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Old July 13th, 2013, 09:40 PM   #21121
ChrisZwolle
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Never in the Netherlands, except in parking garages. Engine braking makes no sense in an ultra-flat country like the Netherlands.
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Old July 13th, 2013, 09:57 PM   #21122
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Never in the Netherlands, except in parking garages. Engine braking makes no sense in an ultra-flat country like the Netherlands.
It saves on fuel.
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Old July 13th, 2013, 09:59 PM   #21123
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I usually let the vehicle roll out as much as possible, but I don't shift down to decelerate ahead of a traffic light or off-ramp.
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Old July 13th, 2013, 10:11 PM   #21124
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I usually let the vehicle roll out as much as possible, but I don't shift down to decelerate ahead of a traffic light or off-ramp.
I try to do it, but I am not always that patient. It also forces one to react to the road beforehand and make the drive smoother, but slower. Most of the time one has to change the gear anyway, so it's quite ok to utilize it a bit.

Although, I use breaks in slowing down for possible priority of those countless right hand side streets. Basically inside build up area it is mostly pointless to use engine break, aside from roundabouts and turning (because that's the only place where one changes the gear anyway).
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Old July 14th, 2013, 12:13 AM   #21125
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I try to do it, but I am not always that patient. It also forces one to react to the road beforehand and make the drive smoother, but slower. Most of the time one has to change the gear anyway, so it's quite ok to utilize it a bit.

Although, I use breaks in slowing down for possible priority of those countless right hand side streets. Basically inside build up area it is mostly pointless to use engine break, aside from roundabouts and turning (because that's the only place where one changes the gear anyway).
I always try to do the same. But still think it might have sense to engine brake in built up areas as the speed limits are set quite low. I have experienced shifting down to second gear may slow down the vehicle from fifty to twenty. Then it is better for brakes preservation.

Obviously if i have to suddenly slowdown eg in case of accident on motorway, i do not bother about engine braking.
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Old July 14th, 2013, 02:43 AM   #21126
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It saves money on breaks maintenance and fuel. I always engine break, I like shifting but one must be moderate on clutch as well.
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Old July 14th, 2013, 02:49 AM   #21127
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How does it save money on fuel? Isn't it the other way around? Less revolutions - less fuel?
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Old July 14th, 2013, 03:27 AM   #21128
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I dont know, but I saw already comsuption computer showing minimal comsuption when using clutch + break combo, instead of engine breaking
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Old July 14th, 2013, 03:43 AM   #21129
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I rarely use the brakes, they even have dusk an oxide on it and the car only have +56k kms…

In fact, I use "shift down & shift up". Yes, I said shift up. My Polo, like TDIs and other engines, has injection system controlled by computer and it has a program that disconnect the fuel injection when the engine can be moved by the movement of the wheels.

So, if the car can be moved by inertia and the wheels are connecter to the engine, the consumption will be zero. That's why I shift up, the car still "roll out" but the fuel injection will be disconnected, plus, my car has a low retention rate.

Also I shift down when I want to reduce speed or stop, or even maintain the speed when I downhill, and the injection will be disconnected.

Obviously the injection is disconnected if I don't touch the accelerator.

But in city normally I roll out, specially if I was in 1st or 2nd gear and the stop, give way or red light is far away.

Also I roll out inside parkings. In my garage (a 4 semi-level underground garage ) I roll out down hill the 8 ramps until my spot.
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Old July 14th, 2013, 04:52 AM   #21130
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Quote:
Originally Posted by Verso View Post
How does it save money on fuel? Isn't it the other way around? Less revolutions - less fuel?
Just ask the expert
In modern engines (let's say all those with electronic injection), when you engine brake, the "cut-off" function is engaged: the engine rotates but no fuel is injected. The engine is moved by the vehicle's kinetic energy, flowing through the powertrain; and that energy is spent contrasting the engine's internal frictions, thus slowing down the vehicle.

In fact you can have three conditions:
- idle, at minimum rpm, with a minimum of fuel injected in order to win the internal frictions
- accelerating (or keeping constant speed), with fuel injected to generate the necessary amount of torque
- coasting (= engine braking), with no fuel injected

Slowing down a vehicle means dissipating the amount of kinetic energy previously gained by burning fuel while accelerating. You have two main options (plus all shades of gray in the middle):
1) you can depress the clutch and apply brakes, which means you will convert kinetic energy to heat generated by the brakes fricton (consuming them), AND you will burn fuel to let the engine idle. This can also be dangerous because getting in a bend without a gear engaged can easily challenge the vehicle's balance.
2) you can lift the gas pedal, so that the cut-off function will be immedately engaged and no fuel will be injected, and energy will be converted into bringing the engine to higher revs, as we said before.
The higher the revs, the higher the amount of energy needed to push the engine (due to more internal frictions), so shifting down to a lower gear will bring to a quicker stop; but also to higher wear, and that's way it's a sporty trick to not exceed with.
A good rule-of-thumb is to keep the same speed-gear ratio you apply when accelerating, or just forcing it a bit down. Shift down before the engine reaches its minimum revs (same way you shift up, but reversed).

