From looking at this http://www.canyon.com/_en/roadbikes/...91#tab-reiter2 I'd be on a medium/56.



[TABLE="class: ausst, width: 100%"]
[TR]
[TD="class: term"][/TD]
[TD="class: term"]Frame size[/TD]
[TD]XS (50)
[/TD]
[TD]S (53)
[/TD]
[TD]M (56)
[/TD]
[TD]L (58)
[/TD]
[TD]XL (60)
[/TD]
[TD]2XL (62)
[/TD]
[TD]3XL (65)
[/TD]
[/TR]
[TR]
[TD="class: term"]A
[/TD]
[TD="class: term"]Seat tube length[/TD]
[TD]465
[/TD]
[TD]505
[/TD]
[TD]537
[/TD]
[TD]563
[/TD]
[TD]585
[/TD]
[TD]610
[/TD]
[TD]635
[/TD]
[/TR]
[TR]
[TD="class: term"]B
[/TD]
[TD="class: term"]Top tube length[/TD]
[TD]525
[/TD]
[TD]537
[/TD]
[TD]549
[/TD]
[TD]566
[/TD]
[TD]583
[/TD]
[TD]600
[/TD]
[TD]616
[/TD]
[/TR]
[TR]
[TD="class: term"]C
[/TD]
[TD="class: term"]Head tube length[/TD]
[TD]125
[/TD]
[TD]138
[/TD]
[TD]150
[/TD]
[TD]170
[/TD]
[TD]190
[/TD]
[TD]210
[/TD]
[TD]230
[/TD]
[/TR]
[TR]
[TD="class: term"]D
[/TD]
[TD="class: term"]Head tube angle[/TD]
[TD]72°
[/TD]
[TD]72.5°
[/TD]
[TD]73.25°
[/TD]
[TD]73.25°
[/TD]
[TD]73.25°
[/TD]
[TD]73.25°
[/TD]
[TD]73.25°
[/TD]
[/TR]
[TR]
[TD="class: term"]E
[/TD]
[TD="class: term"]Seat tube angle[/TD]
[TD]73.5°
[/TD]
[TD]73.5°
[/TD]
[TD]73.5°
[/TD]
[TD]73.5°
[/TD]
[TD]73.5°
[/TD]
[TD]73.5°
[/TD]
[TD]73.5°
[/TD]
[/TR]
[TR]
[TD="class: term"]F
[/TD]
[TD="class: term"]Chainstay length[/TD]
[TD]410
[/TD]
[TD]410
[/TD]
[TD]410
[/TD]
[TD]410
[/TD]
[TD]410
[/TD]
[TD]410
[/TD]
[TD]410
[/TD]
[/TR]
[TR]
[TD="class: term"]G
[/TD]
[TD="class: term"]Wheel base [/TD]
[TD]967
[/TD]
[TD]975
[/TD]
[TD]980
[/TD]
[TD]997
[/TD]
[TD]1014
[/TD]
[TD]1031
[/TD]
[TD]1048
[/TD]
[/TR]
[TR]
[TD="class: term"]H
[/TD]
[TD="class: term"]Stack[/TD]
[TD]534
[/TD]
[TD]546
[/TD]
[TD]560
[/TD]
[TD]579
[/TD]
[TD]598
[/TD]
[TD]617
[/TD]
[TD]636
[/TD]
[/TR]
[TR]
[TD="class: term"]I
[/TD]
[TD="class: term"]Reach[/TD]
[TD]367
[/TD]
[TD]375
[/TD]
[TD]383
[/TD]
[TD]395
[/TD]
[TD]406
[/TD]
[TD]417
[/TD]
[TD]428
[/TD]
[/TR]
[TR]
[TD="class: term"][/TD]
[TD="class: term"]Spacer[/TD]
[TD]25*/15**
[/TD]
[TD]25*/15**
[/TD]
[TD]25*/15**
[/TD]
[TD]25*/15**
[/TD]
[TD]25*/15**
[/TD]
[TD]25*/15**
[/TD]
[TD]25*/15**
[/TD]
[/TR]
[TR]
[TD="class: term"][/TD]
[TD="class: term"]Stem length[/TD]
[TD]80*/90**
[/TD]
[TD]90*/100**
[/TD]
[TD]100*/110**
[/TD]
[TD]110*/120**
[/TD]
[TD]110*/120**
[/TD]
[TD]120*/130**
[/TD]
[TD]120*/130**
[/TD]
[/TR]
[TR]
[TD="class: term"][/TD]
[TD="class: term"]Handlebar width[/TD]
[TD]400
[/TD]
[TD]400
[/TD]
[TD]420
[/TD]
[TD]420
[/TD]
[TD]420
[/TD]
[TD]440
[/TD]
[TD]440
[/TD]
[/TR]
[TR]
[TD="class: term"][/TD]
[TD="class: term"]Crank length [/TD]
[TD]170
[/TD]
[TD]170
[/TD]
[TD]172.5
[/TD]
[TD]172.5
[/TD]
[TD]175
[/TD]
[TD]175
[/TD]
[TD]175
[/TD]
[/TR]
[TR]
[TD="class: term"][/TD]
[TD="class: term"]Seat post diameter[/TD]
[TD]27.2
[/TD]
[TD]27.2
[/TD]
[TD]27.2
[/TD]
[TD]27.2
[/TD]
[TD]27.2
[/TD]
[TD]27.2
[/TD]
[TD]27.2
[/TD]
[/TR]
[TR]
[TD="class: term"][/TD]
[TD="class: term"]Seat post length[/TD]
[TD]330
[/TD]
[TD]330
[/TD]
[TD]330
[/TD]
[TD]330
[/TD]
[TD]330
[/TD]
[TD]330
[/TD]
[TD]330[/TD]
[/TR]
[/TABLE]



as stated above, I'm 174cm tall and normally ride 54cm. The small looks tiny IMHO.