What will I need to do to get the speed o to read correctly if I change to 15" tires from the 14" the 98 came with.

My 17 year old will be driving it so I wont him to know how fast he is going without the Blue Lights on.

Here's a link to a tire size calculator. You put in the original size tires and the size you want to upgrade to. It will tell you if it is compatible and if the size change will throw off the speedometer and by how much.

http://www.1010tires.com/TireSizeCalculator.asp