New size tires, now mpg way off

[JeremyFOwens]

So I just went to a 275/60/20 Perrelli cuz they were on sale at walmart and discount tire matched. They are nice tires and do rub a little at full turn.

My issue is now my mpg on display has dropped 2 mpg. Not sure if speedo is correct or not. I understand I can flash it to correct it but is the display correct in mpg or is it trying to base it off the correct tire size.

To fix this is the best way to buy a RC device to fix both?

 

[Richard320]

If the tires are 10% larger, mpg will appear 10% smaller. MPG is calculated using the odometer and the odometer/speedometer are calculated using revolutions and tire diameter.

Reprogram the tire size and everything should fall into place.

 

[Tchpet]

That's why I am purchasing a Tazer DT. There is a group buy going on if you have interest. Just do a search for Tazer DT Group Buy.

 

[Fantastipotamus]

When I switched my tires in my old Nissan Titan to heavier (but stock size) BFG A/T’s, my MPG dropped from 17.5 to 14.5 highway. Never saw 17 again! My point is some tires just decrease MPG.

Reprogramming probably isnt a bad idea, but before you drop the cash, could just hand calc MPG for a tank as see if its actually inaccurate.

 

[Jako]

When I switched my tires in my old Nissan Titan to heavier (but stock size) BFG A/T’s, my MPG dropped from 17.5 to 14.5 highway. Never saw 17 again! My point is some tires just decrease MPG.

Reprogramming probably isnt a bad idea, but before you drop the cash, could just hand calc MPG for a tank as see if its actually inaccurate.

Went from Pirellis to Firestones and lost mpg with a 1994 Ford Explorer.

 

[aimlowrobin]

Bigger tires means speedometer is off and so is the odometer. Mileage shown will them also be incorrect. Not to mention, if you went bigger, they likely are heavier and will drop your mileage a bit.

 

[sheepdogtrail]

AlfaOBD can reprogram your tire size in mm. Which will be accurate.