General rules of thumb seem to be that steeper gears help with towing (and Dodge towing specs change by 1,000+ lbs just with a gear change), and the steeper gear will help a little with in-town mileage with a small hit to highway mileage.

I thought that the towing increase was due to the engine spinning faster and getting more into the torque curve, but... It looks like 55Mph going from 3.92 to 4.56 gears is only about a 300RPM change and the engine is still spinning less than 2500RPM in direct/drive. The torque peak isn't until almost 2,000RPM later and the HP peak isn't until almost 3,000RPM later. Now, if I drop into 2nd, I'm currently about 4,000RPM at 55Mph. That is definitely at/near peak torque, but that's also only used on a steep grade.

For in-town mileage, it seems to be the same general idea that the steeper gears will get you moving from a stop faster and that's where your mileage gain will be at.

ASSuming that I'm correct with the above, it seems like something like going from 3.92 to 4.56 wouldn't make much of a difference, yet.... it's huge. What am I missing?

I'm half-heartedly considering going from 3.92 to either 4.10 or 4.56 but my gut and my brain don't agree on the performance difference.

Thanks!

 

well the steeper gears are gonna help you with acceleration and towing for sure (steeper gearing runs the RPM's up and gets more torque to the ground) you'd be pretty suprised at the difference it'd make going to a 4.10 or 4.56 gear from 3.92....also, if you plan on going to a bigger tire, then going with a steeper gear is gonna help your truck with gettin goin

 

Heres a perpective: My toyota mini truck, stock gears are 4.10s. stock tire size equates to about 29". Im running 35s and 5.29s bring me back to stock ratio. All neccesary to keep that little 4 banger happy. V8s, gas or diesel are less fussy. Mathematically the change in rpm isnt all that much, but when 300 more rpm equals say 30 (nice round number) more ft-ibs of torque to the wheels thats a sweet improvement!