Suspension Recommendation ~$2,500

[Eritas]

I re-read my posts from last night and I'm thinking that I was harsher than needed to be and I apologize for that. Anyhow, I'm liking where this threads heading as we are now having an actual technical discussion on merits on VLs.

I'm sure some of my posts could have been written better too.

I took a picture of the backside of a stock VL and you can see that it has a good amount rubber bushing on the top side and I can stick a screwdriver through and wiggle it a bit. The bottom side has very little rubber and feels pretty solid. So my theory is that if you go with aftermarket VLs without supporting mods, you won't feel any difference because extra firmness will be observed by soft cradle bushings or as SlaughterOfTheSoul mentioned, by stock LCA bushing.

The rubber really isn't all that thick and I can't tell if it's solid or not. I've done that too, but sticking a screwdriver though the hole and twisting it around (conical movement) is not representative of the load path when installed on the car. The vertical link is a compression/tension link. To feel the play of the bushing in this sense, you would need to try to compress the bushing by pushing down on both ends of the screwdriver, which would bend it. You really need a hardened bolt or rod and even then, you're not going to feel any play in compression. To properly test the deflection of the stock bushing, you need a potentiometer and a load cell to measure deflection vs load. It's not that difficult to do for any credible race shop or parts manufacturer. Then compare those results to aftermarket poly, spherical and delrin links.

Once I get my subframe bushing inserts (which are amazing on my friend's car) I'll probably then back to back the poly VL to stock and see if it makes a difference then. Based on the Steeda video, the subframe bushings should be addressed before anyone installs a vertical link.

I know this isn't an apples-to-apples comparison, using an unscientific fingernail test, 80 durometer polyurethane inserts feel a bit firmer than the OEM rubber, and 90 durometer ones feel almost as hard as a rock. Not sure what's the rating for OEM rubber bushings, but this site says they generally range between 50 to 70 durometers. And since OEM rubber bushings are known to degrade over time, perhaps the biggest improvement comes from having a fresh set of bushings. I'll bet Ford race cars get their bushings refreshed often, if not between every race, unlike the street cars.

I'd agree with that. I'm pretty sure Ford's racecars use solid aluminum inserts on the subframe and diff, and probably have a lot of spherical bearings in the control arms. I'll have to go back to the Dean Martin GT4 page and check. But either way, I find it really intriguing that Ford changed out all of these bearings and bushings except the VL. Maybe minor compliance in that link helps put power down for road racing? If so, I still stand behind the idea that aftermarket VL's aren't necessary for street/HPDE cars. Maybe drag cars, but I don't drag race, don't know the needs of drag racing, or have seen failures or improvements from drag racing, or care much about drag racing. That's just an opinion (on stock VLs) and lack of experience/interest (drag racing), and no one has to agree with it.

Sponsored

 

[TheLion]

Just playing devil's advocate here, but remember because something is firmer does not necessarily make it better. I think we get too caught up in "because this part has some compliance we must make it firmer because all compliance is bad" and the only reason we tolerate any compliance is to avoid excessive NVH. There are areas where some small compliance may actually result in more desirable traits. A small amount of compliance in the vertical links keeps your breaking from being overly edgy, same with on power, which makes the car easier to drive. Easier to drive is better for the less skilled drivers like most of us. That's the very reason I will probably go with BMacIL's suspension combination once the time comes (Track Pack Dampers with BMR SP083 springs, stock PP sway bars). It's an easy to drive setup that's very similar in overall characteristics to the GT350.

I would highly reccomend before anyone starts digging into vertical links and RLCA bushings they simply try the IRS Cradle Lockout of their choice AND Ford Performance Outer Toe Link Spherical Bearings. If you have a PP car you only need the outer bearings that go into the knuckle as the inner toe link ends already have spherical bearings. If you have a non-PP car you'll need to buy some toe links of your choice or upgrade to PP toe links + the outer bearings.

