Do Harleys Need Premium Gas? (Solved & Explained)

Many people don’t think about this, but the quality of the fuel you put in your Harley is vital to its overall performance.

Using the wrong fuel for your bike will affect its performance and may damage the engine. Some Harley owners believe “premium gasoline” is the “best stuff” for Harleys.

Do Harleys Need Premium Gas?

Harley-Davidson advises owners to use only premium fuel for their motorcycles. Large V-Twin engines have higher compression ratios and excessive compression in the engine can cause fuel to ignite prematurely and run rough on regular gas.

With its high octane content, premium gasoline is more resistant to compression-induced ignition and is better for Harleys.

Gasoline contains octane, which is a chemical that prevents the premature combustion of engine fuel.

What Type Of Fuel Should You Use On A Harley?

The different types of fuel include:

  1. Regular fuel [85-90 octane rating]
  2. Premium fuel [91-95 octane rating]

On paper, premium fuel sounds like it’s better than regular fuel. After all, “premium” is always better than “regular,” isn’t it? However, both fuel types are actually similar and offer the same benefits.

The only difference is that one has a higher amount of octane than the other does. Premium fuel has more octane than regular fuel, making it more resistant to pre-detonation caused by compression in the engine.

Regular fuel has less octane and a lower octane rating. The reduced octane content in regular fuel means it is more prone to premature ignition.

What Is Premature Ignition?

Premature ignition, also called pre-detonation, occurs when the air-fuel mixture in your engine starts to burn before it should. Ideally, the fuel should burn only when the spark plug produces a timed spark in the engine.

However, other elements in your engine can cause the fuel to ignite ahead of time. Heat and pressure caused by compression can force the fuel to “detonate” before the spark plug produces the spark.

If the fuel in your engine starts burning, early engine components, such as the pistons, will be affected severely.

Piston rings, ring lands, and big end bearings may also suffer substantial damage in the process.

Pre-detonation causes increased engine pressure, which in turn raises the resistance in the engine. High resistance causes the temperatures in your engine to rise.

Excess heat in the engine will affect the metal components in the engine and cause them to wear out faster. A symptom of premature ignition is a “pinging” or “knocking” sound.

We also have more about this in our article about whether SUVs need premium or regular gas.

The large V-Twin engines used in most Harley motorcycles are more prone to premature ignition than other motorcycle engines. V-Twin engines have higher compression rates and produce enormous heat and pressure.

These two elements can detonate the fuel in the engine before a timed spark occurs. What happens afterward is what we’ve described as premature ignition.

Premium fuel prevents detonation in high-compression engines, which makes it the best fuel to use on your Harley.

Compression occurs when your engine’s RPM increases after you start it and start revving it.

What Are The Benefits of Premium Fuel?

Many fuel makers and gas stations advertise premium fuel as being “better” than other types.

Apart from preventing early ignition, premium fuel does not offer any more benefits than regular unleaded fuel. Nonetheless, if your motorcycle’s engine is designed to run premium fuel, using regular fuel will only decrease its performance or even damage the engine.

Some people claim that premium fuel will increase horsepower or lead to increased fuel savings, but experts have debunked these claims. Yes, premium fuel may allow for some gains in performance or fuel economy. These gains are, however, too negligible to justify deciding to spend more on premium fuel.

Some companies also say that premium fuel contains extra additives that prevent dirt from building up in the engine. However, this is not true as all fuel types [both regular and premium] have additives that remove dirt from fuel.

The only reason why your Harley bike needs premium fuel is that its design makes it susceptible to pre-ignition. Pre-ignition will cause your Harley engine to knock, leading to further damage. High-octane premium fuel prevents pre-ignition from happening, and that’s the only benefit it has for your bike.

Common Misconceptions About Premium Fuel?

Fuel type is one of the most commonly talked about issues in the motorcycling world.

One thing you’ll notice is the amount of misinformation and disinformation on the topic of fuels.

Here are some of the popular misconceptions about premium fuel:

1. Premium Fuel Improves Performance

This myth is quite popular among motorcycle owners, including those who own Harleys.

According to the proponents of this idea, a bike’s performance will increase if the owner uses high-octane fuel. However, much of the evidence of the facts to support this theory is mostly anecdotal and unverified.

Premium fuel will only bump up performance numbers if the manufacturer made the engine run on premium. High-performance engines like those in sportbikes run better on premium fuel and may get some performance gains from using higher-octane fuel.

The minimal increase in performance may reduce a racer’s lap time by, say, one-tenth of a second in sports bike racing, where every second counts, premium gasoline may help.

With your Harley [which is not a sports bike], premium fuel will do nothing to increase the torque or horsepower available to you.

It will only allow the motorcycle to achieve its intended level of performance. Using regular fuel when your Harley calls for premium fuel will affect its performance and fuel efficiency.

