This week on Car Talk, can Dave put two snow tires on his girlfriend's car, or does he need to buy a full set, as his tire dealer insists? Tom has a two-tire solution that may qualify for next year's Nobel Prize in Bad Advice. Elsewhere, Cathryn's car is going "boom boom" whenever her mechanic isn't around to hear it; Helen's Toyota gained and then lost an extra 100 miles per tank of gas after she moved to Salt Lake City, and, can Keith install an air conditioner in his Geo Metro, and still make it up a hill?  Also, on Stump the Chumps, we find out if Tom and Ray got Pam's Volvo to stop smoking. All this and more, this week on Car Talk.