A guide to motorcycle exhausts | Everything you need to know if you're considering an upgrade

There are a number of ways that we can upgrade and customise our bikes to make them our own, from smaller motorcycle accessories to one of the most popular motorcycle upgrades, an aftermarket exhaust, be that the a full system or a slip on can. One of the more expensive modifications that you can make to your bike, however one of the most transformative to the look and sound.

Jump to:

• What does the exhaust do?
• Why fit an aftermarket exhaust?
• Types of exhausts
• The law surrounding aftermarket exhausts

What does the exhaust do?

As you probably already know, the exhaust is the exit pipe, usually at the rear of the bike, be it under the seat, mounted to the rear peg hangers or an underbelly mounted can. The main purpose of the exhaust is as an outlet for the gases from the engine during the combustion process. You may be familiar with the suck, squeeze, bang, blow of the combustion engine, well the exhaust is where gases from the blow bit are released.

Some exhaust systems, especially those engineered for race bikes, will play a part in improving the motorcycle’s performance. One way that they achieve this is by being made or more expensive, lighter metals like titanium but another is by reducing back pressure. A full exhaust system replacement can increase power by up to 15% (if you make sure to recalibrate the fuelling, too), perfect if you are chasing lap times at the track.

Exhausts are also a key part of converting harmful gases produced from the fuel burning process into more environmentally friendly ones to allow the motorbike to meet the tight emission standards that are required these days.

Various sections of the system contain catalysts made from precious metals that clean up your emissions as they pass through, removing some of the more harmful gasses. Exhausts can also deal with particulates and any unburned hydrocarbons that make it through your engine.

Emissions aren’t just about gas, though, and another job an exhaust does – much to many riders’ disapproval – is to reduce the noise of the motorcycle, by use of mufflers or silencers.

Why fit an aftermarket exhaust?

There are two main reasons that aftermarket exhausts are so popular: stock exhausts can be ugly and sound gutless. We’re into Euro5+ emission regs as of this year and stock pipes have grown larger and less attractive over the years.

A simple end-can swap can be enough to improve the look of your rear end, but some riders take it further with a full system that can really streamline things, as well as knock kilos off the bike’s weight.

Sound is also a big motivation. It’s worth pointing out here that technically, any modification that alters the sound output of your motorcycle from its type approval is illegal in the UK. More on the law around exhausts…

Police can also act if your silencer does not work correctly or you are riding in a way that creates excessive noise. Under the Road Traffic Act 1988 (Section 42) the penalty for not complying with these rules is a £50 on the spot fine.

Types of exhausts

There are many manufacturers of aftermarket exhausts, with some of the most well known being Yoshimura, Akrapovic, Arrow, Scorpion down to the lower end of the market with brands like Lextek There are two main types of exhaust upgrades for a motorcycle. The first being a full exhaust system and the second is called a slip on. Which you choose will depend on your needs and budget.

A slip on

The slip on exhaust is the end can portion of the exhaust system, which can be removed from the motorcycle and attaches to the stock exhaust system. Many people will replace the exhaust silencer themselves as it requires fairly minimal experience and tools. This type will not have a significant impact on performance, however it will likely change the sound of the motorcycle.

A full exhaust system

This is when the entire exhaust system of the motorcycle is replaced, including the muffler, exhaust pipe and the header. This option will inevitably cost more than a slip on and require a much more involved fitting process. The benefit of a full exhaust is the reduced weight and often increased performance to the bike.

What the law says

It’s a murky and grey area and, clearly, many riders push the boundaries of what’s acceptable on the road without coming to grief, but there is a legal framework you can work to.

Under Euro5 rules, when big bikes leave the factory they need to meet a ride-by noise limit of 77dB(A) when measured at 50kmh +/- 1kmh. The Government says: “It’s illegal to modify the exhaust system to make a vehicle noisier after it has been ‘type approved’.”

They add that the police can act if your silencer does not work correctly or you are riding in a way that creates excessive noise. Under the Road Traffic Act 1988 (Section 42) the penalty for not complying with these rules is a £50 on the spot fine.

Getting an MOT

If you’ve got an aftermarket pipe, what happens when it comes to the annual MoT test? Well, here’s where things get a little bit vague…

There is actually no maximum volume to which exhausts have to adhere. Instead, it is down to the discretion of the tester. That said, those stamped as ‘not for road use’ will fail the test.

According to the Government’s own information for testers: “If possible, you should assess the exhaust noise by revving the engine to approximately half the maximum engine speed. The engine should be warm before you carry out this check.

“The exhaust system and silencer should be in such condition, or of such a type, that the noise emitted from the motorcycle is not clearly unreasonably above the level expected from a similar motorcycle with a standard silencer in average condition.”

Race tracks will also enforce sound restrictions on exhaust noise with most UK tracks limiting to 105dB so it is worth checking with the race track before you go.

Some manufacturers like Yamaha and Akrapovic are upping their exhaust game to increase power without breaking racetrack noise limits. With some modification companies facing fines for noise boosting exhaust modifications.

In addition to the noise restrictions there are other legislations that you should be aware of. The law states that it is illegal to alter an exhaust from manufacture to make it louder. So this means removing the baffles or collector boxes. It goes on to explain that it is illegal to use an exhaust that has words to the effect of ‘not for road use’ on a motorcycle that is being ridden on the road.

So while many motorcyclists will replace their exhaust in favour of a louder, sexier one, it is worth being aware of the potential trouble that you could run into. Generally speaking most police officers will not pull you over simply for a loud exhaust, unless you are causing trouble or being obnoxious in others ways, but frankly speaking if your exhaust is too loud, police can penalise riders for exhaust noise and you could face an on the spot fine of £50.

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