2. Premium Fuel Cleans the Engine

Another popular misconception about premium gasoline, this one’s not entirely untrue.

Premium fuel contains detergent additives that remove carbon deposits from the engine. Regular gas has detergent additives too, but the concentration is lesser than that found in premium gas.

Filling up with premium fuel may give some assurance that your engine won’t suffer from a buildup of carbon deposits. The problem is, there are cheaper ways to keep your engine clean.

Products like fuel system cleaners can help rid your engine of carbon buildups and the likes. Fuel system cleaners are over-the-counter additives that you can buy at any spare parts shop.

They improve overall performance [deposit buildups affect performance] and are viable alternatives to purchasing premium fuel every time.

Conducting regular maintenance is another cheap and more effective way to ensure your engine is always clean. Even if you use premium fuel, carbon may still build up on engine components.

The best way to prevent carbon deposits from accumulating is to clean the engine components at periodic intervals, as specified in the service manual.

3. Premium Fuel Increases Mileage

The premise that premium gas lasts longer is perhaps the biggest draw for those who use it.

Like the increased performance assertion, this one, too, doesn’t hold. There’s nothing to suggest premium fuel lasts longer than regular fuel.

Like we said before, the only difference between ordinary and premium fuel is the octane content, and octane does not affect fuel economy. The only exception is when you use regular fuel for an engine that demands premium fuel.

In such cases, the fuel economy will drop significantly.

Much of the misconceptions surrounding premium fuel arises from the psychological expectation of owners. They believe they are getting more from premium since they are paying extra for it.

Research reveals that premium fuel doesn’t provide any unique benefits, except protecting your engine from knocking.

Should I Use Ethanol Free Gas On My Harley?

The ethanol gas vs. non-ethanol gas debate has been raging for years among motorcycle owners.

Some believe using ethanol gas will harm your motorcycle, while others see nothing wrong with using it on bikes. Should you use ethanol gas or ethanol-free gas on your Harley? Let’s answer these questions.

Ethanol is an alcohol-based fuel made mostly from corn crops in the United States. Oil producers add ethanol to gasoline to boost its octane rating [ethanol has high octane content].

Ethanol is a biofuel that’s cheaper to produce and is cleaner than standard gasoline. It also reduces emissions, which is one reason the Environmental Protection Agency supports its use.

Harley-Davidson recommends that owners use pure gasoline. According to experts, ethanol gasoline reduces the performance and fuel economy of motorcycles. It can also make owners spend more money on maintaining their bikes.

The alcohol in ethanol gas, also called E10, can absorb water, which will corrode the components in the fuel system and other parts of the engine.

Despite this, the U.S Government’s support of ethanol fuel means more gas stations now sell only E10. Only a handful of outlets in the U.S still sell pure ethanol-free gas anymore.

So, you’ll probably not have a choice whether to choose between ethanol and non-ethanol fuel. However, they have the facts about each fuel to make an informed decision.

Benefits and Drawbacks of E10

As we said earlier, ethanol contains alcohol, and this is where most of the problem with it lies.

E10 doesn’t have a long shelf life and breaks down quickly when stored for long in the engine.

When it breaks down, the alcohol rises to the top and attracts moisture [E10 is hygroscopic]. Once this happens, components exposed to the gas will start to corrode.

In particular, gaskets, fuel lines, seals, etc., are most likely to suffer damage. Besides, ethanol produces less energy than gasoline and gives lesser mpg than the latter [around three percent less].

However, ethanol gas isn’t as bad as some would have you believe. Pure gasoline may give you better mileage and performance, but the gains aren’t considerable enough to defend the high cost.

Moreover, Harley-Davidson and other motorcycle companies now use ethanol-resistant fuel system components on their bikes. Therefore, using ethanol gas will not harm your Harley’s parts.

The only way your Harley may have problems with ethanol gas is if it is an older model. Harley-Davidson didn’t design its earlier models to run on ethanol-based gasoline as it does on new models.

In such instances, E10 may cause fuel-system components to wear out. However, you can remedy this by using stabilizer additives that prevent E10 from breaking down.

So, there you have it. Use ethanol gas on your Harley if that is what’s available. Buying pure gasoline is good but unnecessary.

If your Harley is an old model, you will do well not to store ethanol gasoline in the engine for long. E10 doesn’t have a long shelf life and breaks down quickly. If this happens, it will become corrosive and cause engine parts to decay.

If you have to store your Harley for long, say, during winter, you should empty the tank. Winterize it and fill it with fresh fuel next time you want to ride the bike.

How Far Does A Harley Go On A Tank Of Gas?

There’s no standard answer to the question of how many miles a full tank of gas will take you on your Harley.

This is because many factors influence the fuel economy of your bike, but if we use the average mpg of Harleys to calculate, it is possible to determine how far you’ll go on a filled-up tank of gasoline.

