Gear Change Needed!

[txhotrod]

I am running 35's on a Ram 1500, 5.7 what gears do you recommend? Trying regain some pep and mileage back, 12 MPG sucks! LOL. I was leaning towards 3.90 or a 4.10.
I pull lots of trailers, from an RV @9k loaded to flatbeds. I want to get the transmission back into the proper RPM range, so it will quit downshifting on every overpass and hopefully gain some MPG back, gas aint cheap! LOL
What are your suggestions? My local supplier was recommending 4.56, which I think is a too tall, for pulling and highway. Thanks!

 

[crash68]

Your not going to get any fuel economy back, the transmission is going to speed up and the downshifting on inclines will always happen. To alleviate all those issues the true solution isn't gearing, but switching to a diesel.
As for 4.56 with 35s, it won't be a problem for towing but for highway driving the engine rpms will be about 2100 rpms at 75 mph(6th gear).

 

[DILLIGAF]

4.56 and 35s is perfect.

 

[caulk04]

With the RFE trans, 4.56 or nothing.

8spd? It's good enough that 3.92 should be no issue.

Your milage is going to suck. Just know that going in to a lifted truck on big tires.

 

[txhotrod]

My 2011 only has a 5speed transmission. Right now diesel is not an option, just got rid of the one I had.
I have installed gears in other vehicles and the mileage has increased along with driveability., you just gotta hit the sweet spot, between power and MPG. Jeeps I know well. These trucks still learning I just dont want to be turning 3000 rpms on the highway. According to the gear chart I looked up my 3.55 gears with the original 275/60 is at 2349 @65mph. I believe mine is a bit lower in 5th (overdrive) Charts use a 1-1 ratio

 

[Wild one]

My 2011 only has a 5speed transmission. Right now diesel is not an option, just got rid of the one I had.
I have installed gears in other vehicles and the mileage has increased along with driveability., you just gotta hit the sweet spot, between power and MPG. Jeeps I know well. These trucks still learning I just dont want to be turning 3000 rpms on the highway. According to the gear chart I looked up my 3.55 gears with the original 275/60 is at 2349 @65mph. I believe mine is a bit lower in 5th (overdrive) Charts use a 1-1 ratio

Multiply 2349 X 0.67 = 1574 rpm in 5th. Both 4th and 5th are overdrive ratio's in your 5 speed RFE.

• Gear Ratios:
  • 1st 3.00:1
  • 2nd 1.67:1
  • 2nd Prime 1.50:1 (Only used when a kickdown acceleration)
  • 3rd 1.00:1
  • 4th 0.75:1
  • 5th 0.67:1 (545RFE only and 45RFE reprogrammed)
  • Reverse 3.00:1

 

[Daw14]

I went from 3.55 to 4.56 with 33” tires and 65rfe , it’s a different beast now.. mileage in town went up a little 1-2 mpg .On highway at 80 probably lost 1-2 . Pretty much a wash except on long trips .

 

[WY-Dave]

Here is the page that I used when I was in the Jeeping work https://4lo.com/calc/geartire.php
and great RPM calc https://www.crawlpedia.com/rpm_gear_calculator.htm
And a few calcs under "trans calcs" https://www.randysworldwide.com/

 

[62Blazer]

You need to know what gear ratio the truck currently has and then calculate what gearing should be. Based on the increase in tire size you can determine what gear ratio is need to bring the RPM back to stock, though often people will go a little bit further on the gearing change to help compensate for the added weight and rolling resistance of the larger tires. In regards to gaing back MPG just don't have any high expectations for that. The larger tires and presumably a lift since take more power to move down the road, and more power means more gas. Gears mainly just compensate for the perceived power loss and transmission downshifting. Also keep in mind that the transmission downshifting for grades doesn't necessarily mean a reduction in MPG. Lugging the engine at a lower RPM and requiring 100% power output has the possibility of using more fuel as compared to the engine running higher RPM but only requiring a percentage of the power output.