GT350R Springs for GT (high rate, minimum lowering)

[SteedaTech]

Hi All!

I'm new here, and there's a lot of great information on this thread and across this forum. Hopefully this is the right place to post this!

I'm looking to stiffen-up my car and make the steering more responsive - while still being daily-drivable.
I daily drive a 2017 Mustang GT PP completely stock (with the exception of the Steeda clutch assist spring and a Corsa Sport cat-back)
I currently do a lot of spirited driving through Bay Area backroads and in the future I plan on taking my car to auto-cross events.

Based off of research gathered from this forum, my build proposal so far is as follows:

• APEX SM-10 19x10 + Michelin Pilot 4S @ 285/35r19
• FRPP Track Dampers
• Steeda Tension Link with Bearing
• Steeda Roll Center Correction Lateral Link + Bumpsteer kit
• Steeda Stop-The-Hop Kit (IRS Alignment, Brace, Bushing Supports)
• FRPP Knuckle to Toe Link Bearing
• BMR SM760 Rear Shock Mount

I am holding off on the RLCA bearing for now due to concerns over NVH.

The only decision remains is what springs to choose, namely GT350R springs or BMR SP083 springs.

• GT350R - 240f/920r lb/in @ .7/.3 inch ride height drop
• SP083 - 250f/980r lb/in @ .88/.75 inch ride height drop (or .5 inch rear if used with a Steeda 1/8 inch spacer)

I am hung up on the following reasons:

- The GT350R has less of a drop front and back, but Steeda's Extended Ball Joint is *ideally* designed for a 7/8 inch drop; the joint is .625 inch more than stock whereas a GT350R ball joint is .5 inch more than stock. Given the design of a McPherson strut cg to rc drop ratio is roughly ~3:1, I would be raising the roll center probably .6-.7 inches higher than Steeda and/or Ford deems is ideal, and I am not sure how far off from 1:1 the motion ratio would be. I am also not sure what other unintended effects this would have, such as increased camber gain under braking or faster tire wear from scrub during suspension travel if the motion ratio is far off from 1:1. Seems like @BmacIL runs GT350R fronts with this and doesn't have issues, I would love his input

- The BMR SP083 front spring matches PERFECTLY with Steeda's Extended Ball Joint @ a 7/8 inch drop. However, the rear drops too far for my liking and I would probably want to run it with a 1/8 inch spacer to raise it 1/4 inch (total .5 inch drop). I'm still worried that this may be too low of a drop in the rear, as the rear roll center drop is worse than the front roll center when lowering the same distance. I know @Bluemustang runs this without a spacer and loves it, I would love to hear more on his thoughts

- The BMR SP083 springs are 5% stiffer, but this is probably unnoticeable and a non-issue.

Please tell me if I'm over thinking this too much and I should simply choose one or the other!
My gut is also telling me I would probably also not notice the difference, which would mean I should choose the GT350R springs for the extra .2 inch of ride height gained, as I'd prefer to lower as little as possible.

Thanks!

Another great choice great choice is the Steeda Comp Dual Rate Springs. They are remarkable on track and street. Especially coupled with the adjustable Steeda Pro Actoin Dampers!
Also, our IRS subframe support braces are substantially lighter than other offerings providing outstanding control.
Steeda Tech

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[Norm Peterson]

Based off of research gathered from this forum, my build proposal so far is as follows:

• APEX SM-10 19x10 + Michelin Pilot 4S @ 285/35r19
• FRPP Track Dampers
• Steeda Tension Link with Bearing
• Steeda Roll Center Correction Lateral Link + Bumpsteer kit
• Steeda Stop-The-Hop Kit (IRS Alignment, Brace, Bushing Supports)
• FRPP Knuckle to Toe Link Bearing
• BMR SM760 Rear Shock Mount

I'm guessing it'll run in CAM-C or C-Prepared unless there's a novice class you can run in.

