Euro 4 and exhaust flaps

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Motorcycle noise

Debate about the volume of motorcycles

Euro 4 and exhaust flaps


traffic & business

Euro 4 and exhaust flaps

Euro 4 and exhaust flaps
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Euro 4 has been in effect since January 2017. In addition to stricter exhaust gas limits, the standard also sets other noise limits. Many fears have arisen, especially with regard to flap systems in the exhaust. Completely unfounded, as we explain here.

Michael Orth


The black Harley babbles discreetly while idling. It rattles and rattles – the running noises of the engine. They are more audible than the exhaust: inconspicuous, quiet and elegantly reserved. It’s a bit like someone at the table talking to a neighbor with his hand in front of his mouth so that not everyone can hear what is being said. Then Mr. Thomas goes there and presses a button on the handlebar. The button lights up, the rattling and rattling goes down, and the exhaust sounds as if the machine it is screwed to is now twice as big. He’s no longer just bubbling. The man at the table pushes his chair back when he gets up, takes his hand from his mouth, takes a deep breath and makes a clear announcement. He doesn’t speak loudly, but clearly. He opens the door.

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“Euro 4 stricter? You cant say it like that.”

Just like Bastian Thomas with the push of the little button. Bastian Thomas is Head of Development at the KessTech exhaust experts. What he says and, above all, how he says it, is the exact opposite of all the shitty house slogans that have been around long and loud enough and are still doing: With Euro 4 everything will be really bad. Limit values, complicated measurements, no one will see through any more, but it must be clear to everyone that everything is going to be really bad, no, even worse. The Sound of Silence will be everything that motorcycles are allowed to utter. What was a nice tone before will then have to sound like a jammed fart. Exhaust flaps will be banned, in principle, all. And it will not matter whether any retrofit pot was okay according to the previous provisions – with Euro 4 there will be an obligation to retrofit and the fun of sound will go. Euro 4? A bogeyman.

“Euro 4”, says Bastian Thomas, “no issue at all. Measurement procedures have changed compared to Euro 3, it is more complex to homologate new systems. But we have already done it for many models, for others we are currently at it. All good no problem. It sounds good and it’s nice to drive. And always legal.” Then Mr. Thomas smiles a friendly, satisfied smile. He has every reason to. “Let’s talk about the noise, it’s actually even better than before”, he says. The objection that Euro 4 is stricter than Euro 3 is commented on first with a shake of the head, then with an explanation. “Stricter? You cant say it like that. The limit value for driving noise is down from 80 decibels to 77 and 78 respectively. But there is also a completely different measurement method. Therefore the values ​​are not directly comparable.”

Idle noise does not mean idle

So far, the issue of exhaust noise was regulated under Euro 3 as follows: With Directive 97/24 / EC, the European Parliament laid down the maximum permissible noise level for motorcycles and the measurement methods for determining it in 1997. There is no absolute limit value for stationary noise. What was measured as part of the homologation is binding for all specimens of this type and for accessory systems for this type. And: idle noise does not mean idle. It’s called half the rated speed.

For the driving noise, 97/24 / EG specifies a maximum value of 79 db (A), with a tolerance of one decibel. The procedure: In second and third gear, the machine drives at 50 km / h in a 20-meter-long measuring section. The gas is fully drawn from the beginning to the end of the route. The microphones are located 7.5 meters away from the passing motorcycle in the middle of the measuring section, one on the left and one on the right. There are two drives per aisle, usually from both sides. A measured value is averaged after four journeys. The norm does not regulate what happens outside of this framework, i.e. the motorcycle may then be louder than 80 db (A). Loud and legal are not fundamentally in contradiction to one another. The theoretical basis of exhaust systems with flap systems is that both are in order according to the letter of the law. Electronic sound management can be perfectly adapted to the requirements of the directive and ensures that a system in the metrologically relevant area meets all legal requirements. If the electronics recognize that the machine is moving in this area, a flap in the exhaust closes and thus regulates the sound pressure down.

Why is it still here when 97/24 / EC has been replaced by Regulation 168/13 and UNECE R41.04, which now define noise limit values ​​and measurement methods within the framework of Euro 4? Firstly, because the old regulations still apply, namely for motorcycles that were registered before 1.1.2017 and homologated before 1.1.2016. And even if someone is going to screw retrofit dampers with flaps onto such a machine in the near future, the old regulations will still apply.

