My old 91 on Racing Beat Street springs and Billies:
On paper, the RBs should be -35m. More like 45-50mm. Low at the front. I actually got stuck on a few high speed humps.
Check for leaks, check they rebound ok. Check the bottom bushing is in good condition; though they can be replaced with one from a Mini Metro :shock: .
I didn't bother cutting the bumpstops; just fitted a set of standard new ones. Car was firm, handled fine. If the shock looks in really crappy order (rusty etc), I wouldn't fit it. I've seen people trying to pull a fast one with GABs in really shocking order.
I have the billies too, car came imported with them and rsr springs, dont know how much they lower the car by though to be honest. The billies are very stiff, great on smooth roads and B roads, not so good on potholes!!