i have heard that bigger tires cause your gas consumption to increase is it true

 

definitely true, although not always as exaggerated as some might have you think. but when you started jumping inches you add a lot of weight so you start losing anywhere from 1 to 5 mpg in most cases..depending on what size you run. like if you went to say 285/70 from a stock tire you might lose 1 - 1.5 mpg...but if you went to a 315/70 from stock you might lose 2-4mpg...

 

Yes this is true when I went from the stockers to 34s. Mine went down about 3mpg.

 

Just as much as weight is the fact you will have more rolling resistance due to the amount of rubber on the road. More friction due to wider widths.

 

I went from stock to 33x13.5 to 37x13.5.

15 mpg stock. Either of the larger tires I'm around 13.5. The width and rolling resistance has more effect (in my experience) than the height.

 

Keep in mind that a lot of people go to a taller tire and never correct their speedometer/odometer. So the odometer is off when they figure their MPG's.

 

My buddy got 35" **** Cepeks on his Jeep and his speedometer shows him goin 10 mph under what he really his. And yeh his gas went down bout 2 mpg

 

2 to 3mpg loss mainly in city driving is not unusual for larger heavier tires.