Advice: Understanding oil

You understand very little of the technical jargon and every brand available claims it's the superior choice for your bike. Is it all the same?

No. What's more, using the wrong oil can cut the service life of your bike's engine in half. Bike makers don't always help. It would solve many problems if they all said something like, "We've tested all the oils available and the best one for this model bike is Kendall 20W-50".

What bike manufacturers will tell you, though, is what grade of oil to use and what classification. Honda, for example, recommends 20W/50SE for its early 1960s scooter range.

The 20W/50 numbers basically tell you the viscosity of the oil, ie how thick or "heavy" the oil is. Notice how light the olive oil is you use for salad dressing compared with the oil you put in your bike? Olive oil might be something like 2 or 3W.

The "/50" part of the description tells you that when the oil is heated to the high end of the operating range, it will have the lubricating qualities of a 50W oil. Oils for bikes tend to range from 10W to about 70W.

The "SE" on the end of the numbers is a classification by the American Petroleum Institute (API) and means that, if tested, the oil would meet a certain standard. These classifications change fairly regularly and have gone from the original SA through SB, SC, SD, SE, SF, SH, SJ, SL, SM and so on to the current classification level of SN. The closer the last letter is to the end of the alphabet, the more sophisticated the oil is likely to be.

Related: Changing your oil

SN-classified oil, for example, will have better wear resistance and increased oxidation stability over SM-classified oils.

If you own an older bike, the manufacturer might have recommended something like a 10W/40SF oil. This doesn't mean you should deny the engine better oil as it's developed but does give you a guide to the minimum requirements. SF-classified oil is still widely available, even though SG, SH and SJ-classified oils have since come on the market.

When it's extracted from the ground, oil is dark and heavy. It then gets "distilled", a heat-driven process which separates the oil into components. The light end of the separation can be used for petrol while the heavy end becomes the base stock for the oil you eventually pour into your bike.

At this point oil makers put a pack of additives into the oil to improve its suitability as a lubricant. The type and quantity of these additives is what makes oils different and provides at least one explanation as to why prices for oils can vary so much. At the top end of the scale manufacturers can produce a lubricant which isn't mineral-based. These oils we know as synthetics.

Additives can include detergents to keep the inside of the engine clean, dispersants to stop the crud produced in the combustion process from sticking together and forming sludge, viscosity index improvers, anti-oxidants, pressure and anti-wear agents, corrosion inhibitors and plenty more. The "miracle" oil additives you see advertised everywhere and on supermarket shelves are more of the same - the stuff's already in the oil you're using but probably in better proportion.

Air-cooled engines in particular need an oil which keeps its body at high operating temperatures, which means a reasonably heavy base weight. 20W is suitable but 25W is also okay as long as you're prepared to warm the engine properly before you start asking it to perform, especially in colder weather. Your engine will appreciate a 50 or 60 number at the other end of the scale.

Liquid-cooled engines have closer tolerances so 15W isn't a bad starting point – thin oil flows through tighter spaces. Because liquid-cooled engines operate at a more stable temperature, big numbers on the end aren't as critical - 15W/40 or 15W/50 would be normal.

Because of the peculiar nature of motorcycle engines and the conditions in which they operate, the type of oil a manufacturer specifies for a particular model will often be something of a compromise. Your job is to follow the manufacturer's recommendations, and you'll be close to the right decision. Match the oil's specification and how often you change your bike's oil to your riding conditions.

Unless the manufacturer of your bike specifically tells you to use a full synthetic oil, you can safely leave it alone. It has been developed for car applications and some racing applications but isn't necessarily better for bikes than conventional oils.

I know I just criticised bike manufacturers for not specifying brand names, but I'm not going to name names either, the main reason being that what suits my bikes and riding conditions may not suit yours. I own six motorcycles and use four different brands and specifications of lubricating oils. On one of these bikes I change the specification of the oil for winter and summer riding.

One thing's for sure, though. The oil you use must be motorcycle specific – it must be made for motorcycle use. General automotive oils won't do. Trust companies which have an established history of making oil for bikes - they understand the special nature of motorcycle lubrication and its usually reflected in the quality of their products.