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Cigarlover 1

Do The Rising Gas Prices Effect The Speed You Drive?

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Speeding on the highway adds a surprising amount to your fuel costs.

With gas prices rising, gas-saving advice abounds: Drive more gently, don't carry extra stuff in your trunk, combine your shopping trips.

This is all sound advice but there's one driving tip that will probably save you more gas than all the others, especially if you spend a lot of time on the highway: Slow down.

In a typical family sedan, every 10 miles per hour you drive over 60 is like the price of gasoline going up about 54 cents a gallon. That figure will be even higher for less fuel-efficient vehicles that go fewer miles on a gallon to start with.

The reason is as clear as the air around you.

When cruising on the highway, your car will be in its highest gear with the engine humming along at relatively low rpm's. All your car needs to do is maintain its speed by overcoming the combined friction of its own moving parts, the tires on the road surface and, most of all, the air flowing around, over and under it.

Pushing air around actually takes up about 40% of a car's energy at highway speeds, according to Roger Clark, a fuel economy engineer for General Motors.

Traveling faster makes the job even harder. More air builds up in front of the vehicle, and the low pressure "hole" trailing behind gets bigger, too. Together, these create an increasing suction that tends to pull back harder and harder the faster you drive. The increase is actually exponential, meaning wind resistance rises much more steeply between 70 and 80 mph than it does between 50 and 60.

Every 10 mph faster reduces fuel economy by about 4 mpg, a figure that remains fairly constant regardless of vehicle size, Clark said. (It might seem that a larger vehicle, with more aerodynamic drag, would see more of an impact. But larger vehicles also tend to have larger, more powerful engines that can more easily cope with the added load.)

That's where that 54 cents a gallon estimate comes from. If a car gets 28 mpg at 65 mph, driving it at 75 would drop that to 24 mpg. Fuel costs over 100 miles, for example - estimated at $3.25 a gallon - would increase by $1.93, or the cost of an additional 0.6 gallons of gas. That would be like paying 54 cents a gallon more for each of the 3.6 gallons used at 65 mph. That per-gallon price difference remains constant over any distance.

Engineers at Consumer Reports magazine tested this theory by driving a Toyota Camry sedan and a Mercury Mountaineer SUV at various set cruising speeds on a stretch of flat highway. Driving the Camry at 75 mph instead of 65 dropped fuel economy from 35 mpg to 30. For the Mountaineer, fuel economy dropped from 21 to 18.

Over the course of a 400-mile road trip, the Camry driver would spend about $6.19 more on gas at the higher speed and Mountaineer driver would spend an extra $10.32.

Driving even slower, say 55 mph, could save slightly more gas. In fact, the old national 55 mph speed limit, instituted in 1974, was a response to the period's energy crisis.

It was about more than just high gas prices, though. The crisis of the time involved literal gasoline shortages due to an international embargo. Gas stations were sometimes left with none to sell, and gas sales had to be rationed. The crisis passed, but the national 55 mph speed limit stayed on the books until the law was loosened in the 1980s. It was finally dropped altogether in 1995. (The law stuck around more because of an apparent safety benefit than for fuel saving.)

Despite today's high gas prices, don't expect to see a return to the national 55 mph speed limit. The law was unpopular in its day, and higher speeds have become so institutionalized that even the Environmental Protection Agency's fuel economy test cycle now includes speeds of up to 80 mph.

Driving 10 miles per hour faster, assuming you don't lose time getting pulled over for a speeding ticket, does have the advantage of getting you to your destination 50 minutes sooner on that 400 mile trip. Whether that time difference is worth the added cost and risk is, ultimately, up to you.

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Around town my driving hasn't changed much. For the majority of the time on the high way I set the cruise on the speed limit which is usually 55 around here and let it be.

So has anybody changed the way they drive since gas prices have started going up? If not do you plan to if it reaches a certain point?

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I hear ya key chain. I use to be horrible for going 15 to 20 over the speed limit. Now when I set the cruise at 55 I feel like a turle going down the road. I like to think I'm saving my self an adequate amount of money. Plus it's safer and don't have to worry about getting a speeding ticket.  ;)

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Yup, 100%. There is a big difference if I'm going 55 and spinning 2000 rpm's, or 70 and spinning 2500 rpm's. I can just see my gas gauge going towards E. I would rather just drive 55, save some gas, not have to worry about smokey's, and be safer.

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I also know that not letting your car idle for a long time is a good way to save gas, and yet I still let it warm up in the driveway for a good ten minutes on those below 30 mornings.  Can't stand shivering while I drive.

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Time is money.

I don't drive particularly fast on the highway, but the gas prices aren't high enough to make me drive more slowly. Speeding tickets, on the other hand.... :P

The few bucks I might save are not worth the extra time I'll have on my hands when I do reach my destination 8-)

Over a year, yeah, I could save 100 bucks or 200 bucks.  But that translates into many more hours spent in the car as well...

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I also know that not letting your car idle for a long time is a good way to save gas, and yet I still let it warm up in the driveway for a good ten minutes on those below 30 mornings. Can't stand shivering while I drive.

But it's better for the life of your engine to let it warm up rather than drive it form a cold start. At least that's what I've heard. I'm no mechanic. lol

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Time is money.

I don't drive particularly fast on the highway, but the gas prices aren't high enough to make me drive more slowly. Speeding tickets, on the other hand.... :P

The few bucks I might save are not worth the extra time I'll have on my hands when I do reach my destination 8-)

Over a year, yeah, I could save 100 bucks or 200 bucks. But that translates into many more hours spent in the car as well...

So Tokyo I just have to ask is there a price that gas would reach that would make you slow down. Say $4.00 a gallon.

I'm just kinda getting intrigued by this whole gas price thing. When I started driving you could get gas for .99 a gallon and I'm just getting to the point where I'm fed up with the prices.

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I hear ya key chain. I use to be horrible for going 15 to 20 over the speed limit. Now when I set the cruise at 55 I feel like a turle going down the road. I like to think I'm saving my self an adequate amount of money. Plus it's safer and don't have to worry about getting a speeding ticket.  ;)

I don't think it's any safer.  In fact , I believe it's more dangerous by not keeping up with the flow of traffic.  I'm not saying do 15 or 20 over to be like everyone else but doing 15 under the limit is deffinately a hazard.

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Sorry I guess that reads wierd. 55 is the speed limit on the road I travel. I don't drive under the limit. I usually just set it at the limit.

People that drive under the speed limit make my blood pressure spike. That's one thing I don't understand and there seems to be alot of people that do that here in MA.

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we are wasting a lot of gas here in florida then. Along a lot of our interstates it is 70 mph, which means a lot of people are going 80 - 85. I usually keep my cruise on the interstate at 76.

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i just do the speed limit, which is mainly 65(night)70(day) where i drive, but even during the day i usually keep it at 65, no cruise control either, which does kinda suck.  in my truck it costs me about $40-45 to fill it up, i can go almost two weeks on a tank driving to and from work and one fishing trip on the weekends.  if i go fishing more than once then i might go a week and a half.

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I can't afford a ticket,so speed limit or just under is how i roll.Gas prices effect how far i want to travel.I'm with muddy,i'm on "p" a lot now.

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