Higher gears in rear axle to increase gas mileage

[mcrews]

See what different rear end options the factory offered..... if they offer a factory option......

If so then you might be alright.

[darcane]

Originally Posted by 98frontier

Hello, this is my first post as I just registered today, I was curious to know what kind of mileage increase I could expect if I were to install a 3.54 rear axle in my 1998 Nissan frontier in place of the 4.33 axle I have now, my engine is a stock 2.4 Dohc with a four speed auto, my truck is 2wd and I am running 235 75r15 tires in place of the factory 215 65r15.

That is an 18% drop in rpms. Try reducing your speed by 18% (if you normally drive at 60mph, drive at 49mph) and see if your tranny is happy staying in your top gear with the converter locked up. If it is keeps downshifting or unlocking the converter, you will waste more fuel than if you left it as is.

This isn't a perfect test, since you will have higher loads from aero drag at the higher speed, but it should at least give you an idea if you can stay in your top gear with the higher geared axle.

Oh, picking up an Ultragauge would be a great idea. They are inexpensive and will tell you RPMs, instant and trip mileage, and a bunch more. The Torque app and a Bluetooth OBDII adapter also work well if you have a smartphone.

[mcrews]

yes that^^^^^^^ what darcane said.

[IsaacCarlson]

I say go for it. I had a 3.55 in my truck and swapped it out for a 4.10 for better pulling torque and my mileage dropped about 5 mpg BUT this is a work truck and it works HARD)

[Hersbird]

If you drop the rpm too much on the 4 speed auto it may not hold overdrive or lockup the torque converter on the highway. With a manual you can always force it to stay in whatever gear you want. 4.33 gears are pretty steep but you already tamed them somewhat with the bigger tires. What might be best for economy would be to swap the gears and go back to the small tires. If you are paying $500+ to swap gears it will take a long time to pay for itself, if you found a $100 junkyard rear end with the taller gears then easier to justify.