand the impact of the contact area of the tire on the rolling resistance, you must have a strong knowledge of Physics. I will try my best to keep it simple.
So, as I discussed above the resistance between tire and surface is directly proportional to the ground reaction.
Rolling Resistance = Friction Coefficient x Ground Reaction
The friction coefficient depends on the rubber mechanical characteristics of the tire and its treads pattern while the ground reaction depends on the tire weight.
For example, an aggressive off-road tire will get worse mpg than a street tire.
Since the tire is a deformable object, increasing the tire load also leads to more deformation and therefore, to increased rolling resistance.
If the contact patch between the tire and road is bigger and wider, it makes it difficult to roll the tire forward as it causes more deformation. So, higher power will be required from the engine, which will increase the fuel consumption and decrease the MPG.
3. Larger Torque
The engine in a car gives a turning force that spins the tires around. This turning force is called torque. Bigger tires are like having a bigger gear connected to the wheel.
The car designers very carefully pick the gear ratios to help the car get good gas mileage.
When you step on the gas pedal, the engine gives the same amount of turning force to the wheel, no matter if the tires are big or small.
But bigger tires make that turning force spread out more before it pushes on the road. So less force from the engine actually pushes the car along.
So, with big tires, the engine has to work a lot harder to make enough force to push the car down the road. All that extra work uses more gas.
4. Aerodynamics or Air Drag
Think of driving like moving through water. The larger the object, the more water it has to push out of the way. Air acts similar to water. According to engineering rules, air drag depends on two things – how fast the object is moving and how big its surface area is.
Your car’s rotating tires push air along as you drive, causing friction that makes drag. How much drag happens is based on the tire size, its speed, and overall vehicle size.
Bigger tires mean more air resistance since there’s more surface for air to push against. So your engine works harder to force air past the tires, burning more fuel.
Raising the car’s height with bigger tires also increases air drag that the engine must beat with more power. And more power equals more fuel.
Wide Tires vs Narrow Tires Gas Mileage
If both narrow and wide tires have the same diameter, the same material, and the same tread pattern, the wide tire will cause less gas mileage as the wide tire produces more drag on the vehicle.
Moreover, wide tires do weigh more which puts more of a strain on the engine and transmission, thus decreasing gas mileage. Check out this forum thread for more details.
Despite affecting the gas mileage, wide tires are still preferred as they offer better handling and shock absorption due to the flexing of the sidewall.
How Much does Bigger Tire Affect MPG?
Increasing a tire size by two points i.e. from 35″ to 37″ can decrease gas mileage by 1-3mpg, depending on whether you are driving on the highway or in the city, and the surface on which you are driving.
The mileage can even decrease by 5 to 6 MPG if you’re going up several sizes in both width and diameter of the tire, with aggressive treads pattern and several inches of lift.
Some First Hand Experiences Shared By People In Different Communities
Our team conducted research across various online communities, forums, and subreddits to gather user comments and opinions on “effect of bigger tires on mileage”.
User 1:
Swapped my Toyota Tacoma’s tires to a larger set last year. I did see a noticeable drop in MPG, probably around 2-3 miles per gallon. I think it’s because the larger tires add weight and rolling resistance, which makes the engine work harder. It’s a trade-off for better off-road performance, but definitely something to consider if fuel economy is a big concern for you.
User 2:
I recently upsized the tires on my 2016 Honda CR-V, going from the standard 17-inch to 19-inch. Honestly, I haven’t noticed a significant change in my gas mileage. It’s pretty much stayed consistent, maybe a slight drop but nothing alarming. It seems like as long as you don’t go too extreme with the size, the effect on fuel efficiency isn’t drastic.
User 3:
I’ve always been curious about this, so I experimented by fitting larger tires on my Ford F-150. To my surprise, the effect on gas mileage was minimal, maybe a drop of 1 MPG at most. I think as long as you keep them properly inflated and aligned, the impact isn’t as big as some people make it out to be.