Sunday Mystery: where did this grommet come from?

[GothicCastle]

Not really a weight weenie concern, but thought I'd tap into the forum's vast collective wisdom.

Was just rinsing off a bike and this fell off. It is flexible rubber. Fingers shown for scale. It is split, but I suspect it wasn't supposed to be (and why it fell off something). I was thinking that it might have been sealing housing somewhere, but I don't remember doing that when I put the bike together.

Any ideas?






The bike is a Cinelli Nemo Tig

• Dura Ace 9100
  Reynolds wheels
  Zipp cockpit / post

[TobinHatesYou]

Might just be a damping o-ring placed between a bottle cage and its bosses.

[Calnago]

You don’t have newish Campy wheels by chance do you? They use those o-rings in the little valve nuts that screw on to their valve extenders. They fit into a little groove of the nut but they don’t come already installed in that groove. I’ve seen some wheels where the person didn’t know where they were supposed to go and just placed them between the nut and the rim itself. If yours was like that I could easily see it breaking and falling off. If so, you’ve possibly got a valve extender that may be clanging against the rim. I’ve also seen them used around brake housings or derailleur housings just to help keep the entire housing from rubbing on the paint. Does the same thing as the rubber “bumpers” that you used to fit on derailleur/brake cables that weren’t enclosed in housing as they were externally routed between stops on the frame. Or, it could be from something completely different but without seeing your bike those would be my two first guesses.

[LouisN]

Did you put air with a Co2 cartridge "head" ?
They sometimes "blow" this litlle gasket out and it lands around the valve.

Louis

[TobinHatesYou]

Or if he were running tubeless, sometimes there's an o-ring under the valve nut

[spdntrxi]

Or if he were running tubeless, sometimes there's an o-ring under the valve nut

this gets my vote if tubeless

[GothicCastle]

These are all excellent guesses.

I had thought about a bottle cage nut, as well. This bike has supacaz fly cages on it, but I don't remember a grommit coming with them or the stock Cinelli bolts.

The bike isn't tubeless; GP 4000's with latex tubes (no extenders). The wheels are older Reynolds Assaults. I do have the Silca Speed Shields on these wheels; maybe it was on one of these.

It is entirely possible that it was on the valve and that I didn't notice it.

[Calnago]

Running Shimano? Check your brake adjuster nuts. They use o-rings to keep the nuts from falling out when there’s no cable attached.

[Alex2012]

Running EE Brakes?

[spdntrxi]

These are all excellent guesses.

I had thought about a bottle cage nut, as well. This bike has supacaz fly cages on it, but I don't remember a grommit coming with them or the stock Cinelli bolts.

The bike isn't tubeless; GP 4000's with latex tubes (no extenders). The wheels are older Reynolds Assaults. I do have the Silca Speed Shields on these wheels; maybe it was on one of these.

It is entirely possible that it was on the valve and that I didn't notice it.

did you buy just the shields or the kit... because that is designed with tubeless in mind.. so you might not use the valves... but didn't notice the oring was still in there.

[GothicCastle]

Running Shimano? Check your brake adjuster nuts. They use o-rings to keep the nuts from falling out when there’s no cable attached.

Yes, 9100 brakes. This is a good possibility.

[GothicCastle]

did you buy just the shields or the kit... because that is designed with tubeless in mind.. so you might not use the valves... but didn't notice the oring was still in there.

Just the shields. I'm not confident in these rims running tubeless.

[jfranci3]

what pedals?

[GothicCastle]

Speedplay zero pedals. The dust caps look intact.

[LouisN]

Maybe your bike's cheating on you....

LOuis