With financial markets in a historic tailspin, it's a good time for belt-tightening. One of the best ways is to tame that cash-eating monster: your car. I was perusing the OneThingCT Web site, which offers a collection of one-off things anyone can do to reduce personal energy consumption. One suggestion is to put your car on a diet, and the idea appealed to me. It's a strategy with numerous benefits: It can save money, help the environment and make you healthier, too. Estimate how many miles you drive every week or month. Then give yourself a budget -- the total number of miles you allow yourself to drive over a period of time. The point, of course, is to be stingy. At the very least, you want to allow yourself only enough miles for commutes and errands that are absolutely necessary. But if you want to cut costs and perhaps spur a change in your lifestyle, allow yourself a mileage ration that's between 10% and 25% less than what you drive now. Seeing how much you're saving can provide good inspiration. So here are calculators and other resources to help you. RideShareOnline shows you how much you spend on gas while commuting, alongside how much you could save by splitting the cost with carpool buddies. DriveLessSaveMore goes one step further by showing you how much you would save per month, week or year by cutting down on driving by 40%. These calculators require mileage estimates, as well as your car's fuel consumption and the price of gas. If you don't know these things offhand, you can use Google ( GOOG) maps to find distances. The Department of Energy lists weekly gas prices nationwide, regionally and in select states and cities. The DOE also provides fuel consumption stats for most cars.