Looking for Gear Ratio Help
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New User
Joined: Apr 2019
Posts: 2
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Looking for Gear Ratio Help
Hey guys, I just joined and have a question on my F-250.
I currently have a 2012 Lariat FX4 with the 6.7L:
- 8' lift
- 40x14.50r22 tires
- current gear is the stock 3.55 w/ electronic locking
- truck is tuned and deleted
- primarily used for highway and towing my boat and race car (both are under 10k pounds)
The truck feels sluggish so I know my next step is adjusting the gear ratio. I have tried calling a few vendors and not gotten much help. I've looked a the charts some people have posted and it looks like I should be in the 5.13's but that seems very low for what I do.
Any help would be appreciated!
I currently have a 2012 Lariat FX4 with the 6.7L:
- 8' lift
- 40x14.50r22 tires
- current gear is the stock 3.55 w/ electronic locking
- truck is tuned and deleted
- primarily used for highway and towing my boat and race car (both are under 10k pounds)
The truck feels sluggish so I know my next step is adjusting the gear ratio. I have tried calling a few vendors and not gotten much help. I've looked a the charts some people have posted and it looks like I should be in the 5.13's but that seems very low for what I do.
Any help would be appreciated!
Mountain Pass
Joined: Sep 2004
Posts: 101
Likes: 5
If you do the ratio math, 40"/34" * 3.55 = 4.17. You could go 4.11 or 4.30 and be back at the same RPM as stock LT275/65r20. I don't think I'd go higher than 4.30 with a tuned 6.7L. Those charts you probably saw are dated and based on older engine power levels.
Cargo Master
Joined: Sep 2007
Posts: 2,470
Likes: 535
From: Chandler, AZ
If you have the $$$$ and want to re-gear I would do 4:30s. 4:11 is only 2 steps up from 3:55 and may not be as noticeable as you may think for the same money.
40/34 is +17.6% increase
Here are 6R140 ratios
GEAR RATIO STEP
1, 3.974
2, 2.318, 1.714
3, 1.516, 1.529
4, 1.149, 1.319
5, 0.858, 1.339
6, 0.674, 1.273
At highway speeds the steps are only about 30% because you have 6 gears. Your 40s put you in the middle of that. A variable vane turbo will make optimal boost/power regardless of engine rpm due to tire size.
I went from 32s to 37s which is +15.6%. Loaded to 18k my truck makes about the same speed up 7% grades. I didn't feel a ~$3K gear change was justified. YRMV.
40/34 is +17.6% increase
Here are 6R140 ratios
GEAR RATIO STEP
1, 3.974
2, 2.318, 1.714
3, 1.516, 1.529
4, 1.149, 1.319
5, 0.858, 1.339
6, 0.674, 1.273
At highway speeds the steps are only about 30% because you have 6 gears. Your 40s put you in the middle of that. A variable vane turbo will make optimal boost/power regardless of engine rpm due to tire size.
I went from 32s to 37s which is +15.6%. Loaded to 18k my truck makes about the same speed up 7% grades. I didn't feel a ~$3K gear change was justified. YRMV.
Hotshot
Joined: Jul 2013
Posts: 14,266
Likes: 2,187
With an 8” lift....what are you doing to correct the drive line angles
options are plates that correct the axle angle back to what it should be
adapters to drop the transfer box
if you have no drive line angle correction I would start there before doing a gear change.
options are plates that correct the axle angle back to what it should be
adapters to drop the transfer box
if you have no drive line angle correction I would start there before doing a gear change.
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