Before you spend the cash to have them swaped back, consider doing this, which could pay YOU!.

Maybe somebody local who has 4.10's would consider swapping complete axle assemblies. This would be fairly simple (not much harder/more work than a lift install. I'm sure somebody would gladly pay you several hundred $$$ and help you do the swap. That would save both of you cash.

Just an idea. Alot of people wouldn't be up for the hassle, but I like to save a buck when I can.

 

Don't know if it matters, but did you do the Hypertech reprogram?

 

x2 you computer is confused.......programer should help....

 

This makes me nervous about getting mine installed. I'm re-gearing for the same reasons- the hills of CO.

 

Just installed a MOPAR CAI - It does help with both power and fuel economy - power when you get on it and more MPH when you lay off the throttle.

lot easier and cheaper than changing out gears.

not going to turn it into a hemi - but at least it helps a little on the overall performane side.

someone had a dyno chart - 5.13 's are better if you are only off-roading - 5.13's your RPM's are too high and a 3.73/4.10 your RPM's are too low with 35" tires. think it was 4.54? is supposed to best for 35" tires overall (like stock).
not sure they make a 4.54 kit for the JK yet - but they do have a 4.88.

 

I know I've mentioned this a few times...but there is a tendency to over gear on an upgrade, the thinking is that if a little more is good, a lot more must be better, etc.



The Auto's and the 6 speeds have shown a definite preference range, as the auto's have a numerically lower final drive ratio than the manuals, etc.

Essentially, the 42 RLE Auto Magic Box has:

1st @ 2.84

2nd @ 1.57

3rd @ 1.00

4th @ 0.69


and the NSG 370 six shooter has:

1st @ 4.46

2nd @ 2.61

3rd @ 1.72

4th @ 1.25

5th @ 1.00

6th @ 0.84

________________

So - as you can see....obviously, the 6 spd has more flexibility as far as gearing than the auto does, simply more available ratios....and, therefore, the increased ability to re-gear (For Free), on the fly....as needed.



Flat landers can get by with taller gears, CO and mountainous terrain people generally like lower gears...if they can simply allow themselves to drive slowly enough to keep the rpms down, or, can afford the go go juice to make up for the extra mph, etc.

Driving more slowly also reduces wind resistance...which on a brick like Jeep, adds up FAST.

So - the more tractor-like you make your gearing, the more tractor-like you need to adjust your driving.

---------------------------------

Going from 32's to 35's essentially changes your final drive ratio by dropping your rpm in every gear by about 8.6%.

Going from 4.10 to 4.88 essentially RAISES your RPM by about 16%.

So - Going from 4.10 gearing to 4.88 gearing, and from 32's to 35's at the same time, results in an overall INCREASE in RPM in every gear of about 7.4%.

IE: To simply MAINTAIN stock final drive ratio if starting with 32's and going to 35's...and starting with 4.10's, all you'd need to break even is about 4.45 ratio diffs....not a worth while change in ratio so as to be worth it...its so close to stock anyway, etc.

If you started with 3.21's, or 3.73's, etc...well, the difference starts to be worth it for 35's, etc.

 

 

The extra resistance of the 35's vs 32's is not bad enough for me to regear from 4.10's per se with my 6 spd....

LARGER than 35's tend to have LOTS more hysteresis to overcome, and with 35's at about the break point for that issue, sure, we need to take it into account.

I just up the PSI for larger tires for Street Work to reduce the rolling resistance/use a set of AT's for DD duty, and a set of MT's for 'Froad Work.



Your driving more tractor-like with the deeper gearing makes perfect sense, and is the way to adapt your driving to the deeper gears....so, its all good.



I've been playing with the mpg meter as I drive....my mpg is maxed when I'm under 2k on the tach....essentially about where the stock 3.21 gearing and 32's would have put me at hwy spds.

As the tach climbs, the mpg drops....as I'm simply pumping more gas through the engine for any given speed when the rpm is higher than the beginning of the torque curve.

The point of diminishing return is when a steep hill makes it such that the gas pedal is starting to be depressed too far to MAINTAIN rpm, and a down shift is needed to maintain speed, etc....but, down shifting to a 1.00 from a 0.84 ratio (6th to 5th) for example - raises the rpm ~ 16%....essentially the same as if I dropped in 4.88's, but was still in 6th....

....the difference is that after the hill, I can still go back to 6th....and reap the mpg harvest.

 

I think some of you might be missing the point. My 4door rubi with 35s/5/13s in 3rd gear will put out aprox 2800 rpm at 60mph. However, the engine does not have enough power to maintain this speed/rpms on the high country highways. Someone suggests just driving slower. How slow - 30 mph in 2nd gear?? 5.13s are undoubtedly good somewhere. But moving a JK unlimited up I-70 aint it.

Not trying to start an argument. Or, suggest I know more than other people. But I have first hand experience on this one. And am certain there are people out there that think 5.13s will solve their steep grade power problem (I was one of them). Just trying to save someone some time and hard earned $$$.

 

fyi - here's a chart for calculating true RPM/MPH

http://www.angelfire.com/fl/procrastination/rear.html

RPM Gear ratio 4th (auto) Tire MPH
2000 4.10 .69 34.6 73
2000 4.56 .69 34.6 65
2000 4.88 .69 34.6 61
2000 5.13 .69 34.6 58

* 2000 is a good cruising rpm