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Di2 allows a 52:32 to be used with a SS rear mech?

by razor77
Mon, Mar 20, 2017 10:41
3

My set up Di2 52-36 & 11-28.  Using the di2 6870 short cage the max chain capcity is 33, exactly what my set up has.

I'd like to try the 11-32 without the cost of a new rear mech, the rear 32 with the front 36 should be fine but not with the front 52 which would increase the chain capcity to 37, and could cause damage/won't work as documented on many other threads.

Using the new 6870 firmware, I believe the syncro modes can be set to prevent 52:32 happening.

I am adding the bluetooth EW-101 di2 componant tomorrow, and will be able to test the scinerios using the existing 11-28 before I try swapping out for the 11-32.   

Whilst I believe my logic is correct, is this idea flawed in any otherway?

 

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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razor77 | 7 years ago
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Thank for the replies.

VeloUSA; 33t chain capacity, or more correctly "chain take up limit" for my current set up and derived from the sum of 28 less 11, and 52 less 36.  Shimano publish this detail as a spec for their rear derailleurs.  this increases to 37t if I switch out the 11-28 for the 11-32.

I've read many similar comments to yours Pablo, regarding use of a 32 with a 52, and although it "can work" I don't want the associated risk.  I am only considering now because the di2 sync mode can prohibit that ratio.

You have both drawn my attention to this fact, I'll still likley need to adjust the b screw for the physical larger 32 cog (despite limiting the use of the 52:32 to keep the max 33t), which has too many cons/compromises from my reading.  

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pablo | 7 years ago
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11-32 works and I briefly tried it with a 52 mid compact on ultegra di2 short cage. You really need to be careful with 2 things.
Chain length especially cross chaining you could end up ripping the derauiler off and if you have short chainstays when cross chained you can get rubbing or damage the front derailleur.

I didn't like it and had some SRAM compact rings i picked up cheap so run in like that in the mountains.

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VeloUSA | 7 years ago
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A short-cage Shimano 11-speed rear derailleur can work with a 11-32 cogset by tightening the b-screw in quite a ways.

I am unsure how you measured "chain capacity" or what is meant by "33 & 37 chain capacity". 

If you're questioning chain length then you might try Machinehead Cycling online chain length calculator and convert the final results from inches to mm. MC calculator has 52/28 to 52/32 as a one link increase.

http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc....

You can also double check by using Park Tool's chain length manual equation. Again, you will have to convert from inches to mm.

http://www.parktool.com/blog/repair-help/chain-length-sizing#article-sec...

 

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