Can you de-cat a Euro 5+ motorcycle?

 Euro 5 vs Euro 5+ on Petrol Motorcycles – What’s the Difference? And What’s Coming Next?

If you ride a modern bike, you’ve probably seen Euro 5 or Euro 5+ in the spec sheet… but what does that actually mean?

Here’s the quick breakdown 👇

Euro 5 (introduced 2020)

Euro 5 set strict limits on emissions for new motorcycles, especially:

• Carbon monoxide (CO)
• Hydrocarbons (HC)
• Nitrogen oxides (NOx)
• Particle numbers on some direct-injection engines
• Stricter noise and durability requirements

Most modern bikes already have:

✔ catalytic converters

✔ lambda sensors

✔ precise fuel injection and ECU mapping

 Euro 5+ (also called Euro 5b)

Euro 5+ isn’t a whole new standard—it’s a tighter second phase of Euro 5.

For petrol motorcycles, this mainly means:

✅ more accurate real-world testing

✅ tougher on-board diagnostics (more sensors, stricter fault detection)

✅ more stringent durability of emission controls

❗ stricter testing of particulate numbers on direct-injection engines

What riders actually notice:

• ECUs are fussier
• Catalytic converters are more integrated into the exhaust design
• Exhaust mods trigger engine lights more easily
• Bikes must stay cleaner for longer during their life 

What About Euro 6? And When Will It Hit UK Motorcycles?

Euro 6 already applies to cars, but motorcycles have not yet moved to Euro 6.

The EU is preparing a “Euro 6 for motorcycles” (known as Euro 6 for L-category vehicles). The UK usually follows EU standards for bikes with some delay.

Expected UK timeframe:

• No official published date yet, but most industry analysts expect around 2027–2030
• It will likely mean:
  
• Stricter NOx limits
• Wider use of particulate filters on petrol bikes
• More complex ECUs and lambda sensors
• More real-world (RDE-style) emissions testing 

When Euro 6 arrives, exhaust and ECU modifications will get even trickier.

Thinking of Removing the Catalytic Converter? Here’s What You MUST Know

Removing the cat (“de-catting”) is common on older bikes, but modern Euro 5/5+ bikes depend on it for tuning and legal compliance.

If you remove the cat on a Euro 5/5+ bike and still want it to run properly:

You will generally need

• ECU remap or fuel controller
• Lambda sensor adjustments or eliminators (if used)
• Correct fueling to avoid running lean
• Sometimes a modified mid-pipe to ensure proper exhaust back-pressure

What happens if you don’t:

• Engine warning lights
• Limp mode (on some bikes)
• Overheating exhaust valves
• Poor low-end running
• MOT failure if visible tampering is obvious (see below)

UK Law: What Riders MUST Know About Modifying Euro 5/5+ Motorcycles

On Road Use

In the UK it is illegal to use a motorcycle on public roads if you have:

❌ tampered with or removed emissions equipment (including catalytic converters)

❌ modified the ECU so the emissions exceed the approved type-approval standard

This applies even if the bike still passes an MOT. MOT is not the same as type-approval compliance.

MOT Rules

• Motorcycles currently do not have an emissions test at MOT
• BUT testers must fail a bike if a catalytic converter that was originally fitted has clearly been removed on a bike that required it for approval

Insurance

Removing a cat is a material modification.

If you don’t declare it:

→ insurance can be invalidated

→ claims may be rejected

Police / Roadside checks

Roadside enforcement officers can:

• Inspect for missing emission equipment
• Check for ECU tampering
• Issue fines or prohibit the bike from being ridden

Final Thoughts

• Euro 5+ is basically Euro 5 with stricter testing and tougher ECU diagnostics.
• Euro 6 for motorcycles is coming later this decade and will push emissions even lower.
• If you modify your exhaust and remove the cat, be prepared for ECU work, sensor issues, and legal risks.
• Always declare mods to your insurer and make sure you know the legal implications.