I've been curious about this myself, so checked out Wikipedia
Shell Rotella T - Wikipedia, the free encyclopedia
I'd probably buy the synthetic referenced below (Multigrade synthetic oil -- in SAE 5W-40). Maybe someone else will chime in.
Shell Rotella T is a line of heavy duty engine lubrication products produced by Shell Oil Company. The line includes engine oils, gear oils and coolants. The oil carries both the American Petroleum Institute (API) diesel "C" rating as well as the API gasoline engine "S" rating. Ratings differ based on the oil.
The Rotella product family is categorized by Shell into the following product families:
* Engine oils
* Tractor fluid (a universal transmission, gear, hydraulic, and wet brake fluid)
* Gear oil
In the engine oil family, there are four basic oil sub-families:
* Multigrade conventional oil -- in SAE 10W-30 and 15W-40 viscosity ranges
* Multigrade synthetic oil -- in SAE 5W-40
* Single grade conventional oil -- in SAE 20, 30, 40 and 50
* Synthetic blend oil
Both the multigrade conventional oil (10W-30 and 15W-40) and the synthetic SAE 5W-40 meet the newest API certification of CJ-4/SM.
Shell is marketing their new CJ-4/SM oil as "Triple Protection," meaning it provides enhanced qualities for engine wear, soot control and engine cleanliness. Shell's Rotella website indicates that on-road testing confirms the new Triple Protection technology produces better anti-wear characteristics than their existing CI-4+ rated Rotella oil. This is achieved despite a lower zinc and phosphorus additive level as called for by the API CJ-4 specification. (The 15W-40 Rotella T with Triple Protection oil has approximately 1200 ppm of zinc and 1100 ppm phosphorus at the time of manufacture.)
Though marketed as an engine oil for diesel trucks, Rotella oil has found popularity with motorcyclists as well. The properties of heavy duty engine oils tend to map to the same requirements of motorcycle oils, particularly those whose engine and transmission share the same oil. (This is called a "shared sump" design, which is unlike automobiles which maintain separate oil reservoirs - one for the engine and one for the transmission). The chemical additives found in heavy duty engine oils work well with motorcycles. In addition, the lack of "friction modifiers" in truck oils such as Rotella means they do not interfere with proper wet clutch operations.
Motorcycle specific oils tend to cost between $8 and $10 per quart. Shell Rotella T 15W-40 costs about $10 per gallon (or about $2.50/quart). The price economy of Shell Rotella T allows a motorcycle owner to change oil more frequently, thus matching the "extended change interval" value of motorcycle specific synthetics.