I want to upgrade my 10 speed to 11. Will my SRAM Red 53/39 10spd rings and 172.5 crank work with an 11 speed upgrade? Looking to upgrade to SRAM eTap with the "kit". I understand the need for a new cassette (11-28), front & rear derailleurs, shifters and 11 speed chain. Do I need new crank and chainrings?
11-speed chain is narrower than 10-speed. You keep the crank but you must put on 11-speed rings which will most certainly fit judging by the pictures on SRAM's website. The shape of the cranks remains the same and the BCD is identical, of course.
Here's an article about it
So, you cannot technically run an 11 speed chain on 10 speed chain rings. As the article says, the chain rings can be swapped out and you can keep the same cranks from your 10 speed set up.
From my own experience however you can run 11 speed chain on 10 speed chainrings, but as advised by SRAM, the shifting is not great, eg. you will get chainsuck and slow shifting occasionally