Four Ways Wheel Selection Affects MPG

There are many factors that help or hinder your vehicles fuel efficiency. Many of the smaller things are overlooked. Wheel selection is one of the issues you almost never hear discussed when it comes to fuel efficiency. Here are 5 reasons that this should be a consideration for someone who wants to drive a vehicle that runs as efficiently as possible.

Rotational inertia

We’ve all heard it before. Objects at rest tend to stay at rest while objects in motion tend to stay in motion. This is true, and it’s truer the more mass something has. The more massive or heavy something is, the harder it is to move, and the harder it is to stop once it is moving. All of this is also true for wheels. Heavy wheels take more energy to get rolling. In our case, the energy is horsepower and torque. The horsepower and torque are generated by burning gasoline. If your wheels are heavy, you’re costing yourself more in fuel than you could be by switching to a lighter wheel.

An added drawback, not directly tied to MPG, of heavy wheels is that they are harder to stop. Once your wheels are moving, they want to keep moving due to momentum. The more mass that is rotating; the more difficult it is to slow down. This added load is put on your braking system. You can expect hotter brake pads and rotors, as well as shorter life spans on both components with heavier wheels.

Ferrari knows how to make a light wheel.

Ferrari knows how to make a light wheel.

Width matters

If your intention is to achieve the best gas mileage possible, you need to run narrow wheels. Aerodynamic drag consumes over 50% of your fuel at highway speeds. One way to reduce aerodynamic drag is to reduce your frontal area. One way to reduce your frontal area is to run narrower rims and tires. Basically, you should try to use the narrowest tires you can safely use that are rated for the speeds and conditions you plan on driving in. A narrow tire requires a narrow wheel. Some vehicles are capable of achieving an additional 5MPG or more simply by switching to a narrower wheel and tire combination.

light F1 wheels

Formula 1 wheels need to be wide for traction, but also need to be light.

Function over form

Aerodynamic drag is also affected by the sides of your wheels. Wheels that have a lot of open areas, spokes, or intricate designs built into them are not great for your aerodynamics. Air has to travel around the sides of your vehicle as you travel. The optimum aerodynamic design for your wheels is for them to be completely flat and fill up all of the area between the sidewalls of your tire. Ideally you want the air to have a straight and smooth trip along the outside of your vehicle. Any detours that you allow the air to take through your rims, or fancy wheel designs, is drag that you are creating and unnecessary fuel you are burning to overcome that drag. Many top speed cars used flat hubcaps from one side of the tire to the other to eliminate aero drag around the wheels. Most top speed cars just enclose the entire wheel now-a-days.

Super light and almost there.

Super light and almost there.

Dial down the diameter

Although larger wheels are very popular, they are less efficient. Part of the reason they are less efficient is that they are almost always heavier and therefore have more inertia. Another seldom thought of reason is that the bigger the diameter the wheel, the more torque it takes to turn it. Even if a large diameter wheel is the same weight as a smaller one, it’s harder to turn because the outside edge of the wheel is farther from the hub. This distance is called the torque arm. Think of it like this, you could hold a 5lb weight in your hand pretty easily, it would be harder to hold out at arms length, and really hard at the end of a 10 foot pole. The weight is still 5lbs in all cases, what changed was the length of the torque arm. It’s the same way with the distance between the center of the axle and the outside edge of the wheel.

What we’ve covered here basically boils down to the following: Try to pick the narrowest, flattest, lightest, smallest diameter wheel you can safely use. Of course all of these fuel saving attributes of a wheel are almost the exact opposite of what looks nice and is popular, but a tradeoff has to be made if you want to achieve better MPG numbers.

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