How do I know what tires I can fit on my truck?

Understanding Tire Size Classifications

Now that you understand what to look for and where to find it, let's delve into reading and comprehending the actual tire size classifications, IE: what do the various digits represent? 

Tires sizes are separated into two basic categories–imperial (flotation) and P-metric. Each category utilizes three digits to determine the tire size, though they differ in order and preferred unit type.

P-Metric Sizing

To begin, let's look at the more common measurement–metric. Refer to the following example:

EX: P245/75R16 91S

Metric tires are measured using a combination of metric and imperial units–specifically millimeters and inches. The first numerical value, in the above example (245), relates to the tire's width in millimeters. The second numerical value represents the tire's aspect ratio or profile. However, instead of accounting for the entire height of the tire, the aspect ratio is written as a percentage of the tire's profile divided by its width. In the case of the above example, the value (75) tells us that the tire profile is 75% of the total width of the tire. The third numerical value refers to the size of the wheel, in inches, that the tire must be mounted on (16).

The final numerical value on the tire (91) refers to the tire's load index or the weight that the tire can carry. This value ranges from 1 to 150, with each digit having a corresponding value, in pounds, ranging from 99 to 7385 lbs. Non-numerical values on the tire include the tire type, which can consist of P (passenger) and LT (light truck), as well as the tire's construction, which can include R (radial), D (diagonal), or B (bias ply). The final non-numerical is the tire's speed rating.

Imperial (Flotation) Sizing

Imperial, or Flotation tire sizing, is similar to P-metric, though differing in several critical ways. Refer to the following example:

EX: 33X12.50R17LT 120Q

Imperial tire sizes are common if you own a truck or SUV. These sizes utilize three primary numerical values to determine height, width, and wheel diameter, much like P-metric sizing. However, all sizes are displayed in inches rather than a combination of millimeters, percentages, and inches. 

The first numerical digit (33) refers to the tire's height in inches; in the case of the example, the value represents a total height of 33 inches. The second numerical value (12.50) describes the tire's width in inches. The third numerical value (17) represents the size of the wheel, in inches, that the tire must be mounted on.

As with P-metric sizing, a series of other values are also present on an imperial tire. The last numerical digit (120) and non-numerical (Q) refer to the tire's load index and speed rating. These two values are calculated similarly to those on a P-metric tire. The non-numerical value after the tire's width (R) also relates to the tire's construction, just as with the P-metric. The Non-numerical digit after the wheel diameter refers to the tire's type, in this case, LT (light truck).

What's the Biggest Tire Size for Your Truck?

While the largest tire size one can fit on their vehicle varies significantly across makes and models, it's best to follow the 3% rule. This method involves calculating how large of a tire can fit on your truck while keeping variances within the 3% mark. 

In the case of your pickup, the largest tire you should attempt to fit on stock suspension is 3% taller and 3% wider than the factory equipment. But what about modified suspensions? 

One way to skirt this rule is to install a leveling or lift kit. As you raise the height of your pickup, you increase fender well clearances, which allows you to squeeze a larger tire without the risk of scrubbing on body panels. While not fool-proof, a good rule of thumb is for every inch of lift, you can fit an approximately one-inch taller tire. However, most lift manufacturers will specify the maximum tire sizes compatible with each product.

If you're still struggling to select the correct tire size, consider heading outside with a tape measure and taking some quick measurements. With the wheel straightened and at full lock, measure the distances between the tire's edge and various suspension components/body panels; do this for both sides. 

With these basic measurements, you can measure for clearances and make an educated estimate for the largest tire you can fit without clearance issues. And for all of your wheel and tire needs, don’t forget to check out RealTruck’s extensive inventory!

Example: The version/option of a Honda Accord EX V6 is EX V6.

It's important that we have all of your vehicle information. Things like your version/option can affect your tire size, and we want to make sure we're showing you the right results based on the information you've given us.