Springs for STX class AutoX
#1
11-17-2005, 08:46 PM
Springs for AutoX (STX class only!)
Suspension Gurus, I call for your wisdom!
I autocross my G in STX class. The biggest limitations in this class are 8" rims and 245mm width tires. I have 17x8 wheels and raced this last season on the new Hankook Z212 tires. I'll probably will stick with the same tires next year since they are significantly less expensive than Azenis and other tires in that class.
Having said that, I would really like to keep this thread's discussion geared toward STX class only. BS, BSP, or higher classes have different tire/rim allowances (all wider and stickier) than STX; thus different advice would apply.
My current suspension mods are 350evo sways (front and rear) and Tokico D-Spec dampeners. I've also been keeping my car aligned with zero toe and about -1.6 camber in the rear. The rest are the stock nominal specs. I've found the best settings for me personally are with the sways both at medium and the D-Specs set at 4 turns from full stiff (f & r). I tried full stiff on the sways one day, but the car was too twitchy and unforgiving for a driver with my skills.
Now, I'd like to take my setup a bit further to the next level. I have decided to put some different springs in mainly to get more negative camber out of the front of the car. In all my research, I have found two springs that will meet my spring rate and lowering dimension requirements: 350z Tein H-Techs or OEM 350z Springs. From what I have read in all my searches, I should be able to use either type of springs and be OK without aftermarket camber adjustments.
The question is which do you think the best setup would be?
1. First, the older 2002-2004 OEM 350z springs share the same spring rates (314/342) as my coupe. By installing these there should ultimately be negligible changes to the load balance of the car (ignoring camber changes).
2. By going with 2005+ OEM 350z springs (314/427), I add 25% more roll bias to the rear and increase the overall stiffness ([f%+r%]/2) from springs by 12.4%. This setup concerns me since power-on oversteer is already a slight issue. Perhaps more negative camber in the rear and stiffer front sway to compensate?
3. 350z H-Tech springs (358/375) result in 3.8% roll bias to the front and increase the overall stiffness by 11.8%. This seems like a favorable setup, except the rear may be dropped too much for the stock camber/toe adjustments. The bias should help the power-on oversteer a bit assuming the sways are kept on med/med.
4. Finally, the last option is using 350z H-Techs in front and 2005+ OEM 350z springs in the rear giving a balance of (358/427). This results in a 9.5% bias to the rear and an overall stiffnes increase of 19.4% To me, this seems like a winning setup - better camber up front and rear (at least more adjustability for rear). This setup does favor power-on oversteer a bit over my current setup, but increasing the negative camber in the rear near -2 degrees and some rear dampener adjustment should help.
OK, OK, I'm going somewhere with this
My question is: given the limitations in tire size and compound (245mm width and wear rating >140) which of the above choices do you think best? Will the newer 350z springs alone be too stiff in the rear? Will the higher spring rates of the H-techs up front be too much for the front tires to handle? Overall, I'm leaning toward the 4th option of mixing the front H-Tech springs with the rear 2005+ OEM 350z springs.
I know this is a pretty long post. I think I've made up my mind now, but I wanted to share my homework with the class and get the teachers' feedback for all to see. This should be useful info for all the STX folks out there.
TIA!
I autocross my G in STX class. The biggest limitations in this class are 8" rims and 245mm width tires. I have 17x8 wheels and raced this last season on the new Hankook Z212 tires. I'll probably will stick with the same tires next year since they are significantly less expensive than Azenis and other tires in that class.
Having said that, I would really like to keep this thread's discussion geared toward STX class only. BS, BSP, or higher classes have different tire/rim allowances (all wider and stickier) than STX; thus different advice would apply.
My current suspension mods are 350evo sways (front and rear) and Tokico D-Spec dampeners. I've also been keeping my car aligned with zero toe and about -1.6 camber in the rear. The rest are the stock nominal specs. I've found the best settings for me personally are with the sways both at medium and the D-Specs set at 4 turns from full stiff (f & r). I tried full stiff on the sways one day, but the car was too twitchy and unforgiving for a driver with my skills.
