Thx, Dave.
Refering to ETKA there are both 22.22 and 23.81 mm. Possibly some GTIs exported overseas had the 22.22.
Found some more - Boxster S and 993/996 Turbo:
piston size/area 1. stock front caliper:Golf/GTI - Ate FN3 54 mm caliper:
2290 mm²S3/R32/R - FNRG 57 mm:
2552 mm²2. aftermarket - proper match:AP Racing 6-pot CP7068-00 (355x32 ) >
2350 mm²Boxster: 40 mm + 36 mm > 1257 mm² + 1018 mm² =
2275 mm²Boxster S: 40 mm + 36 mm > 1257 mm² + 1018 mm² =
2275 mm²993 Turbo: 36 + 44 mm > 1018 mm² + + 1520 mm² =
2538 mm² (on the edge)
Brembo GT Satteltyp A: 40 mm + 36 mm > 1257 mm² + 1018 mm² =
2275 mm²Stoptech ST-40: 38 mm + 34 mm > 908 mm² + 1134 mm² =
2043 mm²3. aftermarket - poor match:Forge: 707 mm² + 1046 mm² + 1164 mm² =
2917 mm²996 Turbo: 40 + 44 mm > 1257 mm² + 1520 mm² =
2777 mm²Q7/Touareg/Cayenne (three variants):
34/36/38 mm : 907.920 + 1017.876 + 1134.115 = ~
3060 mm²32/36/38 mm : 804.248 + 1017.876 + 1134.115 = ~
2956 mm²30/34/38 mm : 706.858 + 907.920 + 1134.115 = ~
2749 mm²4. master cylinder diameter:- 22,22 mm >
388 mm² (some Mk.V GTI, Mk.V + Mk.VI Golf)
- 23,81 mm >
445 mm² (Mk.V R32, Mk.V GTI, Mk.VI GTI, Golf R)
- 25,40 mm >
507 mm² (RS3 + TT-RS)
If you know the piston diameter: Pi * radius² = area