... the rear drops too far for my liking and I would probably want to run it with a 1/8 inch spacer to raise it 1/4 inch (total .5 inch drop). I'm still worried that this may be too low of a drop in the rear, as the rear roll center drop is worse than the front roll center when lowering the same distance. I know @Bluemustang runs this without a spacer and loves it, I would love to hear more on his thoughts

I agree that for a typical strut suspension that the geo RC height drops by somewhere between 2 and 3 times as fast as the front ride height drops, but I don't think the boldface part above concerning what's essentially an SLA rear suspension in front view is true (I'm thinking the RC to ride height 'drop' ratio should be much closer to 1:1).


Norm

 

[Rebellion]

Hi All!

I'm new here, and there's a lot of great information on this thread and across this forum. Hopefully this is the right place to post this!

I'm looking to stiffen-up my car and make the steering more responsive - while still being daily-drivable.
I daily drive a 2017 Mustang GT PP completely stock (with the exception of the Steeda clutch assist spring and a Corsa Sport cat-back)
I currently do a lot of spirited driving through Bay Area backroads and in the future I plan on taking my car to auto-cross events.

Based off of research gathered from this forum, my build proposal so far is as follows:

• APEX SM-10 19x10 + Michelin Pilot 4S @ 285/35r19
• FRPP Track Dampers
• Steeda Tension Link with Bearing
• Steeda Roll Center Correction Lateral Link + Bumpsteer kit
• Steeda Stop-The-Hop Kit (IRS Alignment, Brace, Bushing Supports)
• FRPP Knuckle to Toe Link Bearing
• BMR SM760 Rear Shock Mount

I am holding off on the RLCA bearing for now due to concerns over NVH.

The only decision remains is what springs to choose, namely GT350R springs or BMR SP083 springs.

• GT350R - 240f/920r lb/in @ .7/.3 inch ride height drop
• SP083 - 250f/980r lb/in @ .88/.75 inch ride height drop (or .5 inch rear if used with a Steeda 1/8 inch spacer)

I am hung up on the following reasons:

- The GT350R has less of a drop front and back, but Steeda's Extended Ball Joint is *ideally* designed for a 7/8 inch drop; the joint is .625 inch more than stock whereas a GT350R ball joint is .5 inch more than stock. Given the design of a McPherson strut cg to rc drop ratio is roughly ~3:1, I would be raising the roll center probably .6-.7 inches higher than Steeda and/or Ford deems is ideal, and I am not sure how far off from 1:1 the motion ratio would be. I am also not sure what other unintended effects this would have, such as increased camber gain under braking or faster tire wear from scrub during suspension travel if the motion ratio is far off from 1:1. Seems like @BmacIL runs GT350R fronts with this and doesn't have issues, I would love his input

- The BMR SP083 front spring matches PERFECTLY with Steeda's Extended Ball Joint @ a 7/8 inch drop. However, the rear drops too far for my liking and I would probably want to run it with a 1/8 inch spacer to raise it 1/4 inch (total .5 inch drop). I'm still worried that this may be too low of a drop in the rear, as the rear roll center drop is worse than the front roll center when lowering the same distance. I know @Bluemustang runs this without a spacer and loves it, I would love to hear more on his thoughts

- The BMR SP083 springs are 5% stiffer, but this is probably unnoticeable and a non-issue.

Please tell me if I'm over thinking this too much and I should simply choose one or the other!
My gut is also telling me I would probably also not notice the difference, which would mean I should choose the GT350R springs for the extra .2 inch of ride height gained, as I'd prefer to lower as little as possible.

Thanks!

There is no shame in mixing spring brands and using spacers. With the rate difference being negligible, it's up to you to decide on the right look with choosing the drop. The small difference in front roll center with the R spring vs the BMR is also not a lot, as you can tune balance with other means (alignment, mainly).