Euro 4 noise limit at 78 db (A)

Second, the principle has not changed. Even within the framework of Euro 4, there is no absolute noise limit, but a precisely defined range in which a maximum sound pressure must not be exceeded. “However, the measurement procedure is now more complex”, says Bastian Thomas, the KessTech developer. If a driving noise measurement with a known machine according to Euro 3 took about 20 minutes, it can now take three to four hours. Because according to the new regulation, the metrologically relevant area is sometimes different for each type of motorcycle.
How come? In a very simplified way, Regulation 168/13 says: For machines with initial approval after 1.1.2017 or type approval after 1.1.2016, a noise limit value of 78 db (A) applies. The UNECE R41.04 directive is the associated instructions for use. It describes the procedure for noise measurements and thus defines an exact range in which the 78 decibels must be adhered to. As follows: In principle, nothing changes in the measurement setup. But instead of entering the measuring section at 50 km / h as before, this speed (+/- one km / h) must now be at the level of the microphones. That describes the beautiful word “Acceleration of aim”.

Using a complicated formula, taking into account weight, performance and a rider weight standardized to 75 kilograms, each motorcycle has its own run-in speed. For example, on an R 1200 R it is 38.1, on a GS 38.6 and on a Harley-Davidson Street Glide 34 km / h. Also relevant: the gear to be engaged for the measurement. Measurements are made in the gear in which the target acceleration is reached. If it is above in one aisle and below it in the other, it must be measured in both the one and the other aisle. The results must then be evaluated taking into account a so-called gait weight factor. In addition to determining the stationary noise, there is also a constant speed measurement at 50 km / h.

“If you chew your way through the legal texts, your head will smoke until you understand what they are trying to tell you”, tells Matze Rudling from the exhaust manufacturer Jekill and Hyde. “It takes a while to adjust to the new features, but nobody pees their pants when it comes to Euro 4. It is even the case that in normal driving on the road you rarely get into the areas where the flap closes.”

When exhaust flaps and hollow bulbs come together …

Bastian Thomas from KessTech is of the same opinion. “The electronics now regulate the flaps differently. But that’s a matter of taste. Most people – drivers and residents alike – are likely to like it better now.” In fact, he says, there are some models that are legal tested according to ECE 41.04, while they would not be under the old directive. For some machines, tightening the upper limit is not a problem. Because measurements are made differently than before, they even do better. A 300 ninja, for example, uses the old method to measure a driving noise of 78 decibels. According to the current methods, it comes to only 72.

In terms of volume, has the legislature put a rotten egg in its nest with Euro 4? No, neither yourself, nor the exhaust manufacturers or those who are completely right to be upset about too loud motorcycles because they have to suffer from the noise pollution. “It’s annoying because some of the machines are screaming like hell. On a Sunday you take a break in a Black Forest cafe and think you’re racing on the Isle of Man”, says someone who likes to drive himself, but does not want to drive others crazy. “It’s just a misery when exhaust flaps and hollow bulbs come together.” Mario Muller, CTO of Jekill and Hyde, sees it no differently. He says: “Sheer volume is the last thing we want. What we want to achieve with our systems is a deep, dull, rich sound. And a sound that is legal in every driving condition. These loud noises and high frequencies hurt your ears. It’s not healthy, and it’s not fun either.” He enjoys what he does “socially acceptable sound” names. This is also important to KessTech. Bastian Thomas just puts it differently. In contrast to the flap systems from the original equipment manufacturer, with a controllable system the customer can at least determine when and how quietly he wants to be on the road. And with the “Responsibility in the hands of the user” connects very expressly “Appeal to their social skills”.

With the flap closed, it is even quieter than the original

However, this can only be influenced very indirectly with guidelines. “The new regulation”, says Bastian Thomas, “is not a step backwards, but neither is it progress. It has a very vehicle-related effect. In terms of noise, it tends to benefit the low-speed machines with large individual cubic capacities rather than the small short-stroke machines that live from the speed.” One of the particular difficulties of development is that this is exactly the opposite with regard to the exhaust gas values. In any case, the emissions behavior cannot really be separated from the sound management. And that’s why it’s often not enough just to adapt the electronics to the new specifications, even if that would be complicated and expensive enough. At KessTech, for example, they have also changed the design of a whole series of dampers, because in the original systems the catalytic converter was relocated from the manifold to the muffler or had to be larger there in order to meet the new emission standards. “In many Harley models, the Kat is no longer in the collector and the flaps have been removed. We had to”, says Bastian Thomas, “take a further step in development.” And that costs.

How much? For the price of the measuring equipment alone, Mario Muller from Jekill and Hyde speaks of a sum of around 50,000 euros: GPS devices, interface to the machine’s canbus, computer, calculation programs. In addition, there are five-digit fees for renting official routes and equipment for acceptance, plus investments for the required reports, which Muller estimates between 8,000 and 15,000 euros. If you allocate the costs to the development and the reports for a single model, you get around 40,000 euros, says Muller’s colleague Matze Rudling.

