'Petrol efficiency experiment; an increase of 20%' blog discussion

Options
1…2526272830

Comments

  • silverwhistle
    silverwhistle Posts: 3,791 Forumite
    First Anniversary Name Dropper First Post
    Options
    Idiophreak wrote: »
    I'm fairly sure "driving sensibly" includes sticking to the speed limit, reading road signs, stuff like that...

    Or as a motorcycle Met plod once told me over a beer about a booking he once made: "I'm not booking you for doing 90 mph down Hyde Park, [n.b. at 4 in the morning] but because you didn't see me!"
  • wiggers
    wiggers Posts: 83 Forumite
    First Anniversary Combo Breaker First Post
    Options
    4. The brake is a money burner. Where safe, allow yourself to slow naturally When you press the brake you are effectively converting the energy you’ve paid to put into the car into heat. Instead if you can slow naturally you’re using all the stored energy most efficiently. Good road positioning is crucial for this.

    This is nonsense! It makes no difference if you use the brake, engine or just let friction slow you down. You use fuel only to a) increase momentum (accelerate) and b) to overcome friction (air resistance, mechanical losses, tyre rolling resistance). Putting your foot on the brake does turn momentum to heat, but it is not until you press the accelerator to speed up again that you use fuel.

    The important thing about braking is to anticipate, think ahead and to not brake unnecessarily. Use the Cruise Control (if fitted) or concentrate on your speed to keep momentum constant. Lift off a bit earlier so the hazard has cleared before you arrive in order to keep your speed up.
    If your outgoings exceed your income, your upkeep will be your downfall.
    -- Moe Howard of The Three Stooges explaining economics to brother Curley
  • Skools_Out
    Skools_Out Posts: 258 Forumite
    First Anniversary Combo Breaker First Post
    Options
    wiggers wrote: »
    This is nonsense! It makes no difference if you use the brake, engine or just let friction slow you down. You use fuel only to a) increase momentum (accelerate) and b) to overcome friction (air resistance, mechanical losses, tyre rolling resistance). Putting your foot on the brake does turn momentum to heat, but it is not until you press the accelerator to speed up again that you use fuel.

    The important thing about braking is to anticipate, think ahead and to not brake unnecessarily. Use the Cruise Control (if fitted) or concentrate on your speed to keep momentum constant. Lift off a bit earlier so the hazard has cleared before you arrive in order to keep your speed up.

    Wow! This thread appears to be a blast from the past :eek:

    Anyway, what you appear to have failed to have considered is where the energy came from that created the original speed.

    What is being suggested is, as you suggest, to think ahead and adjust your speed accordingly to avoid use of the brakes as much as possible. Then you are not using energy only to waste it by using the brakes.

    Finally, if you are a good driver who can drive economically, use of cruise control actually uses a little more fuel in real world driving. That is because cruise control attempts to maintain the car's speed no matter what the road or ambient conditions are.
    What that effectively is doing is constantly opening and closing the throttle to take into account those conditions such as change in wind speed/direction as well as hill and bends in the road in an attempt to maintain the set speed.
  • Cayman_Iguana
    Cayman_Iguana Posts: 3 Newbie
    Options
    In a large car park with 'back-to-back' double rows of spaces, e.g. at a supermarket, try to find a pair of spaces so you can drive through the first and end up facing outwards from the second. This means you when you leave you just switch on and drive away. Saves that slow reversing out process with a cold engine, which uses more fuel.
  • TeeJAy17
    TeeJAy17 Posts: 4 Newbie
    Options
    Has anyone tried coasting (is it legal?) I do this a lot and my fuel computer is very happy with the results. Most engines while turning use a little fuel. If, for example approaching traffic lights you take the car out of gear it well sit at around 800 rpm, whereas leaving it in gear it could be running at 2,000 until it drops to 800 when you are stationary.
  • almillar
    almillar Posts: 8,621 Forumite
    Photogenic Name Dropper First Post First Anniversary
    Options
    There's no law against coasting, but you'll be taught not to do it - it's bad practice as you're not in full control of the vehicle. The engine is disconnected, so you're not getting any engine braking.
    So rule 1 - don't do it.
    Rule 2 - know when you can! Don't coast down a bendy hill. But if you're approaching red lights, that you know will change, you want to slow down as little as possible and go through on green. Coasting may be appropriate here.
    For efficiency, you want to not speed up or slow down.
    It doesn't work like that for revs. You could be at 5,000 RPM and using zero fuel, if you're slowing down via engine braking.
    There's no point in coasting if you're just losing speed you have to get back again, see above, that involves changing speed, which is inefficient. Would be better to stay in gear and hold a constant speed.
  • charlieheard
    charlieheard Posts: 522 Forumite
    First Post First Anniversary Combo Breaker Mortgage-free Glee!
    Options
    Coasting is dangerous according to motoring experts, because you do not have control of the vehicle. Plus the engine uses fuel when you're coasting to keep it idling. If you leave it in gear, modern engines will turn off the fuel supply if the engine is above a certain speed, so coasting can use more fuel
    Jumbo

    "You may have speed, but I have momentum"
  • almillar
    almillar Posts: 8,621 Forumite
    Photogenic Name Dropper First Post First Anniversary
    Options
    Coasting is dangerous according to motoring experts, because you do not have control of the vehicle. Plus the engine uses fuel when you're coasting to keep it idling. If you leave it in gear, modern engines will turn off the fuel supply if the engine is above a certain speed, so coasting can use more fuel


    Have another read at my post above, where I cover all of this.
  • charlieheard
    charlieheard Posts: 522 Forumite
    First Post First Anniversary Combo Breaker Mortgage-free Glee!
    Options
    Ahh, but I said it more succinctly ;)
    Jumbo

    "You may have speed, but I have momentum"
  • almillar
    almillar Posts: 8,621 Forumite
    Photogenic Name Dropper First Post First Anniversary
    Options
    Ahh, but I said it more succinctly ;)
    Sorry, but I disagree - I said MORE! You merely said that you shouldn't coast, and that it uses more fuel than engine braking. Correct.
    I went further, and explained that in certain circumstances coasting can be beneficial, you left that entire part out.
This discussion has been closed.
★ ★ ★ Meet your Ambassadors

Categories

  • All Categories
  • 343.3K Banking & Borrowing
  • 250.1K Reduce Debt & Boost Income
  • 449.7K Spending & Discounts
  • 235.3K Work, Benefits & Business
  • 608.1K Mortgages, Homes & Bills
  • 173.1K Life & Family
  • 248K Travel & Transport
  • 1.5M Hobbies & Leisure
  • 15.9K Discuss & Feedback
  • 15.1K Coronavirus Support Boards