I recently got a compact crank for my wifeís road bike, a Shimano FC-4550 (Tiagra level) 50/34. This is specifically labeled a nine-speed crankset. Now we are looking at getting her a 10 speed triathlon bike, but the crankset on it is a 53/39. I would love to put the original triple back on the old road bike and move the new compact to the Tri bike and just sell the 53/39, but will a 9 speed Tiagra compact work with the new 10 speed drivetrain or am going to need to pick up another crankset? I didnít know if there was something to be concerned about with the chainring spacing or chain widths. I know 10 speed chains are narrower than their 9 speed counterparts. Since this will be a racing bike, itís important that it run smoothly.