Then work out from there. You might be really surprised at how just removing IRS compliance and Toe angle changes completely alters the handling the car. The rear end becomes far more communicative, consistent and you can apply power noticeably earlier. Remember those reviews from MT saying you could hang the tail out on the 2016 Camaro SS at will and it was easy to do while with the Mustang it was like balancing a spy plane at the edge of stall (aka it was extremely difficult)?

Well those two IRS modifications completely reverse those negative traits. The rear is in sync with the front 100% (IRS lockout) and the edge is very defined and easy to access (toe links). While hanging the tail out (aka drifting) isn't the fastest way around a track (unless your on dirt), the fact that you can do that predictably means you know precisely where the edge is at and how far you can push.

Regarding diff bushings just be careful to re-torque them after install and then check and re-torque them after the first 100 miles, then also after every track event. Those instructions and warnings are from Steeda's own mouth.

Otherwise you'll end up shearing a bolt like I did and have to drop the whole IRS and replace the diff cover, a complete PITA. And I'm not even FI, I'm just running a Power Pack 2 and Corsa Sport Cat Back exhaust. I would only recommend diff bushings if your willing to do the maintenance on them and for most dual purpose cars it's not worth it in my opinion.

Sure it firms up the drive train / power delivery a bit, but handling wise I'd take toe links over diff bushings any day if I had to choose. Yes, for race applications, aluminum IRS bushings and differential bushings is what you'd want, but there is a quite substantial increase in NVH. It'll sound like you have a basket ball rolling around in the trunk during city driving and if you have a 3.73 you're almost guaranteed to get substantial diff whine.

I want to be able to cruise in my GT 500 miles and still enjoy the car, so if a modification makes the car un-enjoyable it's a no go for me. I don't mind small increases in NVH, it's a sports car, but something drastic is going to ruing it's street enjoyment factor which is 90% of it's use.

Right now I'm running on three basic suspension tweaks that really capitalize on the handling already build into, but hidden within a PP GT. 1. SP080 lowering springs 2. CB05 cradle lockout and 3. FP Outer Toe Link Spherical Bearings. A PP GT really comes alive with just those three simple modifications and it's a good starting place to build outward from.

So for race applications, don't assume everything in the IRS is all hard spherical bearings. They may use poly or even rubber in certain cases to induce a specific handling trait to make the car easier to drive or to handle a certain way under braking or acceleration or mid-corner etc.

There's a reason the GT4 uses OE vertical links. To induce a specific handling trait. I'm not sure however if the inner rear lower control arm bushing is rubber or spherical. It would be interesting to see that part. I believe it is rubber on the GT350 and GT350R stock and both of those cars can out handle most of our GT's even with modifications.

So I'm suggesting we pay much more attention to struts, springs, sway bars, wheels and wheel offsets and tire choices.

 

[TheLion]

By the way I found this for those wondering what the GT350 runs stock: http://www.fordservicecontent.com/F...350-Supplement-version-1_su_EN-US_07_2015.pdf

Front spring rate GT350 34 N/mm (194 lb/in) GT350R 42 N/mm (240 lb/in)
Rear spring rate GT350 160 N/mm (914 lb/in) GT350R 160 N/mm (914 lb/in)
Front stabilizer bar GT350 34mm DIA x 5.7mm wall (1.34 x 0.22 in) GT350R 34mm DIA x 5.7mm wall (1.34 x 0.22 in)
Rear stabilizer bar GT350 22.2mm DIA x 3.9mm wall (0.87 x 0.15 in) GT350R 22.2mm DIA x 3.9mm wall (0.87 x 0.15 in ) with 8mm (0.31 in) shorter arms than GT350

Does anyone know how the stock PP sway bars compare? It looks like BMR's SP083 spring rates are nearly identicle to the GT350R spring rates, probably why they pair so well with FP Track Dampers valving / damping rates. Also since the BMR rear springs are a bit stiffer, it might explain why you don't need a whole lot more, if any, rear bar as they are slightly stiffer than the GT350/R rear springs (914 lbs/in vs. BMR's 980 lbs/in).

