How to Measure a Motorcycle Exhaust

Written by alexander poirier
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How to Measure a Motorcycle Exhaust
Measuring the noise level of your motorcycle's exhaust will ensure that your motorcycle is not in violation of the federal noise law. (Motorcycle exhaust image by Crisps85 from

By federal law, a motorcycle's exhaust cannot "exceed a noise level of 84 decibels when travelling more than 35mph on a paved street or highway." Any motorcycle whose exhaust exceeds this amount of noise is subject to citation and a fine. Because of this, it is important to check the noise level of your motorcycle's exhaust to ensure it does not exceed the designated federal noise level. Luckily, this can be done with a few tools in a matter of minutes.

Skill level:

Things you need

  • Type 1, Type S1A, Type 2, or Type S2A sound level meter
  • Sound level calibrator
  • Tachometer
  • Assistant

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  1. 1

    Park the motorcycle on a flat, even, solid surface. The location should be quiet and should not have any obstructions that could reflect the sound coming from the motorcycle exhaust -- this includes walls, cars and signs.

  2. 2

    Turn on the sound level meter and the sound level calibrator. Aim the calibrator towards the sound level meter's microphone. The calibrator will emit a specific frequency, indicated somewhere on the calibrator. The sound level meter will then calibrate using this frequency. If the sound level meter fails to display the correct frequency, contact the meter's manufacturer for repair instructions.

  3. 3

    Connect the tachometer to the motorcycle per the instructions that came with it.

  4. 4

    Position the rider so that he is straddling the motorcycle seat with both of his feet touching the ground, in normal riding position.

  5. 5

    Position the sound level meter exactly 20 inches behind and at the same height as the motorcycle's exhaust. The microphone must also be parallel to the ground and positioned at a 45 degree angle when compared to the motorcycle's normal line of travel.

  6. 6

    Place the motorcycle's gears into the neutral position. Have the rider run the engine at 35mph, displayed on the tachometer.

  7. 7

    Record the decibel output of the exhaust at 35mph. If it exceeds 84 decibels, the motorcycle's exhaust is in violation of the federal noise law.

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