Actual mpg change: 37 bfg

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SlickMachine

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Coming from other lifted trucks: The weight increase from larger tires/wheels contributes to decreased MPG but not nearly as much as the effect of the change in final drive ratio caused by the larger tires. The engine is no longer running in the sweet spot with regard to RPM. Seems like everyone is talking about weight....
Returning the final drive ratio to near stock while running larger tires requires regearing the diffs. MPG would then return to near stock, although still reduced slightly because of added unsprung weight (especially rotational).

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Truckzor

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Coming from other lifted trucks: The weight increase from larger tires/wheels contributes to decreased MPG but not nearly as much as the effect of the change in final drive ratio caused by the larger tires. The engine is no longer running in the sweet spot with regard to RPM. Seems like everyone is talking about weight....
Returning the final drive ratio to near stock while running larger tires requires regearing the diffs. MPG would then return to near stock, although still reduced slightly because of added unsprung weight (especially rotational).

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37" BFGs are only 6% larger than stock and that lowers your cruise RPM, as an example, from ~ 2000 RPM to ~ 1900 RPM. That isn't going to hurt your fuel mileage.
 

SlickMachine

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37" BFGs are only 6% larger than stock and that lowers your cruise RPM, as an example, from ~ 2000 RPM to ~ 1900 RPM. That isn't going to hurt your fuel mileage.
Yes it does and without a doubt. Also in play is the increased mechanical difficulty of turning a larger diameter tire

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Truckzor

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Yes it does and without a doubt. Also in play is the increased mechanical difficulty of turning a larger diameter tire

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Yes, bro(dozer), there is a doubt. A 6% difference in effective gearing isn't significant in a truck with a 10 speed transmission. I'd wager jacking your truck up cost more in fuel mileage due to aerodynamic losses. Your experiences in the past are nothing like moving from 315/70s in a Raptor to BFG 37s. You were moving from, what, 31 inch tires to 35s? (and probably still rubbing)

And even if you were right, which you aren't, the next lowest set of gears available is 4.56, which is an 11% difference from stock, which moves your overall gearing down by 5% (with BFG 37s), increasing your cruise RPM by about the same 100 RPM difference at cruise range.

That's not going to help fuel mileage. :shrug:

I agree there is a slightly larger contact patch. I don't see that making much difference, though.
 

SlickMachine

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Yes, bro(dozer), there is a doubt. A 6% difference in effective gearing isn't significant in a truck with a 10 speed transmission. I'd wager jacking your truck up cost more in fuel mileage due to aerodynamic losses. Your experiences in the past are nothing like moving from 315/70s in a Raptor to BFG 37s. You were moving from, what, 31 inch tires to 35s? (and probably still rubbing)

And even if you were right, which you aren't, the next lowest set of gears available is 4.56, which is an 11% difference from stock, which moves your overall gearing down by 5% (with BFG 37s), increasing your cruise RPM by about the same 100 RPM difference at cruise range.

That's not going to help fuel mileage. :shrug:

I agree there is a slightly larger contact patch. I don't see that making much difference, though.
Holy shit I'm out. This got retarded.

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SlickMachine

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Yes. Yes it did...
In your mind, were does the loss in MPG come from when moving up in tire size.. the 130 pounds in extra weight in wheels and tires? Following that logic: when your girl jumps in your truck adding 200lbs to it, do you see a 2 mpg drop in fuel economy? No you don't. When her AND her 250 pound mom jump in your truck at the same time, do you see a 5 MPG drop when driving around? Again, no. :Shenanigans:

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ChevyChad

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In your mind, were does the loss in MPG come from when moving up in tire size.. the 130 pounds in extra weight in wheels and tires? Following that logic: when your girl jumps in your truck adding 200lbs to it, do you see a 2 mpg drop in fuel economy? No you don't. When her AND her 250 pound mom jump in your truck at the same time, do you see a 5 MPG drop when driving around? Again, no. :Shenanigans:

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Sprung vs unsprung weight is a huge difference. You are not doing apples - apples comparison here brodozer dude.
 

SlickMachine

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Sprung vs unsprung weight is a huge difference. You are not doing apples - apples comparison here brodozer dude.
You're absolutely right. At this point I'm just trolling the village idiot.

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