I know mathematically it seems only 6mm but while sitting in the car it feels a lot though. The earlier tyre was totally worn out and second thing is when you buy a 98+100 PCD alloy The actual height what you are mentioning is from the center of the wheel to the edge. but the hub dia plays an important role so that can not be standard. So height from ground to center of the wheel for 15" can vary from 375mm M i right..!! But one thing i wanted to share with you : hub dia 58.1mm (punto) hub dia 73mm (multi-pcd alloy) so when you add the diff of these to the total height it actually increase your GC by another 15 mm. And i think thats is why i am feeling is much while i am sitting in my punto. I hope you got it, may be i am wrong but i understood it like this. ---------- Post added at 04:57 PM ---------- Previous post was at 04:54 PM ---------- Rather the 15mm diff in the hub dia will be 15/2 for the height/GC so it will be 7.5mm so 6mm actual + 7.5mm hub dia diff = 13.5mm thats what i was talking about earlier.