A time trial bicycle is very similar to a triathlon bicycle. In fact, because the market for time trial frames is so small, many manufacturers are currently making triathlon bikes that are adjustable enough that they can be set up in such a way that they are legal to ride in UCI events. The main differences are that a triathlon bicycle will sometimes have a steeper seat tube angle (and thus a more forward saddle position), which places less stress on the hamstring leg muscles, thereby saving strength in the hamstrings for the run which follows the bike portion of the race. Several frames come with a seat post that when installed one way, give the UCI required 5 cm distance from the saddle nose to the center of the bottom bracket and when installed the other way gives a better tri geometry some triathlon frames do not meet the strict rules governing the design and overall shape of bicycle frames specified by the UCI and adopted by USCF for use in sanctioned event. The bike leg of a triathlon may be hilly and long (112 miles in the Ironman), and so the higher gearing, higher weight, and less comfort mentioned above for time trial bikes may not apply to a triathlon bike.