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Old 07-08-2007, 02:05 AM   #1
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Question higher gear+lower rpm=worse gas mileage?

my mom keeps telling me that driving around in a higher gear at lower speeds is just eating up more gas than i would if i just had it in the lower gear at a higher rpm whilst going the same speed. i.e. if i was cruisin at 55 in 5th at 1500rpm, she says that I would be using less gas if i were in 4th gear doing 55 at 2-2200 rpm. It just seems counter intuitive to me.
Is there any validity to this claim, and if so, why?

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Old 07-08-2007, 09:04 AM   #2
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nope, you're having almost double the explosions, so almost double the gas

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Old 07-08-2007, 09:17 AM   #3
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low rpm = better fuel economy. Why do you think they put those idiot arrows to shift in a lot of cars with standards in them. Because most people want to run the rpm's real high, before shifting. Very bad practice, if you are wanting to conserve fuel. It is very old school to wind the piss out of the motor, before shifting. Now you just get going enough, to get the next gear.

That is what I like about my YJ, with the V8, all I do is idle over everything. No skinny pedal required. Can wheel all day, on 18 gals.
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Old 07-08-2007, 10:26 AM   #4
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her reasoning, and others have said the same, that the engine works harder to turn that higher gear, so you have to press the pedal down further, thus using more gas.
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Old 07-08-2007, 10:55 AM   #5
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Quote:
Originally Posted by bluvikng View Post
low rpm = better fuel economy
but only if the engine is strong enough.
after putting some 32s on my TJ the RPM at the same speed is about 15-20% lower. but now i need about 25% more gas in the city and about 15% more on the highway.
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Old 07-08-2007, 01:39 PM   #6
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but the tires weigh more, and the gearing is off so you probably use more gas then with restored gearing

every extra 100# - 10% from ur mpg
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Old 07-08-2007, 09:37 PM   #7
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It all depends on power of the engine. Just because your running low rpms does not mean your running the most fuel efficient. An engine running inside its power band it will do much better then one struggling at 1500 rpm.

A high load, low RPM, the engine will burn more fuel than if it were at high RPM no load
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Old 07-08-2007, 10:23 PM   #8
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I know for a fact that my Jeep gets better gas mileage when revved out to 3,000rpms (our peak torque in the 4.0) than driving it at 2000 in every gear. The 4.0 is a torquey engine sure, but it just doesnt have the power to move the Jeep around in the wind. Low speeds its great, but its not exactly the most efficent motor for moving our refrigerators down the road. Rev that bad boy out a little to help out. Lugging the engine is not a good idea in ANY vehicle. 1/8 throttle at 3,000 rpms is going to burn much less gas than 1/2 throttle at 2,000. In a Jeep, throttle position is much more important than Rpms. Now in a Camaro, its the opposite. Reason being is that the motor has more than enough azz to move the vehicle forward, so the less gas AND RPMs the better (less fuel consumption period). This works, because the motor will pull the vehicle through a flat road at 1/8 throttle 1800 rpms, as well as up a hill at 1/8 throttle 1800 rpms.


Short and sweet, in your Jeep, rev is out a little with less throttle opening. In an over powered vehicle, drive with an egg under the throttle and shift early.
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Old 07-08-2007, 10:29 PM   #9
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Quote:
Originally Posted by debruins View Post
every extra 100# - 10% from ur mpg
Using this logic if I added #1000 pounds to my Jeep it would get 0 MPG.
That is not the case. I don't believe your math is based on any factual information.
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Old 07-09-2007, 01:10 AM   #10
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Originally Posted by Scoob View Post
Using this logic if I added #1000 pounds to my Jeep it would get 0 MPG.
That is not the case. I don't believe your math is based on any factual information.
Actually no it wouldn't scoob. Say you were getting 20 MPG. Add 100 lbs and you would be getting 18MPG, 200 would be 16.2, 300 = 14.58, 400 = 13.122, 500 = 11.81, 600 = 10.63, 700 = 9.57, 800 = 8.61, 900 = 7.75 and 1000 lbs would equal 6.98 MPG. You would have to add a whole lot of weight to get to 0 using his formula.
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Old 07-09-2007, 03:52 AM   #11
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Actually, I don't know if strictly mathematically you ever would reach zero. Mechanically you could add so much weight that the vehicle just wouldn't be able to move, but if we're talking just numbers, there would always be some kind of theoretical distance that the vehicle could go.
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Old 07-09-2007, 03:59 AM   #12
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Just like in lifts, every Jeep is differant, has it's own comfort zones. When you find the spot in the powerband that suits your particular vehicle, that is where you should run it for the most efficiency. However, the lower the RPMs are (without lugging) the lessor the fuel flows...
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Old 07-09-2007, 06:49 AM   #13
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Thank you jjseel, that is all I was trying to say, you just said it more clearly. I get too excited sometimes.......... Lugging is not going to get you good fuel mileage, neither is over revving.

Just a foot note: there is no such thing as an overpowered vehicle......... A fuel injected V8 is not too much power when it is powering a 5,000 lb. jeep.
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Old 07-09-2007, 07:07 AM   #14
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define "lugging"
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Old 07-09-2007, 07:14 AM   #15
coilovers are damn flexy
 
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Lugging is being in too high of a gear for the power you need, to sustain forward momentum. When the RPM's are too low, and you try to compensate with more throttle, and nothing happens, there is no increase in speed, then you are lugging. It is more fuel efficient, to down shift, and then give half the gas.
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Old 07-09-2007, 12:49 PM   #16
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I hate math.
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Old 07-09-2007, 01:01 PM   #17
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roger that fox.

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