just 6" lifted my 11 ecoboost and have a question about gearing. If i were to regear for ease on the tranny and possibly a little better gas, what gear should i go with? The truck came stock with 3:55s and my stock tires were 275-55r20. new tires are 35x12.50x20. 275-55 are 31.91 inches tall

I did a calculation of percentage increase in tire, times the current gear size, and came up with 3.90s for the new gear. (35/31.91=1.10% 1.10%x3.55=3.90)


so is this calculation correct and what gear would be most efficient in bringing back to stock feel. recomendations? thanks in advance

 

Now that they have a 6 speed auto, the need for regearing is a lot less than it used to be. I doubt you can get the gas mileage any better, the folks with EB's with 3.15 gears are getting better mileage than anyone else. What's going to help more than anything is when someone comes out with a programmer that works on the EB so you can correct the vehicle speed. It's not the gears that's causing the loss in "feel", it's the wind resistance and heavier rolling weight.

 

i knew that was gonna be a big factor too, i just didn't want to be putting an extra large strain on the tranny. thought a regear may help. planning on keeping this one for a while.

 

I don't think you would be putting a strain on the tranny - being that they ARE available with 3.15's and 1st gear in the 6 speed is a stump puller to begin with.

 

If you regear I wouldn't go higher than 4.10 with 35s on the new 6 speed.

 

And 3.73's aren't worth the expense.

 

x2

 

Your math is correct, so 4.10 is the way to go. With what you're wanting to accomplish, you want to get as close as you can to your target (3.90), but then select the next lowest gear that gets you close to your target, not higher (which would be 3.73). Although I have no e-boost experience, the principles are the same, thus I slightly disagree with GLC. Based on my own learning experience, it's amazing what a gear swap will fix. Regardless of what the truck/tranny will make up for, it's still not a "recovery" of the performance (no matter how minimal) you've lost to taller tires. Gears is the only way to recover that. Yes, tuners in the right hands with the rights settings are incredible, but it's a band-aid when used to cover gearing loss.

Look at it this way...imagine a tuner WITH gears (starting from stock performance instead of from a handicapped situation) instead of the tuner having to "make up" for lost gearing.

I will never go with taller tires on my next truck without budgeting for gears at the same time...but that's just me.

 

Disagree if you want, but have you ever owned a truck with a 4.17 low gear? Your 4R70 has a 2.40 low gear.

 

but the trucks with the 3.15 gears have a lower tow rating and are slower to accelerate. besides, who wants to slow their truck down?

 

George, I'm in no way disagreeing with you that it's an extremely capable truck and tranny; night and day from what I'm driving. I'm just making the point that regardless of what's in front of the driveshaft, adding taller tires starts you at a handicapped position vs a level playing field. Two guys with identiacl trucks and 35" tires; one with gears returing the truck to a stock-ish rpm range and the other did not re-gear. Add an identical tuner to both. Who has the advantage? Is it required or near as critical as on the older trucks?? Absolutely not, but it's still a handicap.

 

Definitely. I have both and its far stronger than when it was 100% stock.

 

well i dont think itd be worth the money just to go to 3.73s at all. so itd have to be 4.10s if i was going to do it. thanks for all the info!!. appreciate it

 

No, you're absolutely right. That would be almost downright stupid. But 3.73's isn't even your best choice. You'd want 4.10's anyways...which would most definately be worth it. I went from 3.55's to 4.10's and to this day, still kick myself for waiting so long.