Setup
GC coilovers, Koni single adjustable, 440F/400R #/in (this is about 45% stiffer than stock and 20% than my old Dinan III)
Dinan rear bar in middle position
Dinan front strut brace
TC Designs sway bar brackets
SSRs with 275 RA1s (track) - Dinan 275 PS1F/2R (street)
aligned at 1 degree negative in front at about 1/8 inch higher than Dinan III (adjusting front camber to 2 1/2 for track results in just enough toe-out for nice turn-in without being "twitchy")
Track
Pretty much everything i had hoped for and maybe more
More forgiving - able to make fine adjustments to line and drive different lines passing or being passed - better response and control approaching limit (exceeded expectations)
Very well balanced
Better behaved under braking
Quicker -- i'd only been to Buttonwillow once, a year ago, on street tires -- my best laps were 7-8 sec quicker. allowing 3 sec for tires and 2 sec for experience, leaves 2-3 sec for suspension. However, i was still overbraking at least half the turns and believe that i can more safely work on further improvements. Will have a better idea of speed when i get to Thunderhill where i've got some history. Hopefully will see KJK at the track this summer and he can drove it for an informed 2nd opinion.
Anecdotes
had the pleasure of gradually closing on an (old) viper (compently but not expertly driven) under braking and cornering with enough extra speed through the corners that he couldn't pull me on the straights, then passing and going away
driver of stock Boxster S (experienced, but not expert) came over after session to find out why he couldn't close on me in corners
Street
Not bad but not great - at low speeds ride is FIRM but not harsh, "busy". Drove about 500 mi on varied freeways and good secondaries to track - high speed ride is quite acceptable.
The front suspension travel is reduced from about 4 1/2 inches to 3 1/2 inches (depending on how the bump-stops are factored in) and that at the slightly lowered but not extreme ride height there is only and inch of travel to the stop. This make speed bumps and potholes a problem -- fortunately i don't have too many of either. i may try raising the car a bit more, but don't want to reduce the rear camber too much.
The track handling improvements carry over to the street.
Conclusion
if you really want to track an M5 and you don't have a serious pothole problem, this is the way to go (double adjustable Konis would be better, but who knows when they'll deliver them)
if you're never going to the track, buy a Dinan stage III (with JRZ shocks if you can afford it)
if you're thinking about tracking the M5 or track a couple times a year i'm really not sure if the Dinan III with adjustable camber plates (as reputably available from GC) or the GC coilovers with "street" springs (and Dinan rear bar) is better. The GC linear springs are going to be more predictable on track, but i'm concerned about the front spring travel for street use (i'm assuming spring travel is the same 3 1/2 inches and with less stiff springs there it will be even easier to bottom out)
GC coilovers, Koni single adjustable, 440F/400R #/in (this is about 45% stiffer than stock and 20% than my old Dinan III)
Dinan rear bar in middle position
Dinan front strut brace
TC Designs sway bar brackets
SSRs with 275 RA1s (track) - Dinan 275 PS1F/2R (street)
aligned at 1 degree negative in front at about 1/8 inch higher than Dinan III (adjusting front camber to 2 1/2 for track results in just enough toe-out for nice turn-in without being "twitchy")
Track
Pretty much everything i had hoped for and maybe more
More forgiving - able to make fine adjustments to line and drive different lines passing or being passed - better response and control approaching limit (exceeded expectations)
Very well balanced
Better behaved under braking
Quicker -- i'd only been to Buttonwillow once, a year ago, on street tires -- my best laps were 7-8 sec quicker. allowing 3 sec for tires and 2 sec for experience, leaves 2-3 sec for suspension. However, i was still overbraking at least half the turns and believe that i can more safely work on further improvements. Will have a better idea of speed when i get to Thunderhill where i've got some history. Hopefully will see KJK at the track this summer and he can drove it for an informed 2nd opinion.
Anecdotes
had the pleasure of gradually closing on an (old) viper (compently but not expertly driven) under braking and cornering with enough extra speed through the corners that he couldn't pull me on the straights, then passing and going away
driver of stock Boxster S (experienced, but not expert) came over after session to find out why he couldn't close on me in corners
Street
Not bad but not great - at low speeds ride is FIRM but not harsh, "busy". Drove about 500 mi on varied freeways and good secondaries to track - high speed ride is quite acceptable.
The front suspension travel is reduced from about 4 1/2 inches to 3 1/2 inches (depending on how the bump-stops are factored in) and that at the slightly lowered but not extreme ride height there is only and inch of travel to the stop. This make speed bumps and potholes a problem -- fortunately i don't have too many of either. i may try raising the car a bit more, but don't want to reduce the rear camber too much.
The track handling improvements carry over to the street.
Conclusion
if you really want to track an M5 and you don't have a serious pothole problem, this is the way to go (double adjustable Konis would be better, but who knows when they'll deliver them)
if you're never going to the track, buy a Dinan stage III (with JRZ shocks if you can afford it)
if you're thinking about tracking the M5 or track a couple times a year i'm really not sure if the Dinan III with adjustable camber plates (as reputably available from GC) or the GC coilovers with "street" springs (and Dinan rear bar) is better. The GC linear springs are going to be more predictable on track, but i'm concerned about the front spring travel for street use (i'm assuming spring travel is the same 3 1/2 inches and with less stiff springs there it will be even easier to bottom out)
