Fueling Up: A Dirt Bikers Guide to Gasoline

When it comes to fueling your dirt bike, the right choice can significantly impact performance, longevity, and overall enjoyment. Let’s dive into the different types of fuel available and their implications.

Regular Unleaded Gasoline

Octane Rating: Typically 87
Suitability: Most dirt bikes will run on regular unleaded gas.
Pros: Widely available, cost-effective.
Cons: May not optimise performance for high-compression engines.

Mid-Grade Gasoline

Octane Rating: Usually 89–90
Use Case: Suitable for some dirt bikes with moderate performance requirements.
Pros: Slightly better combustion stability than regular gas.
Cons: Limited benefits unless your bike specifically requires it.

Premium Gasoline

Octane Rating: Typically 91–94
Recommended for: Performance-oriented dirt bikes, especially those with high-compression engines.
Pros: Protects against premature ignition (knocking or pinging).
Cons: Higher cost, unnecessary for most stock bikes.

What fuel is best for dirt bikes?

The best fuel for your specific dirt bike is what the manual recommends. For example, a Honda CRF250F is made to work well with regular 87 octane pump gas. In general, most bikes will run just fine on 87, unless you have a more race-bred motorcycle or performance modifications done to your engine.

What about Race Gas?

It’s expensive, smells pretty good, but you almost certainly don’t need it. This high octane fuel is only going to benefit you if high performance modifications have been done to your engine and has been properly set-up to run race gas. Otherwise, save your money.

What happens if you use regular 87 in a dirt bike that requires 91 or higher premium gas?

You may or may not notice the effects right away, but if you use the wrong gas or too low of octane for your dirt bike, the fuel will burn too quickly and potentially cause overheating, detonation, more rapid fuel consumption, backfiring or bogging. If you hear a pinging or knocking sound coming from your engine under load, you likely need higher octane gas or a retune.

What about Ethanol?

One type of gas to avoid, if possible, is ethanol-based (yes, it’s becoming increasingly difficult to avoid). Ethanol, commonly found in E10 gasoline (which contains up to 10% ethanol), can significantly impact your dirt bike’s performance. The big concern using ethanol-based fuel is corrosion. Ethanol attracts moisture which, over time, corrodes vital engine parts. Ethanol-blended fuels have a shorter shelf life and can gum up carburetors and accelerate rubber deterioration. So, go ahead and use ethanol blends if that’s all you have access to, but do not run gas with an ethanol concentration above 10%. And above all, don't let these fuels age in your bike, or in your fuel cans.

Dirt bike at the top of a mountain with sunset in the background

Does elevation affect what fuel you should use?

Does elevation affect what fuel you should use?

As you ascend in elevation, the air contains less oxygen, resulting in reduced compression in your engine. The compression ratio doesn’t change with elevation, but the effective pressure does change so it will have the effect of a lower ratio. So, as elevation increases significantly, you could run a lower octane gas (say you’re running 91 octane at sea level, above 5,000 ft you’d be safe to switch to 89 octane instead). It may be best to run above the minimum octane the manufacturer recommends, then either adjust your carb or let the fuel injection system take care of things.

In closing, check your manual to see what fuel the manufacturer recommends for your specific bike, but generally speaking, running regular or mid-grade gasoline will work best for most. Try to avoid ethanol blends if at all possible, but if not, at least ensure it’s no more than 10%. Don't let fuel sit in your bike tank and carb to avoid gel and corrosion. Use fresh gas, especially in a more race/higher performance engine.

Reprinted with permission from British Columbia Off-Road Motorcycle Association (BCORMA)

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