One for the Shimano gurus.

bianchi928
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Joined: Tue Jun 09, 2009 3:17 pm
Location: Perth

One for the Shimano gurus.

Postby bianchi928 » Mon Nov 12, 2018 5:22 pm

Hi all,

I recently acquired a second hand Dura Ace 9070 (Di2) groupset to replace my mechanical Ultegra R8000.

My Ultegra is running 50/34 with an 11-28 cassette with the Dura Ace coming with standard 53/39.

I am buying anew chain and thought I might go to a 30 tooth cassette at the same time.

My research (ie Google) tells me that the 9070 cannot run anything bigger than a 28 at the back without a long cage conversion kit (K-Edge or alike).

I'm not too stressed, 28 will be fine for now (no trips cycling in the mountains planned for a long time) but I thought it would be nice to know.

Thanks in advance.

Travis
Stand on my dog I cut off your head

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Duck!
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Re: One for the Shimano gurus.

Postby Duck! » Mon Nov 12, 2018 9:49 pm

It's not the cage, it's the main body geometry that limits maximum sprocket size. Shimano used to be pretty precise with their actual maximum sprocket capacity vs the recommendation (i.e. if they said 28T max, they meant it, and the derailleur would get really narky at anything bigger), but in more recent times they've built a bit more tolerance in. The 9070 WILL fit a 30T without trouble. That said, Dura-Ace does still seem to have tighter tolerance than the lower groups; I have fitted short Ultegra and 105 derailleurs with 32T cassettes and they've worked fine, but I'd be hesitant to try that big with 9000-series D-A. R9100 maybe due to its different geometry, but not 9000.

Where the cage length becomes important is the combined difference across the cassette and chainrings. The 14T difference of 39/53 allows a slightly wider cassette, as long as it stays within the actual maximum sprocket capacity than the 16T difference of 36/52 or 34/50.
I had a thought, but it got run over as it crossed my mind.

bianchi928
Posts: 657
Joined: Tue Jun 09, 2009 3:17 pm
Location: Perth

Re: One for the Shimano gurus.

Postby bianchi928 » Tue Nov 13, 2018 7:25 pm

Cheers Duck, much appreciated
Stand on my dog I cut off your head

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