QuickSpeed is a barebones, simple to use speedometer/odometer (iPhone only), for bicycling. It is completely free, with no in-app purchases required for full funtionality. Save or load your favorite routes with .gpx exporter/importer feature. Get true elevation changes and elevation profile via USGS. Retro mode with analog speedometer and odometer.
Continued use of GPS running in the background can dramatically decrease battery life.