GT car style suspension setup?

[Yoshoobaroo]

2017+ non-Sachs suspension is very good. I paired mine with Perrin adjustable sway bars to tighten up the cornering without sacrificing straight line suspension travel.

[churchx]

For me B6+stock springs of MY2013. I find it a bit better on larger road defects, and a bit worse on small "vibrating" road pavement uneventies. Also +1 to car seeming a bit more composed & firmer, especially when pushed. For pure daily only driving .. don't know .. slightly but stock everything seemed overall a bit more comfortable, as often public roads are very bad and often driving is slow, letting feel out every road defect. Maybe it's because of overly soft stock springrates and with springs like RCE yellows it's better matched? Maybe that firmness is just thing to be gained at expense at handling slow/small extent road defects? Not sure, but cannot claim that B6 is universally 100% everywhere better then stock either.

[Calum]

Originally Posted by Racecomp Engineering

^ My car back when it was in GT mode.



This was RCE SS1s, Perrin steering rack lockdown, Cusco rear lower control arms, adjustable toe arms, Whiteline rear diff inserts, Whiteline rear subframe inserts. And Braid Fullrace A 17x8 with 225/45/17 Michelin Pilot Sport 4s. And a very good alignment.



That was pretty terrific all around. A little low in this pic, but a better overall ride than it was stock.

The rear diff and subframe inserts do add some noise (gear whine). Not that annoying to me, but it would be nice if it were a little quieter for a true GT car.



All pre-2017 OEM dampers are just too stiff and very easily unsettled. I've been swapping back and forth between 2016 OEM and Bilstein B6 during our RCE Rally lift springs testing and the Bilsteins are such a big step ahead. The roads I drive on are terrible crap, and the OEMs can't keep up in certain sections.



So swapping in Bilstein B6 on their on makes a really nice difference. Add RCE Yellows if you want something a little lower and a performance improvement.



The Bilsteins add a lot of "composure" when there's a series of bumps or section of rippled and broken pavement. One intersection near me has massively rippled pavement alllll the way across. On OEM suspension right now you do a "oh...geez...ow...dang!" On Bilsteins it's more of a "oh...geez." A section like that in a corner gives the skating sensation on OEM stuff that is not confidence-inspiring.



On a single bump, say a small speed bump or a single ripple the Bilsteins are noticeably better, but it's not that terrible on the OEMs.



I'd be hesitant to go with a poly front control arm bushing, and would either stick with fresh OEM bushings or STI Group N front control arm bushings.



I'm putting my SS1s back on this Thursday as we await the next prototypes of the Rally springs. Really looking forward to taking off the OEM struts.



- Andrew

The poly bushings for the control arms are already in place, have been for a long time. Is there an objective reason to remove them? Or just subjective? If it's just for nvh I'll take things one step at a time. Right now I want to tackle the major things and then fine tune after I get back to a better starting place for me.

I ended up taking my diff and subframe inserts out a while ago in an effort to reduce noise. I'm guessing I'll end up doing the same with the control arm bushings, but again, one step at a time.

I'm surprised you liked the lockdowns for a GT car. Is there added mass to dampen vibrations without losing the direct connection?

Is the 17×8 wheels something that aids in comfort? Or just stating what you had on the car? Would it be a bad idea for my goals to run a 225 tires on stock rims? Or an advantage?

Would you suggest anything different about my proposed alignment specs?

[Calum]

Originally Posted by Turdinator

I have the pedders strut tops and I don't think you'll need more castor than that. At the very least install them without the whiteline bushes and give it some time to see if you still want more.



If you go the B6 with RCE yellows, make sure you open up the front struts and trim the bumpstops to a similar height to the RCE ones.



You may even want to look at some 16x7.5 wheels instead of the 17s for a smidge more comfort that with the right tire will still feel good.

Unfortunately I already have the whiteline bushings installed. And I hate doing control arm bushings so I'm thinking I'll leave them for now and once I get the major items in I'll make a call then if the nvh is worth fixing.

[Racecomp Engineering]

Originally Posted by Calum

The poly bushings for the control arms are already in place, have been for a long time. Is there an objective reason to remove them? Or just subjective? If it's just for nvh I'll take things one step at a time. Right now I want to tackle the major things and then fine tune after I get back to a better starting place for me.

Not a huge deal, but they do add a slight bit of harshness.

