As a motorbike track day enthusiast and rider myself, I have friends regularly asking me for advice when it comes to what is the maximum sound level their bike exhaust noise level can be.
When I reply with the question, ‘what circuit are you racing at?’ they seem surprised that this is relevant and that I was unable to provide them with a simple dB Level!
A circuit has individual noise levels in force depending on their surrounding environment; these considerations can include how close they are, for example, to residential properties, a hospital or a school. The decision of what this noise level will be is based on calculations on the levels coming from the track and how the noise propagates to these properties.
Circuits do not enforce levels just to spoil the fun of those wishing to enjoy the track. They will be enforcing noise limits to try to reduce as much as possible the environmental impact of their activities and to reduce the number of complaints from local residents. These limits are in place to protect the surrounding residents from intrusive noise. If a circuit continues to be a problem for local residents, there is a risk that the number of track days available to you and me could be reduced, or worse stopped completely.
To try and ensure the noise levels out on track do not breach the limits, you will normally have to be ‘noise tested’ in attempt to prevent any complaints.
This is sometimes referred to as a ‘static’ noise test as you are stationary and would usually be carried out after your safety briefing and before you are let out onto the track.
This test will be carried out in a designated part of the paddock. You will be tested in neutral gear and asked to hold you throttle open at around 2/3rds rpm. You will be told the actual rpm as this varies depending on the type of engine you have and will be different for different types of bike. You can ask your event organiser what rpm you will be tested at and what the dB limit is for your bike for a particular day as they will know.
There are some venues that have noise monitors around the siteconstantly monitoring the noise levels while you are out on track, so it is not advisable to tune your engine to have a ‘quite spot’ just for the static test if it’s a lot louder on track. It’s also not a good idea to take your baffle out or change your exhaust after the static noise test. It is quite likely that you will be spotted and possibly asked to leave the event.
Here are helpful pointers to consider:
1) Check with the venue, organiser of the race event or track day as they will know the level you will be tested at.
2) Note that just because it was a set level last time you were there; it may be different the next time you visit.
3) If you have access to a sound level meter, test your vehicle before visiting to save any disappointment.
4) Test your exhaust using the guidelines in the latest ACU (Auto Cycle Union) or MSA (Motor Sport Association) hand book. .
- Hold the instrument as advised as this can vary your reading considerably.
- Use a windshield (this is not an obvious requirement in some guidelines)
- Do not do your test in your garage or on your driveway if you have a façade or wall close by as this will give you a higher reading.
- Try and be considerate when doing this test as it can sound very loud in a built up area.
- If you have access to an acoustic calibrator, use it. This way you can check your meter is working properly.
5) If you are on a track day and are not an experienced racer, the chances are that having the baffle in or a quieter exhaust system will not actually alter the performance of your bike to a degree that you can notice. If you do find that there is a considerable drop in performance, it may be worth getting your engine re-mapped or tuned to suite the exhaust.
6) If you are a racer and are lucky enough to have enough money to buy a new race exhaust system, many new systems do consider noise without losing performance.
One last important point that has resulted in many a disappointed rider being sent home is the misunderstanding that just because that an exhausts noise level is ‘road legal’, it does not mean that it will necessarily be suitable for every circuit.
Remember my point at the beginning. The noise levels limits that a circuit will use are determined by the environment in which they are situated and the type of events that they run, so if they are close to sensitive buildings or houses they may need to impose levels lower than those for a road legal exhaust.
The noise limits that a circuit will work to will usually be imposed and monitored by the appropriate local authority (usually the local council). As these bodies are responsible for dealing with noise complaints, they are the empowered to impose noise limits and to possibly restrict the activities of the circuit if these limits are not kept to.
Remember that a loud bike riding round and round a track really fast is going to be more annoying to local residents than the same bike riding past a house, once!
If you require a pdf of the correct positioning of your microphone, you can contact me using the form on this page. Please put in your message “Exhaust noise blog”.
If you have any questions, please let me know!