Britax Marathon Convertible Car Seat The standard length for a marathon is 26.2 miles. The Britax Marathon Convertible Car Seat will cover more than 100 times that distance. This durable, long lasting convertible car seat is one the most functional seats to ever hit the market. A little bit larger than other Britax Car Seats, the Marathon is legendary for safety and comfort. Since the shell of the Britax Marathon is a little bit bulkier than others, parents should allow about 31 inches of seat space when used rear facing. Some of the unique features of the Marathon Convertible Car Seat include a five point polyester harness with no tangle polyester webbing, built in lock-offs and a push button LATCH system with Versa-Tether. The Versa-Tether provides the most security in both forward and rear facing installations. Now, the Marathon has Expanded PolyStyrene (EPS) to increase available shoulder width room. EPS foam also adds helps to soften a blow to the head in case of a collision. The patented HUGS System is designed to better distrube webbing loads to reduce head movement and minimize the chance for the webbings edge to load on the child's neck. The Britax Marathon provides parents with an all around all-star car seat. It is the reason that parents have stayed faithful to Britax for more than 30 years.