Whether you drive a classic muscle car, a vintage pick-up or a brand spanking new 4 X 4 off-road vehicle, you should think about upsizing your wheels. Upsizing your wheels improves vehicle appearance because larger wheels better fill the wheel well and can increase the handling and performance of your ride. Better look and better performance are why upsizing wheels is one of the most common aftermarket modifications.
Why Upsizing Improves Performance
As your wheels get larger, the standing size of the tire gets smaller (keep reading to learn why). It is the lower standing size of the tire that drives the improved performance. A lower standing size means your tire can get a better grip on the road. Also, the added width of the tire gives more surface area to grip. The surface area under the wheel is a very important piece of real estate when it comes to performance. In independent Car and Driver tests, wider wheels and tires showed improved grip, braking, and ride comfort. If you drive an off-road vehicle, you also get the benefit of less sway and more stability. The only real downside is that larger wheels may weigh more. Added unsprung weight decreases fuel efficiency. But that is a small price to pay when upsizing looks so good.
How to Calculate Tire and Wheel Size
Your ride was carefully engineered before the first bolt was tightened at the factory. The designers took into consideration the total outside diameter of the wheel and tire that would be installed. This was used to calculate the distance the wheel would travel in one revolution. That one bit of information feeds into the calibration of the speedometer and odometer, the transmission shift points, traction control, and torque. A lot of things happen with every revolution, so if you change the size of the wheel it is important to maintain the overall diameter of the wheel and tire combination.
Wheel sizes are expressed in diameter and width. A 17×9 wheel has a diameter of 17” and a width of 9”. When you upsize the wheel, you must decrease the standing height of the tire by the same amount to maintain the same overall diameter. In other words, for every inch you increase in width you must decrease standing height by one inch as well.
Other Factors to Consider
Every good thing should be enjoyed in moderation. Upsizing is no different. It is possible to upsize your wheels so much they no longer fit the wheel well or cause other problems.
Wheel Offset. Offset refers to the distance of the centerline of the wheel to the mounting surface. Offsets can be neutral, positive or negative. If you change where the wheel sits, you can stress the bearings. Always make sure the offset matches.
Brakes. Don’t crowd those calipers. This is especially true if you are upsizing the wheels on a truck that is used for heavy hauling. If you haven’t lifted the suspension, keep in mind the changes to the suspension when the bed has a heavy load.
Spacers. Most aftermarket wheels have a very large center bore to accommodate fitment on a wide variety of vehicles. Make sure to use hubcentric rings when installing your upsized wheels to reduce vibration and protect wheel bearings and ball joints.
Chuck Krause is Wheelfire Blog’s managing editor. Since the early 2000’s, he has managed and owned a number of internet retail stores in the automotive parts industry. He is an especially enthusiastic owner of his off-road “monsterized” Jeep Wrangler. A fixture in every summer’s Jeep jamboree, (where his reputation for extreme mudding and trail riding are legendary) Chuck is well known for his infectious passion and knowledge about all things automotive.