First are the obvious temperatures, for which some cars already have readouts; coolant, oil, automatic transmission fluid, cylinder head, interior and exterior air. The information obtainable here is at two levels; a safe vs. danger distiction- the traditional "idiot light"--or a quantitative good/bad/best measurement. With a quantitative measurement available, the car can be adjusted/ modified to achieve the best values.

Some areas are perhaps best just monitored to avoid harm. Transmisssion, differential, and wheel bearing temperatures for example. As long as they don't overheat you aren't really concerned. nor will big variations in running temperatures have much effect on performance. Brakes usually fit this category, too. These are areas where the aforementioned products are handy. Looks at them after practice and an event, then either things are O.K., or you make a modifications to reduce or survive the excess heat.

On the other hand, there are areas where you can use the measurements to dial the car in to maximum performance. For instance, maximum power demands minimum temperature fuel and intake air. Scoops, ducts, cool cans, intercoolers, raised manifolds, insulated carb. spacers-all are for this express purpose. And how do you know they work until you measure before and after temperatures?

One of Smokey Yunick's puzzling speed secrets was a small hole drilled in each exhaust header pipe just outside the exhaust port. How did this get him more power? He could stick a small pyrometer sensor into exhaust stream and compare exhaust temperatures cylinder by cylinder. Minimizing variations called for different cylinders to have different carb. jetting, head porting, manifold runner designs, spark plugs, even cam timing! But the results was an engine with all cylinder to its peak independently.

The racing automotive temperature area that has gotten the greatest attention recently has been tire temperatures. This one area of measurement has gone far towards making suspension tuning a science to the average racer, away from the "it feels good" school of chassis tuning.

The basic idea is simple, and spelled out in the first sentence. The more work a tire, or portion of it, is doing, the hotter it gets. Since a tire will have optimal temperature to get maximum traction, we need only adjust the suspension so that all portions of all tire treads are at this optimal temperature. Only then is the car getting all the cornering and traction it's capable of.

This is largely unobtainable, but let's look at the problems and solutions.

First, we need a tire pyrometer. No problem, a number are available with fixed or interchangeable probes from Check-it Electronics Corp. Designed by a racer, it exemplifies what's needed. All solid state electronics, it;s rugged and can survive in a tool kit, while very compact and light. Very quick sensing of temperature, and with a big crystal display that's easy to read while giving an over 1000 hr. battery life. Like all tire pyrometers, it uses a sharp needle--like sensing probe, that may be struck and about 2 millimeters into the tire tread, to measure the temp. just under the surface. The useful temperature range for tires is about 100 F-350 F/40 C-175C. Such a pyrometer may also be used for almost any other temp. measurement you may want to make, if the temperature range covers it, so it's a very versatile tools, and well worth the investment it you're serious about care work. Besides, it's a ball of fun to play with, especially when you haul it out of your pocket to back up your claim that the coffee isn't hot enough!

Secondly, we must get the tires up to temperature. This means quite a bit of hard running. The exact length of time will depend on the course and car and tires and speeds and weather. On racing tires a fairly sensitive drivers can feel the tires warming and sticking better over the first 1/2 dozen or so laps. The car should then come in quickly for a temperature measurement, without any violent pitting maneuvers that might affect the temperature. Have a data table handy to record tite temps. and tire pressure and other pertinent information. Try to get a complete set of three readings across each tire surface within about 30 seconds of stopping. If there's any doubt that the tires are at their running temperature, pit again every few laps for further data, until the temperatures stabilize. Remember, we want the temperatures just under the surface, on the outside and inside edges of the tread surface, and the middle of the tread surface. If the tire has a tread pattern, rather than a sticker, try to get readings from similar tread pattern elements in the three positions, and stay clear of the sidewalls or edges where the treads curls up from the road.

