bostonaudi
Go Kart Champion
- Location
- Charleston, SC
- Car(s)
- 1995 BMW M3
So, in my spring rate testing orgy of late, I've tested a bunch of combos. These are all in the context of a street car that's a daily driver that hits the track occasionally. These are not rates that would generally apply to a stripped out dedicated track car with roll cage etc. I used stock upper strut mounts, with Audi TT control arms with the TT bushings, so front and rear suspension still linked to body through rubber.
The 450's and 350's are 7" length, the 300's and 250's are 8". All are straight linear 2.5" inner diameter from HyperCoil:
front rear
450 350
450 300
350 350
350 300
300 250
300 350
General conclusions: the front of these cars are very sensitive to rate changes. With higher rates it whacks bumps and smaller cracks and fissures in road are all felt. I felt 350 on front was about the most you want to run for a daily driver that hits an autocross or track once in a while. 300 is about perfect, plenty firm and the edge is taken away, smoother and compliant with bumps. At the 450/350 rate my track times were identical (1:47's) at Road Atlanta with the previous 350/300 setup so I did not see any performance advantage at that venue. The car also got more upset running over the gators at turns 3 and 5. It did feel a little better with tighter springs coming down turn 12 as that's a compression corner but it didn't help overall time. I had sway bars set in middle for both spring rates. Even with 450 front, the car felt better with Hotchkis bar in middle.
For the rear, you can run higher rates to help suggest tighter turn in and rotation without incurring as much harshness as front. At 250 rear, its smooth, but perhaps a little soft, 300 better, and 350 makes car turn in very well. Gets a little harder on bigger bumps but manageable.
The 450/300 test was interesting, I ran this combo at VIR and the car was very tail happy coming into turn 1. With a flick of the wheel the rear would come around quite easily. While fun, it wasn't the ideal setup. At 450 front, the Eibach's need to be set near full rebound to control them.
The 350/350 is a good combo as well, a little more aggressive, not a bad ride on the street, handling quite neutral. This is the combo H2Sport is shipping with the Ohlins.
300/250 felt very good on the street, smooth and firm, and you feel the ride of the shock more than the spring. Rear felt like it needed a little more tightness.
With 300/350, the rear is tight, front not crashy at all, car feels a bit like my old 84 GTI with a big rear bar, wants to dive into corners! Rear is a little stiff but manageable. Having the Unibrace with the tighter rear springs seems to work great. Staying with this combo for now for next track event coming up at CMP. CMP has some rough spots that the 450 front springs really didn't like, especially coming out of turn 13, ripply pavement that caused loss of traction accelerating to turn 14.
Eibach supplies the R1 kit with 275f/300r, which isn't bad, the only real issue I had were the supplied springs in my kit were too short, front and rear were 7", at those rates they need to be 8" to avoid coil bind in the front and to have enough ride height in rear. So in a sense I circled back to their original rates, with a slight tweak of +25 to fronts, +50 on rears, with a 1 inch increase in length front and rear.
So for anyone shopping for coilovers for a good daily/occasional fun car, rates around the 300 lb/in range will work well, as long as the damping quality is good ride will be firm and not crashy. With these spring rates the damping very much determines the ride quality, so again get best damping you can afford. Bilstein PSS-10's come with very similar rates as well, and should work great. AST and H2Sport are also using rates in this ballpark. I would not suggest anyone get rates such as the KW Clubsport or H&R RSS Clubsport unless car is more or less a dedicated track rig and you don't want to compromise (and don't have whiny wife or GF).
Note that if you are going to venture into the world of very high rates, I'd suggest getting a kit already setup from the start this way (like Clubsports) or custom springs from a company like Eibach. When you get into a range of 600 or more, for the front the springs need to be very short, and a straight linear spring won't always cut it. For that rate a bell shaped spring (usually what comes in most coilover kits for fronts) is typically better as it will have more travel, and Eibach can supply ERS springs in that shape. You can have a company like Ground Control help with a custom setup as they have Eibach make springs for them in pretty much whatever configuration they require.
The 450's and 350's are 7" length, the 300's and 250's are 8". All are straight linear 2.5" inner diameter from HyperCoil:
front rear
450 350
450 300
350 350
350 300
300 250
300 350
General conclusions: the front of these cars are very sensitive to rate changes. With higher rates it whacks bumps and smaller cracks and fissures in road are all felt. I felt 350 on front was about the most you want to run for a daily driver that hits an autocross or track once in a while. 300 is about perfect, plenty firm and the edge is taken away, smoother and compliant with bumps. At the 450/350 rate my track times were identical (1:47's) at Road Atlanta with the previous 350/300 setup so I did not see any performance advantage at that venue. The car also got more upset running over the gators at turns 3 and 5. It did feel a little better with tighter springs coming down turn 12 as that's a compression corner but it didn't help overall time. I had sway bars set in middle for both spring rates. Even with 450 front, the car felt better with Hotchkis bar in middle.
For the rear, you can run higher rates to help suggest tighter turn in and rotation without incurring as much harshness as front. At 250 rear, its smooth, but perhaps a little soft, 300 better, and 350 makes car turn in very well. Gets a little harder on bigger bumps but manageable.
The 450/300 test was interesting, I ran this combo at VIR and the car was very tail happy coming into turn 1. With a flick of the wheel the rear would come around quite easily. While fun, it wasn't the ideal setup. At 450 front, the Eibach's need to be set near full rebound to control them.
The 350/350 is a good combo as well, a little more aggressive, not a bad ride on the street, handling quite neutral. This is the combo H2Sport is shipping with the Ohlins.
300/250 felt very good on the street, smooth and firm, and you feel the ride of the shock more than the spring. Rear felt like it needed a little more tightness.
With 300/350, the rear is tight, front not crashy at all, car feels a bit like my old 84 GTI with a big rear bar, wants to dive into corners! Rear is a little stiff but manageable. Having the Unibrace with the tighter rear springs seems to work great. Staying with this combo for now for next track event coming up at CMP. CMP has some rough spots that the 450 front springs really didn't like, especially coming out of turn 13, ripply pavement that caused loss of traction accelerating to turn 14.
Eibach supplies the R1 kit with 275f/300r, which isn't bad, the only real issue I had were the supplied springs in my kit were too short, front and rear were 7", at those rates they need to be 8" to avoid coil bind in the front and to have enough ride height in rear. So in a sense I circled back to their original rates, with a slight tweak of +25 to fronts, +50 on rears, with a 1 inch increase in length front and rear.
So for anyone shopping for coilovers for a good daily/occasional fun car, rates around the 300 lb/in range will work well, as long as the damping quality is good ride will be firm and not crashy. With these spring rates the damping very much determines the ride quality, so again get best damping you can afford. Bilstein PSS-10's come with very similar rates as well, and should work great. AST and H2Sport are also using rates in this ballpark. I would not suggest anyone get rates such as the KW Clubsport or H&R RSS Clubsport unless car is more or less a dedicated track rig and you don't want to compromise (and don't have whiny wife or GF).
Note that if you are going to venture into the world of very high rates, I'd suggest getting a kit already setup from the start this way (like Clubsports) or custom springs from a company like Eibach. When you get into a range of 600 or more, for the front the springs need to be very short, and a straight linear spring won't always cut it. For that rate a bell shaped spring (usually what comes in most coilover kits for fronts) is typically better as it will have more travel, and Eibach can supply ERS springs in that shape. You can have a company like Ground Control help with a custom setup as they have Eibach make springs for them in pretty much whatever configuration they require.
