rite, firstly, u decide on the alloys and then the size of the tyre can be decided!
to make sure any alloys u choose will fit, u've gotta make sure that u get these things matched up:
PCD 4x100
(basically the "4" denotes the numbers of studs (bolts) that the alloys have and the "100" is the diameter between two opposite studs.
ET 37-43 (i think)
this is the offset of the wheel and the lower the offset, the further the wheel is moved away from the hub.
wheel diameter
this one is really upto you and depends what sorta size alloys you want! most people with the mk5 get 15s or 16s. 17s will fit but they look slightly big in my opinion.
once the size of the wheel is decided, you can then choose tyres to fit.
usual figures for tyre sizes are something like this
15s.........195/45/15
16s.........195/40/16
"195" denotes the width in mm of the tyre
"45" denotes the profile of the tyres where "45" is a % of the width
"15" denotes the diameter of the alloy wheel
when choosing alloys and tyres, it is best to try and keep the rolling radius as close to, or the same, as what you already have otherwise it will mess up your speedo!
hope some of this helps, any questions just ask!
