Characterization of the OE Suspension Springs
05-19-2014, 05:52 PM
#101
as per your advice last year, when I went with a square setup, as you said, there was a huge transfer of grip to the front, so I went with an AP2 rear bar. I also went with the CR wing to balance higher speed oversteer, and found a used Gendron front bar (using #4 setting) to help with lower speed balance and am very happy so far.
Although, I've only done one track day I found that the amount of front end grip I have now is greatly increased, but the balance is about the same as before the square setup/frontbar/rearwing.
09-23-2014, 11:42 AM
#103
So I wanted to take the latest numbers from the original post, and come up with a ratio that identified the rear-biased-ness of each generation suspension combo. An 'oversteeredness ratio'.
So I used the formula listed, and the spring and bar rates, and came up with the total WR front and total WR rear (not counting the stop bushing). I then simply divided the one by the other, to come up with a ratio of front to rear bias. Below are my results. Feel free to check my math (FYI I suck at math).
Model Year---|---Front WR---|---Rear WR---|---Front:Rear ratio
================================================== ============
2000-2001----|----214-------|-----197-----|--------1.09
2002-2003----|----201-------|-----200-----|--------1.01
2004-2005----|----208-------|-----172-----|--------1.21
2006-2007----|----208-------|-----168-----|--------1.24
2008-2009----|----232-------|-----179-----|--------1.3
CR-----------|----292-------|-----208-----|--------1.4
What the above attempts to quantify is the amount of rear vs front bias there is. To put a number to the tendency to understeer vs oversteer, strictly as a function of ratio of WR front to rear. This is probably oversimplifying things, but I still think it could be useful. Since the suspension is basically unchanged, and wheelbase, weight, CG, etc, mostly the same, this seems like a valid way to compare WR to oversteeredness.
To try and analyze, the lower the number (of the ratio), the more rear bias. This shows the '02-'03 cars should be more rear biased than the earlier cars. Not sure that makes sense, but this is what the numbers show. As each model year progressed from there, they kept going more and more front biased. Less oversteer, more understeer. The CR being the most front biased according to these numbers.
The big jump being from '02-'03 to '04-'05, where the ratio jumped from 1.01 way up to 1.21. It slowly climbed up more from there. Its interesting to note that its not just the ratio that changed, but how much of the WR came from the coils, and how much from the bars. Also what changed is how stiff things were overall. As time went on, each model year change the coils mostly got stiffer, and the bars mostly got softer.
So I used the formula listed, and the spring and bar rates, and came up with the total WR front and total WR rear (not counting the stop bushing). I then simply divided the one by the other, to come up with a ratio of front to rear bias. Below are my results. Feel free to check my math (FYI I suck at math).
Model Year---|---Front WR---|---Rear WR---|---Front:Rear ratio
================================================== ============
2000-2001----|----214-------|-----197-----|--------1.09
2002-2003----|----201-------|-----200-----|--------1.01
2004-2005----|----208-------|-----172-----|--------1.21
2006-2007----|----208-------|-----168-----|--------1.24
2008-2009----|----232-------|-----179-----|--------1.3
CR-----------|----292-------|-----208-----|--------1.4
What the above attempts to quantify is the amount of rear vs front bias there is. To put a number to the tendency to understeer vs oversteer, strictly as a function of ratio of WR front to rear. This is probably oversimplifying things, but I still think it could be useful. Since the suspension is basically unchanged, and wheelbase, weight, CG, etc, mostly the same, this seems like a valid way to compare WR to oversteeredness.
To try and analyze, the lower the number (of the ratio), the more rear bias. This shows the '02-'03 cars should be more rear biased than the earlier cars. Not sure that makes sense, but this is what the numbers show. As each model year progressed from there, they kept going more and more front biased. Less oversteer, more understeer. The CR being the most front biased according to these numbers.
The big jump being from '02-'03 to '04-'05, where the ratio jumped from 1.01 way up to 1.21. It slowly climbed up more from there. Its interesting to note that its not just the ratio that changed, but how much of the WR came from the coils, and how much from the bars. Also what changed is how stiff things were overall. As time went on, each model year change the coils mostly got stiffer, and the bars mostly got softer.
