Springs for koni STR.T struts?
#11
For an S197 being lowered and using STR.t's, I'd be a bit careful about getting too close to 1.5" or going too high with the spring rate. There is some information on S197 springs, but have been a few questions concerning some of the numbers.
The S197 front suspension already is a sort of coilover arrangement, and what that means is that the spring rates are going to have much softer numbers than you'd see with the Fox/SN95 "conventionally located" springs (midway out the lower control arm). Most LCA-mounted springs are about midway out the arm, and to get the wheel rate from that it involves the distance ratio squared. So a 600 lb/in Fox/SN95 spring is going to be about 150 at the wheel. A strut motion ratio is generally around 0.95, and the ratio squared about 0.9, so a coilover or S197 spring giving 150 at the wheel is only going to run in the 160 - 175 lb/in range. FWIW, quite a few of the "lowering springs" run just a little higher than that.
For a mild drop, I'd suggest the Steeda HD upper strut mounts, as these already contain provision for adjusting camber up to about 1° either way from its center position. They're also more durable with lowered cars than the OE strut mounts and you have to take the OE mounts off to get at the spring isolaters anyway, so it's kind of a no-brainer. With them, plus a digital angle finder, you can do your own alignment if you feel like experimenting a bit. If not, make sure that whoever you have do your alignment knows how to work with camber plates (the Steeda mounts work just like C-C plates). Not all places understand this, and may tell you that "camber can't be adjusted" simply because there's no OE provision to do so.
Do at least the front springs and struts together - the same labor is involved, including alignment, so you might as well do it all just once. Rear shocks, rear springs, and sta-bars can all be done at separate times (althoiugh if you do the rear springs before the shocks the rear might be a bit bouncy until you do since your 5+ year old OE shocks aren't going to be up to the task of controlling the stiffer springs.
I suggest that you get in touch with Sam Strano by phone (he's a forum sponsor and his online catalog is at www.stranoparts.com ). I suspect that a particular Steeda sport spring or possibly the ultralights will end up being his recommendation. While you're there, look for his 3-way adjustable sta-bars, and probably the kit with the 22mm rear bar given that your car is a bit lighter up front. Sam wins his autocross class at least as often as not, so I think you can assume that the bar kits that he's put together are going to work well in that environment as well as on the street. FWIW, I have a set of his bars on my '08.
You do realize that swapping springs or both the front and rear bars will move you out of F Stock into either STX/STU or ESP? But if the autocross is mostly going to be for fun rather than any serious effort at winning a class championship, just do it and enjoy the way the car turns out.
Norm
The S197 front suspension already is a sort of coilover arrangement, and what that means is that the spring rates are going to have much softer numbers than you'd see with the Fox/SN95 "conventionally located" springs (midway out the lower control arm). Most LCA-mounted springs are about midway out the arm, and to get the wheel rate from that it involves the distance ratio squared. So a 600 lb/in Fox/SN95 spring is going to be about 150 at the wheel. A strut motion ratio is generally around 0.95, and the ratio squared about 0.9, so a coilover or S197 spring giving 150 at the wheel is only going to run in the 160 - 175 lb/in range. FWIW, quite a few of the "lowering springs" run just a little higher than that.
For a mild drop, I'd suggest the Steeda HD upper strut mounts, as these already contain provision for adjusting camber up to about 1° either way from its center position. They're also more durable with lowered cars than the OE strut mounts and you have to take the OE mounts off to get at the spring isolaters anyway, so it's kind of a no-brainer. With them, plus a digital angle finder, you can do your own alignment if you feel like experimenting a bit. If not, make sure that whoever you have do your alignment knows how to work with camber plates (the Steeda mounts work just like C-C plates). Not all places understand this, and may tell you that "camber can't be adjusted" simply because there's no OE provision to do so.
Do at least the front springs and struts together - the same labor is involved, including alignment, so you might as well do it all just once. Rear shocks, rear springs, and sta-bars can all be done at separate times (althoiugh if you do the rear springs before the shocks the rear might be a bit bouncy until you do since your 5+ year old OE shocks aren't going to be up to the task of controlling the stiffer springs.
I suggest that you get in touch with Sam Strano by phone (he's a forum sponsor and his online catalog is at www.stranoparts.com ). I suspect that a particular Steeda sport spring or possibly the ultralights will end up being his recommendation. While you're there, look for his 3-way adjustable sta-bars, and probably the kit with the 22mm rear bar given that your car is a bit lighter up front. Sam wins his autocross class at least as often as not, so I think you can assume that the bar kits that he's put together are going to work well in that environment as well as on the street. FWIW, I have a set of his bars on my '08.
You do realize that swapping springs or both the front and rear bars will move you out of F Stock into either STX/STU or ESP? But if the autocross is mostly going to be for fun rather than any serious effort at winning a class championship, just do it and enjoy the way the car turns out.
Norm
Last edited by Norm Peterson; 02-15-2012 at 04:48 PM.
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