Tipping Sensation During Hard Cornering (roll center?), SP080 springs, PP swaybars and Struts

[Bluemustang]

I am extremely satisfied with my setup of SP083s, Ford Racing track dampers and BMR sway bars. I'm also running 285/35 R19 as Norm suggested to you.

Don't overestimate the value of a good alignment. I am using Kelly's alignment spec plus about about .2-.3 negative camber front & rear.

-1.8 front camber and -1.5 rear camber. -0.01 and -0.02 front toe and 0.14 rear toe on both sides. This is honestly the best the car has felt and the wider tires and solid alignment. I think running less negative camber in the rear has made a big difference for the handling balance.

I feel the effect of the roll center is overplayed. If you car is lowered an inch or more, then it might be more beneficial. But with my setup I don't feel that I need it.

@BmacIL runs the same setup as I do and he didn't feel the need to install Steeda roll center corrected control arms. There are most likely other factors at play which makes it hard to decipher the real effects. I don't doubt that they work, but it's just a matter of determining whether or not it's needed.

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[BmacIL]

I think that there is an equation that is being overlooked here .

With progressive springs and bumpier than all get out the ride quality is far better while DD ing every time 1 has to drive to A to B twice a day . Lineers just keep bouncing trust me I drive 294 and it plain sucks on these PP springs and shocks ..
Figuring out that 1 needs to correct Roll center is an ideal plan and 1 should give careful thought to while lowering to go along with correcting the alignment ..

So give me the ideal alignment Specs . For lowering an inch in the front and a half inch in the back plus the correct valving shocks and struts with BMR SPO80 Springs ......

The bounce you feel on 294 isn't linear vs. progressive. It's a poorly damped suspension causing oscillation. Better dampers + getting rid of the rubber spring that is the stock shock mounts is key.

 

[Norm Peterson]

If linear springs are bouncing, it's because their dampers aren't providing enough damping at low suspension velocities. The same shocks used with dual-rate or true progressive springs is going to do a better job of quieting any 'bounce' because the spring doesn't have enough rate in its softer region to push the suspension as fast or as far up. As you go up with spring rate, I suspect it gets tougher to meet both performance and ride harshness targets with either fixed or manually adjustable shock valving.


Norm

 

[Bluemustang]

I think that there is an equation that is being overlooked here .

With progressive springs and bumpier than all get out the ride quality is far better while DD ing every time 1 has to drive to A to B twice a day . Lineers just keep bouncing trust me I drive 294 and it plain sucks on these PP springs and shocks ..
Figuring out that 1 needs to correct Roll center is an ideal plan and 1 should give careful thought to while lowering to go along with correcting the alignment ..

So give me the ideal alignment Specs . For lowering an inch in the front and a half inch in the back plus the correct valving shocks and struts with BMR SPO80 Springs ......

My experience with progressive springs might be different from yours. I switched from progressive/dual rate Ford Racing springs to SP083 high rate linear springs and the ride quality is far better and controlled IMO but YMMV. For me, I've learned the linear rate springs are far more predictable which leads to a better ride and better handling.

 

[Bluemustang]

The bounce you feel on 294 isn't linear vs. progressive. It's a poorly damped suspension causing oscillation. Better dampers + getting rid of the rubber spring that is the stock shock mounts is key.

Agree fully here.

 

[Norm Peterson]

On the matter of roll center correction for small amounts of lowering . . . it's not likely to be worth the bother. Maybe it would if you were at the pointy end of your competition and looking for hundredths of a second in a minute or two at autocross or time trialing, but if that was the case you might not be discussing it publicly for competitive reasons.

FWIW, when I finally swapped to firmer springs on my '08, the strut-suspended front only dropped by about 0.6", so I wasn't even going to think about doing RC and bumpsteer corrections. If I'd felt I had to do anything, I'd have shimmed the front suspension back up by a quarter inch or so.


Norm.

 

[Brian V]

The bounce you feel on 294 isn't linear vs. progressive. It's a poorly damped suspension causing oscillation. Better dampers + getting rid of the rubber spring that is the stock shock mounts is key.

I am running the Steeda rear shock mounts with the PP from @rum_punch_ruby ..steeda rear sway bar set to full soft . I am looking for a less gap in the front .

 

[BmacIL]

I am running the Steeda rear shock mounts with the PP from @rum_punch_ruby ..steeda rear sway bar set to full soft . I am looking for a less gap in the front .

PP shocks and springs? PM me. We'll get ya figured out.

 

[Brian V]

Shopping list ............


Ford racing track shocks and struts for lowering springs
Steeda rear camber adjustment attachments ......

BMR front camber bolts . SPO80 springs .

 

[Bluemustang]

Shopping list ............


Ford racing track shocks and struts for lowering springs
Steeda rear camber adjustment attachments ......

BMR front camber bolts . SPO80 springs .

