The only acceptable way to do this is with factory parts if 15" wheels were a factory option. Different wheel sizes are usually a part of a complete package that includes changes to the brakes and suspension system.
You didn't say why you wanted to do this. The concern has to do with the handling, braking, and steering response changes that will occur. What you have to look at is if anything changes "scrub radius". If you draw an imaginary line between the two steering pivots, (typically the lower ball joint and upper strut mount, or the lower and upper ball joints, when used), that line is designed to intersect the road surface in a very specific point on the tire tread. Changing the width of the tire, the outer circumference, of the offset from the hub, will change scrub radius. Lawyers and insurance investigators know to look for these kinds of changes when trying to shift the blame for a crash from their client to you. They will convince a jury that you were partly at fault for the crash because you were less able to avoid it, and they will be right.
If the tires are larger in outer diameter, that will raise the car's center of gravity and that will upset the carefully-designed-in front-to-rear brake balance. That will increase stopping distance. The higher center of gravity will increase the tendency for the car to lean when cornering.
Sunday, February 22nd, 2015 AT 3:34 PM