Possible?: Dura-Ace 7900 Crankset (10sd) for Ultegra 6800 FD, RD, Cassette

Triathlon Forum
1

I have an Ultegra 6800 group (crankset, both derailleurs, cassette, brifters, etc) on my 2014 Giant Defy.
Now I picked up for cheap a Dura-Ace 7900 Crankset with stages PM and am wondering whether, instead of just using the left crank arm (with the PM), I could replace the whole crankset and convert it to Dura-Ace 7900 (which is 10spd).

Thank you for your advise.

2

Spacing stays the same on the front, shouldn’t have any issue.

3

chain is narrower on the 11 speed group so your shifting may not be as crisp when you use an 11 speed chain with 10 speed chain rings. I think it will also accelerate wear on the rings, chain.

Here is what Sram/Quarq says:
Ten-speed chainrings can be installed on an 11-speed crank, just as 11-speed chainrings can be installed on a 10-speed crank. The spiders are identical. However, all of our groups are designed to function as complete groups, so if a 10-speed crank is installed in an 11-speed group or vice versa, we strongly recommend changing to the appropriate chainrings. Ten- and 11-speed should not be mixed. Our 22 groups actually have the chainrings slightly farther apart than our 10-speed groups, in order to ensure that all cogs can be safely reached in the small ring, and the chain and front derailleur are specifically designed to work with that gap. Running a 10-speed chain on 11-speed rings or an 11-speed chain on 10-speed rings could cause chain jams or derailments.
Read more at http://velonews.competitor.com/2013/11/bikes-and-tech/technical-faq/technical-faq-follow-up-on-10-and-11-speed-compatibility_307163#1C0LYO6wJB4P90Ft.99

4

It will work just fine.

5

I know they say that, but I have never experienced nor read about anyone having a problem. My suspicion is that this is just marketing talk. In fact no one had ever demonstrated any dimensional difference. I have used my micrometer and can find no difference in thickness or gap. I call bs on the whole thing. The manufacturers say there a difference but refuse to state the so called differences in actual measured numbers.

6

I ran an Ultegra 6700 and had no issues. I recently switched to a Power2max with SRAM Red 10 speed chainrings and have had no issues with that combination either.

7

I run ROTOR Q-Rings and NoQ Rings and they don’t ever mention which “speed” they are for. If thats the case for 3rd party manufacturers I call bullshit on the marketing message of “it’s a system”.

8

Yup. Agreed. In fact Praxisworks chainrings went from being 10 speed compatible, to being 10/11 speed compatible. How? They changed the label on the chainrings! No change to the actual design or shape. And guess what, they work perfectly on 11 speed systems.