Originally Posted by
bldegle2
I am running a 50/33 on a 5 bolt 110 BCD on both of my road rides. The 33 is a special ring made in France, an engineering marvel. Running a GS derailleur 11/34 cassette in the rear on both. So I would say 17 would be the max or one will run into problems with chain wrap formulas...
Tigermom, what rear derailleur are you running to get the `19T differential to work?
You should look at the specs for your RD to find your chain wrap capacity.
https://productinfo.shimano.com/#/sp...r%20Derailleur
The formula is not difficult. cassette difference, plus the chainring difference. Your chain wrap is 40T. Compare it with the Shimano specs.
I have a 12-34T 10 speed cassette, with 44/24T chainrings, so my chain wrap is 42T. I have a Shimano RD-4700-GS with long pull cable ratio. It has a chain wrap capacity of 41T. The outermost cog when on the big chainring just barely drags the pulley cage. It will depend on how close you are to the next length of 1 inch chain link.
Even if the outermost cogs drag while on the big chainring, it doesn't matter for me, because with a 20T jump between the double chainrings, the outermost 3 cogs will have chain rub anyway. So I don't use those 3 cogs.