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February 28, 2010

Car Talk

Despite conventional wisdom, cars don't really move faster in cold weather

Syndicated columnists

Dear Tom and Ray:

Was it just me, or did my Jeep really seem faster this morning in the cold, -15 F air? I've always heard that the colder the air, the better the combustion. Is there any truth to my observation this morning, or was I just driving faster so I could get out of the cold car quicker?
--Matt

Ray: The car wasn't moving faster, Matt. Your brain was moving slower.

Tom: It's true that colder air is denser than warm air, and that means you can put more air into the cylinders when it's cold. But I don't think the difference is detectable by the average driver.

Ray: Right. Turbo-chargers give you more power using a similar approach. They compress the air, and force a lot more of it into the cylinders. That allows you to burn more gasoline, and the result is more power. But that takes a tremendous amount of external pressure. It's not something you can duplicate just by lowering the temperature, even to the butt-chattering level you just experienced, Matt.

Tom: So, what made it feel like your car was faster that day? Well, it could have been that your car stayed in high-idle or warm-up mode longer than usual. If the engine were idling at 2,000 rpm instead of 1,000, the engine would sound louder. It also might feel more powerful to you because you'd have to step harder on the brakes to stop it, and press less hard on the accelerator to get it moving.

Ray: Or, maybe your speed just seemed a lot higher because you were barreling down the road, trying to peer through the only four-inch hole in the ice that you were able to scrape off your windshield.

(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk Web site.)

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