It's recommended I use a ester oil in my drz400e. I do all trail and dirt riding what would you guys recommend to use! What are the benefits of using an ester oil. The bike is knocking in it's bottom end and I think it's due to using the wrong oil. I used spectra 4 10w40 which is the recommended weight of oil but everybody I talk to on the drz forum are using a way hevier oil like a 10/50 Full Synthetic ester or 20/50 Full Synthetic ester. I am looking to get rid of the knock or tone it down but I am not so sure on using that heavy of oil. Any recommendations! Thanks for the advice.