Why is 'hard' braking bad for fuel economy ?

[wagonman76]

Mine only cuts the fuel every now and then, and only on a long steep downhill. My fuel cut is very noticeable and is a pretty powerful engine brake. Sometimes I can hold the throttle just right where itll fuel cut all the way down the hill and now slow down as bad.

[greentea]

Can someone clear this up for me? The OP asked why "hard braking" was bad; obviously, going from point A to B, you want to brake as little as possible because braking is pure wasted momentum.

But is hard braking bad in itself? That is; if you have to stop at a light, is slowly braking superior to slamming on your brakes (safety aside)? A strategy I like to use is slowing down to 15 or 20 well in advance of a light so it takes me longer to get there, the light turns, and I'm able to not be forced to brake to 0. Is there a reason not to brake hard when I do this?

Also, does braking itself decrease FE? I read on one of these websites that you could circle around a parking lot to bleed off extra momentum instead of just braking but that sounds ridiculous to me.

[NiHaoMike]

Originally Posted by greentea

Also, does braking itself decrease FE? I read on one of these websites that you could circle around a parking lot to bleed off extra momentum instead of just braking but that sounds ridiculous to me.

They do that to get a higher "score". Since it does not actually save fuel over a trip, I consider it cheating.

[MetroMPG]

Originally Posted by greentea

But is hard braking bad in itself? That is; if you have to stop at a light, is slowly braking superior to slamming on your brakes (safety aside)? A strategy I like to use is slowing down to 15 or 20 well in advance of a light so it takes me longer to get there, the light turns, and I'm able to not be forced to brake to 0. Is there a reason not to brake hard when I do this?

What you're describing is the same as the tip from the hypermiling/ecodriving list, posted above. Sound strategy.

I read on one of these websites that you could circle around a parking lot to bleed off extra momentum instead of just braking but that sounds ridiculous to me.

Yes, that was this web site! Yes, it is a bit ridiculous, and it's splitting hairs. Orbiting a parking spot and coasting to a stop won't reduce your fuel consumption, but it'll increase your MPG. That specific technique is essentially a numbers game - something to do if you have come in with too much momentum.

[KJSatz]

Say you got a sudden red light a few hundred feet in front of you, and you're at speed. No matter what you will have to come to a stop because it's a hella long red. Also allow the condition you want your engine to stay on this whole time--you aren't into EOC and don't want to use the ignition when the light turns green. Finally say if you just coasted in neutral you would still be going very fast when you got to the light.

Under these circumstances the most fuel efficient option is to use DFCO for the longest time possible, using brakes minimally or not at all until you come to a complete stop.

[MetroMPG]

In that kind of situation, some people will even downshift their transmission (as speed drops), to extend the DFCO opportunity.

[wagonman76]

Originally Posted by greentea

Can someone clear this up for me? The OP asked why "hard braking" was bad; obviously, going from point A to B, you want to brake as little as possible because braking is pure wasted momentum.

But is hard braking bad in itself? That is; if you have to stop at a light, is slowly braking superior to slamming on your brakes (safety aside)? A strategy I like to use is slowing down to 15 or 20 well in advance of a light so it takes me longer to get there, the light turns, and I'm able to not be forced to brake to 0. Is there a reason not to brake hard when I do this?

The only advantage I can see to hard braking is as follows. Youre coasting up to a stop sign with the engine idling, downhill. Youve gotta stop anyway, and your wait time will probably be the same regardless of how long it takes to get there. So the faster you get there and make your stop, the less time your engine will be idling to get there and burning gas.

[KJSatz]

That makes sense, but alternatives of starting coasting earlier, or using engine breaking to slow down, would probably yield better results (if you stay in a moderate gear in relation to your speed and can DFCO most of the way to the stop you use LESS fuel on the journey from where you are to stopped-at-the-stop-sign).

[wagonman76]

Yes you would likely use more fuel if you gave it gas to get your speed up only to get to the stop sign faster.

I guess I just keep thinking of this one road on my way to work. Ive gotta crest a hill, then its downhill for like 1/2 mile to the stop sign and during that I can just idle in N. I can only crest the hill so slow. After that, the faster I let the car roll to the stop sign, the less fuel I use. If I gradually brake and take longer to get there, I burn more. If I EOCd, itd be a moot point, but I dont EOC for a few reasons.

[KJSatz]

I guess if you can't DFCO then that's a good option.