Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie
Please note that it is not permitted to have referral links posted in your signature. Keep these links contained in the appropriate forum. Thank you.

https://www.boards.ie/discussion/2055940817/signature-rules

Why is using neutral or (freewheeling) bad

Options
2»

Comments

  • Options
    #32
    colm_mcm
    Registered Users Posts: 73,456 ✭✭✭✭colm_mcm


    peasant wrote: »
    Not exactly true. After a long, hot idling period in heavy traffic there's nothing like a good downhill stretch (if you can get it) with a bit of engine breaking to cool things down again.

    Engine braking - good :)
    Engine breaking - bad :mad:


  • Options
    #33
    JHMEG
    Closed Accounts Posts: 7,686 ✭✭✭JHMEG


    peasant wrote: »
    Not exactly true. After a long, hot idling period in heavy traffic there's nothing like a good downhill stretch (if you can get it) with a bit of engine breaking to cool things down again.
    Or the fan.


  • Options
    #34
    peasant
    Registered Users Posts: 17,819 ✭✭✭✭peasant


    colm_mcm wrote: »
    Engine braking - good :)
    Engine breaking - bad :mad:

    ooops ..ze spellink again :D


  • Options
    #35
    Pete67
    Registered Users Posts: 1,257 ✭✭✭Pete67


    Extra engine wear from engine braking is marginal if it exists at all. The engines moving parts are lubricated. The braking effect comes primarily from the energy absorbed in compressing air and discharging it through the exhaust. An engine can do this almost indefinately without ill effect.

    On the other hand, sustained braking using wheel brakes can result in severe overheating of the friction materials in the pads or shoes, can distort or warp discs and drums, and in severe cases can lead to total loss of braking effect. This can happen when to brake fluid is heated to the extent that vapour forms in the wheel cylinders, and is much more likely when the fluid is old and has absorbed a quantity of water from the atmosphere over time. Hence the oft ignored requirement to replace brake fluid periodically.

    Anyway, this is getting away from the OPs original question which related to coasting. Apologies for that.


  • Options
    #36
    peasant
    Registered Users Posts: 17,819 ✭✭✭✭peasant


    JHMEG wrote: »
    Or the fan.

    All the fan does is shovel more air over the hot coolant. I prefer the faster turning water pump for more effective cooling. Faster coolant flow means better dissipation of heat from the entire engine.


  • Advertisement
  • Options
    #37
    Steve
    Moderators, Category Moderators, Entertainment Moderators, Sports Moderators Posts: 22,584 CMod ✭✭✭✭Steve


    JHMEG wrote: »
    You are putting extra wear on your engine by using it for braking, and brake pads are cheaper to replace.


    -snip- sorry.

    /note to self: read the thread properly.


  • Options
    #38
    JHMEG
    Closed Accounts Posts: 7,686 ✭✭✭JHMEG


    peasant wrote: »
    All the fan does is shovel more air over the hot coolant. I prefer the faster turning water pump for more effective cooling. Faster coolant flow means better dissipation of heat from the entire engine.
    The fan blasts cooler air over a radiator that's extremely efficient at dissipating heat. That's why the fan goes off again so quickly.

    Faster coolant flow - but only through an efficient radiator - will cool the engine a tad quicker until the thermostat closes (a cold engine is less efficient), then you can circulate the coolant at a million miles an hour and it won't cool the engine.

    The fan/radiator/thermostat do a fine job and are adequate.


  • Options
    #39
    JHMEG
    Closed Accounts Posts: 7,686 ✭✭✭JHMEG


    Pete67 wrote: »
    Extra engine wear from engine braking is marginal if it exists at all. The engines moving parts are lubricated. The braking effect comes primarily from the energy absorbed in compressing air and discharging it through the exhaust. An engine can do this almost indefinately without ill effect.
    When you are dissipating the kinetic energy of a 1.2 tonne car through the wheels, clutch, transmission and engine then of course things will wear quicker.


  • Options
    #40
    Dr.Millah
    Registered Users Posts: 582 ✭✭✭Dr.Millah


    When ye say 'engine breaking' do you mean the car slowing itself when its in the gear. Or coming down gears to slow the car down, because the latter has bad effects on the transmission.


  • Options
    #41
    Lord Nikon
    Registered Users Posts: 3,610 ✭✭✭Lord Nikon


    *Kol* wrote: »
    Opel Vectra for example. If you coast in gear the fuel is cut off. You can see it on the trip computer the instantaneous fuel consumption goes to 999.9 mpg.

    Not a very accurate trip computer then.

    I too from time to time try to economise on fuel consumption. Best I can get is 47mpg.

    Best place to coast in neutral is going up a slip road off a motorway, I also anticipate traffic too.


