The Four Main Types
| Type | Centre Electrode | Lifespan | Price Each | Best For |
|---|---|---|---|---|
| Copper/Nickel | 2.5mm | 20,000–30,000 miles | £2–4 | Older engines, budget option |
| Platinum | 0.8mm | 40,000–60,000 miles | £4–8 | Mid-range, most modern cars |
| Iridium | 0.6mm | 60,000–80,000 miles | £6–12 | Modern fuel-efficient engines |
| Double Iridium | 0.4mm | 80,000–100,000 miles | £8–15 | Premium/performance engines |
Why Electrode Size Matters
A smaller electrode creates a more concentrated spark, which means better ignition of the fuel/air mixture. This translates to smoother idling, better fuel economy, and more complete combustion. It’s why iridium plugs (0.6mm tip) outperform copper (2.5mm tip) despite both producing the same voltage spark.
Can I Upgrade?
You can upgrade from copper to platinum or iridium — they’re physically the same size and thread. The benefits are longer life and marginally better performance. However, some engines are specifically designed for platinum and running iridium won’t provide noticeable improvements.
Frequently Asked Questions
Are iridium spark plugs worth the extra cost?
Yes for most cars. The longer replacement interval (60K vs 20K miles) means you change them 3x less often. The lifetime cost is actually similar to copper, with better performance throughout.
Can I use copper plugs instead of iridium?
Physically yes, but the shorter lifespan means more frequent changes. If your manufacturer specifies iridium, it’s because the engine is optimised for iridium’s finer spark.
What about ruthenium spark plugs?
NGK’s Ruthenium HX is their latest technology, offering even finer electrode tips. They’re premium-priced but represent the current state of the art in spark plug technology.
