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S197 Spring and Sway Bar Rates

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Grant 302

basic and well known psychic
S197 Springs Front/Rear:
OEM:
Boss 302 ................... 148F/186R lbs/in
Boss 302 Laguna Seca 137F/191R lbs/in
Brembo GT/ GTPP ...... 131F/167R lbs/in
GT and V6PP............... 123F/156R lbs/in
P Springs (1" drop) 230-260/202 (est - may be same as published K below)
K Springs (1.5" drop) M-5300-KA Front: 228 lb/in. Rear: 199.5 lb/in.
T Springs (0.6/1.4" drop Boss reference) M-5300-T Front: ??? Rear: 199.5 lb/in. (uses K spring rear)
GT500 -

Aftermarket:
Steeda Ultra Lites 555-8206 (1.25/1.5" drop) - 195lb front, 175lb rear
Steeda Sport Springs 555-8215 (1.0/1.25" drop) - 200lb front, 175lb rear
Steeda Comp Springs Boss 302 555-8245 (0.2"/0.8" drop-Boss reference) - 225lb front, 195lb rear
Eibach sportline 4.12535 (1.6"/2") Front: 183 lb/in. Rear: 103-217 lb/in.
Eibach Pro kit GT/Boss 35125.140 (1.0/1.5" drop)
Eibach Pro kit 35101.140 '05-10GT/'10V6 Front: 171-228 lb/in. Rear: 180 lb/in.
MM R&T Lowering Coupe 435H0 (1.9/2" drop) 320-360F / 260-380R ('vert same rates)
H&R Super Sport 51655-77 (1.7/1.9 drop) ~250lb/in / rear: ~200lb/in
H&R Race 51655-88 (1.5/1.4 drop) ~300lb/in / rear: ~275lb/in
BMR Lowering SP009 (1.5" drop) 165 lb. - Front, 160 lb. - Rear
BMR Handling SP065 (1.5" drop) 240 lb/in front (linear), 200 lb/in rear (dual-rate)
BMR Handling SP072 (1.5" drop w/GT500)(~0.5"F/~1"R on GT) 260 lb/in front (linear), 220 lb/in rear (dual-rate)
SR Performance (1.5" drop) Front: 230 lb/in. Rear: 200 lb/in.
Pedders SportsRyder 1" lowering F: 200.8 lb/in R: 186.2 lb/in


FRONT S197 Bars:
34.6mm GT/Boss/LS .................. 436 lbs/in
34mm '05-'10GT/GT500/'11 V6 ... 385 lbs/in
33.2mm '12+ V6
28.6mm 2010 V6
Ford 35mm 'Blue' bar M-5490-AF (Part of M-5490-A kit)
Eibach 36mm: 340, 400, 450 lbs/in
BMR-SB022 35mm: 441, 506, 587 lbs/in
BMR-SB041 38mm: 706, 788, 886, 1002, 1144 lbs/in
Strano Performance 35mm hollow: 472, 547, 642 lbs/in

REAR S197 Bars:
Ford 13mm Solid (Boss 302S):............ 18 lbs/in
Ford 18mm Solid (Convertible):........... 55 lbs/in
Ford 20mm Solid (2005-2010 GT):....... 96 lbs/in
Ford 22mm Solid (2011+ V-6):........... 147 lbs/in
Ford 23mm Solid
Ford 24mm Solid (2011+ 5.0, GT500): 193 lbs/in
Ford 25mm Solid (Boss 302):............. 250 lbs/in
Ford 26mm Solid (Laguna Seca):........ 275 lbs/in
Ford 22mm 'Blue' bar M-5490-AR (Part of M-5490-A kit)

Eibach 25mm: 130, 145, 175 lbs/in
Strano Performance Parts 8419 1" tubular: 162, 185, 225 lbs/in
BMR-SB023: 146 lbs/in
BMR-SB042 25mm: 224, 259, 302, 356 lbs/in
Whiteline 27mm 'calculated' from stated increase over 24mm?GT bar: 266, 309, 357, 411 lbs/in

Been meaning to do this for a while now...
Please post any additions and corrections, I'll get to updating and reformatting as info gets added.
 
Last edited:

Norm Peterson

Corner Barstool Sitter
939
712
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
BMR "Handling" springs - 1.5" lowering, 240 lb/in front (linear), 200 lb/in rear (dual-rate) . . . Part # Sp065

It may still be possible to get "GT500 Handling springs", Part# SP072, which are 260 lb/in front (linear) and 220 lb/in rear (dual-rate). Searching by part number still finds them. Front lowering on a "regular GT" is only a little over 0.5" and the rear lowering is a little over an inch, maybe as much as an inch and an eighth.