Third, you should know at what temperature the tire should be. This may be something you have to work out for yourself, by seeing what works best with respect to lap times. Or, you may be able to get data from the tire manuacturer. For racing tires it's likely to be in the 200F-260F range, and can be quite critical with some tires. Too hot tires show it, by getting greasy-slippery feeling while driving, and by loosing portions of the tread surface, "chucking". If your tires get too hot you have three choices, Driver slower, fit bigger tires, or go to tires of a harder rubber compound. And do it quickly, before you lose traction or a tread.

If the tires don't get hot enough, go smaller, softer, or faster! Cold tires are a special problem for time trials cars; the few laps of running time don't allow tire temps to stabilize. Often such cars must go to very soft compounds, or tires designed for much lighter cars. The tires will then heat up very quickly, and would probably disintegrate in a very few more laps from overheating. In such cases get a temperature and pressure reading at the end of each timed run, and don't get into any long pratice sessions!

Luckily, we can often get more information from differences in temperatures than from absolute values, so it is not vital that we know that exact best temperature. Difference both across a single tire and between different tires are valuable in letting us get the most out of the tires we have. Here's where we get to the real nitty-gritty.

On a single tire(no, not an unicycle-one of the four) usually three temps. are taken across the tread surface. As said, hotter equals harder working. We wants the same temperatures right across the tire, within about 2 degrees. If the center is hotter than the average of the two edges, the center is carrying most of the weight and doing most of the work. The tire is overinflated. Test the pressure, let a little out, and repeat the whole testing procedure when the car pits again. Should the edges turn out to have a higher average temperature than the middle, then the itres underinflated. This will then get the tire at the pressure where it provides maximum traction on your car. If you must adjust oversteer-understeer balance by playing with tire pressures (an obsolete practice, now that adjustable anti-roll bars are so common), keep the tires at one end at this maximum traction pressure, and raise or lower the other end's pressure to decrease its cornering power.

Should one side of the tire be hotter than the other, then adjust the camber. The wheel is improperly tilted to get maximum tread contact with the road. If the insider is hotter, adjust towards more positive camber, to put more weight on the outside edge, and vice-versa for a hotter outside. With a solid axle, where camber is zero and not adjustable, edge-to-edge differences may indicate an incorrect alignment, or a roll steer conditi on, with the wheel pointing slightly towards the hotter side.

Variations from let side to right side tire temperatures are usually more a function of the track than the car. An oval track with all left hand turn will obviously give higher right side temperatures. Weight jacking here would tend to make the two ends behave differently; jacking would tend to equalize rear tire temperatures on the oval, while making front end differences larger. In the extreme the inside front tire will lift off the ground and show no heating!

Keep good records records of tire temperatures, along with pressures, and the other variables you should be keeping, such as camber and toe settings, bump steer, anti-roll bar sizes and/or adjustments, individual wheel weights, weather, track condition, and lap times, along with drivers comments. The end result with be to quickly allow you to dial in your car to its maximum on each track. Good Luck!!

 

 

 

The Second Law of Thermodynamics says that all forms of energy eventually degrade into heat. A thermometer, then, is a supremely useful tool for analyzing what's going on, any place energy is being used.

"Thermometer" is used here in its most general sense, of a temperature measuring device. Such devices commonly use a sensing material in which temperature causes a change in its volume, optical properties, or electrical properties. The first category includes old Dr.Farenheit's mercury-in-glass gadget and the bimetallic strip. The second type includes liquid crystal displays, Mood rings, and the very useful cranyons, paints, and stickers, calibrated to permanently change color or appearance at a designated temperature. The third category includes the most recent developments, of greatest concern to this article, of the electric pyrometer (means the same thing as thermometer, only from the Greek word for fire instead of heat.) The thermocouple and solid state electronics has allowed design of instruments that are accurate, quick reading, portable, sturdy, and realatively cheap.

With such a pyrometer a whole lot of diagnostics are possible around the automobile. Some things even become possible to analyze that were purge guesswork before. These appilications have been one of the major breakthroughs in car "tuning" of the past couple of decades. In recent years inexpensive instruments have become available to very many more mechanics, who have learned a lot. Let's take a look at some applications where knowledge of temperatures is useful around the car.