Now, I'd like to take my setup a bit further to the next level. I have decided to put some different springs in mainly to get more negative camber out of the front of the car. In all my research, I have found two springs that will meet my spring rate and lowering dimension requirements: 350z Tein H-Techs or OEM 350z Springs. From what I have read in all my searches, I should be able to use either type of springs and be OK without aftermarket camber adjustments.
The question is which do you think the best setup would be?
1. First, the older 2002-2004 OEM 350z springs share the same spring rates (314/342) as my coupe. By installing these there should ultimately be negligible changes to the load balance of the car (ignoring camber changes).
2. By going with 2005+ OEM 350z springs (314/427), I add 25% more roll bias to the rear and increase the overall stiffness ([f%+r%]/2) from springs by 12.4%. This setup concerns me since power-on oversteer is already a slight issue. Perhaps more negative camber in the rear and stiffer front sway to compensate?
3. 350z H-Tech springs (358/375) result in 3.8% roll bias to the front and increase the overall stiffness by 11.8%. This seems like a favorable setup, except the rear may be dropped too much for the stock camber/toe adjustments. The bias should help the power-on oversteer a bit assuming the sways are kept on med/med.
4. Finally, the last option is using 350z H-Techs in front and 2005+ OEM 350z springs in the rear giving a balance of (358/427). This results in a 9.5% bias to the rear and an overall stiffnes increase of 19.4% To me, this seems like a winning setup - better camber up front and rear (at least more adjustability for rear). This setup does favor power-on oversteer a bit over my current setup, but increasing the negative camber in the rear near -2 degrees and some rear dampener adjustment should help.
OK, OK, I'm going somewhere with this
My question is: given the limitations in tire size and compound (245mm width and wear rating >140) which of the above choices do you think best? Will the newer 350z springs alone be too stiff in the rear? Will the higher spring rates of the H-techs up front be too much for the front tires to handle? Overall, I'm leaning toward the 4th option of mixing the front H-Tech springs with the rear 2005+ OEM 350z springs.
I know this is a pretty long post. I think I've made up my mind now, but I wanted to share my homework with the class and get the teachers' feedback for all to see. This should be useful info for all the STX folks out there.
TIA!
Last edited by CrazyMike; 11-17-2005 at 08:55 PM.
#2
11-18-2005, 12:36 AM
#3
11-18-2005, 08:20 AM
STX allows aftermarket springs and shock absorbers - there are limitations to that, but my D-specs and the other springs I mentioned are legal.
The rules are located here:http://www.scca.org/_filelibrary/File/2005SoloRules.pdf
Here are some excerpts:
14.5 SHOCK ABSORBERS
A. Shock absorber bump stops may be altered or removed.
B. Any shock absorbers may be used. Shock absorber mounting
brackets which serve no other purpose may be altered, added, or
replaced, provided that the attachment points on the body/frame/
subframe/chassis/suspension member are not altered. This installation
may incorporate an alternate upper spring perch/seat and/or
mounting block (bearing mount). The system of attachment may
be changed. The number of shock absorbers shall be the same as
Stock. No shock absorber may be capable of adjustment while the
car is in motion, unless fitted as original equipment. MacPherson
strut equipped cars may substitute struts, and/or may use any
insert. This does not allow unauthorized changes in suspension
geometry or changes in attachment points (e.g., affecting the
position of the lower ball joint or spindle). It is intended to allow
the strut length changes needed to accommodate permitted modifications
which affect ride height and suspension travel
14.7 ANTI SWAY BARS
Substitution, addition, or removal of any anti-roll bar(s) is permitted.
Bushing material, method of attachment, and locating points are
unrestricted. Components such as anti-roll bars and strut housings
that serve dual purposes by also functioning as suspension locators
may not be modified in ways that change the suspension geometry
or steering geometry. Non-standard lateral members which connect
between the brackets for the bar are not permitted.
