I use a Garmin 1000 on 5 different bikes. I have a speed sensor on my plastic road bike, as I often ride in a group where being able to maintain a constant and steady speed is important. A speed sensor in that scenario lends to more accurate speed indication when using a GPS only has a lag as to the current speed. I also use speed sensors on my mt. bikes, as riding in heavily wooded area's or when riding on trails that have a lot of tight and twisty turns, lends to a more accurate distance track. I do not have or need sensors on the 2 bikes I use for commuting.