M5 Expert (>4000)
Join Date: Aug 2002
Location: Raleigh, NC
Thanked 1,505 Times in 1,029 Posts
Everyone's comments on the front ST40 kit is just echoed by me...which got me thinking. If one asks, "what is the single best modification to the E39 M5, taken in isolation?" I think the answer is the Stoptech front BBK. If you include dollar value as a variable, the answer would quickly fall to the Dinan rear sway bar.
However, I'd rate the Stoptech BBK far above square setup in terms of its impact on the driving experience since it is apparent on each and every single brake application (far less "squish", excellent pedal feedback) whereas the square setup, while fantastic dynamically while cornering, has its drawbacks in terms of tramlining, especially as tires wear down. Changing brake pads on the ST40 is super fast and easy also.
2019 M2 Competition 6MT LBB, slicktop
2011.5 M3 sedan 6MT Silverstone, slicktop: Dinan front swaybar, Eibach rear swaybar, pins-out-max-camber-up-front, Dinan exhaust, Michelin PS4S, Apex EC-7 9.5/10.5x19
2007 328i wagon Silver/gray: Eibach 28mm front swaybar, E93 M3 rear swaybar, 219M M3 wheels, Michelin PSAS3+
1975 CanAm 125MX2: Stock, original owner