14.8 SUSPENSION
A. Ride height may only be altered by suspension adjustments, the
use of spacing blocks, leaf spring shackles, torsion bar levers, or
change or modification of springs or coil spring perches. This does
not allow the use of spacers that alter suspension geometry, such
as those between the hub carrier and lower suspension arm.
Springs must be of the same type as the original (coil, leaf, torsion
bar, etc.) and except as noted herein, must use the original spring
attachment points. This permits multiple springs, as long as they
use the original mount locations. Coil spring perches originally
attached to struts or shock absorber bodies may be changed or
altered, and their position may be adjustable. Spacers are allowed
above or below the spring. Suspension bump stops may be
altered or removed.
B. Suspension bushings may be replaced with bushings of any
materials (except metal) as long as they fit in the original location.
Offset bushings may be used. In a replacement bushing the
amount of metal relative to the amount of non-metallic material
may not be increased. This does not authorize a change in type of
bushing (for example ball and socket replacing a cylindrical bushing),
or use of a bushing with an angled hole whose direction
differs from that of the original bushing. If the Stock bushing
accommodated multi-axis motion via compliance of the component
material(s), the replacement bushing may not be changed to
accommodate such motion via a change in bushing type, for
example to a spherical bearing or similar component involving
internal moving parts. Pins or keys may be used to prevent the
rotation of alternate bushings, but may serve no other purpose
than that of retaining the bushing in the desired position.
There's more, but they aren't too restrictive for what I'm trying to accomplish...
Yes, I bought a tire pyrometer (probe type) and tried to get my heat distribution as flat as possible. Fronts like to be at 37 and rears at 34 lbs. This was a surprise to me - I was running 42/36 before the pyrometer for half the season and it killed my tires earlier than I would have liked. Oh well - beginner's mistake...
The rules are located here:http://www.scca.org/_filelibrary/File/2005SoloRules.pdf
Here are some excerpts:
14.5 SHOCK ABSORBERS
A. Shock absorber bump stops may be altered or removed.
B. Any shock absorbers may be used. Shock absorber mounting
brackets which serve no other purpose may be altered, added, or
replaced, provided that the attachment points on the body/frame/
subframe/chassis/suspension member are not altered. This installation
may incorporate an alternate upper spring perch/seat and/or
mounting block (bearing mount). The system of attachment may
be changed. The number of shock absorbers shall be the same as
Stock. No shock absorber may be capable of adjustment while the
car is in motion, unless fitted as original equipment. MacPherson
strut equipped cars may substitute struts, and/or may use any
insert. This does not allow unauthorized changes in suspension
geometry or changes in attachment points (e.g., affecting the
position of the lower ball joint or spindle). It is intended to allow
the strut length changes needed to accommodate permitted modifications
which affect ride height and suspension travel
14.7 ANTI SWAY BARS
Substitution, addition, or removal of any anti-roll bar(s) is permitted.
Bushing material, method of attachment, and locating points are
unrestricted. Components such as anti-roll bars and strut housings
that serve dual purposes by also functioning as suspension locators
may not be modified in ways that change the suspension geometry
or steering geometry. Non-standard lateral members which connect
between the brackets for the bar are not permitted.
14.8 SUSPENSION
A. Ride height may only be altered by suspension adjustments, the
use of spacing blocks, leaf spring shackles, torsion bar levers, or
change or modification of springs or coil spring perches. This does
not allow the use of spacers that alter suspension geometry, such
as those between the hub carrier and lower suspension arm.
Springs must be of the same type as the original (coil, leaf, torsion
bar, etc.) and except as noted herein, must use the original spring
attachment points. This permits multiple springs, as long as they
use the original mount locations. Coil spring perches originally
attached to struts or shock absorber bodies may be changed or
altered, and their position may be adjustable. Spacers are allowed
above or below the spring. Suspension bump stops may be
altered or removed.
B. Suspension bushings may be replaced with bushings of any
materials (except metal) as long as they fit in the original location.
