How do you put 20 inch rims on your cadillac?

When ordering rims for your car its ok to to increase rim size but if overall tire height is bigger than factory size then your going to run into problems. The tire size on my 02 Seville sts is 235 x 55 x 17 I believe, make sure that the rims you order can be fitted with the same tire height. The height on my tires would be 235's, 55 is the width and 17 represents 17in rims. Make sure that you can get the same size height and most of the time width, I believe with my car I can run up to 19in rims and still keep 235 height and 55 width, anything wider can result in your tires rubbing in the wheel wells, you don't want that especially with the cost of low-pro tires. Another problem you may be experiencing depending on how may miles that are on your car is the air ride suspension. The air ride went out on my 96 deville and I could barely get the rear tires off with factory 16in rims. I ordered an air ride conversion kit from arnottindustries.com, now shes sitting at a nice factory height. hope this helps, good luck.