There is a difference between “aftermarket” mufflers and “performance” mufflers.
Aftermarket mufflers are designed in accordance with BMW specifications for mufflers produced after the introduction of new German legislation in the 1950s.
Performance mufflers are designed according to pre-1953 specifications.
Example:
P/N 18124090003 Muffler “Fish tail” – RH – after market
P/N 18124090003RDH Muffler “Fish tail” – RH – for optimal performance
Background:
- Between 1951 and 1953, West Germany introduced more uniform vehicle regulations
- These were incorporated into the Straßenverkehrs-Zulassungs-Ordnung (StVZO)
- Around 1953, stricter requirements for exhaust noise (“Geräuschentwicklung”) were introduced
- Before this (late 1940s / early 1950s):
- Exhaust systems were relatively lightly muffled
- Noise regulations were not strictly enforced
- From around 1953 onwards:
- More effective muffling became required
- Manufacturers had to design quieter exhaust systems
- Noise levels became part of vehicle inspection (TÜV)
There was no legal requirement in Germany to retrofit older motorcycles with newer, quieter exhaust systems after the introduction of stricter noise regulations in the early 1950s.
Motorcycles built before this change were allowed to retain their original exhausts. However, in practice, many were later fitted with the newer (quieter) type, as BMW and its dealers typically supplied replacement parts according to the latest specifications.
As a result, both types can be found on (German) motorcycles from this period.