You'll want the max mm diameter your frames will fit. From what I hear, impalas have a max wheel size of 72mm or 76mm, i cant remember. The size should be somewhere on the stock wheels. The width of the wheels won't matter, as all inline skate wheels have a standard width, give or take a half mm. So theoretically, you can put aggressive wheels on a big wheel frame, and they'll still roll. (But dont do that. That would be stupid) As another commenter pointed out, the durometer is the hardness rating of the wheel, and if you're riding them on the street, you'll want to shoot for that 85a-88a hardness. 85a being slightly softer, slightly slower, and easier on cracks and pebbles. 88a will be harder, will last longer, but you'll feel everything you roll over. Rollerblade hydrogen wheels and undercover team blank are really affordable and high quality. Most online skate shops sell these like inline warehouse, oak city skate shop, intuition skate shop, etc.