 

[TheLion]

And according to LMR: https://lmr.com/products/Mustang-Sway-Bar-Size-Guide

Base 2015 GT has a 32 mm front and 21.7 mm (we'll call it 22) rear. Not sure how thick rear PP sway bars are as I know they are a tad thicker. Knowing how OEM's work, I'm guessing...22.2 mm! Mass production makes more sense.

So it looks to me like running GT350R bars with SP083 springs / FP Track dampers would be a static version (obviously it won't have variable damping rates of magnetic ride control) of the GT350R's suspension setup. The arm length on the GT350R rear bar is 8mm shorter even though diameter is nearly identical to stock PP rears.

You could drill out a stock PP rear sway bar to shorten the arm length about 1~1.5 inches, that might give you pretty close rates to GT350R rears, same with the fronts. Just shorten them up a small amount or buy a used set of GT350R bars.

Interestingly this backs up what BMacIL said about the car not needing more bar. Looks to me like the GT350R isn't running a whole lot more bar than the PP GT. Most of it is sprung which makes the car easier to drive. I have a feeling the SS 1LE is tuned in a similar way. While not as fast as the GT350R, it's not that far behind and some of that difference may just be power as the GT350 has a 70 hp advantage. Suspension wise, if you neutered the power, I'll bet my bottom dollar those two cars would be nearly dead even. (2018 PP2 neck and neck with a 1LE).

Take the ZL1 as an example of how throwing a ton of power at it can make it a substantial difference even with handling deficiencies. A regular ZL1 just does not handle as well as 1LE. It's not as balanced, not as easy to drive, but it's faster on a track...a nearly 200 hp advantage can make up for some handling deficiencies. It even beat a GT350R by a small margin. Albeit it took a 125 HP advantage to do it and I'm betting there's even great advantage average due to the swelling mid-range of the ZL1's super charged 6.2. The NA voodoo 5.2 just cannot compete against the big bore FI chevy.

 

[Eritas]

I'm not buying that ChevyTrend comparison test. As you said, the ZL1 is heavier with worse weight distribution than the SS 1LE (and 350R) and the 350R has a much larger splitter and rear wing, making more downforce. The 350R also has wider and stickier tires, yet looking at the speed traces, the 1LE was faster in most of the corners. You'd think the 125hp advantage would show up on the straights, but most of the time the ZL1 gained on the 350R was in the corners. I call BS.

On another note, the 2015+ GT has proven to be faster than the Boss 302 and even my old E90 M3 on track. These are amazingly capable cars that are far better than 99% of what their owners are able to get out of them. But I agree the subframe bushings are way too soft and should be one of the first mods to do, then focusing on improving the nut behind the wheel rather than throwing money at the suspension thinking that's the cars limitation (and not the driver).

 

[TheLion]

They are stamped steel. Definitely not brittle.

VLs are not a big piece of IRS puzzle at all. To say that the aftermarket versions do nothing would not be accurate, but I will say that it's small. Only under very specific conditions am I able to notice it (under slow corner exit, there's less chatter).

Hence why it's not something that should be modified immediately. Cradle lockout and toe links are the two most beneficial first modifications even with stock PP suspension. It really does transform the rear of the car. If Ford had equipped the PP GT with the following 5 modifications from the factory it would have matched the 6th gen SS in straight line performance and performed on par or a little ahead of the 1SS in handling right out of the box with almost no added NVH:

1. Power Pack 2 - gives you nearly identical power to the 5th gen LT1 in the 2016+ SS - there's nothing unusual about a factory performance car requiring 91 minimum

2. Locked out IRS cradle bushings - gets rid of this delay between the front and rear of the car as they almost work in a "delayed manner" stock due to the compliance and substantial amount of IRS movement, this is also why the car "take a set" in corners, because it's a delay, once the IRS stops moving and settles the cars handling becomes predictable again, but that's no good for performance driving

3. Spherical bearings in both inner and outer toe link ends - this really allows you to put power down earlier on corner exit and even straight line, it also provides some much needed feedback from the rear end as to what the tires are doing. This gives you that precision the SS has stock where you "hang the tail out" at will instead of it being so picky that it's nearly impossible to do predictably. It has a defined and consistent behavior as opposed to this vague unknown reaction to driver inputs.

