The decision to put bigger tires on your vehicle can be a complicated one. For many, it’s about being able to go off-roading. For some, it’s all about speed and performance. And for others, it’s just about aesthetics. But since most of us also use our vehicles for commuting and getting around town, there are other factors to consider. After all, adding bigger tires can affect a vehicle in many ways. One aspect that most people can’t ignore is what a bigger tire might do for their vehicle’s gas mileage.
Putting bigger tires on your vehicle can affect its MPG to some extent. In general, using bigger tires will decrease your vehicle’s fuel economy because they are heavier and require more engine power to rotate. The overall impact on gas mileage depends on diameter, width, tread, and other factors.
This article will go over everything you need to know about how installing bigger tires can affect a vehicle’s MPG.
How Do Bigger Tires Affect MPG?
In most cases, installing bigger tires will bring a vehicle’s MPG down. This is mainly due to their increased weight, larger surface area (which creates more resistance), and the extra engine power required to rotate them, but other factors also play a role.
Rolling Resistance
One key factor in how tires affect a vehicle’s MPG is rolling resistance. Rolling resistance is essentially the force exerted against your tire as it rolls along the ground. It’s a complex subject that involves a lot of math and physics to fully understand, so I won’t go into great detail about it here.
For our purposes, it’s sufficient to understand that a) tire diameter, tread, vehicle weight (among other factors) contribute to rolling resistance, and b) the greater the rolling resistance a vehicle encounters, the more fuel it will require to keep it in motion.
Weight
In general, a bigger tire usually means a heavier tire. Every bit of extra weight in each tire will contribute to the overall weight of the vehicle, and a heavier vehicle will require more fuel to be propelled forward.
In some cases, this can be offset by switching to an after-market wheel made from a lighter material (most standard wheels are steel) – but this isn’t always possible with some vehicles and may open up a whole new can of worms in terms of the vehicle’s overall weight distribution.
Contact Patch
A tire’s contact patch is the part of the tire that’s in contact with the ground – where the rubber meets the road, as it were. The size and shape of the contact patch affect traction, performance, and handling, but can also have an impact on fuel economy. Generally speaking, a larger contact patch will mean more rolling resistance, which means fewer MPG.
This is especially true of a wider contact patch. Wider tires will improve traction (one key reason people like to install them), but that added traction will, by nature, make the tires harder to spin (and keep spinning), ultimately requiring more fuel.
Tread
Tire tread also plays a part in fuel economy. In general, the more aggressive and chunky the tread is, the more rolling resistance it will have, and the worse it will be for the vehicle’s MPG. There are plenty of bigger tires with standard tread, but again, many people want bigger tires for improved traction when off-roading and navigating rough terrain – unfortunately, it does come at a price.
Torque
Most vehicles leave the factory with tires sized for peak fuel efficiency, meaning they are designed to work in perfect unison with the motor, transmission, and axles. Changing the tire diameter will create a discrepancy in the system, in effect changing the force output of the engine.
As the engine revs, it exerts torque or twisting force on the axles and, in turn, the tires. While a larger tire won’t affect the amount of torque being exerted on the wheel, it will lower the amount of effective force that the wheel exerts on the road beneath it. This is simply because the torque is being applied across a larger diameter. The result will be that the engine has to work harder to rotate the larger tire, consuming more fuel.
Here’s a fairly entertaining video that explains this concept well:
It’s worth noting that this is less of an issue when a vehicle is constantly moving at high speeds, like on the highway. This is because the larger circumference of a big tire will allow the vehicle to cover more distance with fewer engine RPM (revolutions per minute). Where bigger tires really eat up fuel is in the city, where you’re moving at lower speeds (less coasting) and frequently get moving from a static position.
Some vehicles, such as certain newer sports/muscle cars and many diesel vehicles, have different gear configurations and torque systems designed to improve acceleration performance, so this isn’t as much of an issue with these models.
Aerodynamics
Bigger tires can also greatly affect a vehicle’s aerodynamics, which can dramatically decrease gas mileage. A bigger tire means a larger surface area, which will encounter greater wind resistance. Even a wider tire that protrudes slightly out of the wheel well will catch more wind than a tire that’s flush with the vehicle body. In some cases, installing bigger tires also means modifying the undercarriage or lifting the vehicle, which can also make the vehicle less aerodynamic and cause drag.
Each of the above factors may seem fairly inconsequential on its own, but they all add up to have a significant impact on a vehicle’s fuel economy.
How Much Gas Mileage Can You Expect To Lose With Bigger Tires?
It’s hard to say exactly how many MPG you’ll lose with bigger tires – it depends on your vehicle, the width and tread of the tires, how many sizes up you go, and whether you add a lift kit. Depending on these factors, the loss in fuel efficiency could be anywhere from 2-25% of your current MPG.
If you’re simply going up a size or two in diameter, you may only see a difference of 1-2 MPG, at most. If you’re going up several sizes in both width and diameter, with aggressively treaded tires and several inches of lift, your gas mileage will likely take a big hit, even as much as 5-6 MPG. In either case, the difference will be more significant when driving in the city than it will be on the highway.
Conclusion
In most cases, installing bigger tires will lower your vehicle’s fuel economy to some extent, especially in the city or at lower speeds. But every vehicle is different, and there are compromises you can make to lessen the impact on your gas mileage. In the end, it’s best to determine what the vehicle will be used for most and consult with your dealer or tire specialist to find what will work best. Thanks for reading!