How much cleaner are Euro 5 bikes?

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Euro 5 emissions rules have been a hot topic since the latter part of the last decade as bike makers geared up for their introduction on 1st January 2020. Thanks to the stepped nature of the rules’ introduction the last of the old Euro 4 models need to be sold by the end of 2022 but the motorcycle industry has come through the toughest set of bike emissions rules changes in history with flying colours.

There was speculation that Euro 5 would kill whole swathes of bikes, eliminating entire classes and hiking the prices of those that remained to pay for additional emissions kit and R&D investment. There’s no question the regulations have been hugely influential on motorcycle design – encouraging a growth in twin-cylinder models and a decline in smaller-capacity four-cylinder bikes and seeing many bike firms opt to increase capacities to claw back performance that’s lost to Euro 5 design changes – but overall, far from being hobbled by emissions rules, the bikes on sale today are better than their Euro 4 equivalents.

To get a handle on how rapid and significant the improvement in motorcycle emissions has been over the last few years, we only need to glance at how the rules that bikes sold in Europe (and the UK, since we’re still very much aligned with EU emissions rules even after Brexit) has been since the first ‘Euro 1’ regs appeared in 1999.


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Above: BMW’s K1 was the first bike to get a three-way catalytic converter back in 1990. A decade later they’d be everywhere (cats, not K1s…)


Back in 1997, the first step towards cleaning up motorcycling was taken, with Directive 97/24/EC of the European Union, which established the Euro 1 rules and the testing procedures that would come into force for all new models that would be type-approved after 17 June 1999. The legislation kicked off a harmonised campaign of Europe-wide motorcycle emissions reduction, following in the footsteps of a similar system already in place for cars.

Those Euro 1 rules were comically lax from today’s perspective, implementing a limit on carbon monoxide (CO) of 13 g/km and restricting combined hydrocarbons and oxides of nitrogen (HC + NOx) of 3.3 g/km. For comparison, the original Euro 1 limits for cars, introduced six years earlier in 1993, limited CO to 2.72 g/km and HC + NOx to 0.97 g/km, and by the introduction of motorcycle Euro 1, cars were meeting their own Euro 2 limits, introduced in 1997 and limiting petrol vehicles’ CO to 2.2 g/km and HC + NOx to 0.5 g/km. That meant those Euro 1 bikes could emit around six times as much as cars of the same age.

Generous though they were, Euro 1 motorcycle emissions limits tore through the bike market, essentially killing high-performance two-strokes instantly despite efforts like the direct-injected Bimota V-Due to meet the restrictions. Euro 1 also meant that bike makers finally had to adopt fuel injection on a widespread basis to get more accurate control over the petrol going into their engines and to protect the catalytic converters that many were fitted with for the first time (although the first three-way-cat-equipped bike was the BMW K1 back in 1990). Despite some initial hiccoughs – quite literally from some of those early injected engines, which often had snatchy throttle response compared to the smooth carbs we were used to at the time – the result wasn’t a castration of motorcycling but an acceleration of technology that saw power levels start to rocket.


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Above: 1997 BMW R1200 exhaust shows another early adoption of the catalytic converter as bikes embraced cleaner emissions


Euro 1 was just a gentle introduction to emissions limits for the bike industry – it was followed by a rapid series of reductions, each slashing the level of emission allowed.

In 2003 we got Euro 2 restrictions, cutting CO from 13 g/km to 5.5 g/km and HC from 3 g/km to 1 g/km (a move that eliminated the last stragglers of the two-stroke era, notably the Aprilia RS250). But it was three years later in 2006 that Euro 3 restrictions really started to get people talking about how difficult it was getting, cutting limits to between half and a third of Euro 2 levels by limiting CO to 2 g/km, NOx to 0.15 g/km and HC to 0.3 g/km.

So significant were Euro 3 restrictions that they were left untouched for a decade after their introduction, leading to a period of calm for bike makers but also a noticeable lack of development in bikes as a result.

