I got a deal on a CF drop bar, and replaced the aluminum ones that came with my bike. I kept my old stem, though, which has a 31.8 mm clamp, while the bars have a 26 mm clamping surface. I'm using shims, partly because I like the stem, and partly to spread the tension over a larger surface, which seems like a good idea for carbon fiber.

The "corners" of the bars have a textured surface, to attach the brake hoods. But the center of the bar is smooth. So, if I'm riding on the hoods, sometimes I'll hit a small bump, and the bars will rotate as much as a few inches. It's a bit scary, and a lot more annoying. Riding the tops or the drops seems to solve the issue, but I like having all three hand positions available.

What should I do to get more friction between the bars and the shim? I was thinking of taking it all apart, and wrapping the center of the bars with electrical tape.