I'm not sure about the additional belt, but the shop told me the "p" tire measures nearly 198 as opposed to the regular M1 at 190 (width). The Bridgestone OEM is the same, 198....my guess is the extra width may provide additional stability at warp speeds? I don't know and I'm tired of guessing so tomorrow I will call Metzler and find out. I'm on my 4th set of M1's and have never gone with the "p" because I'm a twisties rider and don't want the extra width. Oh, ya....my local shop sells the regular M1 at $136 and the "p" at $167 so I'm going to hit them up on the price diff, them folkers!! I have never had a problem with high speed stability and run alot in the 150+ range, just not prolonged periods up there. Will do some research and post the results in the am....