One caveat here, as I found out empirically, the difference on front vs rear drop has a consequence. The more you drop on the front vs the rear, you will gain rear grip and tend towards understeer (if everything else is kept constant). This is what I found out when adding a spacer to the rear spring, I chose to compensate this change in balance by using a R rear bar (could also be tuned via alignment). Not a big deal, but it's something to consider.

As other have said, do the LCA bearing, this makes for huge improvement. Personally I would do the CB005 plus alignment sleeves instead of the kit as the attachment points of the BMR part make more sense.

 

[SlowStangGT]

There is no shame in mixing spring brands and using spacers. With the rate difference being negligible, it's up to you to decide on the right look with choosing the drop. The small difference in front roll center with the R spring vs the BMR is also not a lot, as you can tune balance with other means (alignment, mainly).

One caveat here, as I found out empirically, the difference on front vs rear drop has a consequence. The more you drop on the front vs the rear, you will gain rear grip and tend towards understeer (if everything else is kept constant). This is what I found out when adding a spacer to the rear spring, I chose to compensate this change in balance by using a R rear bar (could also be tuned via alignment). Not a big deal, but it's something to consider.

As other have said, do the LCA bearing, this makes for huge improvement. Personally I would do the CB005 plus alignment sleeves instead of the kit as the attachment points of the BMR part make more sense.

Hi Rebellion, could you briefly summarize or link examples of alignment changes and how they correspond to the balance of the car? I've never thought about using alignment as a tool for this

 

[Bluemustang]

The alignment has a big effect on how the car handles. However it's not that simple as saying do this and it will do that. There are many factors including suspension design/geometry, driving style and intended use of the car.

For example, changing the alignment can give or take away grip from one end of the car. Most people run more negative camber on the front because of the MacPherson strut design. As the car rolls in corners, running more negative camber up front will give it more grip due to there being a better tire contact patch. This can reduce the understeer (tendency for the front tires to roll over into positive camber, thus losing grip). Generally for cornering and track/road course driving you want a lot of negative camber for this reason. Better tire contact patch during body roll event. This is good, but there is no free lunch. More static negative camber decreases stability to a degree and more negative camber in the rear decreases straight line grip because less ideal contact patch.

So what you have to ask yourself is, what is your intended use for the car and what is your driving style? All these changes don't exist in a vacuum. There are many factors at play.

 

[SlowStangGT]

The alignment has a big effect on how the car handles. However it's not that simple as saying do this and it will do that. There are many factors including suspension design/geometry, driving style and intended use of the car.

For example, changing the alignment can give or take away grip from one end of the car. Most people run more negative camber on the front because of the MacPherson strut design. As the car rolls in corners, running more negative camber up front will give it more grip due to there being a better tire contact patch. This can reduce the understeer (tendency for the front tires to roll over into positive camber, thus losing grip). Generally for cornering and track/road course driving you want a lot of negative camber for this reason. Better tire contact patch during body roll event. This is good, but there is no free lunch. More static negative camber decreases stability to a degree and more negative camber in the rear decreases straight line grip because less ideal contact patch.

So what you have to ask yourself is, what is your intended use for the car and what is your driving style? All these changes don't exist in a vacuum. There are many factors at play.

Definitely. My priorities in this order are:

1. Frequent (weekly) spirited driving through backroads.
2. Occasional (probably once or twice a year) AutoCross and/or track events.
3. Meet the above 2 criteria without ruining my spine as a DD (I'm only 26 so I don't mind a firm ride, and my commute is only 10 miles).

I'm thinking of sticking with Kelly's suggestion of having 1.5 front and 1.25 negative, but with zero front toe.
Should be the best balance for now.

Nice to know that if I decide to go SB044, I can adjust my tuning with both the bar setting and the alignment.
Although I'm thinking I wont notice it 99% of the time as I only would want to be driving 6/10 or 7/10 (if that) on backroads

One question I do have is, I'm wondering if those alignment specs should change with Steedas Roll Center Correction lateral links. Since camber gain is going to be much more, would it make sense to dial front camber back to 1.25?

