I use Lucas HP gear oil , non synthetic 90 weight in my 03 vtx 1800 c and it works great.The bike use to pop out of fourth gear sometomes but not any more since using this product . I also for the first time mixed partial 4 cycle synthetic oil with standard 4 cycle oil 50/50 , the bike seems to run cooler , 2k miles since last oil change, alls well so far . I hope this info helps .