i was wondering if someone can explain to me how gears affect gas mileage? ive been lookin for ways to get better mpg (right now 10). Ive been tryin to follow the other threads about that kind of stuff but i guess im just one of the few who doesnt know what type of gears are best- i have 33 inch mud tires, and from what ive read 4.10 gears would help me?? i may be way off but if someone could help me itd be greatly appreciated.

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the higher gears (4.10, 4.56, ext.) will give you worse mileage because the motor is spinning higher rpms. lower gears (3.55, 3.27, ext.) will give you better mileage because of lowerr rpms, but if you go too low the motor will be straining too much and mileage will go down.

 

Depends on your tire size too. For example, I was getting about 14-16 mpg with 3.55 and 31.5" tires. Now I have 4.10's and 33" tires, and I still average 14-16 mpg. If I still had 31.5" tires, I think my mileage would be a little worse due to the higher RPM's I would be turing at higher speeds, like highway speeds.

 

alright big help guys thanx

but also a second question about gears- despite teh gas mileage higher gears are better for wheelin, right? im pretty sure about that- does that mean lower gears help speed though? thanx again

 

lower gears (high speed) only help to a point if you you have too low you will not be able to reach speed ealey cuz it will take too much power to get there (likda like starting a standerd in 2nd or 3rd gear) thats kinda an extream anelagy but thats the idea. also your mpg will suck cuz the moter is working hard to get up and stay the speed

 

Also, unless you have an Off Road edition, you don't have 4.10's. That is unless the person you bought it from put then in there. You probably have 3.55's.

 

like my case...i got 4.10's and using them to roll wopping 265 tires and its KILLING my mileage... ill be getting 35's and prolly help my mileage

 

I have a 97 1500 Sport 5.9 auto, with 355 gears and 35" tires. Now that the tire size to gear ratio has changed, you can forget overdrive. My gas mileage and performance went with it. Try the gas mileage at 70(closer to 77 realistically) without OD. Getting ready to switch out to 410's in an effort to return a little past the original ratio, which was good for mpg. but hook a trailer or load and the trans is in and out of OD.
Bottom line, the gear needs to put the RPM's where you can drive the truck.
Load our trannys down with too much gear, 3.25-3.55 with tall tires and we are calling a tow truck.

 

Yeh,35's and 3.55's don't get along very well in OD. I have a 1994 1500 4x4 5.9 with 4.56's and 35's and can average 14 mpg on flat highways doing 80 mph at around 2300 rpm in OD, but drop it down to 65 to 70 mph and I get around 11. We won't even discuss around town mileage[:'(] Seems like everyone else on the forum gets their best gas mileage at a lower rpm, not my truck tho, it likes it around 2200 to 2500 rpm. Maybe its the mods I've done to it-dunno

 

info from an old post:
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Thanks for posting that guido7.

I have been filling in the specs for 3rd gen 5.7Hemi Rams
in a software program called 'Fuel Economy Calculator'
and was interested in what it would say
with 4.56 gears versus the standard diffs of 3.55 or 3.73

At 71 mph the program predicted 16.57 MPG at 2306 rpm
which matches your experience
and estimated that the engine was at 52% load
and had 48% of maximum torque in reserve for passing or climbing hills.
With this 48% reserve torque the engine could take the truck up a 5.7% grade
hill
(which is fairly steep) without downshifting.

With 3.92 diff gears the program predicts
at 71 mph the MPG would improve to 17.07 at 1983 rpm
and estimated the engine was at 61% load.
With 39% reserve torque the engine could take the truck up a 3.9% grade hill
without downshifting

With 3.73 diff gears the program predicts
at 71 mph the MPG would improve to 17.16 at 1883 rpm
and the estimated engine load was 65%
With 35% reserve torque the engine could take the truck up a 3.2% hill
without downshifting.

With 3.55 diff gears the program predicts
at 71 mph the MPG would improve to 17.22 at 1796 rpm
and the estimated engine load was 70%
With 30% reserve torque the engine could take the truck up a 2.6% hill
without downshifting (most gentle interstate hills are less than 2%)

With 3.21 diff gears the program predicts
at 71 mph the MPG would decrease to 16.19 at 1624 rpm
and the estimated engine load was 80%
which is into the 'fuel enrichment mode' to prevent pinging
where the air to fuel ratio is richened from normal 14.7 down to 11
With 20% reserve torque the engine could take the truck up a 1.5% grade
without downshifting.

This is not to say that 3.21 diff gears cannot improve MPG
under the right conditions.

For example the 3rd Gen Rams (Cd=0.528 and 35.1 sq feet) are
quite a bit blunter and less aerodynamic
than the 2nd Gen Rams (Cd=0.44 and 34.49 sq feet).
If the aerodynamics of the new Rams could be made as good as the
older 1994-2001 Rams then:

The program predicts with 3.21 diff gears, 5.7 Hemi and 1994 aero specs
at 71 mph the MPG would be 19.51 at 1624 rpm
and the engine load would be 70%
and the engine could pull the better aero truck up a 2.3% grade without
downshifting.

DaimlerChrysler recently showed off a high MPG show car called the 'BoxFish'
that imitated the shape of a fish to get the a 'realworld' Cd of 0.19
{the real fish is even better at Cd=0.10}

If a 3rd Gen Ram had the aerodynamic Cd of the BoxFish show car
and its present 35.1 square feet of frontal area
the program predicts
at 71 mph with 2.73 diff gears the MPG would be 28.55 at 1381 rpm
and the engine load would be 57%
with 43% reserve torque at this low rpm
the engine could pull a 2.5% grade hill with downshifting.