Two brothers for my ST1100

So I bought a set of used Two Brothers C-Sireis Aluminum mufflers from a member. Good condition great price. Less than an hour to install. The only comment I have is that the left onee will interfer with the axel removeal.

These TB's have a great tone (very deep) and are relatively tame at 4000 rpm crusing down the high. They do bark however when you get on it. But that sounds great too. Ear plugs are in order as always.


I did some tesitng with a sound pressure meter before and after with. The bike was in my driveway and i was standing 10 feet behind and 10 feet to the side. I am not sure why this shifts and messes with the table. But I think you guys can figure this out.

1991 - ST1100 Distance RPM Back Position Side Position
Stock Exhaust -Decibel Reading 10' 1000 71db 72db
55' Height 2000 76db 78db
3000 82db 80db
4000 84db 83db

Two Brothers - Decibel Reading 10' 1000 75db 75 db
55' Height 2000 84db 84db
3000 90db 87db
4000 89db 88db
I thinks yhese are keepers.

Grabcon said:

The only comment I have is that the left onee will interfer with the axel removeal.

Click to expand...

[Carl]: No problemo. Note the springs abetting easy muffler removal. Two springs, one 12 mm bolt, and you're golden.
Only problem I have encountered is the Ess connectors to the collector rusted through. The left one rusted through 5 years ago. Called Two Brothers for replacements and was told "We don't stock parts for bikes that old."

Carl, Thanks for the heads up on that axel removal. I guess I just should have looked a little closer.

So the jury is still out on these mufflers. I have some 2500 miles on them since I put them on. They do have a nice sound most of the time.

Things that I do know, they have added no noticeable performance gains. I guess I expected that from the forum comments. I am going to say my mileage has dropped a few miles per gallon. Down to 42 to 43 mpg, but that does not seem to change with 1 or 2 up. I used to be 45 to 47 mpg. But that may be related to my throttle hand movement.

What I really find interesting and this is strictly perception from a rider point of hearing is that air density and elevation make a significant difference in the loudness and the tones I hear as a rider. The denser the air and the higher in elevation the louder and deeper the tones get, almost to the point of unbearable even with earplugs. Hot dry days are wonderful damp days are okay at normal elevation which for me is 5280 to 6800 feet. Anything higher than 9500 feet things get real tough with dense air.

So for all of you scientists out there you will probably tell me that this has to do with the Doppler Affect. So it would be interesting to hear the scientific thoughts on this. Although remember it is my perception, nothing measured.

I just bought an ST1100 with the Two Brothers mufflers and it is louder than I care for. Sounds like a Cummins diesel pickup without mufflers. Anyone on here try putting the silencers on?