Question 1

Why can't I use only two winter tires?

Accepted Answer

If you were to put winter tires on only the front or rear of your vehicle, you would create a vehicle with a split personality.   Leading automobile maunufacturers such as BMW, Mercedes-Benz, Honda, Nissan and Toyota recommend in their owner's manuals that you install four (4) winter tires for winter driving.  By installing four (4) winter tires, you maintain the most balanced and controlled handling possible in all winter driving conditions.  It is imperative to keep the same level of traction at all four (4) corners of the car; otherwise, the full benefits of ABS or traction control systems will be lost.

Question 2

When should I mount winter tires on my vehicle?

Accepted Answer

It is recommended to mount winter tires as soon as the temperature remains consistently near freezing.

Question 3

How is the overall tire diameter measured?

Accepted Answer

A tire is mounted on the appropriate rim width as identified by T&RA (Tire & Rim Association) or ETRTO (European Technical Rim & Tire Organization) then inflated to 26 psi.  A calibrated measurement tape if run around the circumference of the tire in the center of the tread (which represents the largest overall diameter).  This measurement of circumference is then divided by the mathematical constant known as PI (3.14126...) to calculate diameter.

Question 4

What is the proper air pressure for my tire?

Accepted Answer

Proper air pressure for a tire is determined by the vehicle manufacturers and is set to best fine-tune a tire's capabilities to their specific vehicle make and model.  The vehicle manufacturer's pressure recommendation can be found on the vehicle's tire information placard label, as well as in the vehicle owner's manua.

Question 5

Can I go to a lower speed rated tire than what came on my vehicle?

Accepted Answer

It is recommended that the replacement tire size speed rating be equal to 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.  It is quite common and permissible during winter driving to use a winter tire with a lesser speed rating that the O.E. tire.

Question 6

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

Accepted Answer

If no instructions for the tire mixing appear in the vehicle owner's manual, adhere to the following guidelines:   *Do not mix sizes.  All four (4) tires must be branded with the same tire size. *Do not mix radial and non-radial tires.  All (4) must be either radial or non-radial. *Be sure that the outside circumference of all four (4) tires is within one (1) inch of each other. *Do not mix tread pattern types such as all-terrain and all-season.

Question 7

What is the difference between P-Metric and Metric?

Accepted Answer

P-Metric sized tires are those with the "P" at the beginning of the tire size (such as P215/65/16).  P-Metric sizes were introduced in the United States in the late 1970's 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 capasity 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 based on the formula for load, vehicle manufacturers can design their new vehicles (weight and wheelwell dimensions) around either existing or new tires.

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