The Wunderlich exhaust deflector »GONZZOO«

We always keep an open ear for our customers. Of course, this also applies to the riders of the BMW R 1250 GS and R 1200 GS LC, which are undoubtedly some of the best all-round motorcycles that money can currently buy.

One point that is always a topic of discussion is the clearly perceptible, low-frequency drone of both GS, which is particularly noticeable in part-load and full-load operation at speeds between 80 and 130 km/h. However, this is exactly the speed range in which most riders ride on the road. Or the range you can avoid the least. Some riders report that the noise can cause discomfort on longer trips.

This was the reason for our developers to investigate the phenomenon - which we knew from our own experience - in engineering terms, in order to subsequently develop a functional solution that reduces and minimizes the effect.

The phenomenon and its cause


During test rides, we were able to identify the resonance chamber, which is roughly formed by the inside of the cases and the entire rear wheel arch, as the source of the noise. The right mounted silencer also protrudes into this space. The resonance chamber turns out to be the sound source because of its geometry, volume and the materials (and their acoustic reflection behavior) that bound it. Accordingly, it is not primarily mechanical vibrations but rather the sound pressure escaping directly from the exhaust that stimulates the described chamber to resonate. This resonance chamber acts like a mechanical amplifier. It is the cause of the droning noise.

After this realization, it was also clear why the noise was particularly noticeable in the partial-load and full-load ranges: these are the operating conditions in which the sound pressure level of the exhaust is physically at its highest.

The aim was therefore to eliminate the resonance chamber described above as the source of the noise. This could only be achieved if the sound pressure and the exhaust gas flow from the silencer were diverted or deflected. We have ruled out a conventional sound insulation - because it was not practicable.

Wunderlich exhaust deflector »GONZZOO«

With this knowledge in mind, our developers considered a deflector solution right from the start. The deflector had to be designed to deflect or shield the sound pressure in a targeted manner so that it would not reach the resonance chamber at all and cause it to drone. This defined the primary requirements of the specifications:

  • The redirection of the sound pressure was to ensure significant noise reduction at head height of the rider and passenger.
  • The shielding upwards and to the side was to have the additional positive effect that the sound waves are radiated downwards and to the rear and are therefore perceived as less loud. 
  • In the subjective perception when passing the GS, a significant noise reduction should be achieved - depending on the free field conditions.
  • The deflector should shield the heat radiation of the exhaust gas stream in such a way that the heating of the right-hand case and the case contents is noticeably reduced.

In addition to the challenges posed by the demanding primary requirements, our developers paid particular attention to further general conditions. After all, only those who unprofessionally manipulate the exhaust system risk invalidating the operating permit. For this reason, the specifications included further technical requirements of essential importance:

  • The exhaust deflector should recieve a type approval certificate (EEC).
  • The solution should not affect the engine performance, especially not negatively, i.e. it should not change the backpressure in the exhaust system compared to the series production.
  • The solution should be simple and effective, especially when riding with mounted cases.
  • The solution should be flexible and small in terms of geometry.

With our now presented exhaust deflector »GONZZOO« we have fulfilled all mentioned requirements. It is model specific designed, to fit the BMW R 1250 GS + Adventure as well as the BMW R 1200 GS LC + Adventure.

The »GONZZOO« – efficient, ingeniously designed and with type approval certificate (EEC)

The deflector »GONZZOO« efficiently reduces the specific drone of the GS described above. And it reduces the noise pollution for the environment. Thus, it complies with the in-house sustainability initiative Wunderlich BLAU. The »GONZZOO« is remarkable because we have managed, to reduce it to the bare essentials at the same time. In doing so, it is easy to misjudge the physical and engineering know-how that goes into it. After all, the extensive preliminary tests for the development of the effective deflector were time-consuming. .

TÜV Rheinland (German Technical Inspection Association) carried out its own series of measurements on the deflector following our measurements as part of the technical tests for the granting of the type approval certificate (EEC). These extensive measurements prove that the limit values of the sound pressure levels of the original exhaust system are not changed. The administrative act at the KBA has been successfully completed and thus the GONZZOO is available for the BMW R 1250 GS (incl. Adventure) and the BMW R 1200 GS LC (incl. Adventure) with German type approval certificate.

Always ready for action: the »GONZZOO« is compact and easy to stow away

A big advantage is that the »GONZZOO« is small and easy to stow away and always have with you. So you can mount or dismount it on the road at any time thanks to the spring clamps and use it flexibly everywhere (Slip-on)!