Tire Sizes: Big Vs. Small

January 27, 2012

Knowing tire sizes is as equally important as having tires on your vehicle. So what tire sizes are right for you? Tires can positively or negatively impact all driving aspects- acceleration, braking, handling, etc. Tire size is secondly important only to tire compound, and should be chosen carefully.  

What You Are Looking for

The first thing to consider is what you want your tire to do. Tires come in all compounds, all tread patterns, and all sizes. When researching tires you will learn that certain compounds come in only certain sizes. You won't find a race compound tire in a 75 profile. There is a string of numbers on the sidewall of the tire that denotes it's size, and it's quite easy to read. For example, a 225/55/16 tire has a width of 225mm, a profile (or aspect ratio) of 55mm, and will only fit on a 16 inch wheel.  

When purchasing tires, you should always pair up your tires to correctly match the size of your wheels, but there are some other aspects to consider. The above tire is optimal for a 16x7.5 inch passenger car wheel, an SUV or truck may use a 225/75/16. This tire is the same width, but has a much higher profile giving the vehicle a cushier ride, and better off-road performance, but will lack the street performance of lower profile tire.

Low-Profile Tires

Lower profile tires have better handling characteristics on the street, but come with some drawbacks. A low-profile tire (anything less than 50mm) will handle better in the bends, but will have a harsher ride over potholes and rough roads. An ultra-low profile tire (30mm) is so thin that if you are to hit a pothole, the impact will most likely dent the wheel and possibly cause a blow-out.

Width Adjustment

The same principles apply to adjusting the width of your tires. If you install a really wide tire on a thinner wheel you will increase the contact patch with the road, thus acceleration and braking will improve. But because the tire is wider than the wheel, the excess tire will bulge over the edge of the wheel and will result with a larger profile. Like the truck tire, this will flex under hard turning and decrease the handling of the vehicle.

Stick to the Factory Size

The best advice is to try to stay close to overall stock tire sizes that the vehicle came with. If you install larger diameter wheels, you should pair them with lower profile tires to keep the overall diameter of wheel and tire combo as close to stock as possible. This will also keep the stock speedometer as close to accurate as possible. With so many tire choices out there it can be a daunting task picking one that is best suited to your goals. To assist you in making an informed decision, many major tire sites offer a tire size calculator to calculate the optimum tire size for your wheels. As always, it's best to stay away from the extremes. Just because a tire fits doesn't mean that it is the best choice.

Related Questions and Answers

What Manufacturer Makes the Toughest Low Profile Tire?

The toughest low profile tire that is made by Bridgestone. After all, this does stand to reason since Bridgestone is part of Goodyear tire, a manufacturer that owns at least half-a-dozen subsidiaries that have equally tough reputations such as Monroe and National. The Bridgestone is used on the Chevrolet Corvette ZR1. Whose eight-inch-plus tire size and low aspect ratio (they are in the 25 to 35 degree range) means that not only do these tires put lots of rubber on the road, there's not a lot of tire to take up the shock. So they have to be tough.

What are the Drawbacks to a Very High Tire Aspect Ratio?

The tire aspect ratio is the ratio of the tire or rim size itself with the size of the tire. It is represented like this on the tire sidewall: P225/65R17. This means this is a passenger tire that is 225 millimeters. It has a 65% aspect ratio because of its 17-inch rim to tire crown size. The result is then used to help determine the second figure, as the tire size and its sidewall size interact. The drawbacks of a high tire aspect ratio is that the tire could rub in the wheel well. It might not be able to turn fully, and it has a much narrower patch of rubber on the roadway for vehicle control.