Need help on gear oil selection, will 80w-90 work in place of straight 80w?. I have had my Raider for two weeks and I am at 1500 miles now and I want to change all my fluids to synthetic. The only gear oil I have been able to find from AMSOIL is 80w-90. I asked the dealership service department and they only carry 80w-90. The guys at CycleGear all think that 80w-90 is fine for an 80w application. Any help is greatly appreciated.