Hey guys. Here is my question. I have an old french track frame, late 70's, so everything is a little off. The stem is 21.1 and there is no conversion for a thread-less headset that I am aware of for this measurement. To make a long story short, there are few stems produced for this size, and I was unable to find one that drops down, so I have a new goal. I currently just converted my stock handlebars into bullhorns, but I am looking to extend them a touch. Does anyone know of any bullhorns produced that extend at the stem then go into the traditional bullhorn shape?
The problem is I am yet to find a conversion such as that which is 21.1, and I have been led to believe by a few bike shops that because 21.1 is such a rare stem size, (only used in French track bikes in the late 70's early 80's), it does not exist. So I am stuck with choosing between a very select group of stems which are 21.1, none of which extend very far.
French stems differ both in the size that fits into the steerer, and the size of the part that clamps on to the handlebar. Thus, if you want to replace the handlebars on a French bicycle, you will probably also need to replace the stem.
French stems are .2mm narrower where they fit into the steering column. A standard 7/8" / 22.2mm stem won't usually fit. In many cases, the limiting factor for fitting the stem in will be the headset locknut, rather than the steerer itself. Try removing the locknut before sanding down a stem. If the headset locknut is slightly tighter than the steerer, it can be enlarged easily with a small grinding wheel.
In cases where the stem really won't fit into the steerer, a few minutes work on the stem with sandpaper will usually do the trick. Wrap the sandpaper around the stem, grip it with your hand, and turn the stem round and round until it fits. You only need to remove 0.1 mm, which is 1/250", not much at all!
If you convert from a French stem to a standard one, you will also need to replace the handlebars, which are a different diameter.