So, i have a standard GTi on 17's
Me too!

What would be your first mods / upgrades?
Mine are:-
1) Forged/Revision 'D', DV,
2) Better Rubber,
3) Better Brakes,
4) RNS510,
5) Colour-Coding work,
6) Re-Map,
7) 18".
All that lot might be over £1k, but that's my order of work & i'm sticking to it!

Personally, the last thing I'll get round to doing is the alloys. I think the MKV looks fine on the standard alloys and the ride is just about a decent compromise between comfort and handling.
I might swap the 18" idea for a refurb & powder coat. I'm not sure yet & SWMBO really get's the final veto on any expenditure.
