Oil Groups Explained

Group I

Group I oils are the simplest, and usually will not be found in motorcycles.


Group II

Group II oils are refined by processes known as hydro cracking and isomerization. They have fewer impurities than Group I oils. These oils are the typical “dino” oils that are used in our bikes.


Group III

Group III oils are synthetic oils so to speak. But they are not the type of synthetics that are built up from scratch but modified from dino base stock. They are actually crude oils from the ground that have been refined by a process known as hydroisomerization.
Basically it means a combination of processes that remove more unwanted impurities from the crude oil.

Notice above that group III oils are called "synthetic".
It took a lawsuit, and a firm of lawyers, and a bunch of law suits to decide that. The hydroisomerization process actually changes certain molecules around enough to create new molecules. These molecules are pretty uniform in size and shape, just like in “real” synthetic oil. These new molecules are more resistant to oxidation, so they’ll hold up better and last longer than before.


Group IV

Group IV oils are synthetic oils and are man made. These are one of the groups that most people think of when they talk about synthetic oil. The largest parts of these synthetic base stocks are known as “PAO”, for polyalphaolefin. This stuff starts with ethylene gas, a molecule with 2 carbon atoms, and builds up to a molecule with 10 carbon atoms. Then three of these 10 carbon molecules are combined to form the actual PAO. Each molecule is exactly like every other molecule. The molecules are long chains, are more stable, flow more readily, better resist heat induced breakdown, don’t thicken as much from high temperatures, better resist oxidation, and don’t “boil” off, than their dino oil base stock cousins.


Group V

Group V oils are ester-based synthetics. They made from diester, polyolestors, polyesters, and complex esters. They are extremely stable under high pressure, and resist heat, often to near 500º F. They are polar molecules, containing an electrical charge that causes them to bond to metal surfaces. These oils are very expensive, and seldom encountered in our motorcycle world because of the price.