Mine works perfectly on the front wheel (road bike). The distance from the rear wheel to the handlebars is probably too great. I haven't tried it but I have a slightly older, identical Sigma on a road bike mounted on a roller on the rear wheel and it doesn't work. As a solution, I removed the display from the handlebars and attached it to the centre of the top tube with cable ties. This shortens the distance and works well.

Mine doesn't even work on the front wheel!