If you havent done too many track days and want to be safe then maybe 18mm might be fair enough, especially if you still have standard springs/dampers.
For folks who want a have adjustable dampers or stiffer springs or simply have more experience on track I think the 20mm ones are hard to beat. You can start off on the softest setting.
Originally Posted by Pax
I think it would be a step in the right direction to fit a thicker rear ARB, the question is, should I go for 18 or 20 mm? I do almost exclusively B-road driving, plus future trips to the Ring (I suspect). For this, maybe a 20mm would produce too much oversteer, which is not so nice in 80+ km/h
