So I just replaced my 21" Arachnids with my 19" cyclones(with Pirelli P7's) for an upcoming trip to Lake Tahoe from LA. I figured I'd take a dB noise measurement over a 5 mile road at exactly 50mph in the same lane and see what the average Decibel reading over the drive. (I used dB meter pro on the ios app store) My 21" wheels came in at an average of 53dB ad the 19" at 52dB. It's a measurable difference! I'm not sure exactly how scientific my measurements are, but the numbers match my experience. The 19"'s are definitely less harsh and quieter.