TIRES AND BAD GAS MILEAGE

[stoushr]

OK, HERE IS MY PROBLEM. I HAVE A 07 EDGE. ORIGINALLY I WAS GETTING AROUND 17 MPG IN CITY. OK, I CAN HANDLE THAT. (17'' TIRES/RIMS)

THEN I GOT A REAL GOOD DEAL ON SOME TIRES AND RIMS BUT THEY ARE 20''

I PUT THEM ON AND THE " TIRE PRESSURE FAULT LITE CAME ON"*.. GUY AT LOCAL TIRE SHOP, RESET THE COMPUTER WITH THE NEW TIRES AND WHEELS.

BUT THEN, GAS MILEAGE DROPPED DOWN TO 14 MPG.

 

I MEAN IS THAT POSSIBLE? THAT THERE IS THAT MUCH OF A DIFFERENCE?

 

 

 

NOW WHAT DO I DO?

 

PUT OLD TIRES BACK ON?

[bbf2530]

OK, HERE IS MY PROBLEM. I HAVE A 07 EDGE. ORIGINALLY I WAS GETTING AROUND 17 MPG IN CITY. OK, I CAN HANDLE THAT. (17'' TIRES/RIMS)

THEN I GOT A REAL GOOD DEAL ON SOME TIRES AND RIMS BUT THEY ARE 20''

I PUT THEM ON AND THE " TIRE PRESSURE FAULT LITE CAME ON"*.. GUY AT LOCAL TIRE SHOP, RESET THE COMPUTER WITH THE NEW TIRES AND WHEELS.

BUT THEN, GAS MILEAGE DROPPED DOWN TO 14 MPG.

 

I MEAN IS THAT POSSIBLE? THAT THERE IS THAT MUCH OF A DIFFERENCE?

 

 

 

NOW WHAT DO I DO?

 

PUT OLD TIRES BACK ON?

 

Hi stoushr. :D Yes, it is certainly possible that switching from 17" to 20" wheels would hurt your fuel mileage that much, due to the added rotational mass, likely added weight etc..

 

Other possibilities? Have the temperatures in your area just recently started to drop quite a bit? Cold weather can adversely affect mpg's. So will using the "AUTO", "AC" and front defroster settings of the HVAC system (even if being used for heat), since they can engage the A/C compressor and it's resulting parasitic losses.

 

The TPMS error was completely unrelated and would have nothing to do with the drop in mpg's. That was just an error of omission by the shop for not resetting the TPMS system in the first place.

 

Unless something coincidentally went horribly wrong with your vehicle at the exact same time that the wheels were changed, or your HVAC or driving habits have changed after the new wheels were mounted, it is the wheels.

 

Let us know what you find out.

 

Good luck. :beerchug:

Edited November 9, 2010 by bbf2530

[MrHappy]

Also, the speedo may be off (and thus your distance calculations which factor into mileage) due to the change in tire/rim size.

[bbf2530]

Also, the speedo may be off (and thus your distance calculations which factor into mileage) due to the change in tire/rim size.

 

 

Hi stoushr. :D Although you have not been back to respond, MrHappy is 100% correct and I should be severely chastised for overlooking that possibility.

 

If you did not properly size your new wheel/tire combination, your speedometer/odometer may be off calibration. That speedometer/odometer error could appear to add to the inherent mpg penalties that usually come with larger diameter wheel and tires.

 

You can use the Tire Size Calculator found here: LINK: Tire Size Calculator to calculate the difference between your old versus new speedometer/odometer calibrations. Simply input your old wheel diameter/tire size and your new wheel diameter/tire size and the calculator will list the percentage difference in the overall diameter and speedometer/odometer error between your old and new setups.

 

Let us know what you find out.

 

Good luck. :beerchug:

Edited November 9, 2010 by bbf2530

[stoushr]

Hi stoushr. :D Although you have not been back to respond, MrHappy is 100% correct and I should be severely chastised for overlooking that possibility.

 

If you did not properly size your new wheel/tire combination, your speedometer/odometer may be off calibration. That speedometer/odometer error could appear to add to the inherent mpg penalties that usually come with larger diameter wheel and tires.

 

You can use the Tire Size Calculator found here: LINK: Tire Size Calculator to calculate the difference between your old versus new speedometer/odometer calibrations. Simply input your old wheel diameter/tire size and your new wheel diameter/tire size and the calculator will list the percentage difference in the overall diameter and speedometer/odometer error between your old and new setups.

 

Let us know what you find out.

 

Good luck. :beerchug:

[stoushr]

well, with the tires , the gas mileage is still the same, got tired of that damm lite so i decided to put the newer tires back on 20". they look better. but i guess i have to just deal with the sucky gas mileage.