 

[Bluemustang]

Definitely. My priorities in this order are:

1. Frequent (weekly) spirited driving through backroads.
2. Occasional (probably once or twice a year) AutoCross and/or track events.
3. Meet the above 2 criteria without ruining my spine as a DD (I'm only 26 so I don't mind a firm ride, and my commute is only 10 miles).

I'm thinking of sticking with Kelly's suggestion of having 1.5 front and 1.25 negative, but with zero front toe.
Should be the best balance for now.

Nice to know that if I decide to go SB044, I can adjust my tuning with both the bar setting and the alignment.
Although I'm thinking I wont notice it 99% of the time as I only would want to be driving 6/10 or 7/10 (if that) on backroads

That's good, and you can also go further more to like -1.8 in front and -1.5 in the rear. A little bit more aggressive but with an emphasis on cornering. I would also recommend caster/camber plates, as the front camber is not adjustable and this will allow you to fully dial in. For autocross/track, you'll want as much front camber as the plates will allow. -2 to -2.5 would be pretty good for this. And then just dial your rear camber to be about 0.5 degree less than the fronts.

Zero toe up front IMO is the best for responsive steering. But just be aware it'll be a little twitchy. Small corrections. If you want more stability use more toe in (i.e. positive toe). You don't want negative toe as that increases instability (also increases turn in/response). Also on the rear make sure you have at least 0.10 toe in per side. Without adequate toe in the rear will feel unstable.

 

[BmacIL]

Definitely. My priorities in this order are:

1. Frequent (weekly) spirited driving through backroads.
2. Occasional (probably once or twice a year) AutoCross and/or track events.
3. Meet the above 2 criteria without ruining my spine as a DD (I'm only 26 so I don't mind a firm ride, and my commute is only 10 miles).

I'm thinking of sticking with Kelly's suggestion of having 1.5 front and 1.25 negative, but with zero front toe.
Should be the best balance for now.

Nice to know that if I decide to go SB044, I can adjust my tuning with both the bar setting and the alignment.
Although I'm thinking I wont notice it 99% of the time as I only would want to be driving 6/10 or 7/10 (if that) on backroads

One question I do have is, I'm wondering if those alignment specs should change with Steedas Roll Center Correction lateral links. Since camber gain is going to be much more, would it make sense to dial front camber back to 1.25?

Even with the improved camber gain, the dynamic camber still sucks (all McPherson struts do). I would suggest -1.5 front for how you're using the car.

 

[Rebellion]

@BmacIL and @Bluemustang have said most of it.

The tuning I refer to is to mainly set the camber of the front and rear to adjust the neutral balance of the car (when cornering and not accelerating or braking). With everything else being equal and your caster and toe being already decided, you add lateral grip by putting more negative camber to the front (decrease understeer, increase oversteer) or the rear for the opposite effect, generally. Keep in mind that there are many factors at play here, I prefer to do this at the very end when all of your major mods (including wheels and tires) have been installed.

There are drawbacks for excessive negative (wear, straightline performance, etc), so don't go crazy with it. When I get my Steeda arms and camber/caster plates done, I will likely start with 0 toe front, 0.1 toe in on each of the rear, -1.7 camber front and -1.2 camber rear. From there I will evaluate the performance of the car in hopefully a track day, and I believe I might need more negative on the front. Also, balance needs to fit well with your style of driving, I prefer a slight neutral understeer so I can control the power oversteer when I need more turn in. I currently have -1.5 front and -1.2 rear, I'm limited on the front since I lack camber plates.

Following the rough guidelines posted here will give a very good baseline to work with, 0 front toe, 0.1 toe in rear, pick some camber between -2 and -1.5 for the front, add 0.3-0.5 positive and use that for the rear. Drive for a while and get into an event or two, then adjust the camber to your liking.

