Exhaust noise is regulated twice, by two governments, using two different mechanisms. The federal rule caps what a street motorcycle may emit when new and makes it unlawful to defeat that — 80 dBA for street machines from the 1986 model year onward. State rules cap what the machine may emit on the road today and generally prohibit modifying the system to make it louder. A slip-on that is legal to sell is not automatically legal to fit, and the label on the can usually tells you which situation you are in. Checked August 2026; state noise provisions vary and are amended, so read your own vehicle code before buying anything.
The federal layer, and the number everything else is built around
The EPA regulates motorcycle noise under the Noise Control Act, in 40 CFR part 205. Section 205.152 sets the standards by model year: street motorcycles other than moped-type machines must not exceed 83 dBA from the 1983 model year and 80 dBA from the 1986 model year onward. Moped-type street motorcycles are held to 70 dBA from 1983. Off-road machines of 170 cc and below run to the same 83 then 80 dBA schedule, while larger off-road machines are held to 86 dBA from 1983 and 82 dBA from 1986.
Those numbers are measured by a specified federal test procedure at a specified engine speed, which is why a roadside meter reading cannot be compared against them directly. What the federal rule really gives a rider is not a number to hit but a definition and a label.
The definition is tampering, set out in part 205's definitions as the removal or rendering inoperative, other than for maintenance, repair or replacement, of any device or element of design incorporated into a product in compliance with the regulations — either before sale or while the machine is in use — or the use of a product after such a device has been removed or rendered inoperative by anyone.
Note what that covers. It is not only the act of removing the baffle. It is also riding the machine afterwards, and it applies whether you did the removing or the previous owner did.
Read the label, because the label is written to tell you
Federal regulation prescribes the exact wording of several labels, and the wording is unusually direct. This is the most useful practical tool in the whole subject.
The vehicle label placed by the manufacturer must state the model year, model code, serial number, the noise emission standard in dBA and the closing rpm, followed by: "Modifications which cause this motorcycle to exceed Federal noise standards are prohibited by Federal law. See owner's manual." It must be affixed so it cannot be removed without destroying or defacing it, and it must not be attached to any easily detached piece of equipment.
The exhaust system label is prescribed by section 205.169, which requires the manufacturer to affix a permanent legible label at the time of manufacture to all exhaust systems distributed in commerce. A compliant system reads: "This (manufacturer's name) exhaust system (serial number) meets EPA noise emission requirements of (noise emission standard) dBA for the following motorcycles: (list of model specific codes). Installation of this exhaust system on motorcycle models not specified may violate Federal law."
That single sentence answers the question most riders never think to ask. A legal aftermarket system is legal for listed models. Fitting it to a machine that is not on the list is a different matter, even though the box carries a compliance label.
And then there is the label that tells you exactly what you are buying: "This product is designed for use on closed course competition motorcycles only and does not conform to U.S. EPA noise emission standards. Used on motorcycles subject to EPA noise regulations constitutes tampering and is a violation of Federal law unless it can be shown that such use does not cause the motorcycle to exceed applicable Federal standards." A separate prescribed variant covers systems sold for pre-1982 model year machines only.
If the can you are looking at carries that competition wording, nothing about the purchase is ambiguous. The regulation has told you in advance what fitting it to a road bike amounts to.
| Federal (EPA, 40 CFR part 205) | State (vehicle code) | |
|---|---|---|
| What it regulates | The machine and the exhaust system as manufactured and sold, plus tampering with them | The machine as operated on a public road today |
| Headline figure | 80 dBA for street motorcycles from the 1986 model year, by federal test procedure | California VC 27202 sets 80 dbA for motorcycles manufactured after 1985, 83 for 1975 to 1985 |
| Main prohibition | Tampering — removing or defeating a noise control element, or using the product afterwards | Operating without an adequate muffler, and modifying the system to amplify noise |
| Cutouts and bypasses | Covered by the tampering definition | California VC 27150 prohibits a cutout, bypass or similar device outright |
| Enforcement point | Manufacture, importation and distribution, plus tampering | Roadside stop, inspection, and registration or transfer in some states |
| Evidence available to you | The prescribed labels on the machine and the exhaust system | The visible presence of a muffler and, in some states, a meter reading |
The state layer, and one detail people misquote constantly
California Vehicle Code section 27150 requires every registered motor vehicle with an internal combustion engine to be equipped at all times with an adequate muffler in constant operation and properly maintained to prevent excessive or unusual noise, and prohibits any muffler or exhaust system fitted with a cutout, bypass or similar device.