Norm
 
Last edited:

Fabman

Dances with Racecars
6,519
8,154
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
This is awesome.
I didn't see the FRPP front blue bar on there though...
 

Grant 302

basic and well known psychic
Thanks for making me look at it again - it still needed another edit (red text).
All the 'drop' figures are from GT/coupe - unless noted otherwise.

This is awesome.
I didn't see the FRPP front blue bar on there though...
Only because I have no data on it.

Reserved space to advise @Grant302:

Outstanding Post, excellent information.

Thank you
Great info! We need an uncluttered thread or sticky for data like this!

LOL. Thanks Dave! Only took me 3.75 *years* from when I originally thought to do so.
 
P Springs (1" drop) 230-260/202 (est - may be same as published K below)
I know this is an older thread, just curious if this is updated information from somewhere? I've seen rates of ~200/165 quoted for the P springs up until now. Including, I think, Vorshlag's testing (I have no test data myself to contribute/confirm).
 

Grant 302

basic and well known psychic
I know this is an older thread, just curious if this is updated information from somewhere? I've seen rates of ~200/165 quoted for the P springs up until now. Including, I think, Vorshlag's testing (I have no test data myself to contribute/confirm).

That's a good question, and part of what I intend(ed) to follow up with the spring and sway bar math.

If you look at the chart from Vorshlag:
spring-rates-shelbygt.jpg

...then look at the delta in force between two values one inch apart near the corner weight of the vehicle, you can see that the force delta is closer to the values that I estimate. I would consider these to be 'working' values since they are the relevant rate for dual-rate or progressive springs.

For example:
Stock front weight is ~1,000 lbs per corner. Looking at the positions 1/2" above and below that, there are force values of 1,167 and 923. The difference between the two is 244 lb./in. Checking the pair of values directly below those two are 1,037 and 806. Difference there is 231 lb./in.

Same thing for the rear near 800 lb. corner weight gets 202 and 203 lb./in.

It seems to me that the 'target'/published rates for the K springs are about the same as I've estimated. Assuming some variability in the above test data, it seems reasonable that is the design intent to use the same rates.
 
Geez... I've looked at that testing chart probably a dozen times now over the course of a couple years without ever catching that the "Rate at position" column numbers at ride height are significantly lower than if you calculate the force deltas yourself.

Thanks for spelling it out!
 

Grant 302

basic and well known psychic
That "rate at position" is what it takes to move the spring the next half inch, up or down.

That's what it *should* be. But the values shown are the total force divided by the total displacement. 1,197lb / 6" = 194.5...and 195 is on the chart in the "rate at position" column.
 

Norm Peterson

Corner Barstool Sitter
939
712
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
↑↑↑ Exactly.

But the rates as tabulated are taken as the force in lbs at each displacement divided by that displacement. Which would be correct for a linear spring (and all of the rates would be the same).

I'm going to guess that the cells containing the first displacement to be subtracted (the zero cells) were accidentally given absolute addressing and the formula then copied into every other rate cell. Here's what running the rate calcs from 0.5" below to 0.5" above provide for mean rates. You get the same answer if you work with 0.5" under and the stated displacement going up and average that with the result from 0.5" above and the stated displacement coming down.

0.0

0.5 75 140

1.0 140 146

1.5 221 163

2.0 303 175

2.5 396 188

3.0 491 201

3.5 597 204

4.0 695 209

4.5 806 228

5.0 923 231

5.5 1037 244

6.0 1167



Norm
 
That's what it *should* be. But the values shown are the total force divided by the total displacement. 1,197lb / 6" = 194.5...and 195 is on the chart in the "rate at position" column.

The actual formula for that is to subtract the force value above from the force value below. To calculate the "Rate at position" for 2" of compression at the front, I subtract the force at 1.5" from the force at 2.5" (396-221) to come up with the 152. For very linear springs, it's very close to dividing the total force by total displacement. For progressive springs it give us more useful data.
 

Grant 302

basic and well known psychic
The actual formula for that is to subtract the force value above from the force value below. To calculate the "Rate at position" for 2" of compression at the front, I subtract the force at 1.5" from the force at 2.5" (396-221) to come up with the 152. For very linear springs, it's very close to dividing the total force by total displacement. For progressive springs it give us more useful data.

Yes, that's what the chart *should* show, but it does not. 396-221=175, and 175 should be on the chart, not 152.
 

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