I have a six-month old Volkswagen T-Roc 4Motion. We really love the car . We bought it new from stock so did not actively choose the wheels. These are 215/50/R18 alloys. The tyres (Bridgestone Turanza T001) are down to 4mm at the front and 4.5mm at the back. So I will need to get new tyres soon, but the choice in this size is very limited, excludes all the current best buy tyres, and the cost is going to be around £600 (or £800 from the Volkswagen dealer according to their helpful quote on the safety report). The alternative wheel spec for the car is 225/55/R17 where there is a lot more choice of tyre. But I am a bit anxious about leaping in and changing the wheels, not least because it will be expensive. Volkswagen sell a set of 17" alloys for the T-Roc but the blurb refers to them being designed for winter use. Other people sell alloys that they claim will fit, but a lot of these seem to be about pimping up rather than practicality and I don't know how to assess quality. Also what would third party wheels do to the warranty? Is this an insurance modification?