The most economical way to shift

"Tompie913" (tompie913) 07/22/2016 at 00:39 • Filed to: None

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I’ve been wondering lately, when is it best to shift for better fuel economy? For example, on a uphill climb is it better to run a lower gear at higher revs, so you will be pushing down less on the throttle, or a higher gear at lower revs, where you will need to push the throttle more?

Daily Drives a Dragon - One Last Lap > Tompie913 07/22/2016 at 00:56

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That’s a really good question. I would be very interested to know the answer as well.

DutchieDC2R > Tompie913 07/22/2016 at 01:01

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all the way in the red....

brianbrannon > Tompie913 07/22/2016 at 01:39

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It depends on the car. Get a scanner and read the fuel injection pulse and test your car

415s30 W123TSXWaggoIIIIIIo ( •_•))°) > Tompie913 07/22/2016 at 01:47

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I think it depends on the car, like in my diesel with a turbo is probably a lot different than my 240Z. I actually keep it in 2nd in the Mercedes and it doesn’t pull as hard but I think it’s not banging away and using more fuel, but the turbo is spun up.

M54B30 > Tompie913 07/22/2016 at 02:06

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I always compare it to a bicycle. Would you rather be pedaling faster but lighter or be in a really tall gear busting balls to make each pedal rotation?

I usually downshift and hold it at the beginning of the point of usable power (2,500-3,000 RPMs in my Corolla depending on steepness). Gives me the option to pass going uphill without having to do an awkward uphill/downshift combo

samssun > Tompie913 07/22/2016 at 04:24

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Generally you want open throttle / low revs / higher gear. Lower pumping & frictional losses.

McMike > Tompie913 07/22/2016 at 05:42

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I remember reading if it’s the most efficient way is to keep the revs low, but accelerate quickly,

So WOT to 3K RPM, then repeat until you reach your desired speed.

As far as climbing hills? I would think you would want to keep the revs as low as possible without lugging the engine.

TylerLinner > Tompie913 07/22/2016 at 07:13

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Ecomodder and other hypermiling sites have threads and threads and threads about this. When you’re racing, you want to stay in the ‘power band’. But when hypermiling, you want to stay in what is called the ‘brake specific fuel consumption’ (BSFC) sweet spot.

This has to do with a lot of factors inside the engine and I’m not an engineer so I won’t try to explain, but it tells you how much torque you’ll make for a certain amount of fuel. But you end up with a chart like this. Throttle position is on the vertical axis and RPMs go horizontal.

The red is where you want to be. Usually for four cylinder engines around 2 liters the sweet spot is is about 2200 RPM and 80% throttle. Adjust your shift points accordingly to keep the engine in this rev range when possible.

Hardcore hypermilers use an “MPGuino” fuel economy meter which gives you OBD data kind of like a stock fuel economy gauge, so if you’re a tinkerer this might be something to play with. And again, Ecomodder has some great threads on this.

Enjoy!

nermal > DutchieDC2R 07/22/2016 at 07:35

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Right. The science behind it is that you get there faster, therefore spend less time burning fuel.

Wrong Wheel Drive (41%) > Tompie913 07/22/2016 at 07:51

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Fuel economy is pointless, just have a car that gets 20+ MPG at WOT and then you are good. I can shift at 5k all day and drive around like a race car and still get at least 25 mpg in my Miata. Plus with how cheap gas is, I just could care less. Sure I could get 30+ if I hypermiled the car but I would rather have fun.

Haha as a real answer though, definitely just keep the revs low, shift up early. As long as the car can move, you are going to be using less gas in most cases. I can drive in 6th gear at 40 mph and easily clock in 35 mpg if I do that long enough.

SidewaysOnDirt still misses Bowie > Tompie913 07/22/2016 at 08:09

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The lower the better to an extent. When I cared about such things and was actively trying to see how far I could beat the EPA numbers by, I would floor it but shift at like 2200ish. Lower in higher gears..

SidewaysOnDirt still misses Bowie > nermal 07/22/2016 at 08:09

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Obviously if you get there faster, you’re going to be burnng less fuel because the car won’t be running as long. That’s why we still have speed limits. It’s a big oil conspiracy.

Aaron M - MasoFiST > McMike 07/22/2016 at 08:14

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This is what I recall as well. WOT, stay in the torque peak until you reach your desired speed, then get to the point in the rev range with the lowest specific fuel consumption and stay there.

TylerLinner > TylerLinner 07/22/2016 at 10:59

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I should clarify, though, that that chart only applies when you’re accelerating. Cruising speed should be the slowest practical speed in your highest gear.

TheBimmerGuyWhoNowOwnsAChevy > Tompie913 07/22/2016 at 14:50

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Don’t know how accurate this is because it’s 80's technology but my e28 has a fuel economy meter and it shows a higher mpg at lower rpm; though it is very indecisive on hills, but I always throw it down a gear because in California it is always better to be prepared to get away from some maniac quickly.