L7 Sierra

I have a 2007 GMC that with the stock 245/70/17 steel rims I averaged 19-20 mpg doing the daily jog into work and traffic home. The tires went bad so I scored some escalade aluminum 18's with 265/65/18 tires, and now I get 17.5 mpg. I was not expecting that at all which is why I never got a 22/24 wheel combo even when I had the money.

Is this normal with 17's vs 18's. Or has my stock 3.23 gear ratio meet its match and now I need something deeper like 4.11's? Would 275/60/17's cause this same problem?

I have done the mods below in my sig "just a couple" plus maintance on the mark, and weekly checks of my truck. So if it keeps this way I wish I had my old 496 powered 2500 back it never got above 16, but it had the power to make it worth it.

I know the exact distance to work, and verified according to earlier data not my slightly incorrect speedo now.

outlawz2004

iTrader: (18)

I dont think it would make that much of a difference with just the height, but it could I quess with those gears. With the 18s, your ratio is about 3.137.I have 3.42s and went from 19/20 to 17/18, but I went from a 29" tire to a 33" tires. Your 17s are about 30.6 and your 18s are about 31.5. Are the 18s a bridgestone tire, and if so I know that everytime I have used a bridgestone tires I lost mileage.

95 bright teal

What tires are they, i had 245/70/17 on my stocks, two of the tires were the general ameritracs and the others were bfgoodrich allterrains. the allterains weighed 20lbs a peice more. they were 80lbs, i know lots of 20" wheel tire combos lighter than that.

20lb per wheel can make a huge difference

L7 Sierra

Bridgestone Dueller H/T's. They have a 360 treadware, and maybe 7 lbs heavier then stock tires.

I know it does handle better, but I am not sure if it is worth it though.

outlawz2004

iTrader: (18)

Told ya, Bridgestones are nice tires but suck for gas mileage.

L7 Sierra

Does anybody know what Escalade 18's weigh?

I know the tires weigh 40 lbs, and stock 17 steelies complete weigh 65.

GMCtrk

iTrader: (27)

I run the 18" escos w/ 285/60/18s on all 4s

Coming from 255/70/16s (stock) the thing was a dog. I lost a lot of acceleration, mainly due to the effective increase in gearing. I was running 3.42s at the time and have since changed to 4.10s which rectified the problem.

The escos weigh 28lbs a piece.

L7 Sierra

Must somehow be the 360 treadware and slightly taller combo is just the straw that broke the camels back on my truck.

I might pull my wifes scale out tommorow morning to see what a wheel weighs complete. Other then that start saving for 4.11's.

BLACKND

iTrader: (5)

all terrains also tend to effect mileage alot more than highway style tires. not sure what the overall diameter difference is between what you had, versus what you are running now, but when you add the taller tire/all terrain/heavier tire/wheel package and wider tire, you will feel a loss in power and mileage. Everything tends to add up. a few pounds difference might not seem like a lot, but it all adds to the rotating mass. You're 3.23's certainly isn't helping much.

did you re-calibrate the computer for the larger tire size? Diameters are about 1" larger, might be enough to throw off any readings??

L7 Sierra

No I had to buy tires pretty quick as I had a couple of baldys. There only 1 inch total difference it doesn't make a noticable diff in my speedometerwhen I pass those signs that display your speed.

I will be odering my speed parts here soon and HP Tuners will be one of them. I'll correct it then.