Ok, I might getting a little bit anal here but I had both swingarms side by side while trying to stay open-minded and consider both of them for my nsr250. So, I couldn't resist comparing them... First of, the eternal debate about the weight of both swingarms. A complete Nsr250 mc28 Proarm measures about 9.800Kgr and an almost complete mc21 swingarm measures about 8.500Kgr. So, mc21 swingarm is 1.300Kgr lighter but to make things clear, these measurements are really rough. As you can see from the photo, the mc28 proarm is complete while my mc21 swingarm has quite a few parts missing. Also, I haven't measured mc21 wheel bearings and all 4 metal spacers as these are part of the wheel while on the proarm these are integral parts of the hub-axle assy (hence included on the above measurement). Overall, I believe that both swingarms weight really close with the mc21 maybe ending up being just a bit lighter. I really like the robust looks of the gullarm desig