Originally Posted by
sreten
Hi,
...If the clamp fully tightens against itself without holding the bars,
file away the material in the gap where the clamp meets itself.
This won't fix a wrongly fitting clamp for the bars....
This shouldn't be the issue here, since the OP flipped the same handlebar that had always been there.
Originally Posted by
RandomTroll
Hmmmm... I don't have any of those: how do you know? You like grit: what about adding a piece of aluminum can to shim instead?
If the issue is traction, and not one of fit, (which it shouldn't be since it's the same bar as always) adding another layer can't help unless it's one with higher friction properties. Moreover the added thickness would now mean an incorrect match in the diameters of bar and stem.
Shims are for to match size, traction compound is to improve grip. Neither can do the other's job.