Car geek question

[vettecat]

When I got my summer tires put on, the mechanic told me that winter tires cause higher gas consumption. But he couldn't tell me why, aside from thinking it was somehow related to the wider treads. Now I'm curious. Anyone know?

Comments

[totient]

PV=nRT. When air is colder the molecules move more slowly and so more of them settle to the bottom of the atmosphere instead of being bounced back up to the top. Every degree F it gets colder is 1/500 or so more air your car has to move out of the way; the difference between a 30 degree day and an 80 degree day is a 10% difference in air resistance, and since that's the lion's share of the work your car is doing, a similar change in its mileage.

This effect totally drowns out the ethanol/no ethanol effect, as well as the difference between sticky winter tires and the kind of also sticky tires I rather think you're running in the summer.

[vettecat.livejournal.com]

Fascinating. Thanks for the explanation!