Offset bushings may be used. In a replacement bushing the
amount of metal relative to the amount of non-metallic material
may not be increased. This does not authorize a change in type of
bushing (for example ball and socket replacing a cylindrical bushing),
or use of a bushing with an angled hole whose direction
differs from that of the original bushing. If the Stock bushing
accommodated multi-axis motion via compliance of the component
material(s), the replacement bushing may not be changed to
accommodate such motion via a change in bushing type, for
example to a spherical bearing or similar component involving
internal moving parts. Pins or keys may be used to prevent the
rotation of alternate bushings, but may serve no other purpose
than that of retaining the bushing in the desired position.
There's more, but they aren't too restrictive for what I'm trying to accomplish...
Yes, I bought a tire pyrometer (probe type) and tried to get my heat distribution as flat as possible. Fronts like to be at 37 and rears at 34 lbs. This was a surprise to me - I was running 42/36 before the pyrometer for half the season and it killed my tires earlier than I would have liked. Oh well - beginner's mistake...
#6
11-18-2005, 01:43 PM
Finite changes in spring rate will tune the chassis, moving to understeer or oversteer. But to effect changes that will deliver result’s that bring about improved grip level’s mean's either running very high front camber angles or to prevent front roll in the first place. This is why the front rate increases from the springs you have to pick from will not improve front grip as the front of your car will still roll over and your tires will play dead theirby inducing understeer. Kill the roll with stiffer springs.
So, what can you do?
Every single choice that comes up will involve a rather large investment, this is why I’ve researched the aftermarket and developed the product spec list’s that I have. Fact is most all the stuff you can get is not geared toward real improvements at the track.
1. Tokico does make a linear spring for their 350Z shock and spring system. BUT, are you ok with a 2” drop? Bigger question, will Tokico sell the springs on the side? At 375lbs/375lbs we are still not talking about enough spring to effect roll rates, but the drop will help with the lower CG.
2. Sell the Tokico shocks, since they do not have a removable spring perch and won’t allow for other spring option’s that the rules do allow for. In place of the Tokico’s, TcKline DA shocks ($419 each)
3. Spring option’s for TcKline DA’s
3a.First thing that comes to mind, Nismo T2 springs. But, like the Tokico springs are you going have to be ok with a 2” drop? And you may find that the rear rate they use may be a liability vs. plus. The rules read to me that a spacer above the spring is allowed, this may allow the use of a Eibach ESS spring in the rear to get a lower rear spring rate if needed, but ride height management in the rear is a big unanswered question since the ESS springs are sold in 11” and 13” lengths, would be curious to know the free length of the Nismo T2 rear spring.
3c. Install koni coil over conversion parts on the front TcKline shocks, here’s your payoff for the shocks having separate removable spring perches. Pick the Eibach ERS spring rate that suits you for the front. For the rear run something oem based or work with the Eibach ESS spring instead.
Why not Koni shocks? By the time you revalve them your within $500 of the cost of the TcKline's and you will have rebound only control vs the TcKline seperate rebound and compression dampning control. I can also add that I've run the Koni's with a custom coilover setup on the front with 448lbs rates. From my own experience, the shocks did not enough rebound range to cover that rate. The original set that I had ended up being sent back to Koni for replacement since the left shock was spraying oil out the top. Since I can't find a buyer for the new replacement's I guess I'm going to send them off to propartsusa to be revalved vs getting the TcKline shocks that I want,...sigh.
I went a different route for the front spring instead of using a ERS spring I used a Tein tapered spring with a adaptor I made to fit the spring on the coilover sleave. For the rear I tested the following, with interesting results. Tein 350Z H-tech, oem 05 Z springs, and oem sedan sport springs, 375, 427 and 342 of course respectively.
So, what can you do?
Every single choice that comes up will involve a rather large investment, this is why I’ve researched the aftermarket and developed the product spec list’s that I have. Fact is most all the stuff you can get is not geared toward real improvements at the track.
1. Tokico does make a linear spring for their 350Z shock and spring system. BUT, are you ok with a 2” drop? Bigger question, will Tokico sell the springs on the side? At 375lbs/375lbs we are still not talking about enough spring to effect roll rates, but the drop will help with the lower CG.
