[SirAlec]

Originally Posted by bdman

For front wheel drive or rear wheel drive car?And how is the "balance" affected whether the brakes are used or the engine braking used?

In motorcycles where balance is much more important, slipper clutches are now being fitted to reduce the effect of engine braking which riders found affects the balance when they are leaned over and braking through a corner.

Bro simple reality check. in car you have one pedal that control all brakes. In bikes you have two. So its the biker who decides what to brake first.

Now coming to you main question. All brakes are applied at the same time in cars provided your car brakes are in tip top shape and no alignment or balancing issue. But the traction of tire and the surface its on is not even always Hence the swirl and fishtailing.

To counter that ABS comes in handy, but there were no ABS many years ago still people used to drive in hills and in snow. what they used is a technique called brake pumping to avoid brake locking. That is what the ABS does in reality with the used of sensor and sorts and special master cylinder.

[SS-Traveller]

Originally Posted by bdman

For front wheel drive or rear wheel drive car?And how is the "balance" affected whether the brakes are used or the engine braking used?

In motorcycles where balance is much more important, slipper clutches are now being fitted to reduce the effect of engine braking...

In my experience, a RWD car will always coast in a more stable manner when in gear, than if in neutral (but dynamics under hard braking may not be different, whether in gear or in neutral). Not so much in a FWD car, but still perceptible.

Not a motorcycle person anymore (not ridden 2-wheelers for almost 15 years), so I won't comment about it.

[Ricci]

I don't recommend coasting purely from a safety point of view, otherwise, idling the engine is where least fuel in consumed for a the given distance, as against using engine braking. Say, you see a traffic light about to go red - you put the car in neutral, coast slowing and let speed decay, and then brake to a halt - depending on your initial speed and distance, you will either end up braking a little to stop completely, or time it so perfectly that you coast to a near zero speed and only need a light tap on the brake to halt. At idle, this distance should be covered burning the least fuel , as compared to using the engine , since you'll be doing higher RPM, and thus have more combustion cycles even if your ECU is programmed to reduce fuel injection quantity to a minimum.

I do know the usefulness of engine braking, but I reckon it is a stress on the engine. The engines are for going ahead, the brakes are for decelerating. Given that brakes are powerful enough to lock up the wheels (assuming no ABS), the engine braking isn't going to slow you any quicker.

[bdman]

Originally Posted by SirAlec

Bro simple reality check. in car you have one pedal that control all brakes. In bikes you have two. So its the biker who decides what to brake first.

Now coming to you main question. All brakes are applied at the same time in cars provided your car brakes are in tip top shape and no alignment or balancing issue. But the traction of tire and the surface its on is not even always Hence the swirl and fishtailing.

To counter that ABS comes in handy, but there were no ABS many years ago still people used to drive in hills and in snow. what they used is a technique called brake pumping to avoid brake locking. That is what the ABS does in reality with the used of sensor and sorts and special master cylinder.

I agree with your theory but am having difficulty understanding how adding engine braking will help, rather than hurt the situation.

A key factor in braking is also weight transfer. The harder you brake, more weight is transferred to the front wheels, so rear wheel braking becomes less and less effective, as the rear tires lose grip. So, in rear wheel drive cars, additional braking applied by the engine to the rear wheels will only make the tires lose traction, fish tail etc. etc. etc.

[SS-Traveller]

Originally Posted by Ricci

...even if your ECU is programmed to reduce fuel injection quantity to a minimum.
I do know the usefulness of engine braking, but I reckon it is a stress on the engine.

ECU doesn't reduce fuel flow, it shuts fuel supply down completely when the engine is in deceleration (overrun) mode. And it's the first time I've heard anyone saying engine braking stresses an engine (at least, a 4-stroke engine). Seriously???

[bdman]

Originally Posted by SS-Traveller

.. And it's the first time I've heard anyone saying engine braking stresses an engine (at least, a 4-stroke engine). Seriously???

Well, if the driver down shifts early and the engine over-revs? No? I've heard of valves going through piston heads due to this..

Originally Posted by Ricci

The engines are for going ahead, the brakes are for decelerating. Given that brakes are powerful enough to lock up the wheels (assuming no ABS), the engine braking isn't going to slow you any quicker.

I agree completely!

[bblost]

My first automatic experience in the hill I forgot to shift out of D mode when going downhill.

When I finally stopped the car the smell of burning brake pads was a stark reminder of why we need engine braking.

[SirAlec]

Originally Posted by bdman

I agree with your theory but am having difficulty understanding how adding engine braking will help, rather than hurt the situation.

A key factor in braking is also weight transfer. The harder you brake, more weight is transferred to the front wheels, so rear wheel braking becomes less and less effective, as the rear tires lose grip. So, in rear wheel drive cars, additional braking applied by the engine to the rear wheels will only make the tires lose traction, fish tail etc. etc. etc.

Engine braking has been used in trucks for ages. if engine braking caused wear, consider the fact trucks engine last 5 lac kms plus easily, and that only an average figure.

