Will Cold Weather Affect Car Performance?

You may feel silly racing with mittens on, but at least your car's happy.

Automobiles are finicky beasts: loyal as a German Shepherd when you treat them well, temperamental as a three-year-old when you don't. Extremely low temperatures may not necessarily drive your car to fits, but they'll certainly move it a bit outside of its comfort zone. Where performance is concerned, you should always bear in mind that driving to Publix in the spring involves a no less complicated dance of material physics than bombing down Road Atlanta in the dead of winter.

Engine Performance

Once you get your engine started and up to operating temperature, lower outside temperatures will invariably result in an increase in horsepower and torque. Cold air is oxygen-dense air, as oxygen density continues to increase all the way down the point that the oxygen itself turns into a liquid; that's negative 295 degrees Fahrenheit, if you're wondering. This is particularly true on turbocharged or supercharged engines, which multiply outside air pressure by a factor of 1.5-to-1 to 2.5-to-1. This multiplies the relative change in outside air density and pressure by a concordant amount, which means that the engine can burn even more fuel and make more horsepower. The rule of thumb is that, for non-turbo-supercharged engines, horsepower increases by about one percent for every 10 degree drop in intake air temperature. Multiply that by the turbo-supercharger's pressure ratio as applicable. For example, you might get an 11-percent increase if you're running a 1.1-to-1 pressure ratio or a 15-percent increase in power for a 1.5-to-1 ratio.

Suspension

Generally speaking, suspension will act far harder than it really is in cold weather. The net result is -- hypothetically -- better handling at the expense of a slightly harsher ride. This generally occurs for three reasons. Your car's shocks are filled with oil, and low temperatures will affect shock absorber oil just like they will the oil in your car's engine. Cold oil is thicker and stickier, resisting flow through the metering holes in the shock absorbers and resulting in a functionally stiffer shock. Low temperatures also make metal springs harder and more brittle, which increases spring rate and helps the springs to better control body roll. The rubber bushings in your suspension react much the same way, getting harder and deflecting less under load. These things will remain true up to the point that your shocks, springs and bushings warm up, but they should still remain a bit stiffer than they would under warmer conditions.

Brakes

The news where brakes are concerned is kind of a mixed bag. Brake pads work as a sort of transducer, turning kinetic energy -- movement -- into thermal energy via friction. Brake pads and rotors require a certain amount of heat to produce the friction required to stop your car; anything below that and you might as well be rubbing greased sticks together. This is particularly true of performance-oriented ceramic, metallic and semi-metallic pads optimized to resist fade at high operating temperatures. Fortunately, most brake pads will produce acceptable stopping power at around 50 degrees Fahrenheit, which means that they'll get up to temperature pretty quickly following initial application. The good news is that, while you may lose a bit of braking power during initial braking at the end of a long straight, low ambient temperatures will cool the rotors very quickly and help to negate brake fade after repeated hard applications.

Tires

Same deal as the brakes here: a mixed bag of news that may ultimately benefit you if you know how to apply it. Tires have a temperature operating range just like brakes do; below a certain temperature the tires' rubber gets hard and loses grip, but getting them up to full operating temperature shouldn't take long if you're really pushing the car to its limits. The downside is that performance-oriented tires optimized to work at high temperatures may exhibit an initial loss of grip. The upside is that cooler ambient temperatures will help to keep the tires cooler for greater longevity and increased stability at high speed. If you're racing, you might consider switching to a softer tread compound to create more friction and to capitalize on the cold air and track. Beware of sudden changes in oversteer/understeer balance in cold temperatures, particularly during corner entry and exit. Shifting tire temperatures can alter the tires' friction characteristics faster than you can compensate.

References

• Race Car engineering and Mechanics; Paul Van Valkenburgh
• The Defense Technical Information Center: US Army Developmental Test Command Operations Procedure; Cold Regions, Materiel Effects