FAQ - Technical Info and Definitions

Can I switch to a lower speed rated tire than what came on the vehicle?

It is recommended that the replacement tire size speed rating be equal to or higher than that of the O.E. tire size speed rating. If a lower speed-rated tire is selected, then the vehicle top speed becomes limited to that of the lower speed rating selected. The customer must be informed of the new speed restriction. It is quite common and permissible during winter driving to use a winter tire with a lesser speed rating than the O.E. tire. Still, the customer must be informed of the rating decrease.

Mixing speed ratings on a vehicle is not recommended. If tires of different speed ratings are mounted on a vehicle, the lower speed-rated tires should be placed on the front axle. This is to prevent a potential oversteer condition. Vehicle handling may be affected, and the vehicle’s speed capacity is now limited to the lowest speed-rated tire.

Can I mix radials and non-radials?

Why don’t winter tires have a Uniform Tire Quality Grade rating?

Winter tires are not assigned tread wear ratings. They are designed for cold weather use only, usually when average daily temperatures are at or below 45° F / 7° C.

While the tire operates just fine in warmer conditions, it will wear out very quickly. The life of the tread is impacted by the amount of driving performed in warmer conditions because the rubber compounds that give this tire winter grip are not designed to withstand non-winter conditions over the long-term. In short, winter tires used in the summer wear out very rapidly.

Do you support plus sizing?

Plus sizing must be done with proper care. When replacing tires with optional size designations, be sure to check vehicle manufacturer’s recommendations found in the owner’s manual or on the door sticker. Interchangeability is not always possible because of differences in load ratings, tire dimensions, wheel well clearance and rim size.

However, if you provide the original equipment tire size and the tire size you wish to install to your dealer, they can provide the tire specifications and differences.

How do I determine if my current rim is approved for your tires?

The rim width range represents proper rim widths that will assist the tire/wheel assembly in meeting its performance potential. To achieve the best balance between ride, handling and tread wear, select a rim width in the middle of the manufacturer’s range.

To improve cornering traction and steering response, choose a rim at or near the maximum recommended width. The wider the rim width, the straighter the sidewall and the quicker the steering response. Conversely, using a rim width at the low end of the range will cause the tire to balloon or curve out, slowing steering response.

You can calculate proper tire specification on our website.

How do I read the sidewall of my tire?

Passenger Tire Sizing
Three primary sizing systems exist for passenger tires today: P-Metric, European Metric and Millimetric. Each of these systems evolved from the first tire sizing system: the Numeric Sizing system, which is now obsolete. It was developed when all tires had the same aspect ratio, and it provided only the nominal cross section width of the tire and the rim diameter in inches. Below is more information on two of these commonly seen sizing systems.

P-Metric
This is the metric on the tire that begins with P. The P-Metric sizing system was developed to better align with the European tire sizing system and provides a better description of the tire size.
European Metric
This is the metric to the right of the P Metric, following the forward slash. Essentially, this system was a conversion of the Numeric system from inches to millimeters. Aspect ratio appears in the size designation in most cases where it is other than 82.

Light Truck Tire Sizing
Sizing for light truck tires takes the performance requirements of the vehicle, and the tires, into account. Light truck tires have evolved along with the expanded applications of trucks and vans that have grown to be multi-purpose vehicles that we use for work, for recreation or as passenger vehicles. There are four primary light truck tire sizing systems: Light Truck Metric, Light Truck High Floatation, Light Truck Numeric and Light Truck European Commercial Metric.

Light Truck Metric
This sizing system mirrors the P-Metric system for passenger tires.
Light Truck High Flotation
Light truck high flotation tires have evolved as lower aspect ratio tires and became more popular on light trucks. The combination of lower aspect ratios and high flotation yielded better traction on sand and soft soil found in off-road situations.
Light Truck Numeric
This older system is still widely used, mostly on commercial vehicles.
Light Truck European Commercial Metric
This size system mirrors the European Metric system for passenger tires and is intended for commercial light truck vehicles sometimes referred to as “Euro Vans”. Often these tires are referred to as European C-Type sizes.

How do I read the DOT number?

DOT signifies that the tire complies with the United States Department of Transportation’s tire safety standards and is approved for highway use.

Example: DOT M5H3 459X 065

1^st and 2^nd Characters: tire manufacturer and plant code

3^rd and 4^th Characters: tire size

5^th-8^th Characters (optional): brand and other significant characteristics of the tire.

9^th and 10^th Characters: the week the tire was produced

Final Number(s): the year in which the tire was manufactured

For Uniroyal brand tires, DOT markings related to the week and year of production will have an additional symbol for the decade of the 1990s. It will be shown as a triangle following these last three numbers.

Beginning in year 2000, an additional digit was added to the serial number to allow the year of production to have two digits.

How is the overall tire diameter measured?

What guidelines should I follow when mixing tires on 4WD vehicles?

If no instructions for tire mixing appear in the vehicle owner’s manual, adhere to the following guidelines:

All four tires should be matched for tire size (unless the vehicle was originally equipped with different sizes on front and rear axles), tire brand and tire model.
The tire rolling radius or revs/mile should match for all four tires. This can be achieved by having the same tire size, tire brand and tire model on all four wheels.
Do not mix tire types such as all terrain, all season or winter.
A single tire can be replaced even if the other three tires are worn as long as:
- It is not contrary to the vehicle manufacturer's recommendation/owner's manual
- All four tires have the same size, brand and model.
- The difference in tread depth does not exceed 5/32".
Note: tire rolling radius (or rev/mile) is sensitive to tire inflation pressure. All tires should be properly inflated.

What is a directional tread design?

Tires with directional tread patterns must be mounted so that the primary direction of rotation matches the directional arrows on the tire sidewall. If all four tires are the same size, directional tires can be rotated front to back.

Tires with tread patterns that are both asymmetric and directional require left and right specific tires. Sidewall markings will identify the side of the vehicle and the primary direction of rotation for the tire. If all four tires are the same size, they can be rotated front to back.

What is difference between P-metric and metric?

P-metric sized tires are those with the "P" at the beginning of the tire size (such as P215/65R16). P-metric sizes were introduced in the United States in the late 70s and are installed on vehicles primarily used to carry passengers including cars, station wagons, sport utility vehicles and even light-duty pickup trucks. Their load capacity is based on an engineering formula which takes into account their physical size (the volume of space for air inside the tire) and the amount of air pressure (how tightly the air molecules are compressed). Since all P-metric sizes are all based on the formula for load, vehicle manufacturers can design their new vehicles (weights and wheel well dimensions) around either existing or new tire sizes.

Metric or Euro-metric tire sizes are the ones without the "P" at the beginning, (such as 215/65R16). Using metric dimensions to reflect a tire's width actually began in Europe in the late 60s. However, since Euro metric sizes have been added over time based on the load and dimensional requirements of new vehicles, the tire manufacturers designed many new tire sizes and load capacities around the needs of new vehicles. Not quite as uniform as creating sizes using a formula, but they got the job done.

Euro metric and P-metric tires in the same size (i.e. P215/65R16 and 215/65R16) are equivalent in their dimensions with just slight differences in their load capacity calculations and inflation pressure tables.

What is excessive spinning?

What are speed ratings?

Where can I find the DOT on my tire and what does it signify?

TECHNICAL INFO AND DEFINITIONS