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Feb. 16, 2021, 9:36 a.m. -  AndrewR

The 3 mm difference in chain line means less lateral load on the chain, less micro grinding of the chain ring and the cassette cog teeth. Shift the bike into the gear that used most of the time climbing and look at the chain line from the rear (or take a photo). Shift into the gear that is most commonly used for descending (for pedalling for short sections or cranking into a feature for most riders) and check the chain line (or take a photo). If riders are honest with themselves and consider the time they spend between 50-52T and 28T (most of the ride time given the average S2S climb of 45 - 60 mins with a rolling gut punch of 6% to 25% grades) and the time spent actually pedalling (not pumping when standing on level pedals) in gears between 24T and 10T (12-20 minutes of descending involving about 2 minutes if pedalling for most riders). Unless one is a racer or fast. If one regularly sees one's name in the top 10% of a Strava descent segment (or can keep up with or beat those kind of riders) then one is probably pedalling like a racer on descents and in this case a 'boost' chain line makes sense. The best chain line when producing high levels of power and less lateral load that is likely to contribute to a chain jumping off what ever flavour of NW tooth profile the rider is running (most riders this fast also know to run at least an upper chain guide). The lower/ bigger/ easier gears (we really need to standardise the terminology of the cassette gears) are high torque, large/ long chain wrap and long duration of use gears and anything one can do to reduce these factors, as long as it fits in with the design of the bike/ line of the chain stays/ centred stance (shifting the chain ring line not running cranks out of centre), will lead to a longer lasting, crisper shifting drive train.

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