 

[baevid]

Has anyone tried the FRPP Track suspension paired with Swift R springs? I've been running on Steeda Proactions with Steeda progressives for the past 3 years but want to eventually "finish off" my suspension whenever I decide to take apart my rear end for the rear LCA and toe to knuckle bearing.

I know the FRPP Track + BMR Handling SP083 is a glowing combo but I like the slightly more rear drop of the Swift R and the spring rates seem comparable.

Here's my current setup:
Steeda front Proaction fixed struts
Ford PP rear shocks
Steeda rear shock mounts
Steeda progressive springs
Steeda front LCA bearings
Steeda tension/lateral links with bearings
Steeda bump steer kit
BMR front sway bar
Steeda G-trac bar
BMR adjustable rear camber links
Steeda rear toe links
Steeda vertical links
Steeda rear drag sway bar
BMR cradle lockout
BMR IRS support brace system

 

[BmacIL]

Has anyone tried the FRPP Track suspension paired with Swift R springs? I've been running on Steeda Proactions with Steeda progressives for the past 3 years but want to eventually "finish off" my suspension whenever I decide to take apart my rear end for the rear LCA and toe to knuckle bearing.

I know the FRPP Track + BMR Handling SP083 is a glowing combo but I like the slightly more rear drop of the Swift R and the spring rates seem comparable.

Here's my current setup:
Steeda front Proaction fixed struts
Ford PP rear shocks
Steeda rear shock mounts
Steeda progressive springs
Steeda front LCA bearings
Steeda tension/lateral links with bearings
Steeda bump steer kit
BMR front sway bar
Steeda G-trac bar
BMR adjustable rear camber links
Steeda rear toe links
Steeda vertical links
Steeda rear drag sway bar
BMR cradle lockout
BMR IRS support brace system

The rear spring rate is significantly softer on the Swift springs. I'm sure they will ride extremely well w/ the FP dampers. I think you'd need more rear swaybar for sure to get the balance where it should be, though that comes with the side effect of limiting inside tire loading/putting power down. It's a heavy car though, so maybe it'd be fine.

 

[baevid]

The rear spring rate is significantly softer on the Swift springs. I'm sure they will ride extremely well w/ the FP dampers. I think you'd need more rear swaybar for sure to get the balance where it should be, though that comes with the side effect of limiting inside tire loading/putting power down. It's a heavy car though, so maybe it'd be fine.

Oh yeah you're right, I was looking at the spreadsheet incorrectly as I was paying attention to the front only.

SP083 front 300
SP083 rear 980

Swift R front 279
Swift R rear 782

 

[BmacIL]

Oh yeah you're right, I was looking at the spreadsheet incorrectly as I was paying attention to the front only.

SP083 front 300
SP083 rear 980

Swift R front 279
Swift R rear 782

Also are you looking at the right SP083s? They are 250/980 for rate, but also 0.9" front drop, 0.75" rear drop. The old ones were different.

They were revised:
https://www.mustang6g.com/forums/th...g-springs-revised-and-better-than-ever.95677/

 

[baevid]

Yep.. corrected again. Must be an old spreadsheet that was never updated then but very useful to look at since it had all the specs for nearly every spring. Those height drops are better than the previous 1.25" front .5" rear drop then. I had the original SP080 a long time ago and did not like the rake... which was the only reason why I switched to Steedas at the time.

Another concern for me is that the Whipple weighs down the front end at least 1/8" further so that .9" drop in the front would actually be better for me. Thanks for clearing that up, I'll update my wish list with the SP083 then

 

[Bluemustang]

Also are you looking at the right SP083s? They are 250/980 for rate, but also 0.9" front drop, 0.75" rear drop. The old ones were different.

They were revised:
https://www.mustang6g.com/forums/th...g-springs-revised-and-better-than-ever.95677/

Hey technically 0.875 drop in front. Don't rob me of that extra 0.025" in suspension travel

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