Sound and social compatibility are worth it. In terms of social compatibility, development is not in the hands of the authorities or the manufacturers, but rather in those of the drivers. “When you start, the flap is closed for the time being”, says Bastian Thomas from KessTech. “It only opens when the driver activates the system by pressing a button. The electronics regulate the flap, but it is very easy for me to decide when and where and in what way.” Not a few customers, primarily with BMW, but increasingly also with Harley, says Thomas, it is important that the system is even quieter than the original when the flap is closed. “For example, to drive longer travel stages or to get out of and into the garage in the morning and evening.” Then he turns off the Harley. silence. “Nice too”, he says. Is correct.

Short and sweet

Exhaust systems with a manually operated flap system can only legally be moved on public roads when they are closed according to Euro 3. The switch for operating the flaps must not be on the handlebars. Such systems are completely forbidden under Euro 4.

Exhaust systems with electronic sound management are still legal under Euro 4. For machines that are type and first approved under Euro 3, this standard continues to apply with regard to the retrofit systems. There is also grandfathering, Euro 4 is not retroactive. For models with an initial registration (from 1.1.2017) or homologation under Euro 4 (from 1.1.2016), the retrofit exhaust must also meet the standards of this standard.

Background: What does loud mean?

Sound can be measured, sound pressure a very complex influenced but determinable quantity. But everyone perceives noises and volume differently. Perception of noise is a very individual matter. Noise, says one, sound another. Too much and too intense noise, however, always has a negative effect on the organism. Noise pollution can damage health. Irreparable damage to the ear occurs at a sound level of 150 decibels or more, and it becomes painful at 130 decibels, which roughly corresponds to the noises that become loud when you come close to an accelerating racing car. A sound pressure of 40 decibels is ascribed to soft music. The normal conversation volume is 55, the ringing of a telephone around 80 decibels. A car horn has about the same volume as a symphony concert: 110 decibels, while a fighter jet less than 100 meters away can produce a sound pressure of 150 decibels.

Does that mean a motorcycle whose driving noise complies with the limit value of 77 decibels is not even twice as loud as a conversation and more than half as loud as a jet fighter? No, because an increase of ten decibels corresponds, in very simple terms, to doubling the volume. According to which the symphony concert is three times as intense as a motorbike driving by. Whereby the sound pressure alone is not decisive for the individual perception of the noises.


Good question: Is it sucks or is it loud? Both. Different opinion? Shut up. If motorcycles sound like blocked vacuums, that’s crap. And if they sound so that local residents drop their cups out of the cupboard, that’s crap too. The only difference is: one is a consequence of how the machine is built, the other mainly of how it is moved. It would be nice if it could be said that one thing has nothing to do with the other. Unfortunately, that’s not true. When motorcycles have to meet increasingly restrictive regulations, this follows a general trend towards stricter emission limits.

But not only. It is also a reaction to the behavior of individuals, a few or even a few, who behave in such a way that it certainly does not slow down the official lust for sanction. In other words: people who ride motorcycles in such a way that they can hardly be described as antisocial idiots certainly do not contribute to the relaxation of a conflict that exists everywhere in this way. Here are those who do something they enjoy doing, there those who claim, not entirely wrongly, that they are doing it at the expense of the general public. It’s nice when the smell of sausages, music and the chattering of children waft through the garden while barbecuing on Saturdays. It is also nice to accelerate out of this long left-hand bend down in the valley almost at full throttle, briefly up into the third, already on the brakes, second, next bend. And everything louder than the chatter of the children in the garden. That makes the grill pissed off. And the? Roasting animal carcass pieces in sausage form or marinade makes the neighbors crazy, not to mention the screaming of the little ones. Everyone somehow gets on somebody’s nuts, and everyone somehow gets on somebody’s nuts. The earth is too small for so many people with leaf blowers, chainsaws, jackhammers, pianos, violins, voices, cars, motorcycles. One suggestion: arbitrarily choose and kill two thirds of humanity. But don’t shoot! That would be too loud.

Another proposal, easier to justify ethically and morally, but more difficult to implement from a purely procedural point of view: We all remember a prominent representative of the Enlightenment, Immanuel Kant, and his maxim, which is simple in its wording, according to which the freedom of the one ends where that of the one others begin. That sounds smart. Would be great, a great plan. If not some were petty and the others ignorant. This is not how the enlightened works according to Kant. The only solution that remains is the destruction of a large part of humanity.

Or Euro 5, 6, 7, soundproof windows, motorcycles that sound like clogged vacuum cleaners, working groups that scream so incessantly and loudly for traffic calming that it only rings in the ears of everyone and makes you wish you were deaf, just that you did Don’t have to hear screaming anymore. What nonsense, what crap. But it is probably too much to ask for some to understand that they are not alone in the world and the others too. Loud: is out. And quiet ’: sucks.

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