Some strollers can be easily converted into two wheel mode whenever traveling over rough ground or terrain. (strollerdiva.com)
It had the world's first drive system that could be conveniently shifted in and out of four - wheel mode by working a control lever in the cab. (auto.howstuffworks.com)
If you want something more for running, you will be interested in the Bumbleride Speed, with 3 different front wheel modes for your workout. (stroller-envy.com)