Since gas mileage was recently brought up in the "Where do you normally fill up?
" thread by rookie888
, I thought it would be a good idea to have a discussion about gas saving strategies. His post contains a link to an article in the Toronto Star
, which lists 10 gas-saving ideas from Jim Davidson's book, 75 Ways to Save Gas
. The comments on this article seem to be quite negative, but I hope that the disucssions here can be a little more open-minded. In particular, I'd like to know what you think about nitrogen tires, synthetic oil, and various gas-saving driving techniques. I'm not interested in hearing about how I can use my vehicle less often - I'd just like to share and compare strategies for using less gas per kilometer.
There's no doubt that maintaining a good tire pressure improves fuel economy, and nitrogen makes this easier to do (especially when temperatures fluctuate). I personally use pure nitrogen in my tires, but it's more to avoid the hassle of checking tire pressure and to prolong the life of my tires. I just get the nitrogen levels checked & refilled when I take my car in for maintenance. I use synthetic oil for the same reasons: less engine wear means less repairs and longer lifespan. But it's great to know that these measures might also be slightly improving my gas mileage!
Probably the best driving technique is to avoid going too fast on highways. Most vehicles have an optimum gas mileage when travelling at a speed of 90 - 100 km/h, and gas usage at higher speeds increases quickly (at about 150km/h you're using twice as much gas per km!). I found a chart
with mileage vs speed for 8 different vehicles. The rate that the mileage drops off (the slope) is pretty similar for the 8 different cars, so it stands to reason that most cars will suffer a similar rate of mileage loss.
On city streets, going too fast isn't usually a concern, though you should always think about going a little out of your way to use a highway instead of stop-and-go roads. Besides being stuck in a traffic jam, the biggest waste of gas on city streets is having to constantly stop and accelerate. Here are some of the techniques I use to minimize this penalty:
- Don't waste gas to get to that red light sooner! Preventing the guy in the next lane from cutting into your "shorter lineup" just isn't worth it. Release the gas pedal and coast up to the light. Another advantage to coasting is that the light might turn green before you get there, meaning you won't have to come to a stop at all (while that guy who raced ahead now has to accelerate from zero!)
- Time the lights. Look ahead to the next set of lights and try to determine if it will be green or red by the time you get there. Make use of the pedestrian walk lights (espcially the countdown type), as well as your gut feeling. On your regular commute you'll probably get to know how long each light is. If you think a green light will turn red, let go of the gas (resist the urge to try and beat it). If it's going to stay green, maintain speed or accelerate a little to ensure that you make it. If it is currently red but you think it will change soon, let go of the gas and change to the lane with the shortest line up, to make it less likely that you'll have to brake.
- Leave lots of space between you and the vehicle in front of you. Hopefully you do this anyway, for safety reasons. Drivers on city streets tend to vary their speed, and if you're tailgating them then you're likely applying the brakes every time they slow down a bit, and then re-accelerating to stay on their tail.
Next, there's aerodynamics. Having a roof rack attached can significantly reduce mileage, especially at higher speeds. Most of the air flows over the top of your vehicle, so interfering with it on the roof is going to cost you. Mythbusters showed that using A/C actually uses less fuel than it does to have your windows open, AT HIGHWAY SPEEDS ONLY (I think 80km/h was the break-even point). The Toronto Star article mentioned keeping your vehicle clean for smoother airflow - I'm not convinced that this is going to make a significant difference but I like to keep my car from getting too dirty anyway.
My last gas saving strategy is to avoid uneccessary weight in your vehicle. Don't go removing your spare tire or emergency blanket, but if you've got heavy cargo that you don't need, then unload it before you leave home. That includes a detachable hitch - if you're not going to use it for a while, take it off. A full tank of gas may be heavy, but a low tank is not only more likely to explode in an accident, it also increases condensation (thus diluting the gas and making is less efficient) and can damage your fuel pump which relies on the gas to cool it. I always fill up full, but I never try to go beyond the first click.
Million Dollar Journey also has an older (Jan '07) article about Saving Gas by Maximizing Mileage