They make a speedo big enough to fit a 300lbs man but does it make it right no.Theres a wrong and right way to do everything just slapping bigger wheels on a car with out changing the rear end speedo gear and bigger brakes is unsafe its harder to stop and speedometer will be off and get worse gas mileage.Adding 40 feet more braking distance to a car that didn't have the best brakes to start with is crazy 60-0 matters no matter what your driving.Thank god thats a new mustang if it been a old one id be pissed.