Should i use E5 or E10 petrol for my motorbike in the UK

Choosing the right petrol protects performance, reliability, and the  long-term health of your motorcycle. In the UK, most forecourts offer E5  and E10 unleaded—each with different ethanol content and implications  for your engine, fuel system, and storage habits.

• E5 petrol: Unleaded containing up to 5% ethanol.
• E10 petrol: Unleaded containing up to 10% ethanol.

Ethanol is an alcohol that helps reduce overall tailpipe CO₂, but it  absorbs moisture, can accelerate corrosion, and may degrade older  rubbers, plastics, and sealants used in many motorcycle fuel systems.

• Motorbikes  pre‑2021: Use E5 where possible. Many motorcycles registered before  2021 were not designed around 10% ethanol and are more prone to material  compatibility issues, corrosion, and storage-related problems on E10.
• Motorbikes  2021 onwards: Many newer models are E10-compatible. Always confirm in  the owner’s manual or on the manufacturer’s website.
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• Material compatibility: Ethanol can swell and soften older fuel hoses, O‑rings, seals, float bowl gaskets, and some tank liners.
• Moisture  and corrosion: Ethanol is hygroscopic, pulling water into the fuel.  Water promotes rust in tanks and corrosion in pumps, injectors, and  carburettors.
• Storage  sensitivity: Bikes that sit for weeks or over winter are at higher risk  of phase separation, varnish, and gumming with E10.
• Economy  and feel: Ethanol has lower energy per litre. Some riders notice  slightly reduced mpg and occasional hot‑start or idle quirks with E10.

• Prefer E5 for pre‑2021 bikes: It’s typically more stable for infrequent use and kinder to older materials.
• Check compatibility: Search your exact model/year plus “E10 compatibility” or consult the handbook.
• Use  premium “Super Unleaded” for E5: On UK forecourts, 95 RON is usually  E10; Super Unleaded 97–99 RON is commonly E5 and can help reduce knock  in performance engines.
• Rotate  fuel: If you must run E10, avoid long storage. Ride regularly or brim  the tank and use a reputable ethanol‑safe stabiliser for lay‑ups.
• Upgrade components: Replace ageing rubber lines, O‑rings, and gaskets with ethanol‑resistant materials (e.g., FKM/Viton).
• Mind  carburettors: Carb bikes are more sensitive. If rough running appears  after switching to E10, revert to E5 and consider a carb service with  ethanol‑safe parts.
• Maintain filters: E10 can loosen deposits; replace fuel filters on schedule and monitor for debris.

• Hard starting or lumpy idle after moving to E10
• Fuel weeps, softened hoses, or perished O‑rings
• Tank liner swelling or peeling
• Noticeably reduced range or flat spots under load

• Is E10 bad for all older motorcycles? 
  • Not all, but many pre‑2021 models use materials more vulnerable to ethanol. When uncertain, choose E5.
• Can I mix E5 and E10? 
  • Yes. Mixing reduces overall ethanol content, but consistent use of E5 is safer for older bikes.
• Will E5 improve mpg? 
  • Often slightly, due to higher energy content per litre compared with E10.
• Does ethanol change octane? 
  • Ethanol  has high octane, but pump formulations vary. Follow your manual’s  octane recommendation; many E5 “Super” fuels offer 97–99 RON.

• Choose E5 for bikes stored over winter or ridden infrequently.
• Add an ethanol‑compatible stabiliser to fresh fuel, run the engine to circulate, and top the tank.
• Drain carb float bowls for long lay‑ups to prevent varnish.
• Inspect and replace aged hoses and seals in spring.

• E10 contains more ethanol and can accelerate corrosion and material degradation in older fuel systems.
• For motorcycles registered before 2021, E5 is the recommended, safer choice.
• Many newer bikes are E10‑compatible, but always confirm with the manufacturer.
• If you must use E10, shorten storage intervals, stabilise the fuel, and fit ethanol‑resistant components.

For model‑specific advice or preventative upgrades, AK Motorbikes can  check E10 compatibility, supply ethanol‑resistant hoses and seals, and  set up your bike for reliable running on UK fuels. Bring your make,  model, and year, and we’ll recommend the best E5/E10 strategy for your  motorcycle.