hi everyone
sorry if this is a repeat question, used the search facility but it didnt return anything
question is:
does harsh braking use up petrol? if so why?
thanks to all in advance
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No it doesn't use any fuel.
However, bad driving which leads to the neccessity of harsh braking can.
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thanks.... it was just that when i have had to brake harshly because of hazards the fuel needle dropped a bit and didnt go back up so i thought it may have something to do with that
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thanks.... it was just that when i have had to brake harshly because of hazards the fuel needle dropped a bit and didnt go back up so i thought it may have something to do with that
You see it's a bit like when you buy a couple of pints at the bar and then have to walk very carefully to prevent spillage. Stop suddenly and it slops over the top and spills on your shoes, which is a waste. It's just the same with these new fangled open-topped petrol tanks we have these days. Or something like that.
By the way, did you know petrol in the North of England is chilled and has a head on it?
;-)
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Surely as you brake suddenly all the petrol rushes towards the front of the tank? It will stay there until forced back again so, after braking harshly, you then need to accelerate harshly to even things up.
You may find the back of your neck covered in sick though.
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Having had Boddingtons I can well believe it. "Its the water that makes it special" yeah right, wherefrom, the Manchester ship canal?
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does harsh braking use up petrol? if so why?
No, harsh braking doesn't use petrol.
It's the harsh acceleration afterwards, to get back up to speed that does.
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Err....anyone seen the name of the thread author?
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Espada III - well if you have a family and need a Lamborghini, what else do you drive?
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And the first registered date? 01 April?
Puh-lease.....
No Do$h - Alfa-driving Backroom Moderator
mailto:moderators@honestjohn.co.uk
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No Do$h... yes i just registered a few months ago, whats with the Puh-lease?
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Espada III... what about my name?
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Big Pun? Pun?
April 1st?
Perhaps I should have put [groan] after the "Puh-lease" to signify my appreciation at the humour and/or terrible coincedence.
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You guys are being very unfair. Its a very reasonable question about petrol conmsumption that BP has posted on here, and deserves a sensible answer.
Now BP its like this.
The handling and road holding pixies that live in and around your suspension get jiggled about a lot. One of them has probably ended up in your petrol tank.
Now picture the poor guy floundering in your tank, nearly drowning when you suddenly brake. He get flung forwards and finds the safety of your fuel guage sender float. Naturally he climbs on it, and hence with the extra weight (some of these pixies weigh a bit) your float sits lower in the petrol thereby causing a lower reading on your guage.
When your tank gets empty enough for him to paddle, he will climb off the float and out the tank and all will be back to normal.
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Virtual Edit (TM) bought to you by No Do$h
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who needs an edit button when you have a tame mod
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Big Pun? Pun? April 1st? Perhaps I should have put [groan] after the "Puh-lease" to signify my appreciation at the humour and/or terrible coincedence.
was a coincedence... i tried many usernames were all taken so chose this one which is short for Big Punisher for those of you who dont know who he was search him up
the date was coincedence aswell because that is the first time i seen the site and thought it would be good to register.
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Coincidence it is then. Still, you have to see the funny side to it.
:o)
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It takes the kinetic energy of the vehicle and converts it into heat (brakes) and sound (screaming from passengers and driver of car(s) behind). This kinetic energy came from the petrol so yes in a sense it uses petrol.
Good advance observation and judgement of appropriate speed can often avoid braking altogether, or reduce the amount needed. (Sorry to state the obvious.)
But, does harsh braking to a given speed at a given point on the road use more energy than gentle braking to the same speed at the same point on the road? It probably depends on the speeds involved: 50mph in 5th is probably more fuel efficient than 30mph in 4th, so harsh braking from 50 to 30 is more efficient than slow braking from 50 to 30. The difference is probably not worth bothering about though.
Leif
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Yes but harsh braking means you were going to fast in the first place. By braking hard you have wasted the fuel that you used building up momentum. The best way to save fuel is never to use your brakes!
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The best way to save fuel is never to use your brakes!
I had an uncle who was a right Scrooge. He had a tendency to use the car in front to stop rather than his brakes - now I know why! :-)
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Tell me if this right?
When you brake at any speed, the servo can use up some power of the engine meaning you stop (in thoery) at a shorter distance because you're sapping power from the engine?
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Its not what you drive, its how you drive it! :-)
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> the servo can use up some power of the engine
Errr... the engine can use up some of the kinetic energy of the car. Just for a moment, imagine:
Say you're sitting at traffic lights. And you rev your car until it is doing 3,000 rpm. And then you take your foot off the accelerator, it will drop to 750rpm tickover.
So the car will always return to tickover speed, as it takes energy to keep the engine spinning at a higher speed. (At tickover you use a small amount of petrol to keep it spinning at 750rpm.)
Soooooo imagine you're doing 70mph at 3,000 rpm. Foot off the accelerator pedal and the car will slow down, immediately.
That is engine braking. You transfer the kinetic energy of the car into heat energy losses in the engine and rotational energy in the clutch.
Don't believe me? Try doing 30mph in 1st gear. Then take your foot off the gas, and watch the car come to a standing stop (almost). That's engine braking.
Try putting your foot on the brakes as well, and you'll stop yet quicker!
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Considering the losses of the servo is becoming really academic! Most cars use a suspended vacuum servo. This means that the vacuum builds on both sides of the diaphragm during normal running, and when you press the pedal, atmospheric pressure is admitted to the side of the diaphragm which assists in pushing the master cylinder piston. Cost in terms of fuel consumption, utterly negligible.
Engine braking just means that it takes more torque to turn the engine over than the engine is producing at that time. So, assuming there is some overrun fuel cut off, the engine produces no output torque, but you still need to provide torque to drive the gas exchange process, and, the dominant effect, compression. You still have to compress the charge, but you get no payback in terms of combustion for it. Diesels and high compression engines have more engine braking for this reason.
In trucks, for further non-friction braking, a second compression type cycle is obtained by using a valve to restrict the exhaust pipe, an exhaust brake. So, the engine has to compress the charge as it tries to pump it past the closed valve.
At any engine speed in neutral, the torque generated by the engine is balanced by the internal friction torque of the engine - there is none extra until a demand is placed on the engine.
No extra rotational energy goes into the clutch. In a manual car, the kinetic energy of the car, and that of the rotating masses is geared together. If one changes, so does the other. In fact, one can combine the two, and derive an effective mass for the car, which includes the effect of ratoary inertia.
The dramatic effect that repeating the experiment in different gear ratios gives is because, interestingly, the effects of rotary inertia scale with gear ratio squared. So, the engine braking effect, like the engines accelerating effect is much stronger in lower gears.
Number_Cruncher
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braking can actually save you fuel in the case of the Toyota Prius - www.toyota-hawaii.com/vehicles/Prius/braking.html When you brake, it takes the energy lost to deceleration (potential energy) and stores it so it can be used to kangaroo down the road...
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