Wheels and Tires

Within reason, a single tire size can fit on a variety of rim widths. Tires have flexible sidewalls, making the width of the wheel the influencing factor in determining the width of the tire.  A tire mounted on a wide rim would be “wider” than the same tire mounted on a narrow rim.

Wheel sizes are generally measured as DIAMETER (in inches) X WIDTH (in inches) +/- OFFSET (in millimeters). So, a wheel listed as 17 X 8.5 + 35 are 17 inches in diameter, 8.5 inches wide and have a +35 positive offset.  More information about offsets are provided in the offset question below.

Road tires and tires made specifically for off-roading may have different measurements.

• Road tire codes will generally look like this example: 225/70/R14.  Breaking this number down, the first number in the code (“225”) represents the nominal tire WIDTH in millimeters. The next number (“70”) is the HEIGHT of the sidewall shown as the aspect ratio/percentage of the nominal tire width. “R” represents the RADIAL tire construction and (“14”) is the WHEEL DIAMETER measured in inches. The overall circumference of the tire can change by changing any of the tire’s specifications.  For example, increasing its width will also increase its circumference because the sidewall height is a proportional length.  Similarly, increasing the aspect ratio will increase its height with a simultaneous increase to circumference. NOTE:  Most passenger road tires are manufactured in the standard ply/load range (the amount of load the tire is designed to carry at the industry specified pressure) and will have nothing branded on the sidewalls or may be branded SL (Standard Load). Passenger road tires may also be branded XL (Extra Load) or LL (Light Load) in various circumstances and uses.
• Off-roading, light truck and some other tires may contain a secondary size and look like this example: 35 /13.50/R16 or 35/1350R16/E.  Breaking this number down, the first number (“35”) indicates the tire’s DIAMETER in inches.  The second set of numbers (“13.50” or “1350”, expressed with or without the decimal) is the tire WIDTH measured in inches. The “R” represents the RADIAL tire construction.  The WHEEL DIAMETER is the last number (“16”), with the “E” representing the ply/load range of the tire relative to its construction (how much load the tire is designed to carry at the pressure specified by industry standards).  “C” indicates a 6-ply load carrying capacity, “D” is an 8-ply, “E” is a 10-ply rating and “F” is a 12-ply rating. If there is no letter, the tire has a standard 4-ply “B” rating.

As we discussed in a prior question, wheel measurements are expressed as DIAMETER (in inches) X WIDTH (in inches), plus the allowable positive or negative (+/-) OFFSET. The offset is clearly the tricky part! Offset is the distance in millimeters plus (+) or minus (–) from the hub (where the wheel is bolted to the vehicle) to the true center of the wheel.  Let’s use this example:  22 X 12 -51.  (“22”) is the DIAMETER, (“12”) is the WIDTH and (“-51) is the offset.

• This example uses a negative offset, meaning that the mounting surface of the wheel is closer to the inside (brake area) of the wheel. A lot of custom truck wheels come in significant negative offsets, meaning that the wheels will “poke” outside of the fenders for an aggressive stance. The more negative the offset, the more the tires and wheels will “push” out.
• Conversely, a positive offset would be where the mounting surface of the wheel is closer to the outside (fender area) of the wheel, which would push the wheels inward, thus “pulling” the tires and wheels into the fender well opening.

A vehicle’s speedometer gives the driver an accurate estimation of the vehicle’s speed. Stock vehicles are calibrated for use with the stock parts that came with the vehicle, so if you change the size of the tires and wheels, your speedometer calibration can be thrown off. Larger tires cause the speedometer to read SLOWER than the vehicle’s actual speed, while smaller tires cause the speedometer to read FASTER.  In many cases, Renegade Customs can recalibrate your speedometer in a few simple steps.