Maximizing MPG while slowing down - MT

jandree22

Member
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2007 Mazda5
Lately I've been trying to drive as efficiently as possible to see what kind of MPG numbers I could squeeze out of my 5. Last tank I wasn't even really trying too hard and got a pinch over 26 and I THINK this tank I may have hit the magical 30mpg... it's on the quarter tank mark with 338mi on the trip odo.

ANYWHO, my question is this. While I understand it isn't the safest thing to do, I've been coasting in Neutral where appropriate such as gentle hills on highways and when approaching a distant red light. I know this is bad as I couldn't punch the gas to escape an emergency situation, but that aside, what I was REALLY concerned about was going too hard on the brakes by putting all that momentum on the brakes alone.

But I stumbled accross something interesting on a post at StandardShift.com. They said that it is MORE fuel efficient to coast to a stop in gear with an engine braking load on the engine, than it is in neutral. The reasoning is that while coasting in neutral, your car is using gas to idle the engine. However when engine braking with a small load, say 2-4k revs, the rolling momentum of the car will trigger the compression to move the engine, thus causing the engine to completely stop injecting gasoline. The theory sounds plausible.

What do you guys think about this?
 
Our injectors do cut off when engine braking (at least they do on my car so I'm guessing they wouldn't leave that out on any cars)
 
I use the engine to slow down the car all the time.

edit: What I meant is that I coast to lights while in gear all the time.
 
Hm, learn something new every day. This seems like something I should have known (scratch)

oh well, thanks!
 
It's not the right thing to do because you will wear down your clutch and the cost is much more greater than replace the pads and turn your rotor. My wife was doing the same thing and she wore out her clutch which cost me 1200.00 dollars. Its ok to coast down from (45 to 30 mph) but don't use it to slow down to almost to a complete stop, you will be repairing your clutch and i don't know how much it is for a mazda5, for me i would do it in neutral. Its only my .02 cents.
 
no, you won't wear down your clutch at all, if you know what you are doing. You aren't touching the clutch at all...
 
is this the same with sport shifting in an automatic?

i shift down, and do what im assuming is engine braking when im coming to a stop becuase as i shift down the i see the revs go up, and i apply brake at the same time

is this bad for my car?

dont mean to thread jack but it seems to be an appropriate question
 
Only if your not using your clutch, in neutral you won't but if your using the clutch to much you will wear it down. And your right.
 
no you're not jacking the thread... that's totally relevant. I'd assume you're getting the same response. Your tranny is behaving different but you're still netting the same result at your engine.

And yeah... rev match when you downshift and your clutch will be happy. It's when you go and dump it into 3rd at 65mph and the revs skyrocket to 6k that pisses it off. Literally every time you shift, up or down, some friction is made onto the clutch unless you're perfect like Mario Andretti ;)
 
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Yeah well at 80k miles my stock clutch was still mint.. like I could sell it to someone, and it could easily go another 100k+ miles... and I learned to drive stick on this thing :p

rev match every single downshift, all the time, no excuses :)

As for doing it in an automatic.. I don't know how "real" the engine braking is, so not sure if it'll actually cut the injectors.
 
our autos can actually engine brake, unlike alot of slushbox's, because it leaves the torque converter locked up until you slow way down. The only time I use that "manual" mode is in bad weather, works great.

+1 for the fuel shut off when engine braking. My Hyundai does it, not 100% sure if the mazda does but I know its a more advanced ecm so Id have to assume it does.
 
lol, if you look closely even the fetus in my avatar is double clutching when he downshifts thats my boy btw, I taught him well, no? :D
 
Kansei said:
rev match every single downshift, all the time, no excuses :)
.

Could you please elaborate on this?

I was thinking you should rev match only if you want to downshift for the following acceleration but not for breaking.
Needless to say I almost never rev match because there is no need and I can't do it perfect anyway (screwy) Am I missing something?
Could somebody give examples when rev match is a MUST?
 
Doesn't matter if you are downshifting to accelerate or to slow down, it's the same to the car.. only difference is that after you are in the next gear, you're either on the throttle or off. Practice revmatching more, and constantly. You'll get it smooth.
 
Rev matching isnt a MUST only in that if you dont do it, your car wont die on the spot. But it is a MUST if you want to get the most life out of your clutch possible. It takes a little bit of practice, but when you downshift, clutch once to pop it into neutral, blip the throttle to raise the revs about 1-2k higher, then quickly clutch again and downshift into the next lower gear, and take your foot of the clutch before the revs have a chance to drop. Its a little funky coordinating at first and getting quick enough to engage the clutch in the next lower gear while the revs are still high, but you will get the hang of it if you practice. Now that Ive taught myself, I actually find it funner :)

If you really want to get further instruction, there are videos out there on YouTube that have multiple camera angles (on the shift knob and pedals, generally) that actually demonstrate this.

ha, there's this one that's actually good and the car it's demonstrated on is a C5 Vette... but the guy looks really wierd when they show his face and it looks like he's getting a little too intimate with his shift knob the way he caresses it... funny stuff!
 
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jandree22 said:
Rev matching isnt a MUST only in that if you dont do it, your car wont die on the spot. But it is a MUST if you want to get the most life out of your clutch possible. It takes a little bit of practice, but when you downshift, clutch once to pop it into neutral, blip the throttle to raise the revs about 1-2k higher, then quickly clutch again and downshift into the next lower gear, and take your foot of the clutch before the revs have a chance to drop. Its a little funky coordinating at first and getting quick enough to engage the clutch in the next lower gear while the revs are still high, but you will get the hang of it if you practice. Now that Ive taught myself, I actually find it funner :)

Or just push in clutch, and as you are moving the shifter to the next gear, rev to the RPMs that it'll be at in those gears, then drop clutch when in that gear.

I don't do it to save clutch wear (I don't care if it lasts 200k miles or 300k miles if I rev-match every shift frankly), I do it because it's the only way to smoothly downshift. DSG transmissions do it automatically all the time because it can make every shift perfectly smooth. When I drive automatics (ok, well not my mom's CVT) it pisses me off how rough they shift, even nice new electronic fancy ones.
 
Kansei said:
Or just push in clutch, and as you are moving the shifter to the next gear, rev to the RPMs that it'll be at in those gears, then drop clutch when in that gear.

I don't do it to save clutch wear (I don't care if it lasts 200k miles or 300k miles if I rev-match every shift frankly), I do it because it's the only way to smoothly downshift. DSG transmissions do it automatically all the time because it can make every shift perfectly smooth. When I drive automatics (ok, well not my mom's CVT) it pisses me off how rough they shift, even nice new electronic fancy ones.

Are you of the gas during dropping clutch?

Also I think it can be very confusing for drivers behind if you brake without stop lights. (shrug)
 
After i got used to rev-matching, I started to heel and toe ... brake and downshift (with rev match) at the same time. it's fun when you want to go around that corner and scrub off some speed for your entrance. takes a bit of practice, but it's not hard. just make sure you're wearing the right shoes. i can't do it with my big floppy dress shoes. i need my running shoes to do it.
 
PolarBear said:
Are you of the gas during dropping clutch?

Also I think it can be very confusing for drivers behind if you brake without stop lights.
I don't understand your first question, but you should always use your brakes even just lightly to activate your brake lights. Even if you're completely stopped at a redlight on a level surface, keep the brake on so A) approaching cars know your not moving forward (as an automatic would be doing w/o the brake light on) and B) if heaven forbid someone DOES hit you, you're not gonna go rolling into the car in front of you. However if I'm stopped in a line of cars at a red light with others already stopped behind me, sometimes I then give my brake foot a rest if I'm lazy.
 
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