So I've had the MX31 up front and 51 in the back for about 3-4 hours of intermediate sandy loam MX track with a firm base in places at Mammoth Bar OHV in Cali. I'm 30+ front of pack Novice and corner somewhat aggressively. I've noticed that the outside row of knobs on both sides of the 31 are starting to separate (crack) at their base from the center of the tire towards the outside. None of the knobs has torn completely off but I'm fairly sure that it will happen soon. Traction is still awesome at this point and I'm very pleased with these tires otherwise. No problem with the 51's in the back. Perhaps I may need to go to the 51 up front. Treadwear is great and at 3-4 hours the drive edge on the 51 is just starting to round, corner edges are still fairly sharp. All edges an the 31 are only slightly worn as well (still fairly sharp). Anyone else having or had this problem? Is it normal? Any recommendations? Anyone riding Mammoth Bar soon? Thanks.