General Drive slower = save fuel?

Discussion in 'General Discussion' started by pastore, Monday 7th Sep, 2015.

  1. pastore Banned ★ ★ ★ ☆ ☆

    United Kingdom pastore London
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    I normally take the big A roads to work everyday but lately i been taking the little roads. SO instead of doing about 50mph i do like 30mph and the thinking is if i drive slower i will use less fuel so i will save money. Takes me a little longer to get home but i don't really mind as long and im saving money.

    BUT....

    Does it really save you money driving slower? your constantly stopping and starting, for example traffic, lights, crossings, ramps etc. so doest that eat up more fuel that way?

    Has anyone ever tried this?
     
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  2. Ichiban Founder Staff Team

    England CJ Leeds
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    Its a know fact that you tend to consume more fuel in stop and go traffic no matter how you drive the car. Consistent speed over long journey with fewer stoppages results in better fuel efficiency.
     
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  3. pastore Banned ★ ★ ★ ☆ ☆

    United Kingdom pastore London
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    so stick to A roads?
     
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  4. Ichiban Founder Staff Team

    England CJ Leeds
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    Yes pretty much since yours is an auto be very gentle with the throttle use, I have a IMA Hybrid Jazz and use the throttle as if there is a egg behind it any harder the egg will crack . If you Brake, come off the throttle and set off from a full stop gently you will see a massive increase fuel efficiency.
     
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  5. pastore Banned ★ ★ ★ ☆ ☆

    United Kingdom pastore London
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    thanks but what do you mean by throttle? you mean the gas pedal?
     
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  6. FirstHonda Premium Member Club Supporter

    ^^Yes, the throttle is just another name for the accelerator ('gas pedal' being the American name for the same).

    I've driven automatic for years and @Ichiban is quite right about how to drive for maximum economy. Try to look ahead as much as possible, and accelerate and brake accordingly - and gently.
     
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  7. pastore Banned ★ ★ ★ ☆ ☆

    United Kingdom pastore London
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    thats what I've stated doing last couple of days.

    what about actually not braking but just taking your foot off the pedal to slow down? is hat better than braking?
     
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  8. jd1959 Valued Contributor ★ ★ ★ ☆ ☆

    Ireland Zack Kilkenny
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    All cars are different in terms of finding the 'sweet spot' in terms of speed for fuel efficiency. In terms of taking your foot off the pedal you car uses -0- fuel as it shuts off the injectors to coast, by putting it in neutral you wind up using a slight amount of fuel to keep the engine ticking over. At least that's my understanding.

    Something that has helped me to increase fuel economy is getting a cheap osb-2 Bluetooth dongle off ebay and using my phone or tablet with torque Torque — OBD2 Performance and Diagnostics for your Vehicle to keep track of what the engine is doing and the moment by moment fuel economy, throttle position, engine load and so on.

    The hypermiling forums have good tips for getting better MPG although some are quite extreme and potentially dangerous.
     
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  9. pastore Banned ★ ★ ★ ☆ ☆

    United Kingdom pastore London
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    i don't understand all this technical talk, are you saying that if you buy this off ebay then it tells you how much fuel your wasting?
     
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  10. jimjams Expert Advisor ★ ★ ★ ★ ★

    United Kingdom nobody zoned
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    Your MPG at a constant 30mph would be worse than at a constant 50mph

    The main points are
    1. If you run the car on your driveway you get 0 MPG (which is really bad). The reason why the engine uses fuel when it is idling is due to pumping losses etc. You can consider this to be like an ideal engine that runs without requiring any fuel when no load is connected, but it leaks fuel from the fuel line
    2. If there was no atmosphere (having enough O2 on-board for yourself and for the engine) then the amount of power required at any speed is proportional to the rolling resistance, which can be considered to be linear
    3. But there is an atmosphere, and the power to overcome drag starts to dominate over ~60mph, and the power to overcome drag is proportional to the cube of the speed

    Using point 1, if you drive very slowly, you are losing more fuel per mile than if you drive faster.
    Using point 2, you will start to require more fuel in the engine to overcome the rolling resistance, but you would have to reach quite a high speed until the power required to overcome rolling resistance equalled the rate at which the ideal engine is leaking fuel
    Using point 3, once the drag starts to dominate, you can forget points 1 and 2.

    So most cars are at their best MPG at 40mph to 50mph, depending on points 1 and 2 and 3
     
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  11. jd1959 Valued Contributor ★ ★ ★ ☆ ☆

    Ireland Zack Kilkenny
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    It will read the cars computer and tell you moment for moment what your MPG is. With that info you can figure out what speed gives the best fuel economy or how fast you can start off before your fuel economy takes a massive drop.

    Example I found for my bus if I drive over 113km/hr the fuel economy drops from 12km/l to 9km/l so driving a bit slower on the motorway can save me a good bit of money without taking a whole lot more time for the journey.
     
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  12. pastore Banned ★ ★ ★ ☆ ☆

    United Kingdom pastore London
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    sounds like a lot of hassle to go through, are you really saving that much money?
     
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  13. jd1959 Valued Contributor ★ ★ ★ ☆ ☆

    Ireland Zack Kilkenny
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    It has helped me to regularly average around 11km/l vs 9km/l when I didn't have it, so about 100km per tank which at today fuel price works out to be 12 euro, over a year it should save me around 500 euro. Yes it is a bit of a pain but at least in my case helping to train my foot not to be so aggressive will pay for most of my insurance next year.
     
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  14. exec Premium Member Club Supporter

    United Kingdom London
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    Yeh that is called engine braking, well its a form of engine braking and you will save fuel. I do it all the time when coming upto lights just take my feet off the gas pedal and let the car slow down then use the brakes to actually come to a halt, also driving in general it comes in useful just taking feet off to let car slow down. Don't do it to save fuel though, it just feels more efficient and fluid driving like that.
     
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