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Old 07-28-2008, 05:18 PM   #1 (permalink)
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What is the ideal RPM to cruise at?

Do you get the best MPG from cruising at the lowest RPM possible without stalling, or is there a general RPM range that gives the best MPG?

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Old 07-28-2008, 05:26 PM   #2 (permalink)
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i want to know the answer to this too.. i try to keep my cruising rpm at about 2100-2500 range nowadays.. but i have no SG.. so i have no idea instantaneously if that is helping or not, although my FE seems to be improving overall from the slower speeds
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Old 07-28-2008, 05:31 PM   #3 (permalink)
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Ideally, 0 rpm is the best (EOC) in terms of FE. If you are not EOC, depends on what car you are driving, road condition and what speed you are cruising, generally, highest gear gives you the best FE. If you are climbing up in low speed, like 25mph or 30mph, 5th gear may not be able to give you enough power. If you don't shift down, you need to press harder to maintain the speed, which will use more gas.
My car's best cruising speed is 35mph to 40mph @5th gear, which is about 1800rpm to 2000rpm.
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Old 07-28-2008, 05:32 PM   #4 (permalink)
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Depends on your car. I was advised to find the right balance between RPM and MPH, so get into your highest gear but lowest speed should be close to the optimal. For me that is around 2000-2200 RPM and between 45 and 50 MPH. But without instantaneous feedback via gauge it's hard to say until you fill up the tank.

(I believe it's also mentioned in the 100+ hypermiling / ecodriving tips to increase gas mileage - EcoModder.com)

Another caveat is that since I'm in an automatic, I don't really have the same control on when I can upshift/downshift as compared with a manual (who can downshift sooner and at more efficient RPMs)
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Old 07-28-2008, 06:55 PM   #5 (permalink)
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The correct rpm is usually "lower".

For context, the Honda Insight runs at about 1950 rpm at 60mph. That's with a 63hp engine. Any larger engine should be able to run at even lower rpm to produce the same power.

My civic runs 2800 rpm at 60. Not ideal. I've actually shifted down to 4th, looking for my missing 6th gear, at 35mph. I like to keep the rpm WAY low - 1000 would suit me fine.
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Old 07-28-2008, 07:02 PM   #6 (permalink)
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lower possible....
anything under 1500 my truck vibrates.?
my truck runs 2k at 60mph

at 55 i get 32-35ish at 65 i get 24-26ish.
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Old 07-28-2008, 07:05 PM   #7 (permalink)
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All of the above. Best FE RPM is vehicle dependent. I can do 20 mph in 5th 60+mpg and <1000rpms, but time is a factor. At 45 mph I get 47-50 mpg at 2000 rpms.

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Old 07-28-2008, 07:14 PM   #8 (permalink)
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Quote:
Originally Posted by PaleMelanesian View Post
The correct rpm is usually "lower".

For context, the Honda Insight runs at about 1950 rpm at 60mph. That's with a 63hp engine. Any larger engine should be able to run at even lower rpm to produce the same power.
FYI, Insight runs that low rpm because IMA gives boost if needed. Without IMA, running such low rpm in small engine doesn't have enough power to pass other cars on highway. That is why Civic runs higher rpm even the engine is bigger. Generally, bigger engine usually cruise with lower rpm for the same reason. Just using insight as an example is not appreciate.

Another observation we see from insight engine is lean burn happens in low rpm. Running less than 2krpm at 60mph saves more gas on highway.
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Old 07-28-2008, 08:24 PM   #9 (permalink)
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IMO, it would be the lowest rpm after the car shifts into its highest gear in an auto. That of course is for city driving not hwy.

For the Vibe its 37mph or 1600rpm, on the hwy I sacrifice that to go 55mph which picks me up to around 2000.
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Old 07-28-2008, 09:06 PM   #10 (permalink)
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The insight being the most fuel-efficient car on the roads today, it's absolutely applicable. It's a no-compromise fuel-economy machine. If the gear ratios are tall, it's for mileage.

See also Civic VX - 2080 rpm at 60. Also built for economy, also geared to run at low rpm.

Accelerating from 1000 rpm in my civic also says that lower rpm is best. Anything that's not bucking and shaking - lugging - is good. I HATE the gear ratios. If I just cruise it at 65mph, I only see mid-40's mileage. Taller gears for lower rpm would give me much better mileage. If I could get gears like the Insight, I would.

I do know a thing or two about the Insight.
Quote:
Andrew 156.8 MPG (1.5L/100km)

-------
Here are a couple MetroMPG posts related to the subject:
http://www.metrompg.com/posts/rpm-mpg.htm
http://metrompg.com/posts/speed-vs-mpg.htm
http://www.metrompg.com/posts/tranny-swap.htm
http://www.metrompg.com/zoom_image.h...fly%20%26%20xB

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