Came across something really perplexing while checking out cranks today. On the Harris site it says that Tiagra triple cranks take a "113 mm UN53" bottom bracket, while the 105 & Ultegra triples take an "Octalink V1 Splined Bottom Bracket 118 mm". Does this mean that the Tiagra cranks are 5mm narrower & may be better for people like me who have dodgy knees???