If I can make a suggestion -- for the BMR SP080 springs, it would be a good idea (although not entirely necessary) to do a bumpsteer kit. With the 1.2" drop in the front I encountered some bumpsteer problems when I used those springs.

Less than 1" I do not think bumpsteer kit is really needed but more than that in my experience it helped a lot especially on the the crappy roads.

 

[BmacIL]

Shopping list ............


Ford racing track shocks and struts for lowering springs
Steeda rear camber adjustment attachments ......

BMR front camber bolts . SPO80 springs .

I'd suggest the SP763 and those dampers. It will give you approx 0.4" of rake from what you have with the lowering of 0.875"/0.5", F/R.

 

[Bluemustang]

I'd suggest the SP763 and those dampers. It will give you approx 0.4" of rake from what you have with the lowering of 0.875"/0.5", F/R.

I agree. I think the min drop springs are a better choice as well.

 

[qtrracer]

I suggest purchasing some double adjustable dampers and work with what you have. The factory damping settings are at best a compromise with stock pieces. Lowering springs regardless of rate changes = toe out and negative camber with no other changes. This should be optimized with an alignment. Moreover, the dampers are not allowed to work in their desired range because they are partially compressed (as in dive). Adjustable dampers will allow the user to put the damper's useful range back in sync with the chassis height. In addition, they will allow the user to control how fast the springs compress in dive and rebound from dive. This is important for keeping the tires on the ground and allowing the chassis to behave predictably.

Another thing to keep in mind is that suspension theory in dive while turning has two schools of thought: (i) high spring rates with light bars; and (ii) light spring rates with heavy bars. Of course "light" and "high/heavy" are relative. For example, Maximum Motorsports likes the heavy spring/light bar approach on Fox chassis Mustangs. For later model Mustangs the light/spring heavy bar seems more optimal. But don't mix these up.

The "light" spring allows the front to travel in dive to take advantage of weight transfer. At turn-in, the heavy bar keeps the inside tire planted for optimal grip (adds nothing to straight line driving). If static caster and camber are set-up properly, dynamic caster will help negate any poor KPI issues and also try to stand both the front tires as upright as possible. Too much dynamic camber hurts the inside tire's grip by going positive (hence too much static camber is not good - and caster may not correct enough).

Finally, the S550s use a unique front dual lower ball joint design (unique from earlier Mustangs). These two joints create a "virtual" steering pivot point. The virtual pivot moves around to optimize both dynamic caster and camber in dive while turning. Keep this in mind when trying to improve handling. The Ford engineers didn't add a lot of static camber to either of the 350s despite lowering.

 

[TheLion]

I suggest purchasing some double adjustable dampers and work with what you have. The factory damping settings are at best a compromise with stock pieces. Lowering springs regardless of rate changes = toe out and negative camber with no other changes. This should be optimized with an alignment. Moreover, the dampers are not allowed to work in their desired range because they are partially compressed (as in dive). Adjustable dampers will allow the user to put the damper's useful range back in sync with the chassis height. In addition, they will allow the user to control how fast the springs compress in dive and rebound from dive. This is important for keeping the tires on the ground and allowing the chassis to behave predictably.

Another thing to keep in mind is that suspension theory in dive while turning has two schools of thought: (i) high spring rates with light bars; and (ii) light spring rates with heavy bars. Of course "light" and "high/heavy" are relative. For example, Maximum Motorsports likes the heavy spring/light bar approach on Fox chassis Mustangs. For later model Mustangs the light/spring heavy bar seems more optimal. But don't mix these up.

The "light" spring allows the front to travel in dive to take advantage of weight transfer. At turn-in, the heavy bar keeps the inside tire planted for optimal grip (adds nothing to straight line driving). If static caster and camber are set-up properly, dynamic caster will help negate any poor KPI issues and also try to stand both the front tires as upright as possible. Too much dynamic camber hurts the inside tire's grip by going positive (hence too much static camber is not good - and caster may not correct enough).

Finally, the S550s use a unique front dual lower ball joint design (unique from earlier Mustangs). These two joints create a "virtual" steering pivot point. The virtual pivot moves around to optimize both dynamic caster and camber in dive while turning. Keep this in mind when trying to improve handling. The Ford engineers didn't add a lot of static camber to either of the 350s despite lowering.

Your right that the GT350 does NOT run a lot more static camber than the regular GT, I actually have the factory alignment spec sheets. But they DID change the roll center on the GT350 to correct for the 0.7" drop in ride height over a normal GT, the GT350 front hub knuckles are different than the regular GT's and I believe the height at which the mounting points for the ball studs mount is lower than the regualr GT's front hub knuckles (also the GT350's are aluminum vs. cast iron). There was no need to change the rear roll center as the change in ride height over a stock GT is less than 0.4" (I think it's 0.38" lower ride height in the rear over a GT PP).