4. Slightly stiffer spring rates and slightly lower stance like the BMR SP763 minimum drop springs - yes a little more ride height is normal for a factory setup, also gives you a bit more travel to soak up rougher surfaces of many street applications. I love my SP080's, however they might be a little low in the front for very rough roads and certainly too low for Super Charger kits even though I've not hand any issues with them per say in my NA car. This would be a really good factory option for stock PP cars.

5. Aluminum bushing in the shifter arm base where it attaches to the MT-82 and better gear oil - this really allows for more precise and consistent shifting (aluminum arm bushing) as it removes the compliance of the stock rubber bushing and allows the syncros to mesh more consistently, making the finnicky MT-82 a fairly smooth shifting and precise transmission. Better quality fluid removes a lot of the notchyness in the MT-82, I'm using BG SyncroShiftII.

Those five simple alterations would have made a stock PP GT an very good entry level track car and far more competitive with the 1SS offerings. Granted I don't believe Ford realized Chevy was cannibalizing the excellent 5th Gen LT1 from the Corvette and the Alpha chassis from Cadillac, both much higher tier platforms. The 5th Gen SS was about equivalent (or slightly inferior) to the stock PP setup on the first iteration of the 6th gen GT's (2015-2017). It's a little heavier and makes a little less power, but is fairly close over all.

Handling wise, with just those 3 suspension modifications the car's nature has completely changed. It's like driving a different car and I've only changed 3 basic components of the suspension. Ford didn't focus too much on real handling traits with the PP1 cars for 2015-2017 years. It was more or less an option that gave you a good foundation to build up from for real performance enthusiast who would do their own suspension modifications or possibly use Ford Performance track upgrades. And it was just enough to make the car decently fun to drive for those who just occasionally hit the gas when merging onto the highway or on a back road and mostly tour with the car. For that it's great even stock as it does have a remarkably refined ride as far as american pony cars go.

But I don't mind a small amount of harshness here or there if it means getting a significant amount of performance back that is locked away as long as it doesn't make the car un-enjoyable to cruise in with the windows down and the music up. It's a pony car, it's about fast, fun and affordable. There lots of fun to be had even if it doesn't have a BMW like refinement to the ride as long as it handles well and delivers the power, sound and looks.

 

[Eritas]

New BMWs don't have that great of a ride of handling anymore. Hence my switch.

 

[TheLion]

My big contention right now is where to go with bars, springs and struts down the road. I'm fine with the bar and spring rates I have now until the PP struts are used up. But I'm still pondering the differences in suspension packages I could either create or buy. There's more motor than suspension right now, which is fun, but I would love to run it a little harder on corners.

There's two paths, I can either create my own package or go with a known good quantity (FP Track Package). Costs are similar however as is mentioned the FP Track Package, as good as it is, may make some compromises in handling for the sake of ride comfort. I'd be willing to go a little bit further for handling so long as the car isn't unbearable. I can deal with some harshness on really rough roads.

Of course tires are a big problem right now and there's more in the current suspension than these tires can manage. The P Zeros do not exactly inspire confidence in the corners. In fact their lateral grip is abysmally low compared to even my worn out Pilot Sport AS3+ all seasons...sad. But they are quite comfy (the P Zero's almost feel more like a "performance touring" tire focused more on all around comfort than outright performance). I'm due for tires next spring, so I'll make due for now, looking for a good dual purpose tire in the Pilot Sport 4S's on the 19x9.5 four square RTR Tech 7 wheel setup.

In a year or two I'm thinking of going with a similar setup to BMacIL's using BMR SP083 springs, FP Track Dampers but going a step further and using GT350R stock bars. That would give a nearly identical suspension setup to the GT350R sans adaptive damping. Rear spring rates are a tad heavier, GT350R's are 914 where BMR's are 980. I could compensate with a bit less bar in the rear and leave the stock PP bar but upgrade the front bar only then tweak from there.