  • Advertisement
  • Options
    #42
    Pete67
    Registered Users Posts: 1,257 ✭✭✭Pete67


    When you are dissipating the kinetic energy of a 1.2 tonne car through the wheels, clutch, transmission and engine then of course things will wear quicker.

    That would be true if the kinetic energy is dissipated by converting it to heat via friction. Thats is not the case here. There is no energy dissipated by the clutch unless it is being slipped. The mechanical efficiency of the gearbox/differential is around 98%, so very little energy is dissipated here either. There is no additional energy dissipated through the wheels, as they are rotating at the same rate whether engine braking is being used or not. That leaves the engine, where energy is dissipated primarily by compression of air, generating heat which is lost to the engine cooling system and the exhaust.

    You are far more likely to wear out the clutch thrust bearing by constantly changing in and out of neutral or coasting with the clutch depressed.


  • Options
    #43
    galwaytt
    Registered Users Posts: 12,776 ✭✭✭✭galwaytt


    coasting means you're a passenger in the vehicle, and not in control of it - on corners you will always understeer more than if under power, and this is an unstable condition, and you have no option to change that condition either easily or readily.

    Consider: if you coast on your test, you fail. Coast on your IAM test, you fail.

    Engine braking is very effective at slowing you down. Relying on brakes alone means you're braking is solely down to pad performance. By using engine braking you're spreading the torque reaction (slowing) through the whole drivetrain - and no, it doesn't wear it more. Proof of this is the proliferation of brake shops in the US - automatics have poor engine braking, and so pads/discs/shoes are consumed as much as gas........takes as much energy to stop a car as to move it in the first place. Stand at the bottom of Lombard Street in San Francisco, and you can smell the pads.......

    Trucks can have air brakes to use in lieu of the road brakes, utilising the huge compression avaialable on big diesels.........

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • Options
    #44
    peasant
    Registered Users Posts: 17,819 ✭✭✭✭peasant


    ermm ..air brakes are only ever an addition to regular brakes, mostly used for maintaining constant speed downhill. You'd have a hard time stopping a truck on airbrakes only.

    (Unless you mean the regular brakes on a truck which are operated via compressed air)


  • Options
    #45
    JHMEG
    Closed Accounts Posts: 7,686 ✭✭✭JHMEG


    Pete67 wrote: »
    That would be true if the kinetic energy is dissipated by converting it to heat via friction. Thats is not the case here. There is no energy dissipated by the clutch unless it is being slipped. The mechanical efficiency of the gearbox/differential is around 98%, so very little energy is dissipated here either. There is no additional energy dissipated through the wheels, as they are rotating at the same rate whether engine braking is being used or not. That leaves the engine, where energy is dissipated primarily by compression of air, generating heat which is lost to the engine cooling system and the exhaust.

    You are far more likely to wear out the clutch thrust bearing by constantly changing in and out of neutral or coasting with the clutch depressed.

    I'm not so sure all that is true. eg, as well as compression there is natural friction in the engine. If there wasn't we wouldn't need oil.

    My point it an engine/drivetrain rotating at high speed and under the load of engine braking will wear quicker than one that is idling.


  • Options
    #46
    peasant
    Registered Users Posts: 17,819 ✭✭✭✭peasant


    JHMEG wrote: »
    I'm not so sure all that is true. eg, as well as compression there is natural friction in the engine. If there wasn't we wouldn't need oil.

    My point it an engine/drivetrain rotating at high speed and under the load of engine braking will wear quicker than one that is idling.

    Yeees ...but on engine braking you are missing the explosions :D


  • Options
    #47
    galwaytt
    Registered Users Posts: 12,776 ✭✭✭✭galwaytt


    you don't need oil for friction reduction (entirely) - it's tecnnically possible to build an engine that doesn't need it, but using the likes of PTFE films, friction modifiers etc.

    However, you need oil as your bearings are hydrodynamic - not mechanical. By dint of that design they are very low friction wise. Besides, they're designed to be at full effect on minimum oil pressure, i.e. idling. Otherwise it'd seize every time you came to a halt..........modern engines are low friction engines. Bikes even more so (slipper pistons)

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • Options
    #48
    colm_mcm
    Registered Users Posts: 73,456 ✭✭✭✭colm_mcm


    If an engine and transmission can handle acceleration, then it can surely handle engine braking.


  • Options
    #49
    JHMEG
    Closed Accounts Posts: 7,686 ✭✭✭JHMEG


    colm_mcm wrote: »
    If an engine and transmission can handle acceleration, then it can surely handle engine braking.
    Yes they can, but not forever.
    peasant wrote:
    Yeees ...but on engine braking you are missing the explosions
    True but you have the same force exerted on everything anyway, just from the other end.
    galwaytt wrote:
    you don't need oil for friction reduction (entirely)
    Yes I do. You let me know how you get on with plumbers tape and I'll carry on using oil.;)


  • Options
    #50
    kaizersoze
    Registered Users Posts: 7,042 ✭✭✭kaizersoze


    peasant wrote: »
    ermm ..air brakes are only ever an addition to regular brakes, mostly used for maintaining constant speed downhill. You'd have a hard time stopping a truck on airbrakes only.