That hiatus came to an end in 2016, when Euro 4 again caused a shake-up. While its reductions weren’t as substantial percentagewise as those from Euro 2 to Euro 3, the limits for CO, NOx and HC were all cut to about 60% of their previous levels. To achieve those levels, we saw the widespread adoption of ride-by-wire throttles, allowing the engine management to modulate the way the throttle butterflies opened in response to the twistgrip. As well as tailoring emissions to meet the new restrictions, ride-by-wire (ably assisted by the creation of inertial measurement units to monitor the acceleration, braking, pitch, yaw and roll of bikes) sparked the rapid evolution of traction control and stability control systems that have become de rigueur over the last few years.


Emissions standard

Euro 1

Euro 2

Euro 3

Euro 4

Euro 5

Implementation date






Carbon monoxide

13 g/km

5.5 g/km

2 g/km

1.14 g/km

1 g/km

Oxides of Nitrogen

0.3 g/km

0.3 g/km

0.15 g/km

0.09 g/km

0.06 g/km


3 g/km

1 g/km

0.3 g/km

0.17 g/km

0.1 g/km






0.0045 g/km

Non methane hydrocarbons





0.068 g/km


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Above: A ride by wire throttle (this one is from Honda’s VFR1200F) – the emissions-based tech that allowed traction control to thrive


All those numbers mean that today’s bikes, compared to Euro 1 models from 1999-2003, emit 92.31% less carbon monoxide, 80% fewer oxides of nitrogen and 96.67% fewer hydrocarbons. That’s pretty astounding, particularly when you consider how much performance has improved over the same period.

If the emissions could be compared to pre-Euro 1 bikes of the 1990s and earlier – which were largely unbound by emissions limits, so figures aren’t readily available as to how polluting they were – the difference would be even larger.

However, the full impact of Euro 5 won’t be felt on an environmental level for a while yet. The average bike in the UK is now over 15 years old, which means a typical machine might date back to 2006, when Euro 3 limits were just being brought in.

There’s also a rule of diminishing returns at play. Even if emissions are halved with every new set of legislation, as limits are reduced the cuts become harder to make but have less impact on pollution. You can see in the chart above that the change from Euro 1 to Euro 2 eliminated more emissions at a single stroke than the combined effect of Euro 3, 4 and 5 since then.

While CO2 (greenhouse gas or GHG) emissions aren’t specifically controlled by Euro limits, they’re a good representation of how much fuel is burnt. In Europe, bikes currently account for 1.3% of GHG from road transport. Add other forms of transport into the equation and that percentage drops to 0.92%. And since transport is responsible for only 27% of total GHG emissions – far less than power generation, and roughly on a par with industrial GHG output – motorcycles can only be blamed for 0.25% of GHG emissions in total throughout Europe. Even if their emissions were eliminated entirely, the impact would be minimal.


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Tighter limits are coming

That’s not to say motorcycle emissions won’t be cut more. In fact, the next rule changes are just around the corner in the form of Euro 5 Phase B or ‘Euro 5+’ regulations that are due to be implemented in 2024 and 2025.

Euro 5+, which is set to apply to newly type-approved bikes from 1st January 2024 and added to existing type-approvals by 1st January 2025, introduces elements of Euro 5 that were delayed when the regulations were initially implements.

The main change is that Euro 5+ will enforce the adoption of ‘OBD II’ (On Board Diagnosis II) standards, which monitors a bike’s emissions performance in real time, alerting you if any element of the system is under-par. When Euro 5 was first agreed, back in 2013, it was believed that OBD II could be introduced at the same time – it’s been on cars for many years – but it turned out to be much more difficult than expected to make the system work on motorcycles, which have used OBD I standards since Euro 4 was introduced.

Where OBD I simply looks out for failed components, lighting the ‘check engine’ lamp if, say, an oxygen sensor fails and puts out the wrong reading, OBD II is much more subtle. The biggest headache for bike companies has been its requirement to monitor for misfires, picking up tiny variations in the engine’s vibrations as it runs. Not too tough in cars, it’s a big challenge in bikes that rev much higher and have much more solidly mounted engines – often structural parts of the chassis – making them subject to external vibrations and movements from road surfaces and bumps, which can set off false alarms in the OBD II system.

