On the notties to himeville race my SRAM X7 front dérailleur decided to give up the ghost. It would not downshift onto my granny gear, I understand from my Lbs that the springs do weaken overtime so this is not unexpected. Finding a SRAM 3x10 front dérailleur direct mount is virtually impossible ( to fit a specialized epic 29er) as it would seem that SRAM are moving towards 2x10 exclusively. In fact, chain reaction inform me that do not stock SRAM 3x10 in a direct mount configuration anymore. This got me thinking of changing to 2x10 and I tried to simulate the top speed and lowest speed (climbing) of my current set up. I found an interesting link that allows you to compare different chainring and cassette combinations http://home.earthlink.net/~mike.sherman/shift.html. The results surprised me and really questions the move to a 2x10 configuration for the average rider. Top speed - the max size for a chainring that can be accommodated by SRAM is 42t while Shimano gives 44t. The smallest cassette I could find is 11t, so to get the same top speed on my bike by getting a Shimano FD this is achievable. But what is significant (for me) is the difference between a 42t and 44t is 5% in top end. Lowest speed - the key variable here is the maximum delta between the two chainrings which for both manufacturers is 14t. So if I maintain my 44t the smallest the small chain ring can be is 30t which means I cannot simulate the 22t x 32t currently on my bike since the largest gear for a cassette is 36t which would lose about 20% climbing ability. If the calc on the link is anything to go by. To get to the same climbing ratio with a 36t gear you would need to change to a 26/40t chainring set up, and this would lose you a whopping 10% top speed. (Even this combo would not quite simulate my current ratio at the low end) So in conclusion if your riding is like mine where I struggle on climbs ( I have a chronic back problem so any potential improvement here is limited) and you try to make up for lost time on the downhills then a 2x10 configuration will not give you an optimal range. Fortunately Shimano still make a suitable 3x10 FD so I can continue with my current set up, SRAM's loss I guess? Ps - it is also quite interesting to see the advantage a 29er gains over a 26er in top speed and what it loses in climbing ability when considering similar gear ratios. My experience is that the 29er makes up for it in terms of rolling resistance but this is an entirely different debate.
