what tyre stretch

[s77ygg]

Hi guys I have a 2002 bmw e46 cabriolet, I have gone and bought a set of wheels and I dont know what Tyres to run as I want to go low on lowering springs, im going 50mm at the front and 40mm rear. I dont want my arches to rub or scrape

The wheels are

Front are 19" 8.5j ET15
Rears are 19" 9.5j ET20

Please help guys