Motorcycle Oil Buyer's Guide: Which is best for your bike?

From the April 2025 AMSOIL Magazine - Dealer Edition.

Modern engines are highly refined and benefit from specially designed protection, but a continuously increasing number of options means shopping for motorcycle oil can get confusing. Owners of more than one motorcycle might be curious if they can use the same lubricants in their V-twin, metric motorcycle and dirt bike. However, different types of motorcycles present unique oil challenges that a single formulation can't easily meet.

Why Choose Motorcycle-Specific Oil

Motorcycle oil serves multiple purposes by maintaining engine and transmission performance while protecting against wear. Increased heat accelerates oil oxidation, leading to deposit formation that robs motorcycle engines of efficiency and power. The shearing forces of the transmission further reduce the oil's lubricating ability, increasing the risk of component wear. Whether you ride a Harley-Davidson® touring bike, Kawasaki® sport bike or Honda® dirt bike, AMSOIL motorcycle oil is designed to prevent oil breakdown under extreme heat and pressure.

V-Twin Oil

The classic air-cooled V-twin engine found in most Harley-Davidson motorcycles gets extremely hot. For example, we saw cylinder temperatures reach 420°F (216°C) in our in-house dyno testing. Heat that intense wreaks havoc on cheap motor oil, causing it to lose viscosity and become thinner, effectively turning a 20W-50 into a 10W-40, or worse. Running an engine on a lighter viscosity than it is designed for increases the risk of internal engine wear.

Extreme heat also hastens chemical breakdown, as the rate of oxidation doubles for every 18°F (10°C) increase in oil temperature. That means for every 18°F increase in temperature, oil life is cut in half. It's imperative that the oil in an air-cooled V-twin can withstand such intense heat. AMSOIL Synthetic V-Twin Motorcycle Oil is formulated with synthetic base oils that maintain viscosity at these extreme temperatures.

Bikes that use the same oil for both the engine and transmission are especially prone to viscosity loss, as the force of shifting gears can also destroy the oil's molecular structure. AMSOIL Synthetic V-Twin Motorcycle Oil is shear stable and does not thin from mechanical activity, providing reliable protection against wear under the toughest riding conditions.

AMSOIL Synthetic V-Twin Motorcycle Oil delivers excellent performance in the engine, transmission and primary chaincase, offering the convenience of a single oil for all three reservoirs. It is available in multiple viscosities as part of our complete V-twin product line, including complete oil-change kits with filter. For bikers who prefer specifically formulated oils, AMSOIL Synthetic V-Twin Transmission Fluid and Synthetic V-Twin Primary Fluid are engineered to the same exacting standards.

Metric Motorcycle Oil

Metric motorcycles are known for delivering high levels of performance and responsiveness. Metric single, twin, triple and four-cylinder engines commonly found in standard (naked), cruiser, adventure (ADV), touring and sport bikes can easily surpass 10,000 rpm.

The mechanical action of the crankshaft spinning that fast can whip air into the oil, causing it to foam. If the oil isn't formulated with fast air-release properties, foam bubbles will travel throughout the engine. When they collapse between meshing gears or bearing surfaces, nothing is left behind except air, which provides zero protection against wear.

Most metric motorcycles require wet-clutch-compatible lubricants to deliver fast, smooth, efficient and consistent shifting performance. Additionally, touring and ADV bikes are designed to provide comfort and luxury for long, cross-country adventures, which benefit from extended drain intervals.

AMSOIL Synthetic Metric Motorcycle Oil is specifically formulated with anti-foam additives that weaken the surface tension of air bubbles, resulting in excellent anti-wear protection. The advanced additive package also delivers superior wet-clutch compatibility, enabling smooth shifts for a more comfortable ride. The advanced synthetic formula maximizes engine responsiveness to help riders confidently push their bikes to redline, for maximum speed, acceleration and cornering ability. It also extends drain intervals up to twice the bike manufacturer's recommendation, allowing riders to confidently wander far from home.

AMSOIL Synthetic Metric Motorcycle Oil enhances motorcycle performance and reliability and delivers superior protection against engine wear. It is available in multiple viscosities as part of our complete metric motorcycle product line, including oil filters and AMSOIL Powersports Antifreeze & Coolant.

Dirt Bike Oil

Unsurprisingly, dual-sports and dirt bikes frequently operate in unfavorable off-road conditions, with ample low-speed stress punctuated by periods of high revving. Off-road racing adds frequent repetition between wide-open throttle on straights and rapid acceleration through corners. Throttling through jumps causes the rear tire to spin freely in the air, which creates a heavy load on the engine when it contacts the ground. Trail riding requires constant clutch and throttle manipulation to maneuver over and around obstacles.

Dirt bike engines are also inherently lightweight designs built for performance. However, removing mass and increasing power adds additional engine stress. Additionally, dirt bike pistons tend to have shorter piston skirts to reduce friction. Shorter pistons want to rock inside the cylinder, which concentrates tremendous force on the tiny contact area between the piston skirt and cylinder wall. Only a microscopic oil film provides protection in this area, so superior oil film strength is needed to help the engine survive.

The combination of high rpm and lighter materials can quickly lead to dirt bike engine failure if the oil fails.

Making matters worse, many dirt bikes hold only about one quart of oil, which is tasked to protect all the engine and transmission components under these severe conditions. Therefore, most dirt bike riders change motor oil frequently. Under heavy use, dirt bike engines may even need to be rebuilt as often as every 15 hours.

AMSOIL Synthetic Dirt Bike Oil is engineered to enhance engine performance and reliability in extreme conditions, while delivering superior protection against engine wear. AMSOIL DOMINATOR® Synthetic 2-Stroke Racing Oil handles two-stroke dirt bike needs, and AMSOIL Synthetic Dirt Bike Oil is available in multiple viscosities for four-strokes as part of our complete dirt bike product line, including oil filters and AMSOIL Synthetic Dirt Bike Transmission Fluid.

Choose AMSOIL

AMSOIL synthetic motorcycle oil meets or exceeds exacting motorcycle manufacturer and industry standards and is WARRANTY SECURE™ to maintain factory warranties. It is as precisely engineered as the bikes in which it is used, for peace-of-mind protection no matter what you ride or how you ride.

• Maximum Performance – Modern bikes produce extreme horsepower and torque. AMSOIL synthetic motorcycle oil preserves the performance and power you paid for.
• Consistent Shifting – Ever blamed missed shifts on your bike? AMSOIL synthetic motorcycle oil promotes smooth, consistent shifting you may have never experienced.
• Ride More – Nobody enjoys breakdowns. AMSOIL synthetic motorcycle oil protects engine components so you can ride longer and farther, worry free.

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For all your V-twin and Harley needs, check out our AMSOIL for Harley Davidson article to help you find the right product for your specific motorcycle.

Riding a 2-stroke bike? Check out our AMSOIL Dominator vs Interceptor vs Saber article to help you choose the right 2-stroke oil for your application.