Is a V-brake lever (specifically the Avid Speed Dial 5) compatible with a side-pull road brake (specifically the Colnago X brake)? The bike is being converted from track bar (bar-end brake levers) to flat bar.
In general, V brake levers are not compatible with sidepull brakes because of different mechanical advantage. Avid Speed Dials have adjustable mechanical advantage, so you might be able to adjust them for sidepulls.
You shouldn't, but it might work. V-brake levers work for mountain disc brakes and v-brakes. Everything else needs a short pull lever.
As in the answer to this question, some people claim Avid brakes have enough adjustment to make it work. The better solution is to buy a standard pull brake lever (look for one marked for cantilever brakes for example), or use a travel agent with the V-brake (long pull) levers.