New wheel and tires results in poor MPG.

Merry Christmas everyone,

My DW let me buy 20" wheels and new tires (285/50R20) for my burb for Christmas.

On our trip to visit family in KS (from CA) I noticed that the MPG I was getting dropped 3 MPG.

On a previous trip from LA to Yosemite we got 19 MPG, with the cruise set at 75 MPH. During the trip to KS, with the cruise set at 75, and MPG dropped to 16. I didn't notice any drop in performance so I don't believe anything is wrong the the engine (but won't know until I look).

My driving style is causal, don't have a heavy foot. The original wheel and tire size I replaced were 16" with 275/70R16.

BTW, I took it out of cruise in the mountains and feathered the pedal to keep the burb from dropping in and out of passing gear.

Does anyone have any idea?

thanks everyone for you input.

If you change tire size you will need to get the speedo reset.

Also the brakes need to be upgraded and it was an option on Avalanches.Had one in one once,had brake problems after putting on 20" rims and tires

I was thinking in the same line as to have the speedo checked out and calibrated to the tire size change. One thing I did notice is that the size difference from 275/70R16 to 285/50R20, the latter was only an inch larger. I checked this out at the tire dealer before purchase. Also I ran through one of those speed trap rader limit signs and noticed that my speedo was reading the same speed that the rader was showing (I know that this is not completely accurate).

Just hoping that might be something else.

Also, thanks for the advise regarding the brake upgrade. Although, so far my brakes feel fine (traveled from CA to KS), I will look into the upgrade.

Happy holidays... ;>]

you did not say what year vehicle got the new tires. I believe you need to have the PCM set to recognize the new size tires.... The truck PCM (if somewhat of a new vehicle) is calabrated with the wheels and tires that came on the truck new.... Ask your local GM shop.

I was thinking in the same line as to have the speedo checked out and calibrated to the tire size change. One thing I did notice is that the size difference from 275/70R16 to 285/50R20, the latter was only an inch larger. I checked this out at the tire dealer before purchase. Also I ran through one of those speed trap rader limit signs and noticed that my speedo was reading the same speed that the rader was showing (I know that this is not completely accurate).

Just hoping that might be something else.

Also, thanks for the advise regarding the brake upgrade. Although, so far my brakes feel fine (traveled from CA to KS), I will look into the upgrade.

Happy holidays... ;>]

bigger heavier wheels take more power to spin, the stock 16" wheels are very light compared to 20" wheels, especially chrome ones.

Merry Christmas everyone,

My DW let me buy 20" wheels and new tires (285/50R20) for my burb for Christmas.

On our trip to visit family in KS (from CA) I noticed that the MPG I was getting dropped 3 MPG.

On a previous trip from LA to Yosemite we got 19 MPG, with the cruise set at 75 MPH. During the trip to KS, with the cruise set at 75, and MPG dropped to 16. I didn't notice any drop in performance so I don't believe anything is wrong the the engine (but won't know until I look).

My driving style is causal, don't have a heavy foot. The original wheel and tire size I replaced were 16" with 275/70R16.

BTW, I took it out of cruise in the mountains and feathered the pedal to keep the burb from dropping in and out of passing gear.

Does anyone have any idea?

thanks everyone for you input.

because you installed tires with a larger circumference your will record fewer miles driven ,,,,hence the lower gas mileage..

going from a 70 to a 50 will not see much change in MPG...
if this where a LT 265 75 r16 to the tires you have now then you should see better MPG ...your traction in rain/snow would be scary...though.