Also keep in mind what the gear split on the specific axle carrier is. If you jump from a 3.54 to a 4.56, you may have to change the differential carrier as well to compensate for the pinion head size...i.e. the split for Dana 60 differentials is 4.10 : 4.56 iirc, meaning that gear sets 4.10 and faster (numerically less, like 3.73, or 3.54) will fit on one style carrier, while 4.56 and slower (numerically greater, like 4.88 or 5.13) fit on a different style carrier to maintain gear mesh with the smaller pinion head. Just food for thought...

 

ok here's the current set-up. The front axle is a dana 60 HP currently running 3.73's with the front drive shaft disconnected. The rear axle is a Sterling 10.5 currently running 4.56's. The reason for the different ratios is because he was previously running 3.73's all around, but decided to upgrade to 4.56's to accommodate for the 40" tires. The front 4.56's were on back order and still havent arrived to him. he still has the rear 3.73's in his garage.

With that said, im not sure as to the gear split on the carriers. honestly, that's something i don't know a thing about. he hasn't mentioned anything about it, but ill certainly ask. since the front 4.56's havent been shipped yet, he told me he could have them switched to 4.10's if i wanted. im supposed to be buying the truck towards the end of next week.

 

I'd get the 4.56's for the front. That way you only have one gearset to change and have steep enough gears to effectively run big tires.

I don't get why people want to drive heavy duty pickups with big tires and worry about fuel mileage in the first place. Then they worry about running taller gears for improved mileage which never happens unless it's running nothing but unloaded highway miles.

 

Thanks for the input. I think its pretty apparent from this thread that there are many different opinions, but that's also why i posted this. i appreciate and want any opinion i can get. Its not so much that im looking to save money on MPG's, but rather not wanting to run at 2k+ rpm's at just 65 mph. That's what the truck is running right now with its current set up. if i go down to 37" tires, those rpm's are only going to go higher. if i planned on doing nothing but city driving, then those numbers wouldn't bother me one bit. id actually enjoy the extra pep. But fact is, ill be doing just as much highway driving. no, this truck will not be my daily driver, but it will be driven fairly regularly. the idea is finding the ratio that provides that happy medium between the two, or at least close to it.

 

Sorry, I translated rpm to fuel mileage. Let me re-state:

I don't get why people want to drive Cummins pickups and worry about rpms, or going 100mph in the first place. They are unsafe at anything approaching that speed - especially with big tires. It's an inline 6 with a fat torque curve and limited rpm range no matter what you do to it. They are happy running rated rpm all day, no sweat.

 

I certainly see your point. This truck im buying is approximately 8 hours away from me. So that means ill have a pretty good drive home with it on its current set up. Im hoping that will give me a little better idea of just what i may want/prefer.

 

Like you said, everyone has their opinion. I just wanted to try and elaborate on mine a 'lil.

One thing I know for sure is from personal experience. My '07 has the stock 3.73's with 35" tires and they are almost too big for it, gear-wise. I do not, nor would I want to try and tow anything very heavy with it.

 

Now, that opinion I'll agree with.

 

appreciate it fellas. We will see how the 4.56's treat me on the way home with the truck next week.

 

Mine wont. MIne bogs down pulling my lawn mower up hills with the 37s ans 3.54