The adding of zddp helps with shifting in my bikes. Since the EPA cut allowed zinc and phos, shifting, for me, went down the toilet. Many trannies became notchy. The oils changed and my bikes no longer shifted well. With zddp added I got shifting back to the levels they were before our wonderful epa took issue 3 or 4 years ago with all our motor oils. Zddplus site has good charts/info to determined how much to add to get back the zinc levels of yesteryear. If you don't mind spending 12 to 22 dollars a quart/liter you can still get good levels of zinc and phos in M/Oil. Or you can use a good quality Motorcycle Oil and add zddp, for half the cost of the fancy m/o oils. Some guys say they have no issue with the shifting in their bikes. I do, and this has greatly helped me and others that want the best shifting their bikes can offer. I have been using zddplus and zddpmax for years and for tens of thousands of miles in my bikes. Works just great for me and mine......Texas Tea 10w40 syn M/C oil with 2oz of zddplus in each bike runs about 7.50 a quart, a lot less than most m/c syn oils. Cost effective and sweet shifting....