I fit the taper rollers to my stem by turning down the stem in a lathe after assembly. When I first made my stems I had the machine shop fit up two stems with a smaller diameter stem so I could fit metric taper rollers. I made my own headstock to fit the taper roller bearings, but when David Tompkins had a problem with his steering head lower bearing, I loaned him one of my taper roller stems.
I don't think there is any difference in the "feel." The "feel" was totally changed by the very fast steering of the 18" wheels and low-profile tires. I also changed the rake of the racers from the stock 30 degrees down to about 25 degrees. Finally, the trail is shortened a bit simply because it is easier to turn up a concentric rather than an eccentric. These mods make the "feel" pretty spectacular and tend to overwhelm whatever minor difference the taper rollers make.
I broke a lower race in my racer and designed the new stem to take a taper roller because I needed the reliability of the taper roller bearing. This helped David Tompkins because ultimately, He modified my stock fat stem by putting the stem in the lathe and turning it down for the metric taper roller. By using the metric taper roller, he had room to make a shim for the top race so the metric taper roller would fit the stock headstock. The shim worked fine on the top race because it is the bottom bearing that takes all the pounding.
I do not feel this is a design issue. I think the cause of the problem is poorly shaped bearing pockets on the lower bearing that allows some movement. Over the years, some bearing pockets are abused to the point that they become unreliable for racing. It is just the luck of the draw. Some stock bearings work fine.
The silver stem on the left is a stock 1-1/8 diameter stem and the one on the right is a 21mm diameter stem.
David