Originally Posted by Calum

I ended up taking my diff and subframe inserts out a while ago in an effort to reduce noise. I'm guessing I'll end up doing the same with the control arm bushings, but again, one step at a time.

Yeah I sometimes forget how quiet other cars can be...but I love the difference in feel.

Originally Posted by Calum

I'm surprised you liked the lockdowns for a GT car. Is there added mass to dampen vibrations without losing the direct connection?

There's the slightest bit of added vibration added through the steering wheel. For me personally it does not add any fatigue on long drives or anything like that.

Originally Posted by Calum

Is the 17×8 wheels something that aids in comfort? Or just stating what you had on the car? Would it be a bad idea for my goals to run a 225 tires on stock rims? Or an advantage?

Just stating what I had on the car. There's a slight argument to be made for 225s on a 17x8 adding some sidewall and therefore comfort but for me it was the improvement in grip.

I would not run 225s on the standard 17x7 wheels, but IMO there's nothing wrong with sticking with standard size wheels and tires for a GT car. Either 17x7 with 215s or 17x7.5 with 225s.

Originally Posted by Calum

Would you suggest anything different about my proposed alignment specs?

Just a smidge more rear camber...-1.5.

- Andrew

[Capt Spaulding]

I went with 17x8s because they were several pounds lighter than the OEMs and would make better use of a 225 tire. In addition to increased grip, the added air volume of the 225s can marginally help ride quality.

Adding a degree and half of front camber made a substantial difference both in turn in and reducing push.

[Calum]

How much do the oem rims weigh? (I'm sure it's been answered here somewhere but don't feel like fighting with the search function.)

Edit, googlefoo to the rescue. They're 20.1 lbs for 2013, a little more than 22 for the 2017 plus.

[Turdinator]

Originally Posted by churchx

As written by RCE about B6:
"Where are the bumpstops in the front?
Since it's inverted, the bumpstop is inside the lower part of the strut body. Yes you can open these up and have a look, but I don't really recommend replacing the internal bumpstop. The non-inverted rear uses a regular bumpstop you can see (you reuse stock)."

Originally Posted by Racecomp Engineering

Shortening the internal Bilstein bumpstop is optional with lowering springs. Basically, I don't want everyone opening up their Bilsteins if they don't have to...

- Andrew

Originally Posted by RToyo86

I didn't do that, didn't seem nesssary from what I read on here. Though it can't hurt.

My thinking was two fold, hitting bump stops isn't ideal for ride comfort and secondly if you keep the full length bump stop in front and use the shorter RCE one in the back, the fronts will hit the bumpstop sooner increasing the effective spring rate sooner possibly creating some understeer.

[Capt Spaulding]

Originally Posted by Calum

How much do the oem rims weigh? (I'm sure it's been answered here somewhere but don't feel like fighting with the search function.)

Edit, googlefoo to the rescue. They're 20.1 lbs for 2013, a little more than 22 for the 2017 plus.

I replaced the wheels on my ‘15 with Konigs. At the time Konig claimed a weight in the low 17s for the 17x8 wheels I bought (Ultraforms - since discontinued). The 225 ECSs I mounted were a bit heavier than the Primacys so I think I saved a pound or two unsprung at each corner.

[itschris]

Since you specified GT, not trackable street, I really think you should look at a flat ride setup (rear wheel rates 10-20% stiffer than the front). There's a reason every modern production GT car uses it. Not knocking the square rate setups suggested, but I don't think I'd classify any of them as GT. Flat ride tends to give up performance in braking zones, which you probably won't miss on the street.

I might look at B16s, highest ride height setting + softish damper setting. Pair with stiffer front bar and MCA traction mod. Could substitute Konis + flat ride lowering springs if you wanted a cheaper option. Gain a lot of comfort, maybe lose a bit of performance. Definitely cut any bump stops you reuse. B16s have a shorter internal stop than the B6/8s and opening those up isn't needed.

