I have the Sigma Cuberider rear blinky:

http://www.sigmasport.de/us/produkte/beleuchtung/standard_lights/cuberider/?flash=1&punkt=features

It is mounted to my seatpost (typical size, 27.2mm) with Sigma's "tool-less" mounting bracket, which involves a little rubber strap that is extremely tight when mounted and is hard to imagine would move. But it shifts position very easily when I'm on anything but the smoothest of roads.

Has anyone with this light encountered this and have any workarounds? I'm thinking of giving up on it and getting a PB SuperFlash.

Thanks,

Scott

IIRC it comes with two different sized O-rings. Try the smaller one.

Use a small peace of double sided tape between the seat post and mount. Just a little will do.

Thanks for the replies. I'll give the double sided tape a try. Getting the large O-ring to attach is enough of a struggle - I don't think it would even be possible to use the smaller one.