My Spitfire 50mm F4 101D wheels has gone down to 45mm, within like 2 months.
Swapped back to some very old wheels I have, that are 51-50mm. Huge difference!
Because of that little more leverage, the board doesnt feel like its not "keeping" up. Moves more with me
Anyway... To maintain a some what consistent wheel size, it seems like you have to A) Buy a wheel thats bigger then you like, or B) Swap wheels often...