Section 27151 then prohibits modifying an exhaust system in a manner that amplifies or increases the noise so that the vehicle no longer complies with section 27150 or exceeds the noise limits for its vehicle type, and separately prohibits operating a vehicle with a system so modified.
Here is the detail that gets misquoted. Section 27151 contains a 95 dbA figure, and it is frequently cited as the motorcycle limit. Read the subsection: it applies to exhaust systems installed on motor vehicles with a manufacturer's gross vehicle weight rating of less than 6,000 pounds, other than motorcycles. Motorcycles are expressly outside it. The applicable motorcycle figures are in section 27202, which sets 88 dbA for machines manufactured after 1969 and before 1973, 86 dbA for 1973 and 1974, 83 dbA for 1975 through 1985, and 80 dbA for machines manufactured after 1985.
Most states have equivalents of all three provisions — an adequate muffler requirement, an anti-amplification requirement, and a schedule of limits by manufacture year. Searching your own code for "muffler" will usually land you on all of them in one article.
How to decide about a slip-on without guessing
- Read the label on the can before the review. A compliant system names the models it is approved for. A competition system says so in prescribed federal wording. There is no third category that is quietly fine.
- Check your specific model is on the list. The label language exists precisely because a system approved for one machine is not approved for all of them.
- Do not remove a baffle to "get the sound". That is the textbook example of rendering a noise control element inoperative, and the tampering definition captures riding the bike afterwards as well as the removal itself.
- Keep the original system. Registration transfers, out-of-state moves and inspections are where a loud exhaust becomes an obstacle rather than an annoyance — the transfer process is in registration and title basics.
- Check the vehicle label at the headstock is intact. It carries the machine's own standard and rpm and must be permanently affixed; a missing one raises questions you will not enjoy answering.
- Treat any state meter-based limit as the operating ceiling and remember the federal figures come from a fixed test procedure, not a kerbside reading.
The trade-off, stated honestly rather than piously: a good aftermarket system can genuinely reduce weight and improve throttle response, and the ones that do both while carrying a proper EPA label exist and are not hard to find. What is not available is a legal path to a machine that is dramatically louder than stock. Riders who want the noise are choosing to be non-compliant, and the cost is not usually the citation — it is being the reason a neighbourhood pushes for a noise ordinance, and being the bike an officer notices when everything else on your machine is fine. What that stop involves is in what happens at a motorcycle traffic stop, and the other items likely to be looked at while you are stationary are in motorcycle equipment laws. Anything involving fuel delivery or the catalyst alongside an exhaust change should go to a technician who can check fuelling afterwards, not be finished on the driveway.
If your reason for a louder pipe is being seen rather than heard, the evidence is better served elsewhere. A recording camera such as the zinc-alloy motorcycle camera does more for a disputed junction collision than any exhaust ever has, and it does not put your registration renewal at risk. Riders still working through the licensing sequence will find it in how to get a motorcycle licence in the US.
Frequently asked questions
What is the legal decibel limit for a motorcycle?
Federally, a street motorcycle from the 1986 model year onward must not exceed 80 dBA when tested by the federal procedure, per 40 CFR 205.152. States set their own operating limits — California's section 27202 gives 80 dbA for machines manufactured after 1985 and 83 dbA for 1975 through 1985. The federal and state figures are measured differently and are not interchangeable.
Are aftermarket exhausts illegal?
Not as a category. Federal regulation requires a compliant aftermarket system to carry a label naming the models it meets the standard for, and warns that installation on models not specified may violate federal law. The illegal cases are competition-only systems fitted to road bikes, and any modification that increases noise beyond the applicable limit.
Is removing the baffle from my exhaust illegal?
It fits the federal definition of tampering — rendering inoperative a device or element of design incorporated in compliance with the regulations — and that definition also covers using the machine afterwards. Most state codes independently prohibit modifying an exhaust system so as to amplify or increase noise.
Does the 95 dBA figure apply to motorcycles in California?
No. The 95 dbA test figure in Vehicle Code section 27151 applies to vehicles under 6,000 pounds gross vehicle weight rating other than motorcycles. Motorcycles fall under section 27202, which sets limits by year of manufacture, ending at 80 dbA for machines built after 1985.
How do I tell whether an exhaust is street legal before buying?
Read the prescribed label. A compliant system states that it meets EPA noise emission requirements at a stated dBA for a listed set of models. A competition system states that it does not conform to EPA noise emission standards and that use on a regulated motorcycle constitutes tampering. The regulation writes both sentences for you.
