UK MOT/exhaust question

I read the MOT requirements in the UK for motos and I find the exhaust "check" to be a bit confusing. It says,

"The exhaust system and silencer should be in such condition, or of such a type, that the noise emitted from the motorcycle isn't clearly unreasonably above the level expected from a similar motorcycle with a standard silencer in average condition."

What the heck does that mean in real life? Obviously , a dB spec at X distance is a more-or-less repeatable and objective. The statement in the MOT reg sounds almost totally SUBjective, on the part of the inspector. IOW, one inspector might call a specific muff OK and another say that it is not. Is that the case?

Of course, a rider could just install the OEM muff for the MOT and put the louder one back on after passing. Is that what is commonly done?

It means you get away with the subjective opinion of the tester, Harleys and classics seem to get away with louder exhausts than other but 100 yds down the road the Police can form a different opinion and the valid MOT is useless. Silencer swapping is common.

Yes it is subjective, totally, but bear in mind that very few testing stations have a place for running drive by noise tests, and consider what the cost, to you, that would be.

So the assessment is mainly done indoors! In the test area, with whatever other noise is going on in the workshop for background.

Also consider that, as continual noise testing for race track use illustrates; you cannot rely on db levels from the same motorcycle measured by the same noise test equipment giving the same result from morning to afternoon let alone all year round between equipment calibrations. Atmospheric conditions have a considerable effect on measured noise, as does background noise level.

Silencer swapping is common in the UK on modern sports bikes, where owners think standard exhaust systems aren't loud enough! So they fit an exhaust which does not have the appropriate British standard marks and revert to the original exhaust one day per year! They also drive a lot of non motorcyclists totally barmy, and often hostile!

On the other hand....with a Norton Commando....MoT testers have been known to have little wee whilst listening to music they rarely get to hear these days!

And on another hand if you have one left!......the 'Controle Technique' MoT test equivalent in France.....is optional for motorcycles....honestly!

So when a piece fell off the rear cylinder exhaust on my road bike last week, I cut the equivalent part off of the front cylinder exhaust to make it even

Are you aware that vehicles over 40 years old no longer require a MOT

Thanks, I wasn't aware of that but it's not about my Norton. I'm thinking of buying a bike in the UK and it would be a fairly recent machine. At the moment we have no place here to keep a bike - no garage and no on-street parking in front of the house - so it's more a thought-exercise than anything else. We are thinking of MAYBE renting/buying a garage nearby but not sure about that yet.

What I have in mind is buying a several year-old Royal Enfield Continental GT and purchasing/installing the necessary mods (from Hitchcocks) to bump the power up to "over the ton" capability. Seems like it would be a fun English back road bike.

But I may get other ideas re a bike for here in a couple of weeks when we're at the IOM for the week of the Manx GP.

Plenty of bikes on the island during The Manx, there are 5 dealers
also on the island.

There are a lot of loud Harleys and modern multis in my town and the authorities seem to care less. My Norton is rather rorty but
as there is no inspection....

I once had an MOT tester tell me my exhaust was much too loud (it was a stock pea shooter setup!!)
It was only after much arguing that he aventualy passed my bike!!

Well, if I do my Continental GT plan, I'll be prepared to reinstall the stock muffler one day a year!