I spoke with Kelly from BMR regarding alignment settings for the SP080's and also on his thoughts regarding how the SP080's are intended to work. One advantage of running a bigger drop in the front is anti-dive, SP080's significantly increase anti-dive because the tension links more or less pull up on the chassis more during braking, giving it an increased anti-dive characteristic.

The lateral links however primarily affect roll center as well as the dynamic camber and unfortunately an uncorrected roll center does increase the leverage on the suspension during cornering and slows down steering response a bit and for a third whammy reduces turn in. It also reduces dynamic camber as the suspension compresses which is a fourth strike against it, forcing you to run more static camber, which negatively affects inside tire grip. Sure, you can again compensate somewhat with caster settings, but they are less ideal over all from the factory geometry if you have an uncorrected roll center.

It's not huge, but enough that it's negative effects do offset some of positives of anti-dive and lowered CG. Correcting the roll center would have a similar effect to running a little more bar up front without reducing independence of the suspension and maintaining a little more inside tire grip by having more optimal dynamic camber.

Yes you can compensate some what for a lowered roll center by running stiffer bars or stiffer springs or both. But I think there are more pros to a corrected roll center than just compensating by running more bar. I can always add some more bar later on on top of the lateral links if needed. GT350 bars are not terribly expensive or hard to install and I hear they pair quite well with SP080's on PP struts for a very flat street setup with a nice ride frequency. But I'd rather work from a more ideal roll center starting out then compensating with more bar than I should need due to a less than optimal front end geometry.

There's different approaches and there are very fast cars with either approach, but some setups are inherently easier to drive than others even if their potential may be similar. I'd take easy to drive any day and I think correcting the roll center first is a better way to get there.

Cons of Lowered Roll Center:
- Increased body roll that can be compensated for to some degree with stiffer springs and bars
- Reduces steering response
- Reduces dynamic camber so you must run more static camber to compensate
- Reduces turn in during corner entry (may be good or bad depending on suspension)

Am I forgetting anything?

 

[BmacIL]

Your right that the GT350 does NOT run a lot more static camber than the regular GT, I actually have the factory alignment spec sheets. But they DID change the roll center on the GT350 to correct for the 0.7" drop in ride height over a normal GT, the GT350 front hub knuckles are different than the regular GT's and I believe the height at which the mounting points for the ball studs mount is lower than the regualr GT's front hub knuckles (also the GT350's are aluminum vs. cast iron). There was no need to change the rear roll center as the change in ride height over a stock GT is less than 0.4" (I think it's 0.38" lower ride height in the rear over a GT PP).

I spoke with Kelly from BMR regarding alignment settings for the SP080's and also on his thoughts regarding how the SP080's are intended to work. One advantage of running a bigger drop in the front is anti-dive, SP080's significantly increase anti-dive because the tension links more or less pull up on the chassis more during braking, giving it an increased anti-dive characteristic.

The lateral links however primarily affect roll center as well as the dynamic camber and unfortunately an uncorrected roll center does increase the leverage on the suspension during cornering and slows down steering response a bit and for a third whammy reduces turn in. It also reduces dynamic camber as the suspension compresses which is a fourth strike against it, forcing you to run more static camber, which negatively affects inside tire grip. Sure, you can again compensate somewhat with caster settings, but they are less ideal over all from the factory geometry if you have an uncorrected roll center.

It's not huge, but enough that it's negative effects do offset some of positives of anti-dive and lowered CG. Correcting the roll center would have a similar effect to running a little more bar up front without reducing independence of the suspension and maintaining a little more inside tire grip by having more optimal dynamic camber.

Yes you can compensate some what for a lowered roll center by running stiffer bars or stiffer springs or both. But I think there are more pros to a corrected roll center than just compensating by running more bar. I can always add some more bar later on on top of the lateral links if needed. GT350 bars are not terribly expensive or hard to install and I hear they pair quite well with SP080's on PP struts for a very flat street setup with a nice ride frequency. But I'd rather work from a more ideal roll center starting out then compensating with more bar than I should need due to a less than optimal front end geometry.

There's different approaches and there are very fast cars with either approach, but some setups are inherently easier to drive than others even if their potential may be similar. I'd take easy to drive any day and I think correcting the roll center first is a better way to get there.

Cons of Lowered Roll Center:
- Increased body roll that can be compensated for to some degree with stiffer springs and bars
- Reduces steering response
- Reduces dynamic camber so you must run more static camber to compensate
- Reduces turn in during corner entry (may be good or bad depending on suspension)

Am I forgetting anything?

You're going the right way, but there are some advantage to a lowered roll center: reduced jacking forces and reduced cornering loads in the suspension members.

One of the reasons I did not want to drop the car much is because of all the negatives you listed. With my setup, I'm only down about 0.7" from stock in the front, which doesn't have the magnitude of the cons as you're seeing at 1.2". Add that to the fact that I still have ~250 lb/in springs up front and there is very good roll control and response.

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