The GT350 does (both regular and R) runs a 34mm bar up front. It's not a huge increase in anti-roll over the 32mm GT bar, but a small amount. It also runs a 22.2mm rear bar, but the arm length is 8mm shorter. I BELIEVE stock PP bars are 22.2mm where base model rear bars are 21.7mm. Not sure how arm lengths compare however. OE bars are pretty cheap so it would be a very good base line dual purpose setup that closely mimics the easy to drive nature of the GT350R and it would still ride half way decent, enough that it's enjoyable to cruise in for a while.

I think that would be a really good match for a Power Pack 2 or 3 equipped 5.0. It definitely moves really well with that nice mid-range of Power Pack 2 on back roads, I use it often.

 

[TheLion]

Here's the GT350 bars front and rear:

https://parts.lakelandford.com/a/Fo...BAR--COMPONENTS-FRONT-SUSPENSION/JC15401.html

and

https://parts.lakelandford.com/a/Fo...-BAR--COMPONENTS-REAR-SUSPENSION/JC15714.html

 

[BmacIL]

My big contention right now is where to go with bars, springs and struts down the road. I'm fine with the bar and spring rates I have now until the PP struts are used up. But I'm still pondering the differences in suspension packages I could either create or buy. There's more motor than suspension right now, which is fun, but I would love to run it a little harder on corners.

There's two paths, I can either create my own package or go with a known good quantity (FP Track Package). Costs are similar however as is mentioned the FP Track Package, as good as it is, may make some compromises in handling for the sake of ride comfort. I'd be willing to go a little bit further for handling so long as the car isn't unbearable. I can deal with some harshness on really rough roads.

Of course tires are a big problem right now and there's more in the current suspension than these tires can manage. The P Zeros do not exactly inspire confidence in the corners. In fact their lateral grip is abysmally low compared to even my worn out Pilot Sport AS3+ all seasons...sad. But they are quite comfy (the P Zero's almost feel more like a "performance touring" tire focused more on all around comfort than outright performance). I'm due for tires next spring, so I'll make due for now, looking for a good dual purpose tire in the Pilot Sport 4S's on the 19x9.5 four square RTR Tech 7 wheel setup.

In a year or two I'm thinking of going with a similar setup to BMacIL's using BMR SP083 springs, FP Track Dampers but going a step further and using GT350R stock bars. That would give a nearly identical suspension setup to the GT350R sans adaptive damping. Rear spring rates are a tad heavier, GT350R's are 914 where BMR's are 980. I could compensate with a bit less bar in the rear and leave the stock PP bar but upgrade the front bar only then tweak from there.

The GT350 does (both regular and R) runs a 34mm bar up front. It's not a huge increase in anti-roll over the 32mm GT bar, but a small amount. It also runs a 22.2mm rear bar, but the arm length is 8mm shorter. I BELIEVE stock PP bars are 22.2mm where base model rear bars are 21.7mm. Not sure how arm lengths compare however. OE bars are pretty cheap so it would be a very good base line dual purpose setup that closely mimics the easy to drive nature of the GT350R and it would still ride half way decent, enough that it's enjoyable to cruise in for a while.

I think that would be a really good match for a Power Pack 2 or 3 equipped 5.0. It definitely moves really well with that nice mid-range of Power Pack 2 on back roads, I use it often.

I think you would love that setup. I also plan on similar, though possibly just the front bar.

 

[TheLion]

That's what I was thinking. Running a stock PP rear bar and a GT350/R front bar (GT350 and GT350R run same front 34 mm bar) because the BMR rear spring rates are a little higher than the GT350R's rear spring rates. That should balance it out. So there's not too much rear bar / spring combo between BMR 980 lbs/inch springs and the rear bar.

I'm doubtful that a little more spring and a little less bar out back would drastically upset the balance over the exact setup the GT350R is running. Anti-roll I'd imagine should be pretty close but with a little better rough road capability as the your back end is slightly more independent with a hair less bar, but then again what do I know?

It doesn't sound like the GT350R runs a whole lot more bar than a PP does, just a bit more, most of it is in the springs and dampers.

@BmacIL , you should be the guinea pig and test out the GT350/R front bar with PP rear on your existing setup. I'd imagine it would be nearly perfection.

