Rubber Impact...
 

I was wondering the impact of larger tires on gas mileage...


Motor: 16 valve I-4 with 95 horse power and 98 lb-ft torque
Gearing: 4.62
Tire: 205/75/15
MPG: 27


Motor will have upgrades (new exhaust, intake, headers, blah blah)

New tires: 265/75/16 (14.35% bigger)


Is there a way to find how much it would hurt?

Hmmm...unless you're a really good mathmetition and can do a lot of tests I don't see a way to calculate it before actually trying it out?
Maybe someone could think up a calculation though. I do know the bigger tires tend to cause worse gas mileage.

I dunno, but for every 1" of extra height on the tires of my full-sized truck, its about 10-15% hit in fuel economy. The real answer is, if fuel economy is what you are looking for, don't do performance mods.

Either it makes the vehicle too much fun to lay into the gas or it adds too much weight.

Besides, you're modding the car to look/drive better right? if you worried about fuel eco, you wouldnt put the money into parts (thats more money you could spend on gas).

Do the mods because you want to do the mods and just accept that you will take a hit somewhere else.

The general answer is that More rubber on the road = more weight. More weight = less mileage. More rubber on the road also = more rolling resistance etc etc.

x2 i get around 10mpg but its worth it

Well, it gets about 29 mpg now....I wanna put a lift and have the 265s under it...I'm just wondering if it will still be above my now 16 mpg average with my '99 Bravada

15 percent is not bad... not bad at all... but it'd still be interesting to hear from someone who'd be able to come up with a computation...

Slightly taller but skinnier street tread tires MAY give you better mileage... The wider and more aggressive a tire is the more rolling resistance it will have.