Increasing the size of your tires and wheels, particularly in terms of diameter, is a popular modification these days. It improves the look and handling of your vehicle, in most cases. Although, there are some important considerations you should keep in mind before you make the decision to do it.
For the purposes of this article, "wheel" refers to the round, metal parts that have spokes radiating from their middles. "Tire" refers to the rubber things that touch the ground.
Your speedometer is calibrated with the vehicle's stock tire diameter in mind. Essentially, when you replace your tires with another set that have a larger diameter, you're increasing the vehicle's gear ratio. If your speedometer is still calibrated for 22" tires, but you now have 25" tires, the speedometer will register a slower rate than your actual rate of travel. Your larger tires are putting more tread on the ground with every rotation, due to their longer circumference, but still turning at the same RPM. The difference between the speedometer's reading and your actual speed could be well into the double digits. Ask your mechanic to recalibrate your speedometer after you get larger tires.
Increasing the size of your tires and wheels usually increases the weight of the vehicle. More weight translates to a lower fuel efficiency, as you'd expect. In a test by Car and Driver, increasing the wheel size by 4 inches resulted in 10% fewer miles to the gallon.
There are some circumstances in which changes wouldn't produce a significant effect on efficiency. Perhaps you want smaller wheels but tires of the same diameter, for example. That may not affect your efficiency much. You'll have to find the weight of all the parts you want and compare it to the weight of your current parts to be sure, though.
The key determiner in the handling/ride tradeoff is the tire's sidewalls, which are on the side of the tire and are usually where the brand name is displayed. Drivers tend to agree that taller sidewalls offer a smoother, more comfortable ride. Shorter sidewalls improve performance, on the other hand.
Increasing the size of your wheels has a direct effect on the size of the tires you can fit in your wheel wells. That's because when you add wheel size, you usually have to decrease sidewall height (which is roughly the length from the wheel to the top of the tire). Therefore, "plus sizing" (getting larger wheels) usually decreases ride comfort but improves handling.
Also, know that you can't fit any tire onto any wheel. Tires are manufactured for every wheel size. Your mechanic or tire tech can make sure the tires you like are the correct width for the wheels you have and the correct diameter for you vehicle. Don't try any of that stretching stuff. It's not safe.
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