Affordable Electronic Pyrometers - Tech Talk

Heat can be a racer's best friend or worst enemy. It is the heat from the combustion process that produces power in an engine. Heat from friction warms tires to the point where they develop maximum grip through corners. Energy being converted to heat is what makes a car stop. But too much heat can melt pistons, fry brakes, and burn up tires in just a few laps. It takes a pyrometer to determine how hot objects are getting and how close they are to the danger point.

Pyrometers have been around for a long time. Going back to World War II, airplane engines were fitted with EGT (exhaust gas temperature) pyrometers and pilots used those readings to adjust fuel mixture as the air thinned at altitude. In a broad sense, a temperature-sending unit screwed into a cylinder head and connected to a dashboard gauge performs the same function as the most complex electronic unit. The difference is in what they measure and how quickly they produce results.

Not too many years ago the only pyrometers you could find at a racetrack were in the toolboxes of the very best funded teams. They were too expensive for most teams and few outside of the Winston Cup level knew what they could do. Advances in electronic technology have reduced the cost to where most teams can afford one or two of them.

"Today they are a must-have for most everyone who is serious about winning," says Jeff Butcher, who operates Longacre Racing in rural Woodinville, Washington. "With a set of scales, a caster/camber gauge, and a good tire pyrometer, you can learn just about anything you need to set up a chassis."

Probe And InfraredThe two most common types of pyrometers are probe-style units that have to touch the heat source, and infrared pyrometers that measure surface temperatures.

"For tires, there's nothing that beats a probe," says Butcher. "Tires lose heat so quickly that the only way to really get an accurate reading is to go under the surface and measure the temperature near the cord."

Goodyear recommends probe-style pyrometers for tire measurements and that is the only style used by its trackside engineers. The most basic probe pyrometer sells for about $100.

"It's all anyone really needs," Butcher says. More expensive ones retain multiple readings and will figure temperature averages. "They are a lot more convenient," he says. "But everything they do can be done with a notepad and a hand-held calculator," he specifies.

Tire TemperaturesThere is no "ideal" temperature for race tires. Readings will vary based on variables like rubber compound, construction, racetrack surface, ambient air conditions, and banking. It is the variation in temperatures that can tell a driver or crew chief what changes to make in toe setting and camber. Sometimes a crew chief can work backward, beginning with a driver's observations about how a car is handling and checking those comments against tire temperatures to determine if a change in pressure, springs, or track bar is needed.

Butcher says he tries for "temperature averaging" across a tire's surface with a target of about 10 degrees difference. Goodyear says the best working range for stock car tires is about 200 to 250 F degrees and that temperatures over 275 F degrees are excessive and could lead to tire blistering.

The tiremaker also suggests readings should be taken in a consistent manner. On an oval track, always begin with the right front tire and work around the car in a clockwise direction. Goodyear advises taking a reading on the inside shoulder of the right-front tire. That reading should be no more than 25 degrees higher than the inside tread reading.

For more information, visit www.longacreracing.com for an extensive discussion of tire temperatures, temperature averaging, and proper use of tire pyrometers.