Fully or Semi Synthetic Motorcycle Oil: Which is the Best Option?

It is another of the commonly asked questions you see asked on the track day scene – almost as much as how often to change your motorcycle oil – but with nothing other than the usual marketing spiel from the manufacturers it’s hard to know which you should plum for, so the question is often justified.

Another problem we have is that there is very little in the way of freely available, detailed test results out there to show the effectiveness of one oil against another. This means that our decisions are often based on word of mouth and on what others are buying.

Here I have put together an article which looks at some of the differences between the oils which I hope will not only help you better understand the two types but also help you make the right decision with your own wonga in mind.

But, to better understand the differences between fully synthetic and semi synthetic first we need to look at how fully synthetic differs from traditional mineral oil.

Fully Synthetic vs Mineral Oil

The names of the two oils tell most of the tale, one being a more natural form of oil while the other is a man-made oil built for purpose. Much like diesel, mineral oil is obtained through the refining process of crude oil (a process that goes on to create petroleum) and through further refinement is made into motor oil.

Truly synthetic motor oils on the other hand are made from the processing and refinement of man-made chemicals, and because they are built for a purpose they can be designed to better deal with things like high temperatures and oil breakdown.

Put simply, fully synthetic oils will perform better and last longer than petroleum-based mineral oils because they have been designed to do so.

What are Semi Synthetics then?

The cost of buying fully synthetic oil over conventional mineral oil can be quite large, sometimes up to twice as much. For this reason a middle ground was found with semi synthetics (also known as part synthetics or synthetic blends). Semi synthetics are made from blending traditional mineral oil with synthetic oil, designed to come with some of the benefits of a fully synthetic while not being quite as expensive. However, having a large amount of mineral base stocks (actual synthetic base stocks in semis are said to be between 10-30%) they will still have some of the drawbacks of a standard mineral oil.

As said, they are a middle ground between mineral and fully synthetic oils in terms of performance, price, quality and durability.

Read my How often to Change Oil guide for a more detailed look at the benefits synthetic oils have over mineral oils.

Fully Synthetic vs Semi Synthetic Oil

Reading the above, it’s clear that purely from a performance and durability standpoint a fully synthetic is going to do a better job than a semi, but before you go running out cash in hand here’s a few points to consider that might help you decide which oil to go with.

Cost – If you’re happy with paying the extra cost that comes with a fully synthetic, then in doing so you will be giving your engine the best protection with the added benefit of being able to extend the time between changes.

Will you see the benefits? – If you drop your oil quite frequently (most track dayers drop their oil between 2-6 days) then there’s an argument that you won’t really see the benefits of the extended oil drains that come with a fully synthetic, which means the extra money you’re spending could be in vain.

Is your engine tuned? – If an engine is highly tuned then it is often recommended that you opt for a fully synthetic as engine internals will be more highly stressed. If it’s completely stock however then many agree that a fully synthetic isn’t entirely necessary, because many bike manufacturers would have taken into account the fact that people will use different types of oil when they designed their engines.

Clutch Slip – There has been a long standing notion that there is a risk of fully synthetic causing your clutch to slip with claims that they are ‘too slippery’. In actual fact synthetic oils are no more slippery than mineral oils, however due to the differences in clutch designs between motorcycles, friction modifiers are added to some oils to cater for this which could cause slipping.

However, as long as you buy the correct grade of motorcycle oil for your bike that conforms to all the correct JASO specifications then you should never experience clutch slip with a fully synthetic.

Synthetics Caveat

One thing that is worth noting is that just because the label on the bottle says fully synthetic, doesn’t mean it necessarily is. Different semi and fully synthetics will have differing amounts of synthetic base stocks, some so low that you wonder how it could be classed as synthetic at all.

This topic though is a massive discussion, so all I will say is make sure you go with an oil from a well-known, high quality oil manufacturer and you shouldn’t go wrong.

As I said at the start of the article it’s very difficult to find hard facts and test data for each type of oil, so really it’s down to personal preference and which you feel most happy using. If you don’t mind spending the extra then you can go fully synthetic, just make sure you have the right one.

However modern semi synthetics are more than capable of keeping your engines safe on track days and if you’re dropping your oil more frequently because of those track days then you may not even see the benefit of going for a top range fully synthetic.

So in essence there’s no right or wrong answer as to which is the best for track days (without full blown test data from manufacturers anyway) and either would be a fine choice from what we know, but I hope that the above has made the decision a little clearer and easier for you personally.