These oils are designed to be used in 2 stroke engines only. Racing oils may not be the best choice in the long run because they lack these additives. Your street oil has different additives that are formulated to extend oil life, and maximize fuel economy.

The racing oils are not always the best oil option for a vehicle engine that is not put under the extreme stress of racing. Racing oils are specifically designed and formulated to protect a racing engine under the stresses those engines are placed.

If your engine is older and is prone to having sludge build up in it.

If you live in an area that has really cold winter temperatures.

If you live in an area that has really high summer temperatures.

Synthetic oils do not accumulate moisture and impurities like this.

Short trips do not allow your oil to heat enough to burn the moisture and impurities that can accumulate in it. If you make short trips only in your vehicle.Synthetic oil can withstand higher temperatures and it flows better in cold temperatures than conventional oil. Synthetic oil resists viscosity breakdown so it lasts longer and does not need to be changed as often. Synthetic oils cost more than conventional oils. Manufacturers will always recommend that you use a particular weight of oil in your engine. When you first crank your engine the oil is thicker than it will be after your engine heats up after use. Viscosity or thickness of oil is affected by the heat. The weight of the oil indicates the thickness of the oil. 50 weight oil has a viscosity of 16.3 to 21.8 at the same temperature. 40 weight oil has a viscosity of 12.5 to 16.2 at the same temperature. For instance: 30 weight oil has a viscosity of 9.3 to 12.4 at a temperature of 212 0F. The weight of the oil is determined by the viscosity of the oil at specific temperatures and under specific conditions. Consider the following things about the oil you are buying and then you can read the labels on your oil choices and determine which one will provide you with the best service. Harley-Davidson makes two types of fork oil for shovelheads. The transmission uses 1.5 pints of HD transmission lubricant, although many people use 75w90 gear oil mixed 3-to-1 with Lucas oil. There are a lot of factors to consider when you are buying oil. Harley-Davidson recommends 4 quarts of SAE 50 or 60 engine oil in all 1966 through 1984 shovelheads.

Best fluid for harley transmission