2. Sell the Tokico shocks, since they do not have a removable spring perch and won’t allow for other spring option’s that the rules do allow for. In place of the Tokico’s, TcKline DA shocks ($419 each)
3. Spring option’s for TcKline DA’s
3a.First thing that comes to mind, Nismo T2 springs. But, like the Tokico springs are you going have to be ok with a 2” drop? And you may find that the rear rate they use may be a liability vs. plus. The rules read to me that a spacer above the spring is allowed, this may allow the use of a Eibach ESS spring in the rear to get a lower rear spring rate if needed, but ride height management in the rear is a big unanswered question since the ESS springs are sold in 11” and 13” lengths, would be curious to know the free length of the Nismo T2 rear spring.
3c. Install koni coil over conversion parts on the front TcKline shocks, here’s your payoff for the shocks having separate removable spring perches. Pick the Eibach ERS spring rate that suits you for the front. For the rear run something oem based or work with the Eibach ESS spring instead.
Why not Koni shocks? By the time you revalve them your within $500 of the cost of the TcKline's and you will have rebound only control vs the TcKline seperate rebound and compression dampning control. I can also add that I've run the Koni's with a custom coilover setup on the front with 448lbs rates. From my own experience, the shocks did not enough rebound range to cover that rate. The original set that I had ended up being sent back to Koni for replacement since the left shock was spraying oil out the top. Since I can't find a buyer for the new replacement's I guess I'm going to send them off to propartsusa to be revalved vs getting the TcKline shocks that I want,...sigh.
I went a different route for the front spring instead of using a ERS spring I used a Tein tapered spring with a adaptor I made to fit the spring on the coilover sleave. For the rear I tested the following, with interesting results. Tein 350Z H-tech, oem 05 Z springs, and oem sedan sport springs, 375, 427 and 342 of course respectively.
Last edited by Gsedan35; 11-18-2005 at 01:48 PM.
#7
11-18-2005, 01:55 PM
Also, I want to post the following exchange I had on my350Z.com
In reply to a clarification on the truechoice coilover spring rates (500/425)
I responded with,
His reply,
to that I replied,
In reply to a clarification on the truechoice coilover spring rates (500/425)
Originally Posted by FritzMan
Their selected spring rate bias is very similar to what I'm now running with my JIC FLT setup. Instead of the standard kit of 10kg front and 12 kg rear (560/672 lbs), I'm running 10 kg up front and 9 kg rear (560/502).
The softer rear provides a lot more corner exit traction while the stiffer front allows agressive turn-in and sharper steering response. Not only has handling improved, but I found that a softer rear really improves the street ride. It seems as though the rear is more sensitive to spring rates than the front.
The softer rear provides a lot more corner exit traction while the stiffer front allows agressive turn-in and sharper steering response. Not only has handling improved, but I found that a softer rear really improves the street ride. It seems as though the rear is more sensitive to spring rates than the front.
Originally Posted by Gsedan35
Thank you for your comments. So you ran the original 560/672 setup first, then you switched to the 502lbs setup and your impression's are drawn on having tracked both setups?
Originally Posted by FritzMan
I ran the 560/672 all last season in Solo2 and felt the rear was too snappy. It was good for rotation but bad for weight transfer/traction when exiting corners. Also, any kind of bump would upset the tire's traction because the rear was just too stiff.
Throughout the '04 season I played with sway bar rates and the JIC's adjustable compression and noticed that a softer rear allowed more traction without ill effects to handling. The car certainly felt different, but the clock (and butt) said it was a good move.
This season I'm setting up the car for Solo1 so an even softer rear is ideal (some understeer). Initial testing with the current setup has been quite favorable.
Note that I'm running 245/40/18 Kumho MXs front AND rear so understeer has been substantially tamed with that setup alone.
Throughout the '04 season I played with sway bar rates and the JIC's adjustable compression and noticed that a softer rear allowed more traction without ill effects to handling. The car certainly felt different, but the clock (and butt) said it was a good move.
This season I'm setting up the car for Solo1 so an even softer rear is ideal (some understeer). Initial testing with the current setup has been quite favorable.
