Does Size Matter When it Comes to Custom Rims and Tires?

Yes it does. However, before one delves further into the subject, one has to understand tire codes. Altering a vehicle’s tire sizes, unlike customizing truck floor mats, dashboard covers, and car seat covers, is not something to be taken lightly.

Unfortunately, a lot of people can’t make heads or tails out of the codes labeled on their tires and therefore do not know what “P225/50R16 91S” means. Tire codes are very important if one intends to change his or her vehicles tires. Unlike changing truck floor mats, changing tires without knowledge of what one is doing could bring about adverse affects. Here’s a breakdown of the sample tire codes:

• The “P” means the tire is meant for passenger vehicles like mini vans cars, small trucks, and SUVs.
• The “225” is the measurement of the widest point of the tire’s outer sidewall to the widest point of its inner sidewall when installed.
• The “50” is the percent of the sidewall height relative to the width. (In this example, since the width is 225 millimeters, the sidewall height from the rim to the tread is 112.5mm)
• The “R” denotes how the internal construction of the tire was fabricated. In this example, “R” means radial.
• The “16” is the size of the rim.
• The “91S” is the service description of the tires. The “91” is the number that rates how much load the tires can handle. (The “91” in this example means that the tire can handle 1356 pounds.) The bigger the number, the greater the tire’s capacity.
• The “S” is the tire’s speed rating. (An “S” speed rating denotes that the tire can operate safely at speeds up to 112 miles per hour. The further down the alphabet, the higher the velocities that are safe for the tire.)

So what does this all mean? Typically, a car that’s made for speed will have a wider width with a low alphabet letter (generally W, Y, or Z) and a low percentage of sidewall for optimal handling and steering capabilities. A passenger vehicle, meanwhile, will have a medium width and a higher percentage of sidewall for a more luxurious style.

Tinkering with tires without knowledge about tire sizes is a dangerous thing to do. Here are some of the reasons:

• Odometers and speedometers are calibrated based on the height of a vehicle’s tires. Taller tires make speedometers read slower than the actual speed of the vehicle.
• More recent vehicles have built-in computers that base calculations on the height of a vehicle’s tires. Changing tires could result to a vehicle’s components malfunctioning.
• Stock suspension systems could suffer additional stress with taller tires, resulting in accelerated wear, tear, and/or failure. If one makes substantial changes in tire height, one should upgrade and bolster the vehicle’s stock suspension.

Below is a list of different tire sizes and what vehicle classes should use them.

• 34" x 8" – Class “A” Motorhome
• 31-1/4" x 12" - Class “C” Motorhome
• 30 3/4" x 10" – Isuzu Rodeo, Honda Passport
• 29-3/4" x 8" – Blazer II 4X4, Jeep Wagoneer
• 30" x 10" – Jeep Liberty
• 29" x 8" – Econoline 150 GM ½ Ton, Dodge Raider, Chevy Van
• 35" x 12 -1/2" - Hummer H2
• 27" x 8" - S10 Blazer, Cherokee Laredo 4X4, GMC S15, Honda CRV
• 25-1/2" x 8" = M - Astro, Safari, Geo Tracker
• 24" x 8" - Pop-up Campers
• 21 1/2" x 8" - Pop-up Campers
• 32-1/4" x 12" – Off Road Extra Wide Tires