jmccart

Thanx Speedshift. Are you saying that the big tires make it stop crappy?

06megacabman

I guess I don't understand the surprise about the mileage drop. If I'm thinking about this correctly larger tires makes the speedo and odometer show less mph than actual. Like your speedo says 55mph when actually you are doing 65mph or close too. Therefore, unless you have recalibrated your speedo and odometer I would expect a lower number. In other words if you drive 1 hour you will see 55 miles versus 65 miles on the odometer in addition to the loss due to friction and weight of the larger tire for the same or more amount of Diesel.

MOJO1

I dont know about you guys but my milge is beter. There is a fine line here you can go to big. Iam still going to 37s with a small lift soon see if it drops the tack some more.Like SPEEDSHIFT said we are geared to LOW! On the highway runing 70 it sucks fuel bad!

Dane Bramage

Are there any after-market OD gearing options for 6-spds other than GearVendors & US Gear? I really just want a 7th gear.

Silver76

I gained about 1mpg with 315s.

jsafe

Not me lost 1.5 mpg

3ton1/4

There is no way going bigger on the tire size will improve mileage. I just came off a 1,000 mile round trip with my new 315's. Ran the same trip two weeks earlier with the stock 265's. Big difference !

4x4not

My milage when I went from 245s to 315s stayed about the same, MAYBE went up 0.5mpg. The higher drag was offset by th lower RPMs. I do have 4.10s and an NV5600, so at 68mph I am right at 2000rpm with the 315s. When I removed the Juice though my milage seems to be down significantly now. I will be filling up today and we'll see.

MOJO1

There is no way going bigger on the tire size will improve mileage. I just came off a 1,000 mile round trip with my new 315's. Ran the same trip two weeks earlier with the stock 265's. Big difference

Not all the trucks get the same kind of milage. BUt i know you can on my truck. Think about it if you are tacking 2400 RPM at 70 MPH What if you could run 1800 RPM at 70 MPH Seems to me RPMs DONT LIE
But i could be wrong

Silver76

Ramble Bee, You're exactly right. (He's got an auto). I used to drive 100 miles/day so I'm very mileage conscious and pay attention to this stuff. My 06 auto got worse mileage than my 06 6spd with 315s. RPMs make a huge difference. Also, the type of tire will make a difference. I bought the tallest skinniest tire I could find.

tbr473

Hey Silver 76,

What tall and skinny tires did you end up going with?

Silver76

I run the BFG T/A KO 315/70/17 Load range D. I keep them inflated to their max psi.(50 psi cold) They are 34.5 in tall and 12in wide when mounted on an 8.5in wide rim. I have them mounted on the stock rims so they are probably a little narrower than 12"

tbr473

Silver76,

Sounds good. I don't think that combo would fit on my truck since it is a two-wheel drive.

Thanks for the info.

bighornram

There are way to many variables with this mileage war. I can tell you my mileage dropped when I went to 315s but I mostly drive short trips mixed city and country road driving. Not to mention I have a cr*ppy STOCK auto and 3.73s with a torque converter that slips way more than it should. So with the added weight of the tires, the extra power used to make them turn, and the increased power loss thru the tranny, I don't really expect better mileage. Now if i had a 6-speed with virtually no power loss due to tranny slippage that i drove mostly on the highway and was geared WAY to low (4.10s) then I would expect a better average MPG with the larger tires to drop the RPMs. By the way, I hover around 15 - hand calculated or not - the friggin overhead is right - i've checked. Please donate to JD's TRANNY UPGRADE FUND to make my mileage increase.

JHardwick

You really impress me with your mechanical knowledge.....

I would sure think that rotating mass would dictate otherwise.

Heck, some of those 54" floaters would really get some fuel mileage