What makes you think the weight transfer is more on front wheels, is it because of the engine placement on front. Well thats where suspension system comes into play.

PS: are we going off topic.

[Ricci]

Originally Posted by SS-Traveller

ECU doesn't reduce fuel flow, it shuts fuel supply down completely when the engine is in deceleration (overrun) mode. And it's the first time I've heard anyone saying engine braking stresses an engine (at least, a 4-stroke engine). Seriously???

If fuel flow completely shuts off, won't the engine stall and quickly stop the vehicle? No, I don't agree that fuel flow is completely shut off, there will always be some fuel metered through to maintain combustion to keep the engine running, but the amount of air-fuel mixture combusted is too low to provide enough net force to maintain current speed (total opposing force greater than motive force), so the vehicle decelerates. As for stress, yes , the inertia of the vehicle and it's rotating powertrain will load the transmission and engine, won' it ? I'm not saying it will very soon require an engine rebuild, but I doubt an engine that's been heavily used with engine braking will be healthier than one with more judicious use of engine braking, other running duties/cycle being equal.

[Gansan]

There is only one vehicle in which this is permitted - trains, and their drivers practice it all the time!

In a road vehicle, you want motive power and traction all the time. Disengaging power train = loss of traction and motive power. Very very dangerous. So never ever do it.

[SS-Traveller]

Originally Posted by bdman

Well, if the driver down shifts early and the engine over-revs? No?

...and braking hard throws non-ABS vehicles into uncontrollable 4-wheel skids? No? That's equally dangerous as, even worse than, 'valves going through piston heads'. I should have added "...driven properly..." somewhere, when talking about stressing out engines on decelerating.

In any case, staying in gear (rather than being in neutral) while coasting - that's the topic of the thread, not downshifting while coasting.

Originally Posted by Ricci

If fuel flow completely shuts off, won't the engine stall and quickly stop the vehicle? No, I don't agree that fuel flow is completely shut off, there will always be some fuel metered through to maintain combustion to keep the engine running...

Will depend on how the ECU is programmed. Most street cars (not racing cars) will cut off fuel 100% on overrun (higher rpm than idle, but no extra fuel required, no A-pedal input), but feed fuel again when an impending stall is sensed (rpm drops below a certain threshold).

[ramzsys]

Originally Posted by Ricci

If fuel flow completely shuts off, won't the engine stall and quickly stop the vehicle?

When coasting in a slope, the power flow is from the wheels to the engine. So the engine won't/can't stall if the rpm is enough to overcome the compression. And as SS-Traveller mentions, when nearing idling rpm, ECU starts injecting fuel.

[Octane_Power]

When I used to observe my dad driving he used to always tell me "Never free-wheel(this included both - turning off the engine and letting the car roll on its own accord and 2nd engine running but the gear in neutral) on downhills and never drive with the clutch pressed when the car is in gear"

The reasons were simple - inadequate braking in the time of an emergency and lack in "complete control" of the car when the need may arise.

Suppose one is coasting with the clutch pressed and the gear slotted in 1st.
Due to the downhill, there is only going to be an increase in the momentum of the car; it may so happen that the car crosses 35-45 kmph without one realizing it and by mistake(or wrong reflexes in emergency situations) if the foot is lifted off the clutch one can imagine what kind of jerk the passengers and the car will suffer from.
Maybe causing some serious damage to the engine too in the process.

Now, If you are coasting in neutral then as SS-Traveller has stated, you may just not need braking to save yourself, you may even need to zip out of that spot. For that, pressing the clutch-slotting in the "CORRECT" gear - releasing the clutch- finally pressing the accelerator" read "correct"
All this even if done at lightning fast reflexes ,if you count the time taken for physically doing all this + the time taken by the brain to realize to do this, it sums up to approx 1.2-1.5 seconds. (can be more but not less)

And when in a tight spot, we all know how precious these 1.5 seconds are.

Finally, how much fuel would one save by doing all this coasting and stuff?
20 rs ? 25 rs? Definitely not more than that.
Come on, You own a 6 lac rupee car which as it saves you alot of money by giving excellent fuel-consumption figures, how much more do you need?
Just drive the car in gear and stay in complete control of it.That's it!
Don't waste so much of your energy in saving a couple of 10-bucks of fuel!

-Bhargav

[bdman]

Originally Posted by SirAlec

What makes you think the weight transfer is more on front wheels, is it because of the engine placement on front. Well thats where suspension system comes into play. .

Simple physics. Since the center of gravity i higher than the axis of the wheels, when you brake the more weight gets transferred to the front and when you accelerate to the rear. Which is why you have stoppies and wheelies. Yes, trucks use engine braking not for "control" bur to prevent overheating of their brakes especially on downhill runs. In my original post, I clearly said that in an emergency, I slam n the bakes and clutch.

For example what help will engine braking be on a a car braked like this?

[bblost]

Bdman, this discussion is about coasting.
Should you coast in neutral or not?

The brakes on a car, bike, truck etc will heat up if you coast downhill in neutral.
They heat up then they will fade and fail.