I run 201/ 503 lbs/in Swift Spec-R springs with Bilstein B8 dampers on my 135i.
According to the Swift web site, the springs are designed for the the upper limits of the OEM shock valving.
Because of this, I assume that the B8's can handle a little more "spring". I have contacted Bilstein to confirm what the maximum spring rate is.
Im looking at options for stiffer front springs to reduce body lean when cornering at the track. Does anyone know if there are stiffer springs options out there which will not overwhelm the Bilstein B8's?
I may keep my 135i-specific Spec-R springs, and opt for a stiffer E93/M3 or H&R Front Sway bar if above is not feasible. Im not interested in spending on coilovers at this time. Besides, I would run into spring perch clearance issues with my 255/35R18 tires. Im not willing to run smaller tires in the front, and spend money on coilovers.
Swift makes stiffers springs for other BMW chassis, but there is no information about the (length and diameter), so I cant tell if the springs would work on the E82 chassis. Ive sent Swift Support an email about this.
As a reference, spring rates for the E82/135i are:
BMW M sport = 120/350 lbs/in.
Dinan = 144/490.
Cobb = 148/457.
BMW performance = 160/420.
Swift Spec-R springs = 201/ 503.
E92/M3 specific Swift Spec-R springs are 279/670.
F82/M4 specific Swift Spec-R springs are 279/726.
http://www.swiftsprings.net/products...ct/spec-r.html