I just received a second HAC4 handlebar mount for 31.8 bars. It seems to secure via a rubber O ring and not hold very snug. I'm afraid the O ring will snap or tear or just wear away over time. Anyone else have this set up? Any suggestions? The original clamp for my 26 bar has held secure without incident for years.

For the version that has the cadence sensor option (I have this setup-which in the HAC4 booklet doesn't show), you do have to use the O-rings...That said there should be an adhesive patch to get it to stick also, but I wouldn't trust it alone...in my HAC4 box there were 3 'rings included; for my ITM 26mm bars I had to use the middle size ring, I think. By the way did you try both stops on the mount?-there should be two tabs on one side of the mounting to hold the rings, so you can have more pull-I had to use the second one.

If the above fails try mounting over something (bar-tape...rubber strips...)

those o-rings are pretty tough, though such things can degrade to UV, but (I guess) the good thing is that if you can find out what size (and grade) you need, o-rings are easy to find.

good luck

ps anyone -why can't the ciclo people make an easy to understand manual in english?

I used a couple zip-ties and wrapped them around the outside plastic flanges; though the O-rings did hold it no problem for months. Really don't trust those O-rings though. =)