More manufacturers building sub 500cc bikes

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I’ve been noticing that more manufacturers are starting to build sub 500cc motorcycles, the latest and most notably the Triumph 250. What they are trying to do is take advantage of the European motorycle license laws.

According to the A2 license regulations, an A2-legal bike can’t have more than 35kW – that’s 47bhp – and it can’t have a power-to-weight ratio of more than 0.2kW-per-kg. So they can forget those ideas of a featherweight GP3-bike-for-the-road – if a bike makes the full 35kW, it needs to weigh at least 175kg.

However, restricted bikes are allowed provided they didn’t make more than twice the 35kW limit in their original form. That means bikes with 95bhp or more as standard is ineligible for restriction, however little power you eventually intend to restrict them too.

A bit of maths comes in handy now. First, since they tend to refer to horsepower instead of kW, you need to remember that 1bhp is 746 Watts. That’s 0.746kW. So to work out what a bike’s power is in kW, multiply the horsepower by 0.746. If the result is less than 35 (and as long as the bike makes less than 47bhp), the motorcycle can classify as an A2-class machine.

Now you need to check the power-to-weight. Divide the bike’s power figure (in kW) by 0.2. The resulting number needs to be less than the bike’s kerb weight – that’s how much it weighs ready-to-run but without a rider or any luggage on board. If you’ve got 35kW it needs to be at least 175kg, but lighter machines can also be A2-legal provided their power drops to keep the power-to-weight ratio right. If they want to ride a 140kg Suzuki RGV250 it will need to make no more than 28kW – 37.5bhp – to be A2-legal. Work out the the maximum possible power of a sub-175kg bike by taking the bike’s weight (wet, unladen or kerb, not ‘dry’), and then multiplying it by 0.2. The result is the maximum power in kW. Divide that figure by 0.746 to turn it into horsepower.

Got it? Right…

When it comes to actually restricting a bike, there are already plenty of workshops with experience, since the last set of licence laws forced many people to restrict their bikes to 33bhp. Normally, if there’s no manufacturer’s kit available, the workshop will limit the maximum throttle opening or fit an air-restrictor, either using data they already have or even by putting your bike on a dyno and tweaking the power down. Although many people make reference to a ‘restriction certificate’ to prove that the bike has been detuned, the only reference that the DSA makes to anything like that is if you’re taking the bike to use it for your A2 test. Then, if it’s a restricted bike, they ask you to bring ‘proof of the restriction’ saying it must be ‘on headed notepaper from a main dealer, official importer or recognised specialist, and must show the motorcycle’s registration number.’

Apparently European laws state : “a dyno test certificate will not be accepted as proof of the restriction.”

Which means that if you’ve got a restricted bike, it’s going to be worth having a document like that, proving it’s restricted, in case you get pulled over by police at any time. Insurers don’t require it, but of course if you’re riding an unrestricted or otherwise non-A2 bike on an A2 licence, you won’t be covered and you’ll be breaking the law.

About the author

Buks has had a passion for two-wheels since childhood. After his first motorcycle, a fire-breathing two-stroke Yamaha TZR250, he realized he was hooked. When Buks isn't writing for UltimateVelocity he enjoys practicing martial arts, gardening and spending time with his family.