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Best Motorcycle Spark Plugs

May 31, 2023

There was a time when spark plugs required constant maintenance or replacement. With improvements such as electronic fuel injection, cleaner burning fuels and more exotic metals such as iridium and platinum, modern spark plugs can last much longer than they used to, with service life stretching to 80,000 miles or more. These technological advances mean these are the best motorcycle spark plugs ever manufactured, and we benefit in several ways when it's time to upgrade.

Still, there are reasons why upgrading from a healthy stock spark plug can be a good idea. Better quality spark plugs can improve starting power, engine performance and fuel economy. Modern spark plugs still use a copper core, but the center electrodes are tipped with platinum which runs hotter and last longer. Iridium tips are even more durable, but also more expensive. That being said, spark plugs are relatively inexpensive compared to other upgrades you can make, and the longevity of iridium spark plugs may make up for the extra cost over time.

We’ve put together a list of some of the top motorcycle spark plugs below. Keep in mind that spark plugs tend to be model specific, so be sure to check your motorcycle's manual to learn what size, heat range, and, most importantly, the gap size between electrodes.

NGK is a Japanese company that has been producing spark plugs since 1936. The company supplies OEM spark plugs for a number of motorcycle and automotive manufacturers, and it is also a popular aftermarket supplier. As such, there's a good chance that NGK will produce a compatible spark plug for your particular bike. NGK also has an American subsidiary that produces spark plugs in Sissonville, WV.

The NGK Iridium IX combines a 98% pure copper core with an iridium alloy tip for high durability and consistent performance. The tapered-cut ground electrode is designed to reduce the quenching effect, where heat transfer from the ground to the center electrode may cause ignition issues. A high-grade alumina silicate ceramic insulator helps with heat dissipation, allowing the Iridium IX to operate over a wide heat range.

E3 is another popular spark plug manufacturer, known for its DiamondFire ground electrode. The electrode is secured to the shell with two legs, which E3 claims helps optimize heat transfer and withstand engine vibrations to deliver consistent performance. The ground electrode also projects farther forward into the combustion chamber, bringing the spark closer to areas with a probable good air-fuel mixture. E3 spark plugs also come pre-gapped to meet specific engine specifications.

Autolite produced its first spark plug in 1936 in Fostoria, Ohio, and soon became a supplier to American automotive brands such as Chrysler, Studebaker and Packard.

Designed for powersports applications, the Xtreme Sport uses an iridium-enhanced 0.6 mm finewire design with a V-trim ground electrode that Autolite claims offers more power and better fuel efficiency than standard spark plugs. Autolite also claims the Xtreme Sport helps engines start 26% quicker than standard plugs, reducing wear on the starter and battery and reducing effort for kick starters.

Denso is a Japanese company that started off as an offshoot of Toyota. The company's name itself is a combination of the Japanese words for "electricity" and "device".

Denso claims its 0.4 mm iridium center electrode is the smallest diameter used in any spark plug. The tapercut ground electrode is designed to reduced quenching and improve ignitability while its U-shaped groove helps generate a flame kernel at a lower voltage, helping with ignition without needing to increase the size of the gap.

Accel has been producing ignition systems for more than 40 years, and is now a member of the Holley Performance family.

Accel does not offer a iridum spark plug, instead offering a copper U-Groove plug or a platinum-tipped plug. Platinum isn't as durable as iridium but is still significantly longer lasting and runs hotter than copper spark plugs.

Most modern motorcycles can go about 15,000 miles before needing new spark plugs, but check the maintenance schedule in your owner's manual to make sure what the recommended intervals are.

However, if you start experiencing engine issues, it may be a good idea to inspect your spark plugs to see if they need replacement.

Common signs of a bad spark plug include misfiring or backfiring. If your engine doesn't seem to have its normal rhythm, then your spark plug may not be arcing at the right time. If you hear loud popping sounds, then your spark plugs may be producing an intermittent spark.

An even more obvious sign is if your engine just won't start at all.

Where standard OEM spark plugs need to be changed every 15,000 miles or so, iridium-tipped spark plugs typically have a service life of 40,000 miles or more.

If cost is an issue, platinum plugs may be a good compromise. Platinum isn't as expensive as iridium but still offer good durability because platinum doesn't wear as quickly as copper.

When shopping for spark plugs, make sure they are appropriate for your particular model. Different engines may have specific needs for heat range or how far a spark plug projects into the combustion chamber.

Make sure you get a spark plug with the correct gap (i.e. the space between the center electrode and the protruding ground electrode. A correct gap prevents misfires and improves efficiency. Most spark plugs come pre-gapped, so make sure you buy one that meets your bike's specifications. Some spark plugs need adjustment, which would require a gap or feeler gauge and a gapping tool.

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I have used NGK standard plugs in my Bandit since new and have always had pre-ignition rattle if I don't down shift when accelerating in the top three gears. A friend gifted me a set of Autolite Iridium plugs for Christmas and the rattle is GONE!

NGK #1 in motorcycle spark plugs