FRICTION MODIFIERS
Motorcycle manufacturers and dealers also refer to "friction modifiers" as being another reason not to
use API SJ rated automotive oils. This MIGHT be the only somewhat valid point they make. However, it
is not justified in all cases. Let me explain the issue more fully.
API SJ specifications mandate increased fuel economy over previous API ratings. In order to meet this
qualification, motor oil manufacturers must add friction modifiers to their motor oil formulations. It is
believed that these friction modifiers MAY cause clutch slippage, although I have not seen any specific
scientific testing to validate this claim.
I have spoken with some motorcycle owners who switched from an automotive oil which may have
contained friction modifiers to a synthetic motorcycle specific motor oil and noticed a significant
increase in top end speeds (10 to 20 mph) immediately. This could be an indication that there was
clutch slippage occurring before the switch. However, it is also possible that this increase is due to
simply switching to a better formulation of oil which provides better performance. I have no way to say
one way or the other.
What is important to note is this: Just as 10W-40 and 20W-50 weight oils are exempt from the
zinc/phosphorus limits put in place by API SJ specifications, these same grade oils are exempt from the
fuel efficiency mandates that the SJ rating requires. Thus, it is not necessary for motor oil
manufacturers to add friction modifiers to their 40 and 50 weight motor oils.
Therefore, it cannot be assumed that just because an oil meets API SJ specs it must contain friction
modifiers. It doesn't have to. Some automotive 10W-40 and 20W-50 motor oils may contain no friction
modifiers whatsoever. This could only be determined by speaking with the manufacturer themselves.
Unfortunately, if that manufacturer also carries a motorcycle specific brand of oil, it is likely that they
would point you that direction and avoid answering the question. This is because their motorcycle
specific oil generally costs more and makes them a better profit.
So, in the real world, here's where you stand. Just because a 10W-40 or 20W-50 automotive oil meets
SJ specs, that doesn't mean that it contains friction modifiers, although it might. There is no scientific
evidence that indicates that friction modifiers cause clutch slippage, although some anecdotal evidence
suggests that it is possible.
Therefore, if you want to take the risk, you could use any automotive oil you wish (although preferably
synthetic) and take your chances in regards to clutch slippage. If slippage does occur, you'll likely need
repairs sooner than if no slippage occurred. If you don't want to take the risk, but don't mind making
some phone calls, you might be able to find an automotive oil which you can be certain does not
contain friction modifiers. This might take some digging though.
If, on the other hand, you don't want to waste your time on all that research but don't want to risk clutch
slippage, find a good motorcycle specific oil that won't cost you an arm and a leg and stick with it.
However, look for motorcycle specific oil that is still SJ rated. This assures you that you've got the latest
in motor oil technology but designed for wet-clutch compatibility.
There is a wide range in pricing for motorcycle specific oils. Petroleum based products can range in the
$2.00 to $5.00 or more depending on who you purchase from. Keep in mind they are still petroleum oil -
nothing all that special, but at least you'll be sure there are no friction modifiers. Synthetic based
motorcycle specific oils range from about $6.00 up to $12 per quart.
Believe it or not, the best of the pack is the least expensive of any of them and offers extended drain
intervals to boot.
