07-08-17, 11:23 PM
The cruncher - literally - with any oil in a motorcycle engine is the shearing of the viscosity index improvers (VII) that takes place courtesy of the gearbox.
Synthetic oils have varying amounts of these depending on the viscosity of the base oil and the desired multigrade viscosity numbers. I picked up on the bit in the article which pointed out that 10w40 synthetics have more VII molecules than say, 15w40 or 20w50 oils. Since the VIIs don't lubricate, the more of these required to produce an extended multigrade viscosity range, the less the oil is able to do the friction reduction thing. Also, with more VIIs to break down in the gearbox, the upper viscosity falls off quicker than in oils with fewer VIIs. Make sense? Anyway, as I understand it those are the main reasons why extended life synthetics can't give the same in-service mileages in bikes as in cars.
Synthetic oils have varying amounts of these depending on the viscosity of the base oil and the desired multigrade viscosity numbers. I picked up on the bit in the article which pointed out that 10w40 synthetics have more VII molecules than say, 15w40 or 20w50 oils. Since the VIIs don't lubricate, the more of these required to produce an extended multigrade viscosity range, the less the oil is able to do the friction reduction thing. Also, with more VIIs to break down in the gearbox, the upper viscosity falls off quicker than in oils with fewer VIIs. Make sense? Anyway, as I understand it those are the main reasons why extended life synthetics can't give the same in-service mileages in bikes as in cars.