09-23-2014, 02:22 PM
#104
So I wanted to take the latest numbers from the original post, and come up with a ratio that identified the rear-biased-ness of each generation suspension combo. An 'oversteeredness ratio'.
So I used the formula listed, and the spring and bar rates, and came up with the total WR front and total WR rear (not counting the stop bushing). I then simply divided the one by the other, to come up with a ratio of front to rear bias. Below are my results. Feel free to check my math (FYI I suck at math).
Model Year---|---Front WR---|---Rear WR---|---Front:Rear ratio
================================================== ============
2000-2001----|----214-------|-----197-----|--------1.09
2002-2003----|----201-------|-----200-----|--------1.01
2004-2005----|----208-------|-----172-----|--------1.21
2006-2007----|----208-------|-----168-----|--------1.24
2008-2009----|----232-------|-----179-----|--------1.3
CR-----------|----292-------|-----208-----|--------1.4
What the above attempts to quantify is the amount of rear vs front bias there is. To put a number to the tendency to understeer vs oversteer, strictly as a function of ratio of WR front to rear. This is probably oversimplifying things, but I still think it could be useful. Since the suspension is basically unchanged, and wheelbase, weight, CG, etc, mostly the same, this seems like a valid way to compare WR to oversteeredness.
To try and analyze, the lower the number (of the ratio), the more rear bias. This shows the '02-'03 cars should be more rear biased than the earlier cars. Not sure that makes sense, but this is what the numbers show. As each model year progressed from there, they kept going more and more front biased. Less oversteer, more understeer. The CR being the most front biased according to these numbers.
The big jump being from '02-'03 to '04-'05, where the ratio jumped from 1.01 way up to 1.21. It slowly climbed up more from there. Its interesting to note that its not just the ratio that changed, but how much of the WR came from the coils, and how much from the bars. Also what changed is how stiff things were overall. As time went on, each model year change the coils mostly got stiffer, and the bars mostly got softer.
So I used the formula listed, and the spring and bar rates, and came up with the total WR front and total WR rear (not counting the stop bushing). I then simply divided the one by the other, to come up with a ratio of front to rear bias. Below are my results. Feel free to check my math (FYI I suck at math).
Model Year---|---Front WR---|---Rear WR---|---Front:Rear ratio
================================================== ============
2000-2001----|----214-------|-----197-----|--------1.09
2002-2003----|----201-------|-----200-----|--------1.01
2004-2005----|----208-------|-----172-----|--------1.21
2006-2007----|----208-------|-----168-----|--------1.24
2008-2009----|----232-------|-----179-----|--------1.3
CR-----------|----292-------|-----208-----|--------1.4
What the above attempts to quantify is the amount of rear vs front bias there is. To put a number to the tendency to understeer vs oversteer, strictly as a function of ratio of WR front to rear. This is probably oversimplifying things, but I still think it could be useful. Since the suspension is basically unchanged, and wheelbase, weight, CG, etc, mostly the same, this seems like a valid way to compare WR to oversteeredness.
To try and analyze, the lower the number (of the ratio), the more rear bias. This shows the '02-'03 cars should be more rear biased than the earlier cars. Not sure that makes sense, but this is what the numbers show. As each model year progressed from there, they kept going more and more front biased. Less oversteer, more understeer. The CR being the most front biased according to these numbers.
The big jump being from '02-'03 to '04-'05, where the ratio jumped from 1.01 way up to 1.21. It slowly climbed up more from there. Its interesting to note that its not just the ratio that changed, but how much of the WR came from the coils, and how much from the bars. Also what changed is how stiff things were overall. As time went on, each model year change the coils mostly got stiffer, and the bars mostly got softer.
I believe there is a ratio called the motion ratio, or something similar, which is used to try to identify the influence of the sway bars.
09-23-2014, 02:42 PM
#105
Thread Starter
Car Analogy, your numbers are correct, but technically they represent only the vertical rate (or ride rate). For handling purposes, roll rate is of greater interest, since that's what determines weight transfer and, ultimately, the load on each tire.
