There are two common types of construction for tires: radial and bias. A radial tire has steel belts under its rubber. These belts radiate out from an imaginary center point in the middle of the tire. They are perpendicular to the direction of the tire’s rotation. A radial tire can be identified by the letter ‘R’ in its size, as in a 275/55R20.
Bias ply tires usually have belts made of a type of fabric. These belts run diagonally from the tire’s direction of rotation. The belts overlap each other in different directions, so that each belt is at a 45 degree angle from the tire’s rotation direction, and a 90 degree angle from the other belt. A bias tire can be identified by the letter ‘D’ in its size, as in a 185/80D13, or by the absence of a letter, as in a 12X16.5.
These differences have a drastic effect on a tire’s performance. Radial tires have a higher resistance to heat buildup than bias tires. Radial tires also have a larger “contact patch”, or the area of tread that is in contact with the ground. This is because of the difference in shape of radial and bias tires. Radial tires have flat tread profiles, whereas bias tires have crowned tread profiles. Although radial tires are stronger, bias tires are often more flexible. This makes bias tires suitable for applications such as small tractors, ATVs, and forklifts, where low-speed traction and shock absorption are concerns.
Let’s use a P 225/60R17 99T tire as an example.
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These three measurements are all descriptions of the same thing: the tire’s carrying capacity. Load ranges use an alphabetic system to describe the tire’s ply rating. A load range B tire has the carrying capacity of a 4-ply rated tire. A load range C tire has the carrying capacity of a 6-ply rated tire. Each additional letter indicates an increase of the rating by two plies, so D = 8-ply rated, E = 10-ply rated, and so on.
However, these load ranges or ply ratings do not necessarily mean that a tire has a certain number of plies in its construction. For example, a load range E, 10-ply rated tire might not actually have 10 plies of material in it. Instead, the tire is rated to carry the same weight that a bias tire of 10 plies could carry.
As an alternative to the antiquated load range and ply rating systems, tire manufacturers have begun to use load indexes to describe carrying capacities. These make no reference to the amount of plies in a tire, but simply correspond to the weight a tire can hold.
For example, a tire with a load index of 88 can carry 1,235 pounds when properly inflated. A load index of 89 corresponds to the ability to carry 1,279 pounds, 90 corresponds to 1,323, and so on. Most passenger and light truck tires have a load index between 75 and 125.
A tire’s speed rating designates the maximum speed at which a tire can be operated for one solid hour before the tire is damaged due to heat buildup.
A tire with a speed rating of ‘S’ has a maximum speed of 112 mph. This applies when the tire is operated at this constant speed for one hour. Some other examples of speed ratings are included below.
T = 118 mph
U = 124 mph
H =130 mph
V = 149 mph
W = 168 mph
Y = 186 mph
(Y) = 186+ mph
It is not advisable to replace your vehicle’s tires with tires that have a lower speed rating than recommended. However, you can safely install tires that have a higher speed rating than recommended. Higher speed ratings often mean better performance and handling, but at the expense of mileage.
The tire industry offers many styles of tread pattern to suit different kinds of driving environments. The name of a tire’s tread design is usually listed on its sidewall. Just like your vehicle, these tread designs often have broad model names and more specific sub model names. For example, you might encounter a Cooper Discoverer AT3. ‘Cooper’ is the manufacturer, ‘Discoverer’ is the generic model name, and ‘AT3’ is the specific model name.
Dry rot is a process by which the chemical bonds that hold a tire’s rubber together break down. This can cause tire separations and blowouts. Dry rot will typically occur about 5 or 6 years after the tire’s manufacture date, but it can be accelerated by environmental factors.
Dry rot occurs completely independently from tread wear. A tire that has never been used is just as susceptible to dry rot as a tire that has been on your vehicle for years.
To identify dry rot on your tires, look for tiny cracks in the tread or on the sidewall. If the cracks are numerous, it may be time to replace your tires.
Most tires list their date of manufacture. This information can be found on the sidewall within the DOT Serial Number. For example, if the tire’s DOT number is:
DOT MA L9 ABC 0301
Foam filling is a process that essentially turns an air filled tire into a solid tire. We pump liquid polyurethane foam into the tire and cure it overnight in our hot room. A foam filled tire will no longer be susceptible to leaks caused by punctures, and it will be much heavier than a pneumatic tire.
Foam filling is only available for non-highway tires, and it is only cost effective for tires that are subjected to frequent punctures. Vehicles that commonly utilize foam filled tires include skid loaders, hand dollies, forklifts, and lawn and garden tractors. Foam filling is not a ‘while you wait’ process.
The ‘P’ means that the tire is intended for use on a passenger car. Alternatives may include ‘LT’ for Light Truck, or ‘ST’ for Special Trailer.
The ‘225’ measures the section width (sidewall to sidewall) in millimeters.
The ‘75’ measures the sidewall height as a percentage of the section width.
The ‘R’ specifies that the tire is of radial construction. If the tire is of bias construction instead, a letter ‘D’, or no letter at all will be visible.
The ‘17’ measures the diameter of the wheel.
The ‘99’ measures the tire’s carrying capacity and will be discussed below.
The ‘T’ is the tire’s speed rating, which will also be discussed below.
Keep in mind that it is important to use the same size tire all around your vehicle unless the vehicle’s manufacturer recommends otherwise.
Many new cars and trucks use a Tire Pressure Monitoring System, or TPMS to alert motorists of changes in tire inflation pressure. There are two main types of TPMS: direct and indirect.
Direct sensors are positioned inside the tire at the base of the valve stem. These electronic devices read the tire’s inflation pressure and relay the information to a module in the vehicle through the use of radio waves.
An indirect TPMS system does not involve any hardware within the tire. These systems sense inflation pressure either by the ride height of the car, or revolutions per minute of individual wheels.
If your vehicle has TPMS, there is a light on your dashboard that will illuminate when there is a problem. It will light up if your tires are underinflated (usually when inflation falls to 75% of the recommended pressure), or if the battery in a sensor is dying. These batteries have a life span of about 6 to 7 years, and when they die, the whole sensor valve stem must be replaced for the system to function properly.
While it is best to stay with the manufacturer recommended size, it is sometimes possible to use larger tires on a vehicle. This question is best answered on a case-by-case basis.
‘DOT’ means that the tire is approved by the Department of Transportation.
‘MA’ refers to the plant of origin.
The ‘L9’ is a code designating the size.
‘ABC’ is a manufacturer code.
‘0301’ means that the tire was made during the third week of 2001.
In addition to all-season passenger and light truck tires, we also offer snow tires. Most of the snow tires we provide can be outfitted with metal studs for superior traction.
Studs can only be installed into new, unused tires. The stud holes in used tires are often deformed or too clogged with debris for proper stud insertion.
In Pennsylvania, it is legal to drive with studded snow tires from November 1st to April 15th. For information about the laws restricting the use of studded tires in other states, refer to the Rubber Manufacturers’ Association.
We do not conduct vehicle alignments, but we have a neighbor who does. We can gladly refer you to him over the phone.