Does down-shifting use more fuel?

Truer words were never spoken.

 

Compression braking is designed to limit a vehicle on long downgrades to avoid overheating the brakes with repeated applications to maintain vehicle speed, thus preventing brake fade and subsequent brake loss. It is not necessary to use a compression brake on a level city street at low speeds, but it is prudent to leave a vehicle in gear until you get under 15mph.

If you weren't aware of the capacity, and perceived it as big - I'd be willing to guarantee you were operating it illegally.

Moot point.

And, if as those brakes get hot enough to smoke, they lose effectiveness. It's called brake fade. Clearances are very tight on a braking system. As the drums heat up, they expand and the shoes cannot make contact with the same force.

No "off-hand" way to calculate a % ratio. Too many variables. % of grade, weight being handled, capacity and specing or brake system, engine horsepower, cubic inch displacement, ambient temperature - density of air... etc.

Idiotic question. No intelligent answer possible.

Sounds to me like none of them know what they are talking about. I wouldn't let them drive a truck for me, nor work on a transmission. Yes, you apply fuel to bump rpms, but the engine is in a 'no-load" mode. (Hey, that rhymed.)

Consider it explained.

They are designed to stop an 80,000 lb. vehicle. And before the invention of engine brakes "skilled" drivers could get through the Rocky Mountains without killing anyone or hitting a run-off ramp. Back then, skilled drivers were more common - because they had to be. The unskilled ones that loved to cruise in what we used to call "suicide overdrive" were weeded out pretty effectively. I miss those days.

They are not subject to the laws of friction and heat. They are using reverse thrust, and/or air friction with flaps. If heat is created, no components absorb heat and lose effectiveness.

Then I'll wrap it up in a nutshell.

Leaving a vehicle in gear creates reverse resistance. No fuel is being used because the fuel to the injectors is cut off. So, in theory, you are using the natural resistance of the drive-line, engine and compression as an aid to your braking system, saving wear and tear on your brake pads and drums. To downshift uses a miniscule amount of fuel to bump the RPM's so you can repeat the process, but as the speed decreases, the resistance increases, and most professional and knowledgeable drivers will not downshift in the lower gears.

Only the cowboys do that, and it's more to show off than is practical. Especially using a compression brake on level roads and "light duty" driving.

I don't think this is a troll at play. I read the entire thread, and I didn't feel that his question was being correctly answered, and he is having a hard time wrapping his mind around something he knows nothing about.

Combine that with the fact that he has gotten some ill-informed advice from people who he would think they know what they are talking about - and here we sit - 10 pages of going around in circles.

As far as the cost of leaving a vehicle in gear, Robert, you can put any loss of fuel in red ink under the "safe operating habits" column.

What's the cost of one dead person vs. saving $500 of fuel equate to? Leave your vehicle in gear. It's the right thing to do.

Peace.

 

OK, to set the record straight: Again, i never said anything about being in neutral----i don't believe in being in neutral when coming to a stop/red light etc.

Here's something funny that has been happening in the past few days since the inception of this thread: i conscienciously tried to NOT downshift when coming to a light to investigate why i have always downshifted when coming to a light and why do i do this in the first place. And to see if, in fact, you could stay in the same gear while decelerating.


i PHYSICALLY COULDN'T GET MYSELF TO DO IT! Wether this was from force of habit or fun---downshifting is fun i'll admit, i could not get myself to do it!!!


Well, last night i said NO i'm going to do it. So i tried staying in the same gear when coming to a light. And here's the scoop on that:

You can't do it

What happened in my case, and what will probably happen if you have a 10 speed like me (FR series roadranger, 10th is overdrive btw) is that if you're in 10th(OD) and decellerate then the engine will start to lug/shake around 25 mph. If you then go into 9th(now in direct drive) the engine lugs at around 19-21 mph, 8th is around 15mph and so on and so on.

NOTE: i have 3.70 rear gearing.

So you can't do it. Ok, so i was wrong and you guys were basically right.

Are you happy now you big macho man you?

 

The guy's question has been answered. Now you can close it, Brick.

Would you like me to fall on the grenade and violate TOS?

 

If that was a YouTube clip instead of a photo, you know, you just know, what would happen. Okay, maybe that wouldn't be so funny.

 

This sums it up for me. He has answered his own question about why being in gear leaves the driver in control. If something happens while you're coasting in neutral and you have to frantically search for a gear, you darn sure aren't in any kind of control, and by that point it may just be too late to avoid an accident that could have been prevented.

 

Original question:

********

No need to do that - I don't remember anyone advising to leave it in one gear.

Yah, we all know with an 80,000 lb. truck, and a 10 speed manual, it is impossible to come to a complete stop in 10th. It's prudent to downshift until 15mph, and then you can lightly use your brakes to stop.

Decelerate and gently change gears. If you practice, you can skip them too. Most veteran drivers will put it in neutral for the last 50 feet of the stop and if the light happens to turn green, give it a rap of fuel and ease her into the correct gear and keep rolling.

Doesn't matter if you have 3:23's, 3:70's or 4:11's. It's gonna stall if you leave it in top gear.

Don't know whom you're addressing that to, but there is no "macho man" stuff going on when experienced drivers tell it like it is. It's not a matter of "we're right and you're wrong..." it's more like, "We'll...now he knows....."

I think the gist of Robert's questions was if it hurt the engine and if it wasted fuel. Good driving habits and setting a good pace to your environment ( Smith system stuff ) do more to save fuel than all the neutral coasting in the world.

Okay, Brick, I'm done. No need to padlock it on my behalf.

 

Well said, SmoothShifter.