And you were absolutely right about the Corsa Sport Cat back. After I swapped axle backs (Sport for Touring) with a local guy, I have to say I love it. At first I thought it was a bit quiet and muted, I almost regretted the swap. However at that time I was still running MC 5W-20 oil and no catch can.

I had issues with oil vapor inhalation causing the ECU to pull timing. I never got any audible knock or had any engine reliability / safety issues, however it was definitely not running peak timing and you could tell as it lost a noticeable amount of it's edge at certain times, especially when things got hot (stop and go traffic and when running it over 4,000 RPM for extended intervals).

I suspected oil vapor was causing the car to pull timing even stock as I noticed power fade even before I had the Power Pack 2 installed. I confirmed this with Ford Performance who said it's a common issue even among stock 5.0's of all generations when you start running them over 4,000 RPM for sustained periods of time or in heavy stop and go traffic and that's why they developed their own catch cans. It's a prevalent issue and your not getting peak timing.

I've seen fuel quality testing on the 5th Gen LT1 and in some cases it lost up to 70 HP due to poor quality 91 causing heavy knock. The ECU just couldn't run much timing and was running at the most conservative ends of the tables and that's on a factory stock LT1. This was testing that was done by engine labs if memory serves correctly back in 2014 when there was still heavy research into LSPI causes on TDI engines. The used the LT1 as a guinea pig to study detonation and pre-ignition (not as severe as LSPI, but not too far from it, more or less a pre-cursor stage leading up to LSPI).

There were times I swore my 5.0 felt like it was making 30~40 HP less despite no audible knock....I'll bet it was.

Interestingly enough however, timing and fueling has some significant affects on the tone, rasp, pop and burble of the exhaust. When ECU is running the more aggressive timing on it's table, the exhaust is much more raspy and aggressive sounding. So a more in-between exhaust like the Corsa Sport may sound too mild on some cars but sound just right on others. I love it now, it has a great balance of rasp without giving up some of the deep basy tones I love where the Extreme went from loud (stock) to insanely loud after the Power Pack 2.

Needless to say, if you have issues with power fade or even suspect it, I highly suggest a passenger side catch can AND a Dexos 1 Gen 2 certified oil. Why? Dexos 1 Gen 2, while a GM spec for resistance to LSPI (Ford uses ILSAC GF-5 Plus which also addresses the same issue) also affects the oil's part in inducing knock. LSPI resistant formulas in all of the testing I've seen (try reading a 450 page engineering report from the engine design summit attended by just about EVERYONE), also reduce knock frequency in NA engines.

That means running LSPI resistant oils provides benefits to NA engines by allowing them to run their most aggressive timing tables more often than oil formulas made to prior standards. That means lower carbon buildup, deposits but also more consistent power, especially when you push it hard and for extended duration (aka track / HPDE).

 

[BmacIL]

That's what I was thinking. Running a stock PP rear bar and a GT350/R front bar (GT350 and GT350R run same front 34 mm bar) because the BMR rear spring rates are a little higher than the GT350R's rear spring rates. That should balance it out. So there's not too much rear bar / spring combo between BMR 980 lbs/inch springs and the rear bar.

I'm doubtful that a little more spring and a little less bar out back would drastically upset the balance over the exact setup the GT350R is running. Anti-roll I'd imagine should be pretty close but with a little better rough road capability as the your back end is slightly more independent with a hair less bar, but then again what do I know?

It doesn't sound like the GT350R runs a whole lot more bar than a PP does, just a bit more, most of it is in the springs and dampers.

BMacIL, you should be the guinea pig and test out the GT350/R front bar with PP rear on your existing setup. I'd imagine it would be nearly perfection.

I'm planning on doing that when I add camber plates. I need some more camber for autocross and track. The front bar will offset some of the midcorner front grip increase from the added camber (the balance is very, very good as it is) but will simultaneously improve transient response (like during slaloms).

 

[TheLion]

Glad I installed camber plates from the get go. I figured at some point when I got more into performance driving I'd need more camber and with a 1.2" drop in the front with the SP080's I didn't want to risk having too much and not being able to adjust it out or tweak the caster, neither of which is really "adjustable" stock.

