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I plan to put a 50T chainring on my bmx but I am afraid to have an interference between the chain and the frame.

Does anybody know what is the critical distance between the seatstay and the chain so as to have no inteferences between the two during riding ?

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    1mm should do it
    – robjwilkins
    Commented Apr 4, 2016 at 21:52
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    I'm curious as to why the chain and seat stay would make contact? A larger chainring should not move it any closer to the seat stay, assuming the chainline is unmodified than the chain should be routed very similar. I would be more worried about the chainring being close to the chainstay if the ring size has increased.
    – Nate W
    Commented Apr 4, 2016 at 22:26
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    @Nate . The fact is that I have a small seat tube (around 160mm). If I increase the diameter of the chainring, the chain will come very close to the seat stay (because the SS is very low due to the small seat tube). I wouldn't had have this problem if the seat tube had been longer.
    – Greg.D
    Commented Apr 5, 2016 at 1:38
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    No idea as to an actual number sorry, but if you measure a 50T chainring, cut a circle from cardboard and tape it to your bike, then hold any chain up where you think it would run. There should be minimal chain bounce on the top length while peddling. A mock-up like this will let you test without wasting money. You'll also see the ground clearance/breakover angles change, and whether the chainring clears the chainstay too.
    – Criggie ♦
    Commented Apr 5, 2016 at 10:37
  • @Greg.D Right on, that makes sense. Thanks for the explanation!
    – Nate W
    Commented Apr 5, 2016 at 14:43

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