Shimano Crankset unsupported configuration
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  1. #1
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    Question Shimano Crankset unsupported configuration

    My son has moved from U15 to U17 category this year and as U17 their max chainring size has moved from 46T to 50T. His bike is currently setup with Ultegra 6800 46/36 crankset. I was looking around do either get him a new crankset or just replace the chainrings, whatever I could find easier and at a reasonable price these days.

    A friend of mine offered a 50T Chainring and said it would work fine in a 50/36 configuration. I know Shimano does not offer this config, but it is also not unusual seeing Pro Riders running "unsupported" gear Ratios.

    My question to you is, would a 50/36 work just fine, or would it cause shifting issues? He races very competitively so I would hate to mess up his bike in a setup that could cause him shifting issues. Any one has used a similar setup before?

    Thanks in advance for your replies

  2. #2
    What the what???
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    Most road compact cranksets nowadays are 50/34, so there's no reason why 50/36 should give you any problems. Know, though, that you might need to get a new chain as well since you're adding 4 teeth on the big ring.
    Last edited by Opus51569; 05-07-2020 at 12:29 PM.
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  3. #3
    tlg
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    I would think it'd be no problem and would shift fine since it's a smaller jump.

    But....
    According to the Shimano Manual (Page 6)
    https://si.shimano.com/pdfs/dm/DM-FC0003-07-ENG.pdf
    • Be sure to use the specified gear tooth combination. If an unspecified gear is used, the chain may fall in between the gears,
    damaging them.


    Not sure why that'd be.
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  4. #4
    .je
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    I've had a bike with a 50-36 (Truvativ Touro) crankset and it shifted flawlessly. It should, in theory, shift better than a 50-34, which shifts flawlessly too.

    I have found that the quality of the chainring is the most important thing. I've used Shimano (Ultegra), which is of course the flawless one, as a direct replacement for FSA (Gossamer), which sometimes was great but most of the time was total ****.

    In response to the above, I think Shimano wants to be absolved of being blamed for people using their own 53-22 set and blaming the company for their 'poor products', even if they are using Shimano.
    Last edited by .je; 05-07-2020 at 09:00 AM.

  5. #5
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    50/34 - 16T Jump
    52/36 - 16T Jump
    46/36 - 10T Jump
    53/39 - 14T Jump

    50/36 - 14T Jump

    Sincethe jump is 14T, I would assume it would work just fine, since it is even smaller than the 16T jump from the 50/34. If the jump increased beyond 16T then I could see the issue of chain falling in between gears. But what do I know...

  6. #6
    tlg
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    Quote Originally Posted by alexm370 View Post
    Sincethe jump is 14T, I would assume it would work just fine, since it is even smaller than the 16T jump from the 50/34. If the jump increased beyond 16T then I could see the issue of chain falling in between gears.
    That's my assumption as well.

    If you've got a friend with a 50, give it a shot. Check out the shift pin/ramps and see if the chain can drop between. I'd bet not.
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  7. #7
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    Thanks Guys for the replies, really appreciated

    I will get the 50T chainring and give it try.

  8. #8
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    Shimano now makes 50/36 cranks so where's definitely nothing wrong with the numbers of teeth per se.
    But I suppose they could have changed the pins and ramps since the ones your friends has to give you were made.

    I'd bet strongly it would work just fine. But either way, rings are pretty easy to change. Best to find out for yourself by slapping them on.

  9. #9
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    If the shifting pins on the large chainring do not match the pins on the small, there could be a small hesitation in the shift when shifting in a high torque situation, or out of the saddle. If that happens, you just have to ease up for half a pedal stroke. The front shifting will be similar to shifting before ramps and pins.
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  10. #10
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    Quote Originally Posted by MR_GRUMPY View Post
    If the shifting pins on the large chainring do not match the pins on the small, there could be a small hesitation in the shift when shifting in a high torque situation, or out of the saddle. If that happens, you just have to ease up for half a pedal stroke. The front shifting will be similar to shifting before ramps and pins.
    I don't think there is a such thing as pins on the small ring. I think it's a matter of if the ramps and pins on the big will pick up as they should when making a jump from a small ring that's slightly bigger than those pins and ramps where designed to pick up from.

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