easier said than done.
I want to use 160 mm disc. Shimano make adapter, quite rare but possible to get hold of, but that will work with 180 mm disc.
KCNC make 3: for 160, 180 and 203 - the 160 should fit my fork/calliper but is red so will clash colourwise. I'll probably get one anyway and just not look in that direction when riding.