220 HP in the rear wheels is way too low. You should be getting between 270-280. Either there is a flaw in the measurements, (instrument error, or measurement error) or your engine is not performing top notch.

Also the heavier tire will drop the measured horsepower at the wheels by about 3-4HP but you will not notice this difference when driving.

A bit of advice: Make sure that the K&N filter you are using is well oiled, because if it is not, it will not provide good filtering and will result in serious wear in your engine. Regardless of what you hear, these filters do not provide good filtering if they are not well oiled.