Will Re-Gearing Pay for Itself in MPG

[Jerry Bransford]

All Points well-taken although a lot of talk of a lot of off-roading where is I probably sit in the majority that drive it on the road mostly and occasionally go on a somewhat maintained Trail, no rock crawling for me.

Let me ask you this, yesterday I tested it a bit at 65 miles an hour in 5th gear I am pulling 2000 RPMs. Do you consider that too low of an RPM and what is the ideal RPM range for that speed?

You're lugging the engine when cruising at only 2000 rpms, I personally would bite the bullet and regear to 4.56 which is the ideal and most recommended ratio with the 4.0, 5-speed, and 33" tires. Gearing recommendations are, generally speaking, always made with highway rpms in mind, not offroad rpms unless the Jeep never sees the highway. 4.56 would give optimal highway rpms and odds are good that you'd even see slightly better mpg once you stopped lugging the engine at 2000 rpms. My own mpg went up to nearly 15 mpg from sub-12 mpg after regearing from 4.88 to 5.38 which is optimal for 35" tires when you have the 4-speed automatic as my TJ does. That ratio produces 2600-2650 at 70 mph & I actually would have liked better to have obtained the 2750 rpms I used to see when I had my previous 5-speed and 35" tires with 4.88 gearing. The bigger the tires, the more rpms that are needed to restore the same power that was available with smaller tires. So rpms that would be fine with 30" tires would be insufficient for 35" tires.

 

[jjvw]

... although a lot of talk of a lot of off-roading where is I probably sit in the majority that drive it on the road mostly and occasionally go on a somewhat maintained Trail, no rock crawling for me.

My Jeep may be built the way it is, but at the end of the day it is my daily driver and spends most of it's time on pavement. Except for the physical climb into it, nearly everything I have done to it has improved it's life on the road as much as it's off-road capabilities. The two are not mutually exclusive.

Let me ask you this, yesterday I tested it a bit at 65 miles an hour in 5th gear I am pulling 2000 RPMs. Do you consider that too low of an RPM and what is the ideal RPM range for that speed?

Yes I do have to drop down into 4th gear to pass anybody on a two-lane road or going up hills.

I take off in first gear all the time and never feel as though it's lagging or struggling in fact I shift out of first fairly quick because I used it all up.

Again, I'm pulling 3000k at 75mph. It is nice to still be able to accelerate if I need to. Even on the mountain highways, I was surprised by how much my need to downshift was reduced after the regear. It made driving far more pleasant. As mentioned earlier, the shorter 1st gear has been great for city driving and rush hour creeping.

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I'm all for having a better driving experience, I'm not sure if the answer is going to 410 or 411 gears from 373 is worth the cost vs The Experience?

Thanks

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Going from 3.73 to 4.10 wouldn't be worth it. 4.56 is the what most would recommend for your setup which changes the discussion a bit. And then there is my recommendation that 4.88/33s/5 speed is really nice on my daily driver.

You're lugging the engine when cruising at only 2000 rpms, I personally would bite the bullet and regear to 4.56 which is the ideal and most recommended ratio with the 4.0, 5-speed, and 33" tires. Gearing recommendations are, generally speaking, always made with highway rpms in mind, not offroad rpms unless the Jeep never sees the highway. 4.56 would give optimal highway rpms and odds are good that you'd even see slightly better mpg once you stopped lugging the engine at 2000 rpms. ....

X2. If you were to regear, it needs to be 4.56 minimum. The lower gears we recommend are for the highway. The off road benefits, while desirable, are largely incidental.