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Crow318
Dodge Dakota
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10/26/2004
16:40:40
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 Subject: Gears vs. Mileage
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I know this is here on the forum somewhere, but I havent had good luck with the search. It brings up quite a few topics from way back in '01.
Anyways, I have a '97 CC 4x4 5.2L
It currently has 3.55 gears.
The truck came with the 235/75 R15
I changed the tire to the 31 x 10.5 R16 and I changed the spedo gear, so everything is accurate.
Most of my driving is in the city. I didnt notice a huge difference in power (it has plenty for everyday driving), but I did loose a MPG or so.
The funny thing is that I lost a MPG on the highway too.
I am planning on switching the gears. I have narrowed the choices to 3.92 or 4.10. The 3.92 will bring me just past where i was with the 3.55 and the 235/75's.
Some actual MPG changes would help the most, as I understand how gearing works and effects power and rpm's
thank you in advnace
John
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Crow 318
Dodge Dakota
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11/04/2004
08:44:09
| RE: Gears vs. Mileage
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No one??
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Rob C
Dodge Dakota
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11/04/2004
09:20:27
|  RE: Gears vs. Mileage
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I know those big tires are hard to turn but, why would you think changing the gears to lower final drive would help your mileage? Before you go through the major work of changing your front and rear gearing, shouldn't you put the original wheels, tires and speedo gear back in to make sure that something else isn't causing your mileage decrease? What other changes did you do to your truck?
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01Motorsport
Dodge Dakota
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11/04/2004
09:34:51
| RE: Gears vs. Mileage
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My situation is a bit different, with a '01 4.7 5-spd 3:92. I recently did the reverse of yours, and went from a 29" tall tire to a 28" height. The city mpg improved, while the highway mpg dropped slightly. Generally, if you have to go so deep into the throttle just to get the vehicle moving (with low numerical ratios + tall tires), the mpg "damage" is done, no matter how you cruise. Also consider that the taller tires are heavier, have more rolling resistance and more aerodynamic drag, all mpg killers. Just getting that larger mass accelerated, and speed maintained, takes more energy/fuel.
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monkey
Dodge Dakota
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11/04/2004
13:59:23
| RE: Gears vs. Mileage
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98 CC 4x4 5.2 with 3.92 gears. Most I ever got with lots of highway was 14.2. Now with mostly city I get 10.5.
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Redline
Dodge Dakota
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11/04/2004
15:24:44
| RE: Gears vs. Mileage
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If your truck runs OK, don't change it for a MPG.
+- one or two MPG still equals horrible gas mileage, so why worry about it?
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Crow318
Dodge Dakota
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11/10/2004
12:47:35
| RE: Gears vs. Mileage
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All good points.
As for my reasoning, I do mostly city driving, stop and go. Most of my time is spent accelerating.
Simply put, higher ratio, easier acceleration, less fuel used.
I have read all the threads and have heard the arguments and have made up my own opinion on how gearing changes affect things.
Fact - more RPM = more fuel used
Fact - more engine load = more fuel used
Changing gears from 3.55 to 3.92 will:
increase RPM and use more fuel
decrease engine load and use less fuel
There must be a balance or every vehicle would have a 1:1 rear ratio and turn 500 RPM's at highway speeds.
From what I have heard. To a certain extent, with these engines (318), unloading them makes a bigger change in fuel consumption than increasing the RPM's. I'm not saying that i should be running 5K on the highway, but in the normal highway RPM range of 1800 to 2700 for a small block v-8
Thanks again for all of your input.
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99Dak5.2L4x4
Dodge Dakota
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11/15/2004
13:38:04
| RE: Gears vs. Mileage
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I have 99 Dak 5.2L 4x4 with Automatic transmission.
I had the stock 3.55 and 32 inch Pro Comp All Terrain tires and was getting 11 city and 14-15 highway consistently.
I Installed 4.10 gears with 33 inch BFG All Terrain tires and now I get 10-11 city and 13 Highway consistently. The 33s I have from BFG are really closer to 32s so that is also swaying things. I drove around with the 33 BFG and the stock 3.55 and it was definitly lagging.
In my opinion, if you do not tow do not change your gears. It will not be worth the money. I only changed gears because of the towing.
The gear change was nice though for power. I was cruising at 1850 rpm at 70 mph before the gear change and now I'm at 2150 rpm with new gear change and 33 BFG. I'm definitely always in the power band however, I can litterally watch my gas gauge go down if I drive faster than 77-80 mph because I'm close to 2600 rpm...sucks.
I pretty much fill up every 200-215 miles.... yickes.. @ twice a week. My gas bill alone ever month is at $250 minimum.
I'm buying a Ford Diesel in about 2 months. I can't wait !!!!! Never DODGE again !!
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Crow318
Dodge Dakota
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11/19/2004
15:12:12
| RE: Gears vs. Mileage
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That is the real life info that I was looking for. Thank you.
Anyone else?
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