My SS bike is pretty damn loud. However I continually check with a Db app on my phone and other high grade decibel reading equipment. It is very loud but still way under
j2825 standards.
That is the only reading they can use to regulate noise.
Most SS exhausts are made to be under this regulation.
Harly's are the ones who should worry.
Why do you think j2825 the only thing they could use? It makes sense to use it, but the city can make up whatever rules and associated test they feel like.
As far as most ss exhausts being made to be under the limit, any stock exhaust I have seen was way under, most aftermarket GP exhausts or with baffle removed are over. A standard full size aftermarket exhaust with baffles should pass.