The only limits of coasting are that the rate of kinetig energy reduction will be lower than by simply braking, so you will need more space/time to reach the same low speed; and, of course, when the engine comes to its minimum revs it can't go down anymore and you'll need to brake anyway.
In real situations you will usually combine the two methods, with brakes integrating the cut-off operation. This way you will have all the advantages of coasting while still perfectly controlling your stopping distance.

Also, never shift down into 1st gear because it's too weak to withstand full deceleration, and you may damage the transmission.
Unless you drive my damn Passat TDI, which thanks to stupid "Bluemotion" engineering has such looong ratios that 2nd gear can't go below 25 km/h only vehicle with which I shift all the way to 1st gear.


I make an intense use of coasting and I can state that it's the main way of reducing fuel (and brakes) consumption. A LOT of fuel.
Compared with my parents (with same cars), who don't use it enough, I burn 30 to 50% less fuel, and I'm in an ultra-flat area
When I first drove an A/T I felt dumb, too much brake pressing and no control when setting up curves... then I discovered the trick for forcing it into lower gears

A good way to improve the system (and general driving safety) is keeping a good distance and anticipate what's going on in front of the car you're following: e.g. shift down immediately when next cars are braking or signalling a turn, or if the traffic light down the street turned yellow (and you won't reach it in time...).
The trick at traffic lights is great because coasting from a long distance means I may still be at 20-30 kph when it turns green*, so I'll speed up immediately and with LOT less fuel.

Other tricks are, of course, keeping a perfectly constant speed (a good distance helps a lot); and my experience says that it's better a strong acceleration, to get quickly to constant speed, than a loooong mild acceleration (less fuel per distance, but for much more time!).


So I find the best possible behaviour is to accelerate quickly, then keeping constant speed and wide distance, and decelerate as slowly as possible.
This will be great both for fuel consumption AND to keep a smooth traffic flow.

There's no need to drive as grandma if you want to save fuel... you may even waste it.

I'm an absolute pro with these issues


*some new Dutch lights fooled me they're permanently red on all directions until you pass the sensor, then they give you an instant but short green.
So I arrived ultra slow on the sensor, very distant from the intersection, then I got an unexpected quick green-yellow sequence and I had to run to catch it
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Old July 14th, 2013, 05:33 AM   #21131
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Too long, didn't read. Thanks for your exhaustive explanation, I learnt a few new things. Once I drove down from a mountain pass in neutral to save on fuel.

Last edited by Verso; July 14th, 2013 at 05:42 AM.
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Old July 14th, 2013, 12:08 PM   #21132
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It's some time already but I remember that when doing the driving license rides my instructor insisted on engine breaking and explained it quite well why.

Besides fuel economy and letting breaks to rest, it is also good for the engine itself as the forces on the engine are smaller than the combustion forces.
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Old July 14th, 2013, 12:16 PM   #21133
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I like automatic transmission. Modern A/T let you up- and down-shift. I drove a car with 6 automatic shifts on A/T, pretty cool.
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Old July 14th, 2013, 12:44 PM   #21134
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Modern A/T are pretty awesome.

Nothing to do with old american 4 speed with torque conversion.
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Old July 14th, 2013, 01:01 PM   #21135
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Quote:
Originally Posted by Verso View Post
Too long, didn't read. Thanks for your exhaustive explanation, I learnt a few new things. Once I drove down from a mountain pass in neutral to save on fuel.
i did it to. and burnt the brakes.
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Old July 14th, 2013, 01:02 PM   #21136
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Most tourists do that around here. The smell of burning brakes is unbearable.
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Old July 14th, 2013, 01:06 PM   #21137
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Most tourists do that around here. The smell of burning brakes is unbearable.


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Old July 14th, 2013, 02:34 PM   #21138
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Old July 15th, 2013, 08:44 AM   #21139
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Quote:
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Modern A/T are pretty awesome.

Nothing to do with old american 4 speed with torque conversion.
It depends on a car. Once I have driven a car with automatic transmission and did not like it. The car was lazy. I stepped on the acceleration pedal with full strength, but the car reacted few seconds late. It was Seat Althea.
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Old July 15th, 2013, 11:38 AM   #21140
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Meanwhile in Košice - wall against Roma erected
http://spectator.sme.sk/articles/vie...in_kosice.html

There is even Wiki article about this kind of wall
http://en.wikipedia.org/wiki/Roma_wall
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