The trek fx s 5 hybrid bike 2018 put simply means fitness offering a best of both worlds combination of road bike speed and city bike comfort making it the ideal fitness bike with an added edge fast fun and agile enough for a multitude of uses from fitness and commuting to errands and mellow sunday loops featuring an isospeed decoupler the 400 series oclv carbon frame of the trek fx s produces an incredible smooth ride by allowing the seat tube to rotate independantly