How Does Wheel Size Affect Tire Aspect Ratio?

Selecting new, high-performance wheels is a cost-effective way to give your vehicle a boost in the aesthetics and performance departments. Choosing the right wheels can be quite an experience, however, even before considering the nearly endless array of styles available. If you haven't purchased aftermarket wheels before, then you may be surprised by the sheer number of new terms that you are likely to come across. Are you familiar with bolt patterns? Offsets? Out of all the terms, aspect ratio often confuses the most first-time buyers. Although this technically refers to a property of your tires, it will have a significant impact on your wheel purchase as well.

Understanding Wheel Sizing

Before diving into aspect ratios, it's first essential to understand how wheel sizing works. When wheel sizes are given in inches, that number refers to the diameter of the wheel measured across the face from edge to edge. For example, if your car is equipped with 16" wheels, then each wheel measures 16" across its face. Every wheel on your vehicle must have a matching size.

In addition to sizes given as absolute numbers, many wheel retailers also list "plus" and "minus" sizes. These values refer to the difference in size between the aftermarket wheel and your factory equipment. If a wheel is plus-1, then that wheel is 1" larger in diameter than your factory wheels. Likewise, a minus-1 wheel would be 1" smaller than your factory wheels.

Tire Aspect Ratio

So, what is aspect ratio and what does it have to do with the size of your wheels? Just like the aspect ratio of a television set, the aspect ratio of your wheels is the ratio of their height to their width. This number is given as a percentage, although you will rarely see the percentage sign when browsing through tires. While it may sound complicated at first blush, the aspect ratio is simply telling you how much sidewall height your tires will have. The larger the aspect ratio, the greater the height of your tire sidewall.

Aspect ratio matters for your wheel purchase because sizing your wheels up will generally mean purchasing tires with a lower aspect ratio. This means that your tires will have less sidewall. This can improve your car's overall handling, but it can also result in a somewhat harsher ride. When browsing wheels, be sure to consider the size of the tire that will be mounted on your new wheels so that you can decide if the trade-offs are worth it to you.