Most manufacturers, with an extra few years’ development under their belt, are now on top of those problems and we’re already starting to see bikes launched that are ‘Euro 5+ ready’ – the Aprilia Tuareg 660 is one such machine to already make that claim.

Another element of Euro 5+ is the addition of catalyst monitoring to ensure that bikes’ emissions kit doesn’t degrade excessively over time – manufacturers will be expected to ensure that the kit works well over an extended period of use, and a failing cat or degrading O2 sensor will also spark a check engine warning.

We’re also seeing increasing harmonisation of emissions rules around the planet, with regulators in Japan and India largely echoing Euro 5 limits and schedules, and CARB (the California Air Research Board) in the USA is also proposing to bring California’s limits into line with Euro 5 in 2024/2025 – potentially leading the way where the rest of the USA might follow.


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Above: Big companies have been slow to adopt electric bikes – Honda’s PCX electric (above) is a rare exception


What about Euro 6?

With Euro 5, motorcycle emissions limits for CO, HC + NOx and non-methane hydrocarbons all came into line with the current ‘Euro 6’ rules that passenger cars have had to meet since 2015. So, while there are still no firm, published plans for motorcycle Euro 6 limits – they’re still under discussion – it’s a fairly safe bet that they’ll closely mirror whatever is introduced as ‘Euro 7’ for cars.

Those passenger car Euro 7 rules are due to be published later in 2022, which will give us a good indication of what to expect from motorcycle Euro 6, but the proposals currently mooted include a halving of CO limits from 1 g/km to 0.5 g/km, along with a reduction in hydrocarbons from 0.1 g/km to 0.09 g/km, and a cut in NOx from 0.06 g/km to 0.035 g/km. Non-methane hydrocarbon levels are expected to be unchanged at 0.068 g/km. However, along with those changes, the Euro 7 rules are due to bring a new focus on real-world usage, so even though the on-paper numbers don’t represent the same massive cuts as some previous steps, there will be substantial hurdles to jump.

While cars are expected to have to adopt those stricter Euro 7 rules by in 2025, bikes will probably be left until the end of the decade before being expected to reach whatever motorcycle Euro 6 limits are settled upon.

However, there’s another factor that doesn’t get a mention in these rules – all aimed at individual vehicles – and that’s overall carbon dioxide (CO2) emissions. For cars, CO2 levels are restricted differently. Each vehicle is tested and type-approved at a certain level of CO2 emissions, often used to set levels of road tax, and manufacturers are expected to meet ‘fleet’ targets. In other words, customers aren’t restricted – apart from by some tax burdens – on how much CO2 their vehicle emits, but manufacturers have to ensure that the average emissions of their vehicles fall below a certain level. It’s this CO2 fleet limit that’s increasingly driving the development of hybrid and fully electric vehicles from major manufacturers: every gas-guzzling SUV they sell needs to be offset by the sale of low or zero-emissions vehicles to keep the fleet average down.

It's a clever system, encouraging companies to subsidise their own electric and hybrid vehicles, perhaps by charging more for the less efficient models. Recently the average CO2 target was cut from 130 g/km to 95 g/km, and it’s set to be reduced by 15% to 81 g/km in 2025 and a further 37.5% to 59 g/km in 2030. Bikes haven’t been subject to this sort of limit, largely because they’re much more fuel-efficient than cars, but it’s quite possible that when Euro 6 rules for bikes are hammered out a similar set of rules for motorcycle fleet CO2 emissions could be brought into play – a move that could encourage major manufacturers who are currently fiddling on the side-lines of the electric bike market to dive in at last.

One thing that’s been repeatedly proven is that with each seemingly insurmountable hurdle put in front of the motorcycle industry in terms of emissions, the engineers and designers tasked with solving the problems have surpassed expectations. Not only have bikes got cleaner, but they’ve got faster and safer in the process. So, far from worrying about tighter emissions rules, perhaps we should be eagerly awaiting the next set of challenges to see what new machines and ideas they inspire.