Need to order 4 new tyres for my A4. Been looking on Camskills and found some uniroyal rainsports that i would like to buy. But they are 235/40 R18, Y rated not 235/40 ZR18 Y rated like the Michelin Pilot Sports that are on the car ATM. Whats the difference and is it ok to fot these to my car? I tried ringing Camskills for their advice but they are shut for the night?