Note that I'm running 245/40/18 Kumho MXs front AND rear so understeer has been substantially tamed with that setup alone.
Originally Posted by Gsedan35
Thank you again for your imput, your comment's are appreciated beyond measure. I especially appreciated where your comming from for several reason's. One your not tainted by a product line or having to only talk in a way to support what you sell and your doing the type of event's I'm more inclined to benefit from since I will never see high speed road course's. Furthermore I've been in need of imput on trial and effor testing before I can relax from the position of being against high transfer's of spring stiffness to the front. Your imput helps a great deal in that regard.
Trending Topics
#8
11-18-2005, 02:16 PM
Some related bookmarks that I've saved
http://www.popularhotrodding.com/tech/0311phr_tire.pdf
http://sccaforums.com/forums/141221/ShowPost.aspx
http://www.my350z.com/forum/showthre...threadid=54918
http://sccaforums.com/forums/56960/showpost.aspx
http://www.my350z.com/forum/showthre...threadid=86520
http://www.popularhotrodding.com/tech/0311phr_tire.pdf
http://sccaforums.com/forums/141221/ShowPost.aspx
http://www.my350z.com/forum/showthre...threadid=54918
http://sccaforums.com/forums/56960/showpost.aspx
http://www.my350z.com/forum/showthre...threadid=86520
#9
11-18-2005, 04:31 PM
#10
11-18-2005, 08:23 PM
Wow - I'm already over my head in here 
Gsedan35 - great information! Thank-you! To answer some of your questions: I can't handle much more drop than 0.8" and 0.7" front and rear, respectively. These limitations are set by the local road conditions and the fact that aftermarket camber/toe adjustments are out of the question for me right now (fiscal constraints). This is my commuter car so I like to be able to get a decent ride out of it for the non-race days.
So now the question is whether or not there is any benefit to the choices I listed over my current OEM spring/D-Spec combo? I was hoping any more negative camber induced by lower springs up front (0.5"-0.8") would be of benefit over the stock springs - which should earn me around 0.7 to 1.0 more degrees of static negative camber up front. Sounds like the benefits are lost in the still prevailent body roll?
636Racer - you do make a good point. On one hand the rules state: "Coil spring perches originally attached to struts or shock absorber bodies may be changed or altered, and their position may be adjustable." However, it also says, "Springs must be of the same type as the original (coil, leaf, torsion bar, etc.) and except as noted herein, must use the original spring attachment points." I guess that means they would be OK in front, but the rear must retain springs in the original locations. I'm guessing that has been discussed somewhere on SCCAforums.com somewhere. Coil-overs just aren't an option for me monetarily now, so I'm not going to bother looking for the that answer just yet.
Gsedan35 - great information! Thank-you! To answer some of your questions: I can't handle much more drop than 0.8" and 0.7" front and rear, respectively. These limitations are set by the local road conditions and the fact that aftermarket camber/toe adjustments are out of the question for me right now (fiscal constraints). This is my commuter car so I like to be able to get a decent ride out of it for the non-race days.
So now the question is whether or not there is any benefit to the choices I listed over my current OEM spring/D-Spec combo? I was hoping any more negative camber induced by lower springs up front (0.5"-0.8") would be of benefit over the stock springs - which should earn me around 0.7 to 1.0 more degrees of static negative camber up front. Sounds like the benefits are lost in the still prevailent body roll?
636Racer - you do make a good point. On one hand the rules state: "Coil spring perches originally attached to struts or shock absorber bodies may be changed or altered, and their position may be adjustable." However, it also says, "Springs must be of the same type as the original (coil, leaf, torsion bar, etc.) and except as noted herein, must use the original spring attachment points." I guess that means they would be OK in front, but the rear must retain springs in the original locations. I'm guessing that has been discussed somewhere on SCCAforums.com somewhere. Coil-overs just aren't an option for me monetarily now, so I'm not going to bother looking for the that answer just yet.
Last edited by CrazyMike; 11-18-2005 at 08:28 PM.
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