I have a little spreadsheet which attempts these calculations. As it happens, the F/R roll rate ratios are very similar to the ride rate ratios. I get:
I should emphasize the second note in the table: the rear rates assume AP1 (MY00-MY03) suspension geometry. I don't have data on the revised geometry of MY04+ cars so you should interpret this table as "what if I put an AP2 suspension in my AP1?". 
That's still not the whole story, though, since even these numbers are just roll *resistance*. The actual amount of front/rear weight transfer also depends on weight distribution, track, roll axis, etc. As an example, at 1.0 lateral g, with a 170lb driver and 50% fuel (and AP1 geometry), I get:
So this table says that in terms of actual weight transfer, all of the OE setups produce more weight transfer at the rear than the front.
But that's still not the whole story, because the total load on each (outside) tire is more than just the transferred weight - there's the static weight too. I get:
Again, despite the AP2's bias towards front spring (and wheel) rate, the rear tires still support more load than the front during cornering (assuming the AP2 rear geometry doesn't have a huge effect on the calculations).
But that's STILL not the whole story, because the front and rear tires are different sizes, with different contact patches. So the "total amount of rubber" supporting the loads is also different. So finally, I get:
I think this last table (or the one before it) probably gives a little more accurate sense of the relative "oversteeredness" of the different model years. For example, the effective difference between MY02-03 and the CR is not really 40%, as you'd think from comparing the raw wheel rates, but more like 15%. In the end they're all pretty close - and all definitely S2000s.
[EDIT 12/2015: The last two tables have been revised. The previous calculations of tire loads unintentionally omitted unsprung weight. However, assuming equal amounts of unsprung weight at front and rear, the relative F/R loads per mm of tread are essentially unchanged.]
I have a little spreadsheet which attempts these calculations. As it happens, the F/R roll rate ratios are very similar to the ride rate ratios. I get:
Code:
S2000 Roll Rates Model Year | Front | Rear | Total | F/R ratio ================================================ 2000-2001 | 791 | 708 | 1499 | 1.12 2002-2003 | 696 | 700 | 1395 | 0.99 2004-2005 | 714 | 588 | 1302 | 1.22 2006-2007 | 714 | 579 | 1293 | 1.23 2008-2009 | 810 | 605 | 1415 | 1.34 2008-2009 CR | 982 | 705 | 1687 | 1.39 Notes: - Roll rates are in lb-ft/degree - Calculations assume AP1 rear suspension geometry. MY04+ rates are probably somewhat different due to revised roll center.
That's still not the whole story, though, since even these numbers are just roll *resistance*. The actual amount of front/rear weight transfer also depends on weight distribution, track, roll axis, etc. As an example, at 1.0 lateral g, with a 170lb driver and 50% fuel (and AP1 geometry), I get:
Code:
S2000 Weight Transfer at 1.0g Model Year | Front | Rear | Total | TLLD F/R ================================================= 2000-2001 | 401 | 484 | 885 | 45% / 55% 2002-2003 | 381 | 503 | 885 | 43% / 57% 2004-2005 | 415 | 470 | 885 | 47% / 53% 2006-2007 | 418 | 467 | 885 | 47% / 53% 2008-2009 | 431 | 454 | 885 | 49% / 51% 2008-2009 CR | 438 | 448 | 885 | 49% / 51% Notes: - Weight transfer in lbs. Calculations assume 170lb driver and 50% fuel, for a total weight of 2933 lbs. - For this car, total weight transfer at 1.0g is about 885 lbs regardless of spring rates. F+R values might not add to exactly 885 due to rounding. - TLLD F/R = total lateral load distribution front/rear. - Calculations assume AP1 rear suspension geometry. MY04+ rates are probably somewhat different due to revised roll center.
But that's still not the whole story, because the total load on each (outside) tire is more than just the transferred weight - there's the static weight too. I get:
Code:
S2000 Total Outside Tire Loads at 1.0g
| Front | Rear | Total | F/R Load
Model Year | Load | Load | Load | Ratio
==============================================
2000-2001 | 1115 | 1236 | 2352 | 90.2%
2002-2003 | 1096 | 1255 | 2352 | 87.3%
2004-2005 | 1129 | 1222 | 2352 | 92.4%
2006-2007 | 1132 | 1220 | 2352 | 92.8%
2008-2009 | 1146 | 1206 | 2352 | 95.0%
2008-2009 CR | 1152 | 1200 | 2352 | 96.0%
Notes:
- Loads in lbs.