If memory serves correctly, BMR suggests 7.21 caster while factory spec is 6.91, just as an example. So here's my question, what is it specifically in the rear suspension motion path that makes the rear more sensitive to ride height than the front?

I recall BMR suggesting that dropping lower than 1" causes issues with handling, but that the rear was more sensitive to it than the front. Yet they sell springs that exceed 1" in the front (1.2" front, 0.5" rear for the SP080's). I'm suspecting the reason they chose the rake for that spring setup is more than just good looks. Having the rear up a bit higher to my understanding keeps it from getting into a range that has some significantly negative effects on handling.

 

[BmacIL]

Glad I installed camber plates from the get go. I figured at some point when I got more into performance driving I'd need more camber and with a 1.2" drop in the front with the SP080's I didn't want to risk having too much and not being able to adjust it out or tweak the caster, neither of which is really "adjustable" stock.

If memory serves correctly, BMR suggests 7.21 caster while factory spec is 6.91, just as an example. So here's my question, what is it specifically in the rear suspension motion path that makes the rear more sensitive to ride height than the front?

I recall BMR suggesting that dropping lower than 1" causes issues with handling, but that the rear was more sensitive to it than the front. Yet they sell springs that exceed 1" in the front (1.2" front, 0.5" rear for the SP080's). I'm suspecting the reason they chose the rake for that spring setup is more than just good looks. Having the rear up a bit higher to my understanding keeps it from getting into a range that has some significantly negative effects on handling.

Well, in a independent multi link or control arm suspension, the lengths of the arms overall, relative lengths between lower and upper arms, height and inclination angles between upper and lower arms, and their inner and outer point locations relative to both chassis centerline and to tire center all affect: roll center height, roll center migration in roll, camber gain in roll and heave (or pitch) as well as anti squat/dive angles and the resulting pitch center of the suspension. Lowering the nominal height of the rear suspension much below 0.5-0.6" lowers the roll center quite a bit more than the CG is lowered, thus increasing the roll couple. It also reduces camber gain, so you'll need both more static camber and/or higher roll stiffness to ensure that the rear tires are always seeing some negative camber in roll. The more extreme the control arm angles, the more the geometry changes with movement.

Ford Performance left the GT350 and GT350R rear suspensions quite close to the stock GT height due to all this, and I confirmed with their folks that the tipping point where it begins to change more drastically is around 10-12 mm from the base height.

The front is an entirely different beast being a strut front end, has poor camber gain to begin with (which is why you need so much static camber for track use) and does not change roll center height relative to CG anywhere near as much. The flip side is, you dramatically improve anti dive when you lower the car, and results in a much flatter car under braking.

 

[TheLion]

That explains why the raked SP080's still offer handling improvements over stock PP springs despite the low 1.2" front. The 0.5" rear drop sounds right at the limits. I'm surprised the SP073's don't use a 0.5" rear drop with a 7/8" front drop...I wonder why they went down to 3/4"?

In respects to handling then, I'd wager the SP073's will out handle the FP Track Springs due to slightly less drop if they had been at the same spring rates due to staying closer to the ideal ride height. Given I'm still on PP struts, I'm quite glad I went with the SP080's out of the other spring choices to keep the rear end sticking.

I was quite surprised at how well the car still handled despite the aggressive drop out front. Still haven't gotten in for an alignment, but next couple weeks I'm planning on running -1.75 front camber and -1.50 rear camber. 0 Toe front, 7.21 caster as recommended by BMR for their SP080's and 0.10 toe rear per side since I have spherical bearings both inboard and out.

Should be a nice balanced corner carver until I get some tires and most of all TIME for a beginners HPDE session hopefully next year. I'm going to do something radical and learn the car as is since the suspension is fairly stock with just a few tweaks to address it's factory quirks before moving onto the SP073's, FP Track Struts and GT350R front bar.

I think there's probably quite a bit more car right now than driver (well and tire at the moment since the P Zeros suck)

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