Ok I love the 1R but it doesn't clamp down the handle bar. I was at a bumpy trail today. Every time I hit a bump, my handle bar rotated forward or backward. What is your trick to clamp the bar down on the 1R stem? Look at the picture below, it was bad. I am about to change it out to a 3ttt stem and bar.

Are you sure that your bar size is the same as the clamp size? That's the only reason I could see this happening.

Do you have a Cinelli bar in the stem?....because I thought that pre-1996 Cinelli bars are a little (26.4mm instead of 26??) bit bigger in diameter than other brands, so if you have a different brand bar in the stem, it might be too small for the stem to grip on it adequately. Or you might also have an older 26.4mm Cinelli stem combined with a newer 26mm Cinelli bar.

Chombi

I forgot to mention the bar is Cinelli Giro 26.4mm.

slip a sliver of a beer can inbetween the clamp and the bar.

+1

Also check the binder bolt to make sure there isnt a burr or damaged thread. Could be you tighten the bolt and its not really tightening on the bars. Had this happen once. It was maddening until I removed the bolt and inspected it.

Lube the bolt threads too, maybe?

Level your saddle so you're not doing a continuous push-up to prevent your butt from sliding forward.

It looks about my size... Send it my way and I will send you a bike with bars that don't slip.