- For this car, total load on outside tires at 1.0g is about 2197 lbs regardless of spring rates. F+R values might not add to 2352 due to rounding.
- Calculations assume AP1 rear suspension geometry. MY04+ rates are probably somewhat different due to revised roll center.
But that's STILL not the whole story, because the front and rear tires are different sizes, with different contact patches. So the "total amount of rubber" supporting the loads is also different. So finally, I get:
Code:
S2000 Outside Tire Loads per mm of Tread at 1.0g
| Front | Front | Rear | Rear | F/R Ratio
Model Year | Tread |Load/mm| Tread |Load/mm| Load/mm
=========================================================
2000-2001 | 205 | 5.44 | 235 | 5.26 | 103%
2002-2003 | 205 | 5.34 | 235 | 5.34 | 100%
2004-2005 | 215 | 5.25 | 245 | 4.99 | 105%
2006-2007 | 215 | 5.27 | 245 | 4.98 | 106%
2008-2009 | 215 | 5.33 | 245 | 4.92 | 108%
2008-2009 CR | 215 | 5.36 | 255 | 4.71 | 114%
Notes:
- Tread widths in mm, loads in lb/mm.
- MY00-MY03 rear tires are rated at 225mm, but are unusually wide and have narrow tread gaps compared to the fronts. The "effective"
rear tread is estimated here as 235mm.
- Calculations assume AP1 rear suspension geometry. MY04+ rates are probably somewhat different due to revised roll center.
[EDIT 12/2015: The last two tables have been revised. The previous calculations of tire loads unintentionally omitted unsprung weight. However, assuming equal amounts of unsprung weight at front and rear, the relative F/R loads per mm of tread are essentially unchanged.]
10-02-2014, 10:58 PM
#107
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Great work!! Very interesting read. I bout my MY04 with stock shocks and Eibach sport pro springs. Last week I switched over to Tein Mono Sport w/ EDFC. Since then, i can't stop tweaking my set up and read up on other suspension set ups!
07-20-2015, 03:45 PM
#109
Thread Starter
No.
The shocks are matched to the spring rates in order to maintain the same ride height. So, mounted on any other OE shock, CR springs will raise the ride height substantially. (Not to mention, they'll be underdamped.)
Now, for non-CR springs, it's often possible to mix-and-match since the rates are all pretty close. (Obviously, don't try switching the 219 lb '00 fronts with the 309 lb '02 rears!). You're okay if you stay within 5% of the original spring rate...*maybe* as much as 8 or 10%. That might not sound like much, but if you go +5% at one end and -5% at the other, you'll get a pretty big change in handling balance.
The shocks are matched to the spring rates in order to maintain the same ride height. So, mounted on any other OE shock, CR springs will raise the ride height substantially. (Not to mention, they'll be underdamped.)
Now, for non-CR springs, it's often possible to mix-and-match since the rates are all pretty close. (Obviously, don't try switching the 219 lb '00 fronts with the 309 lb '02 rears!). You're okay if you stay within 5% of the original spring rate...*maybe* as much as 8 or 10%. That might not sound like much, but if you go +5% at one end and -5% at the other, you'll get a pretty big change in handling balance.
09-15-2015, 06:37 AM
#110
twohoos,
Can you do this calculation for the eibach front bar? I find it hard to believe that the 32mm eibach fsb is only 416in/lbs, barely stiffer than the 00-01 fsb 28.x mm which is 393 in/lbs.
I'm not sure where the eibach rates came from but that doesn't seem right.
Can you do this calculation for the eibach front bar? I find it hard to believe that the 32mm eibach fsb is only 416in/lbs, barely stiffer than the 00-01 fsb 28.x mm which is 393 in/lbs.
I'm not sure where the eibach rates came from but that doesn't seem right.