I switched the stock 2.1" Big Apples on my Big Dummy for 2.35 " can feel the diffference, not huge, but there. I do find them slower, but for an indirect reason. i often don't realize how low the pressure has gotten, until i stick 60# or more on the back. Hmmm.... Feels a bit wiggly. Check. YUP! 20 psi or less! Flats? Not so as you'd notice.