Issue with b-limit on Ultegra 8000 going from 11-34 to 11-30
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  1. #1
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    Issue with b-limit on Ultegra 8000 going from 11-34 to 11-30

    So I decided to go from a 11-34 to 11-30 cassette on my bike, and when I set the b-limit for the 11-30 about 6mm from top of jockey wheel to the 30t sprocket and I ran thru the gears on the 34t chainring, when I got to the 13 tooth gear my chain had a lot of slack in it, so I open up the gap on the b-limit to about 12-14 mm and it seem ok then, is this going to cause me any problems, all the gears seem to shift ok, or do I need to get another chain an size for the 11-30?

  2. #2
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    It sounds like your chain is at its max length for the 34t cog setup. If that's the case, you'll have to either shoerten your existing chain or install anew one cut to the correct length.

    The B screw should be set to its spec for each cassette.
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  3. #3
    MDM
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    When you are in the small-small combination, as long as the derailleur is still able to tension the chain, it's OK. I suspect your chain length is OK as is, since the small-small is the same as it was with the other cassette, but shift into that combination and check. Maybe the B tension adjustment changes things slightly.

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    If you plan on staying with the 30, take a link out of the chain. If you are going back and forth between the two, split the difference on your b tension and stay out of the smallest two cogs in the small ring, you really don't ever need to use those combos anyway.

  5. #5
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    Quote Originally Posted by MDM View Post
    When you are in the small-small combination, as long as the derailleur is still able to tension the chain, it's OK. I suspect your chain length is OK as is, since the small-small is the same as it was with the other cassette, but shift into that combination and check. Maybe the B tension adjustment changes things slightly.
    So I checked the small/small combination on the 11-30 and with the b-limit set were it should be and the chain is a little too slack, then I checked the 11-34 and it was ok in the small/small, as 202cycle said I could split the difference but sometimes I forget were i'm at on the gears an run a little on the 34/12t-13t, so I will put the 11/34 back on and will get another chain for the 11-30 combo as sometimes I need the 11-34 for some of the steeper climbs I do.

  6. #6
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    How could the chain tension be different between the 11/34 (r/f) on one cassette and 11/34 (r/f) on the other?
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  7. #7
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    Quote Originally Posted by duriel View Post
    How could the chain tension be different between the 11/34 (r/f) on one cassette and 11/34 (r/f) on the other?
    I assume you meant (different between 11/34 and 11/30). All I could see was that the b-limit setting on the 34 open up the rd enough to have proper tension in the small/small but when adjusted in toward the 30 it didn't have enough tension, basically I would need a little shorter chain for the 30 as the rd couldn't provide enough chain wrap for the 30, with the b-limit adjusted in.
    Last edited by Ventura Roubaix; 1 Week Ago at 03:58 PM.

  8. #8
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    NO, I meant what I said. Small/Small in both situations should not change the slackness of the chain because the gears are the same.
    That is what the OP said, or I misinterpreted what he said?
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  9. #9
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    Quote Originally Posted by duriel View Post
    NO, I meant what I said. Small/Small in both situations should not change the slackness of the chain because the gears are the same.
    That is what the OP said, or I misinterpreted what he said?
    changing the b limit screw moves the angle of the derailleur thus moving the idler pulleys backwards or forwards.

  10. #10
    'brifter' is f'ing stupid
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    Quote Originally Posted by MDM View Post
    When you are in the small-small combination, as long as the derailleur is still able to tension the chain, it's OK. I suspect your chain length is OK as is, since the small-small is the same as it was with the other cassette, but shift into that combination and check. Maybe the B tension adjustment changes things slightly.
    No. Not w/ the new derailleurs. If the b tension is set correctly and the chain is the correct length your shifting will work properly. If the chain isn't the correct length and you attempt to set b tension by eliminating slack in small/small you might end up w/ too big a gap, especially in the smaller cogs.

    Quote Originally Posted by duriel View Post
    NO, I meant what I said. Small/Small in both situations should not change the slackness of the chain because the gears are the same.
    That is what the OP said, or I misinterpreted what he said?
    Wrong. B tension is set at the large cog/upper pulley. If the chain is the correct length for the large cog, no problem. If you have the chain sized for a 34 and slap a 30 on and adjust b tension for the 30 your chain will be slack in the 11.
    Last edited by cxwrench; 1 Week Ago at 06:26 PM.
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  11. #11
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    Quote Originally Posted by Ventura Roubaix View Post
    So I decided to go from a 11-34 to 11-30 cassette on my bike, and when I set the b-limit for the 11-30 about 6mm from top of jockey wheel to the 30t sprocket and I ran thru the gears on the 34t chainring, when I got to the 13 tooth gear my chain had a lot of slack in it, so I open up the gap on the b-limit to about 12-14 mm and it seem ok then, is this going to cause me any problems, all the gears seem to shift ok, or do I need to get another chain an size for the 11-30?
    Read page 18 of the manual for how to set up your end adjust bolt (not B screw any more).

    https://si.shimano.com/pdfs/dm/DM-RARD001-02-ENG.pdf

    This is for when the chain is sized right for your biggest cog which is a 34 using the big - big technique also in the manual. Now put your 11-30 on and adjust your end adjust bolt as needed to take up the slack when you are in the 11 cog and you are done. There is no reason at all that if you follow this method with a chain sized to your 11/34 correctly that it won't work for you. The only down side to getting your idler pulley further from the cassette on the 11/30 is you can have some not as crisp shifting somewhere in the range as the idler has to move the chain further when the shift is actuated to make up for side play in the chain, to get it to change cogs. But with Mechanical shifting going up the cassette you can just push the lever a tad more and it will go, Di2 can get a little annoying on come set ups because you can't micro adjust for those odd spots in the range by hand at the shifter.

    I have a bike with the chain sized for an 11/36 with Di2, and at times run an 11-23 and it works ok for me, you just need to make sure that idler is close to the biggest cog on the big range cassette, I didn't size the chain using the big / big method, I sized it to the cassette based on the end adjust screw just tight enough to keep slack out on the 11, and the end adjust screw putting the idler as close to the 36 as I could without rubbing the cog and a smidge extra space, maybe a couple mm. The rear DR is pulled fairly far forward in the big big combo (compact crank) but there is still some flex available in the DR tension (like 3 links worth) so not concerning to me.
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  12. #12
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    Maybe I'm confused or have gotten lucky but I've never touched the B limit or chain length when going to a smaller bit cog with that der. 30 to 25 in my case.

    If I'm using a 30 okay I've already proven I can use 25 and below okay with the same set up is they way I look at it.

    Maybe my thinking is off but the results have been perfectly fine.

  13. #13
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    Quote Originally Posted by cxwrench View Post
    No. Not w/ the new derailleurs. If the b tension is set correctly and the chain is the correct length your shifting will work properly. If the chain isn't the correct length and you attempt to set b tension by eliminating slack in small/small you might end up w/ too big a gap, especially in the smaller cogs.



    Wrong. B tension is set at the large cog/upper pulley. If the chain is the correct length for the large cog, no problem. If you have the chain sized for a 34 and slap a 30 on and adjust b tension for the 30 your chain will be slack in the 11.
    I agree, cxwrench said what I was trying to say, thanks.

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