Ok just to add a few points to this thread.
You can run 20mm on the rear on a low car (as I have done) BUT don't be fooled into thinking you can buy 20mm spacers on eBay with the bolts. Why? Cos I did too, came with bolts, but most are normal bolts. You will need radius bolts. My radius bolts cost a further £22 for 10.
DO NOT fit a spacer without radius bolts.
The car looks better, handles alot better, and I suppose it will
help braking stability too (not yet tried that). Just remember to re torque the bolts after a few days as they WILL get looser.
Sent from my iPhone when I should be working....