    (Unless you mean the regular brakes on a truck which are operated via compressed air)

    I presume he/you meant to say exhaust brake.


  • Options
    #51
    Capital Slow
    Closed Accounts Posts: 50 ✭✭Capital Slow


    ianobrien wrote: »
    You're not saving fuel. You do know that at zero throttle, with the revs over a certain figure, no fuel is being injected (a figure of 1600 to 1900rpm, depending on car), so by coasting, you're using fuel (idle) while leaving it in gear and above a certain rev, you're using no fuel.

    You can feel it kicking in if the revs drop. It's at about 1800rpm in my 2005 Almera.

    I don't understand!

    Do you mean your engine is running at 1600 rpm at nothing? That's impossible, the engine needs fuel to keep running, isn't it?

    Just say that's true, my other question is, my car is a 97 KIA, how do I know immediately whether my engine has the same feature as your relatively new car apart from trying it out?


  • Advertisement
  • Options
    #52
    JHMEG
    Closed Accounts Posts: 7,686 ✭✭✭JHMEG


    All fuel injected cars cut fuel when decelerating to improve emissions.


  • Options
    #53
    Pete67
    Registered Users Posts: 1,257 ✭✭✭Pete67


    Do you mean your engine is running at 1600 rpm at nothing? That's impossible, the engine needs fuel to keep running, isn't it?

    The engine needs fuel to provide power to the wheels, but when the wheels are driving the engine, ie when you lift your foot off the accelerator, then no fuel is required. For fuel efficiency and to improve emissions, the ECU shuts off the fuel supply until the engine speed drops to idle, at which point fuel is restored to keep the engine running. You can often sense this as a slight surge of power if you do not depress the clutch as the car slows down to the point where the engine rpm is around 700 - 800.


  • Options
    #54
    Biro
    Closed Accounts Posts: 4,091 ✭✭✭Biro


    maoleary wrote: »
    I don't think that's correct. Best practice at Institute of Advanced Motorists is to brake using your gears. (for instance, if you engage a gear and leave the acc pedal alone, the car's speed drops anyway, and faster than if you were coasting)

    Actually, the IAM say that using gears to slow is no longer needed, as modern brakes are so efficient. They say "Gears to go, brakes to slow" to get people out of the habbit of slowing via the gears, which gives no visible sign to the people behind that you are slowing i.e. no brakelights. However, you do stay in gear while braking!


  • Options
    #55
    ianobrien
    Registered Users Posts: 2,755 ✭✭✭ianobrien


    JHMEG wrote: »
    You are putting extra wear on your engine by using it for braking, and brake pads are cheaper to replace.

    Horse manure. Engines are built to take it, assuming you're not revving it to 7000rpm plus!!!!!!!!!!!


  • Options
    #56
    ianobrien
    Registered Users Posts: 2,755 ✭✭✭ianobrien


    Capital Slow wrote: »
    I don't understand!

    Do you mean your engine is running at 1600 rpm at nothing? That's impossible, the engine needs fuel to keep running, isn't it?

    Just say that's true, my other question is, my car is a 97 KIA, how do I know immediately whether my engine has the same feature as your relatively new car apart from trying it out?

    Simple, the engine is being turned by the wheels, through the gearbox. It's the kinetic energy from the momentum of the car that is turning the engine, via the gearbox, not the energy released by the combustion of fuel.

    Even the 1980's Escort XR3i had that system, and that used an early mechanical fuel injection, a Bosch system I think.


  • Options
    #57
    ianobrien
    Registered Users Posts: 2,755 ✭✭✭ianobrien


    You'll soon learn NOT to free-wheel in the Alps, if you ever drive there. You won't have any brakes left, as they'll have burnt/boiled. That's why they have sand traps at the bottom of the hills.

    That reminds me of a story of a friend of mine who had the habit of freewheeling. He was on holidays in his camper, and just lost the brakes coming down one steep decent in the Alps. We met him in the Campsite later, and he was ranting over the "unsafe design, inadequate brakes etc". We pointed out that we came down the hill in the same type of vehicle, with a bigger load and we hadn't any problems. We had a look at his camper and told him to throw the fancy chrome wheel trims in the bin, as they were not allowing enough brake cooling, and to not freewheel, as the engine will take it. After all, campers engines are designed for lead footed delivery drivers! Needless to say, he didn't like it......


Advertisement