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The Golf R uses 235/35 R19 91Y XL tyres on 8.0J x 19 ET50 wheels.
The R also runs on lowered suspension (front/rear 25 mm) compared to the GTI (front 22 mm/rear 15 mm), so on the face of it, a further front 3 mm/rear 10 mm drop probably wouldn't hurt.
Hopefully someone else will chime in with more info.
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