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enter image description hereBike - Trek DS 8.6 (2016) hybrid. Purchased August 2016

Chain set / chain rings - FSA Dynadrive 48/36/26

Shimano Deore front and rear derailleurs

Chain - KMC

Bike usage - roughly 600 miles since purchased, road and bike trails, but not off road / trail; Some hill work (but generally in small chainring for those), and really only using large chain ring when on flat roads. Novice rider, so not huge power output, and rides average 80-85 cadence rpm, topping out 100-105 very occasionally. Rides are generally between 10-20 miles

Edit re "cross-chaining" - when using the large chainring I would tend to be using smaller cogs of the rear cassette, to avoid cross-chaining

Please take a look at the picture - hopefully you will see what appears to be different shaped teeth on the front large chain ring. Some appear quite pointy, others rounded, and two or three almost flat, as if the apex has been removed.

My question(s) - is this excessive wear and if so, caused by some fault in the drive train? Or has the chain ring been manufactured with these differences in the teeth? If there is a likely fault I can go back to LBS, but what are the likely causes? If deliberately manufactured that way, why?

  • Is there a possibility that the flat tooth is from damage? If you remove the wheels, the bike rests on its largest chain ring. I would imagine that this could damage teeth that way. – Christian Lindig Feb 2 '17 at 13:50
  • @ChristianLindig - I don't think so. I've only taken the wheels off a couple of times (in the garage, on a stand, to practice taking them off and replacing...) That's not to say supplier / LBS hasn't, but would think unlikely... – Mike Feb 2 '17 at 13:59
  • Welcome to Bicycles @Mike. Good to see you have taken the tour. I don't see any unusual wear in your pic. It looks like a typical low end chain ring. AFAIK the flat tooth is to help the chain move when you change gears at the front. – andy256 Feb 2 '17 at 22:47
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More or less all contemporary multi-speed chainrings are like that. The idea is the different profiled teeth correspond to different areas of the ramps and/or pins to create specific assisted areas for shifts to occur.

  • Yeah, from the picture I don't see any evidence of excessive wear on the ring. – Daniel R Hicks Feb 2 '17 at 20:15
  • This is exactly right, notice the correlation between the flat topped teeth and the shifting pins/ramps. The flat tooth comes right before the shifting pin to aid in getting the chain on the teeth more easily. – Nate W Feb 2 '17 at 22:19
  • Gentlemen, and in particular @NathanKnutson, thanks for the answer & comments. Out of curiosity, and hopefully not seen as "new" question - the shifting pin, is what I took to be a meaningless rivet through the chainring, and in the photo is on the outer edge of the chainring, 2 of them in the rough 3 o'clock position? Its purpose is to interfere with the travel of the chain, as the front derailleur moves the chain across, sufficient to give it a "nudge" up (or down) onto the new chainring, and a flattened tooth enables the chainring to "grab" the chain more efficiently? Engineering ingenuity! – Mike Feb 3 '17 at 10:14
  • I don't remember the actual figures, but some awkwardly large percentage of Shimano's patents are dedicated to specifics of shift gates and ramps, tooth design and the like. It's a much larger area of engineering mastery than most people realize. – Deleted User Feb 3 '17 at 16:29
  • @Mike Something like that, yes. I think usually the main idea is for the pins to create something for the chain to briefly ride up on and the flatted teeth create a slightly more open path for the chain to get onto and off of the ring. Smoothing the transfer of power is also a goal of the system in addition to just making it easier to shift. As has been pointed out, there's kind of a lot going on - probably the best way to get a sense of it if you're curious is to get in position to watch it in motion as you shift back and fourth with the bike in a workstand or hung from its saddle. – Nathan Knutson Feb 3 '17 at 17:19

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