Q: I just found out my car has directional tires. What are the benefits? I don’t like that they can’t be rotated.

— Jerry Dawson

A: Directional, also called unidirectional, tires are designed to offer optimum straight line acceleration, dry weather cornering performance and wet weather traction by utilizing large tread blocks and angled grooves and sipes (narrow slits). Tread blocks are the portions of tread between the grooves. During dry weather, widely spaced grooves (larger tread blocks between) allow a greater contact patch and less tread squirm while corning. During wet weather, one typically desires closer spaced grooves to channel water away, lessening the chance of the tire hydroplaning. By optimizing the tread design for a particular direction of rotation, directional tires provide the best compromise between dry and wet weather performance.

A directional tire’s diagonal grooves need to be oriented correctly (as viewed from behind the tire they should point upward), so a directional tire has arrows molded into the sidewall, indicating the proper direction of rotation. When installing and rotating tires, one will adopt right side and left side tires which are not interchangeable. Should a directional tire be installed backwards, it will not hurt the tire, but performance — particularly wet weather traction — will be reduced. Periodic tire rotation is a good idea since front and rear tires are subjected to differing forces and wear accordingly.

Performance oriented tires may also be have one tread pattern on the inside of the tire and another on the outside. These need to be mounted correctly (front side versus back) on each wheel to provide the intended performance benefits. Look for a notation on the sidewall, indicating front versus back.

A: Don R. asked for more information regarding the use of an infrared temperature gun. He was interested in learning more about various temperatures of engine, brakes and other parts. A typical temperature reading at the thermostat housing of an engine at operating temperature is 195 degrees. Validating the proper turn-on point of an electric radiator cooling fan might show a reading of about 215-230 degrees. An infrared gun may also be used to check exhaust manifold temperature, possibly indicating a cylinder misfire should a cooler reading than the siblings be seen. Automatic transmission pan temperature is typically only a few degrees cooler than the ATF inside, providing useful information for those who tow, and aren’t equipped with a transmission temperature gauge (no more than 220 degrees is advised during a mid-mountain check). Observing correct brake temperature should show consistent side-to-side temps and rotors should not exceed 300F during downhill stretches without a cool-down stop. Another favorite is verifying an exhaust restriction such as a failed/clogged catalytic converter — it will be noticeably cooler downstream of the fault. These are only some of the cool things that can be done with this tool!