The Ultegra FC-8000 inner chainrings are OE replacement for R8000 cranksets, however work with all Shimano's 110mm four-arm asymmetric cranksets. One of the nice features of Shimano's new 4 arm 110mm asymmetric bolt circle is the same for compact, standard and TT so this means that one crank arm fits all chainring sizes. If you move from the flats to the hills or try different events, you can keep the same crank and just change the chainrings.

When changing to different size chainrings, you will want to keep the difference between the inner and outer chainrings to 16 teeth or less. The outer ring is generally matched to a specific inner ring in terms of the position of the lifting pins and tooth profile. If you typically run a 52/38 for example and want to use a 36 for a hilly event, you will generally be okay with the same outer chainring. Keep in mind, you will generally need to shorten the chain when going from standard to compact or lengthen the chain when going from compact to standard or TT rings.