How do you know if the car is not put in N? Below 1k rpm is engine on idle which normally when car in P or N position.

Safety rating is just rating. It is still not safe if you drive dangerously. Do you know that coasting (or going downhill in free gear N) is even illegal is some states in the US?

yup just theory.
and turning key off will stop faster rite. why not equal when both are same condition cut off

becos i drove one and it do improve fc.

official channel mention usa version got coasting function ya

Not just theory. If you have OBD scanner, you get get fuel flow rate from the ECU. When engine braking downhill with no throttle, the fuel flow rate is 0.

Yes BMW coasting mode will disconnect the transmission from the engine.

But by doing so, it will need to continue to inject fuel to keep the engine running compared to engine braking which requires 0 fuel.

On the flip side, engine braking will slow down the car and you will need more fuel to re-accelerate back to speed, which the BMW coasting mode doesn't thus saving fuel.

It's a give and take, and either one would work depending on the condition.

But knowing Europe's strict emissions regulation, this coasting function is probably designed to meet those requirements instead of being a genuine effort to save fuel. Like those silly cylinder deactivation tech.

This post has been edited by dares: Oct 25 2021, 11:10 AM

Because those people mistakenly assume lower gear = high fuel consumption

Then give throttle to accelerate to force it to upshift
Then car too fast on downhill, lift off and brake
Then back to step 1, trying to accelerate again

They themselves is the one to blame for the high fuel consumption. Think about it, with 4AT even when drop to 3rd gear on let's say Genting downhill, it would still be 80km/h+ at 3000-4000rpm if you don't apply brake at all. That's plenty fast for normal road user.

Even when I go down from Genting with 7 speed DCT, I also manually downshift 5->4->3->2 approaching the bump. Or 5->4->3 when approaching most hairpin.

the auto downshift thing, normally you fake brake and it will kick in.

for low gear at down hill, it won't increase consumption, if it does, it is your car issue due to when downshifted, your oil valve is not open if you are not accelerating

Actually both are correct, and both are more efficient in respective use case. In the modern days of advance electronics with multiple axis accelerometer to detect acceleration, pitch angle, yaw angle, the ECU will decide coasting vs engine braking.

ECU make decision for efficiency and safety, that the decision would work for most road user. Unless one try to race downhill, or mistakenly assume lower gear = more fuel and do something funny to override it.

Today even 4.0L Audi RS6, RS7 have 48V mild hybrid. The PHEV and 48V cars would coast with engine off. Downhill all modern cars will do engine braking or/and regenerative braking, with 0 fuel used.

Here's something counter intuitive.
Fuel flow rate has directly relationship with throttle body opening, which influence airflow rate/volume. Raise of Engine rpm is the result of increase airflow, and ECU inject more fuel due to more air to maintain close to 14.7:1 ratio (give and take direct injection car would burn super lean at low load, all car burn rich for high load to reduce temperature and prevent knocking). That's why on race series like GT3, TCR, WTCR, BTCC racing etc that don't get standard engine design like F1, everyone get air restrictor (essentially a plastic cone, or metal plate with standard diameter) for balance of performance.

This post has been edited by constant_weight: Oct 25 2021, 12:37 PM

^thanks for ur support.
i pick free gear becos the gliding sensation feel goods.
while engine braking is useful when im racing mood

and i always getting max stars in eco pro mode

I personally think you maybe confused people a bit lah.

Your car would coast during relatively flat or minor down slope.

Definitely not downhill, maybe anything more that 2-3% gradient it would switch to engine braking instead.

Everyone must be thinking about Genting downhill.😅

There is another smarter (At I least think it is smarter) implementation of coasting that doesn't disconnect transmission from engine.

What it does is simply keep the throttle body wide open and don't inject fuel. This case, the engine rpm still high but car would glide pretty long distance, although not as far as transmission disconnection.

Essentially when we do engine braking we are using air to brake. With throttle body fully closed, the pistons are pulling vacuum. Wide open throttle will remove the restriction.

One thing for sure is again if the driver trying to act smart by shifting to neutral him/herself. The engine burn extra fuel for both coasting and engine braking cases literally render the technology useless.

This post has been edited by constant_weight: Oct 25 2021, 01:37 PM

Not really, race car is race car, normal cars cylinder pressures and heat are no where near those race cars you're relating to

On Coast cruise, even with high RPM, injectors typically fully turn off, regardless throttle opening.

And if close, negative pressure induces more engine braking as the RPM can no longer be maintained.

Just ignore the coasting scenario here for a bit. Let's assume the driver is stepping on throttle.

The intention is to tell people engine rpm only has indirect relationship with fuel consumption, not direct relationship.

We have no control on engine rpm. We only control amount of air when we step on throttle. The corresponded fuel is base on the air, and engine rpm is the effect.

The reference to race car is to show with air restrictor, on ball park, that is the max amount of air everyone get. Try to put bigger turbo or whatever, the max performance can't deviate far from the average. Air is the key to to fuel consumption, engine speed is the result.

Aye, I also wanna highlight the amount of air we also no control in modern DBW cars, but that's a topic for another day as you deviate to cruise control/stability controls/hill whatever assist/anti stalling assist (I appreciate this!)/auto rev matching (auto also got ya!) etc

The reality is modern cars take out a lot of driving than what most people think and worse, how "good" of a driver they may think they are.

That's true!!! Bloody bastard electronic throttle.
Most of them are trying to make our life easier, some are super annoying. One example is rev hang, especially on low gears during manual shift.

But think deeper, in the old time people need practice and training to handle 300hp.
Now 200hp+ is entry level, 600hp+ family saloon is not abnormal. Without those electronic assist most of the modern car are probably un-drivable, at least not for normal driver.

I think for flat roads or slight downhill gradient, the coasting function would be more efficient.

But for steeper downhill, engine braking would be more efficient because we are using gravity (which is free) to move the car forward while using no fuel.

Maybe it is not done because even with WOT the TB and valves are still restrictive and the pistons will still be pulling some amount of vaccum? Definitely not as much as closed throttle, but I'm guessing enough to cause deceleration.

Lol reminded the first week of so after my low power car ownership, hero mode turn off everything and spun out even at low speed from traffic light launch.

Lucky no one else was involved and only a slap on the wrist lesson learned fixing back front/rear bumper and wheels scuffed up.

noob