How does temperature affect the speed of a car?

Answer 1

At a drag strip it is very important, too cold <35*f can cause traction problems. Temperature is very important when it comes to horsepower. The rule of thumb is for every 10*f you lower the intake temperature you gain 1% increase in power. That's how cold air intakes/ 60's ram air, cowl inductions work. I've had et's change by 3/10 of a second and 2mph, in the same day- 80 degree track during the day 50 degree track at night.

The way factories rate HP has changed int the last 10yrs. The current SAEJ1349 standards are taken at, " 29.235 inches of Mercury pressure with a higher air temperature of 77 degrees F and zero vapor pressure." The Dyno/gross ratings are at 29.92inches/60*f/and 0 vapor pressure, which equals a 5% difference in power. An example from a magazine, "the new 427ci LS7 Corvette engine rated at 505 hp would probably correct to closer to 530 hp using the performance-industry gross correction factor (C.F.)." So 17 degrees and .685 inches of mercury pressure change equals 25hp. If you want more see link below.

If your talking about top speed..? Aerodynamics and wind direction, are more important.