I've seen everyone write about the pros of changing the gears. Can someone post the possible cons??????

My warranty is almost up and im thinking about doing it. I don't do a lot of hauling....the biggest is a trailer with 4 dirt bikes on it. I am on the freeway everyday, and need my passing power!!!! My average mph is between 70 and 80.....Bay area driving

Thanks

 

if you want to a higher number, like 3.92, 4.10, etc youd loose top end speed and youd prolly get worse gas mileage

 

What about the top end acceleration???? I haven't had my truck above 100mph anyways.....hell, i don't even know what the top speed is To many dang CHP around these parts!!!!

 

if you do alot of highway driving i wouldnt go higher than 4.10's if you are running stock size tires.

 

Well, say for example, I have 33's now and my truck has 3.55's in it stock, recommendations?? Need it back in the right powerband

 

Here's an older post that has some info on the subject:
---
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 unless the PCM computer software instructs it to downshift early (which it probably does).

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.

 

Dude, come on! There is no point of doing a 3.92. If you wanna drag race get 4.56's. If you want a little more accel. get the 4.10's. If you wanna be slow like me get 3.92's. It depends on what you wanna do. If you have a lead foot like me...4.56's won't do much on the gas mileage...I'm getting 14.5 hwy now...New gears won't change much...mabye 13 hwy at worst. I won't give a crap...cause I'll be fast![sm=gears.gif]

 

ok....so clear this up for me plz:

if i go from say 3.55 to 4.10....i'd see a definate low end acceleration improvement, but my top end speed would drop to ???????? and my top end acceleration would be crap?????

 

Low end there will be a big difference.....top end acceleration wont be a big difference, top speed will but I doubt you'll get to high enough speeds to find the difference unless you regularly drive over 100mph. I have 3.92s right now, thinkin about 4.56gears once I get a lift and bigger tires, otherwise the ratio would be too noticeable with 4.56's on stock tires. But its whatever you want, if you are concerned about mileage though I wouldnt get 4.56 gears if you are consistenly on the highway with stock size tires.

 

i am 1 or 2 sizes bigger than stock. all i';m really worried about is my top end passing. i really can't lose to much...otherwise i'll be sitting behind grandma and her 66 cadillac..and be late for work!!!