Larger than normal cog capacity from 7800 short cage RD

[stien]

What would allow a 7800 short cage to be able to shift into and play nice with a 32t cog? I tried it for fun this afternoon with a SRAM 1050 cassette and it worked great. Moved in the b screw but no biggie at all. What is the concern besides the upper pulley bouncing off the cog? I've eliminated that with the b screw. I can even run 50-32 (50/39 crank) safely without ripping the Rd off.

[oldpotatoe]

What would allow a 7800 short cage to be able to shift into and play nice with a 32t cog? I tried it for fun this afternoon with a SRAM 1050 cassette and it worked great. Moved in the b screw but no biggie at all. What is the concern besides the upper pulley bouncing off the cog? I've eliminated that with the b screw. I can even run 50-32 (50/39 crank) safely without ripping the Rd off.

Top pulley banging into the biggest cog and having enough chain for big-big combos are the only real concerns with this sort of thing.

[rice rocket]

You can also install the B-screw backwards to try to gain more clearance if you're on the cusp of it hitting.

[aramis]

It depends a lot on the derailleur hanger/rear dropouts because that determines the placement of the derailleur relative to the cassette (assuming the derailleur is the same). If there is enough room for the pulley to clear the cassette on the biggest cog, it works. If there isn't, it makes noise.

Also you need to make sure that shifting from the small front/big rear to big front/big rear doesn't tear things apart, especially under load.