From users’ reports, the gas mileage of most Harley motorcycles hovers between 35-40 MPG. Using these figures, you can easily calculate how many miles your bike will go with its tank full.

The formula goes like this:

  • Average MPG x Total Gallons

Therefore, if your Harley bike uses a 6-gallon tank, you’ll multiply the average MPG by six, which is the number of gallons your gas tank can hold. You should get 210/240 miles as your result.

This means you can go between 210 to 240 miles on a full tank of gas. If your Harley uses a smaller container, you can calculate using the same formula to get your answer.

It would be best if you exercise caution when using the formula, though. Many things affect gas mileage, and it may vary in different situations.

Factors that influence your bike’s MPG include:

  1. Engine size
  2. Fuel type and quality
  3. Tank capacity
  4. Driving style
  5. Weather
  6. Engine tune-ups
  7. Weight [this includes its dry weight and loaded weight]

One, or a combination, of these factors, can increase or decrease your Harley’s gas mileage. For instance, you’ll get better MPG when you’re out cruising on the freeway than when you’re riding in stop-and-go traffic.

Similarly, you’ll get less gas mileage when you’re tearing down canyon roads, compared to if you were riding at low speeds. How long the gas you buy lasts is entirely up to you.

You should always check the low fuel light and re-fuel immediately; it blinks. And it’s not advisable to wait until you exhaust the gas before refilling the tank.

Always check the “Miles Left To Empty” indicator and fill it up when the gauge number is low.

The area you’re riding in may not have many gas stations. You wouldn’t want to run out of fuel in a remote area, would you?

Do All Harleys Use The Same Type Of Fuel?

Although they share arguably the same V-Twin engine design, Harleys do not use the same fuel.

Yes, we said earlier that Harley engines need the fuel of at least 91 Octane to run optimally.

91 Octane means premium fuel, and it is what Harley advises users to use on the bike. However, Harley may need a different fuel sometimes.

In particular, modifying your engine means it will require fuel with a higher octane rating than the 91 Harley-Davidson recommends. Mods raise your engine’s compression ratio, which will increase its risk of knocking. You’ll need high-octane fuel to prevent the engine from knocking due to compression.

Another case where your Harley may need a different fuel is when it’s a classic model. Much of the premium fuel available nowadays contain 10 percent ethanol.

Although there are ways to use E10 gasoline safely on your classic Harley, it’s better to use pure petrol. It’ll be a little hard, but with persistence and research, you’ll find stations offering pure gasoline for sale.

Apart from the cases mentioned above, all Harleys use the same fuel, which is premium fuel.

When Did Harleys Stop Using Carburetors?

Harley stopped using carburetors fully in 2008. For years, Harley-Davidson used carburetors on its engines.

Every Harley engine, from the older Knucklehead motors to the modern-day Evolution engine, all had carburetors.

That was until the EPA started demanding that motorcycle manufacturers use Electronic Fuel Injection [EFI] systems instead of carburetors in their engines. Due to this, Harley was forced to phase out carburetors on its models.

The first fuel-injected Harley model was the 30th Anniversary Edition Electra Glide, released in 1995. But it was a piece of optional equipment, and most of the bikes in Harley’s lineup still used a carburetor.

Fuel injection became standard on all Harley motorcycles in 2008. By this time, no model in the Harley-Davidson was carburetted.

The EPA mandated motorcycle manufacturers to use EFI on their bikes because fuel injection had more control over the air-fuel mixture than carburetion. It can decrease the motorcycle’s total emissions.

While the EPA’s goal is noble, many Harley purists say they prefer the older carburetted models to the newer fuel-injected ones. EFI robs Harleys of the classic “potato-potato” sound because of its high idle. Moreover, you can repair faulty carburetors on the roadside, but the oxygen sensors of the EFI are more complicated.

Nevertheless, Electronic Fuel Injection is here to stay, so we guess Harley purists will have to get used to it.

Final Thoughts

If your Harley-Davidson service manual asks you to use premium fuel, use only premium fuel.

Buying cheaper regular-grade fuel may save you some money now but will cost you in the long run in repair costs.

Also, using fuel with a higher octane content than your engine requires will make you spend more. You’d be better off saving the money than spending more on fuel, hoping your Harley will run better. It will not, and you may feel cheated.

Your Harley will run ethanol gas without a problem unless it’s an older model. In that case, the best thing to do is to use only pure non-ethanol fuel.

Some online maps and apps contain locations of gas stations that sell pure gasoline. Nevertheless, if your Harley is a newer model, you need not go the extra mile to buy pure gas. Whatever gains you get won’t be enough to offset the increased costs.

Ensure you are buying quality fuel-some fuels contain additives that can harm your bike’s components. We advise you to buy gasoline only from reputable outlets, not no-name indie outlets.

Ride Safe!

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