Just take a pic and show us.
288mm have a thing metal pad spring.
280mm has nothing.
Easy to tell difference just by looking at them
just a pic of the wheel square on? or more of the caliper?
ive just being a bit ingenious as dont wanna go take off a wheel now, as only just got in from work from 7 this morn, so got some wire and fed it around the disc around the middle (so sat on the vents), through the caliper aswell

then took the length of wire, lay it down and measured, and got d = 885/3.14 = 282,
but the groved bit is slightly smaller diameter than the disc, so in actual fact it isnt conclusive but looks like 280s, haha i hate golfs at times, lol

anyway ill go take a pic

just to see what u reckon

edit

