mileage suffers without question once you get big heavy tires with more aggressive tread. look in the readers rides section, i just posted a recent pic of mine up, it's a 2003 2dr.... i used to see 500km on a tank of fuel, now it's more like 400km. power is down noticeably but it really isn't that bad. still quicker than a stock 1.6 older model tracker.. but.. that don't mean much.