Approx ride freqencies for reference, if you go the lowering springs route:

hz      front lb/in     rear lb/in
1.1	94.78515624	118.3383333
1.2	112.8021694	140.8323966
1.3	132.3858794	165.2824655
1.4	153.5362861	191.6885399
1.5	176.2533897	220.0506197
1.6	200.5371901	250.3687051
1.7	226.3876872	282.642796
1.8	253.8048812	316.8728924
1.9	282.7887719	353.0589943
2.0	313.3393595	391.2011017

[Calum]

Originally Posted by itschris

Since you specified GT, not trackable street, I really think you should look at a flat ride setup (rear wheel rates 10-20% stiffer than the front). There's a reason every modern production GT car uses it. Not knocking the square rate setups suggested, but I don't think I'd classify any of them as GT. Flat ride tends to give up performance in braking zones, which you probably won't miss on the street.



I might look at B16s, highest ride height setting + softish damper setting. Pair with stiffer front bar and MCA traction mod. Could substitute Konis + flat ride lowering springs if you wanted a cheaper option. Gain a lot of comfort, maybe lose a bit of performance. Definitely cut any bump stops you reuse. B16s have a shorter internal stop than the B6/8s and opening those up isn't needed.



Approx ride freqencies for reference, if you go the lowering springs route:

hz      front lb/in     rear lb/in

1.194.78515624118.3383333

1.2112.8021694140.8323966

1.3132.3858794165.2824655

1.4153.5362861191.6885399

1.5176.2533897220.0506197

1.6200.5371901250.3687051

1.7226.3876872282.642796

1.8253.8048812316.8728924

1.9282.7887719353.0589943

2.0313.3393595391.2011017

https://www.ft86club.com/forums/show...&postcount=334

I'm gonna go with what Andrew had to say about that. Especially considering how much appreciation the 2017 factory setup gets with its approximately square setup.

Edit: wouldn't resonance frequency also depend on damping?

[itschris]

Originally Posted by Calum

https://www.ft86club.com/forums/show...&postcount=334

I'm gonna go with what Andrew had to say about that. Especially considering how much appreciation the 2017 factory setup gets with its approximately square setup.

Edit: wouldn't resonance frequency also depend on damping?

In the context of "getting around a track the fastest" I definitely wouldn't go for flat ride on this platform. But GT cars aren't benchmarked by laptimes, racecars are, and for a GT style suspension I think it's a no brainer.

The idea behind setting natural frequencies in a flat ride configuration is that you can use less damping (both compression and rebound) to maintain pitch control, which should lead to a more comfortable ride. My opinion, but I think most of the praise for 17+ suspension comes from the improved damping. From the sticky, 86 rates are 2.3f/3.3r - that is still flat ride. No idea what the BRZ/PP rates are.

I think you should look for some ride alongs if you can. I found the B16s near soft to be noticeably more comfortable than yellows and B8s despite the stiffer rear rate. I think they're usually overlooked because most people don't want to pay double for essentially zero laptime improvement. But you did say anything was on the table.

[Calum]

Originally Posted by itschris

In the context of "getting around a track the fastest" I definitely wouldn't go for flat ride on this platform. But GT cars aren't benchmarked by laptimes, racecars are, and for a GT style suspension I think it's a no brainer.



The idea behind setting natural frequencies in a flat ride configuration is that you can use less damping (both compression and rebound) to maintain pitch control, which should lead to a more comfortable ride. My opinion, but I think most of the praise for 17+ suspension comes from the improved damping. From the sticky, 86 rates are 2.3f/3.3r - that is still flat ride. No idea what the BRZ/PP rates are.



I think you should look for some ride alongs if you can. I found the B16s near soft to be noticeably more comfortable than yellows and B8s despite the stiffer rear rate. I think they're usually overlooked because most people don't want to pay double for essentially zero laptime improvement. But you did say anything was on the table.

Ok, I just spent close to an hour going down a rabbit hole of reviews on b16, which also lead to a lot of discussion on KW V3s. Here's what I learned along the way, with regard to me directly.

B16 with progressive rate springs likely aren't for me. I didn't say it in the OP, but predictability is likely the absolute top priority. So those are out. I need to predictability to help mask my poor driving skills on this bad pavement.

V3 would be too low. We have "speed humps" (I need to steel one of these signs. That they actually put that on a street sign is hilarious to me) in my neighbourhood that are huge and I'd be bottoming out if not high centering at their highest setting.

That said, it looks like the factory BRZ springs 151 front/195 rear) from the 13-16 model years give very close to a flat ride setup. Maybe I should just look for a set of those.

At this point my intention is to run Pirelli P Zero All Season Plus tires. The reviews show them to be plenty sticky, but also very comfortable. They give up wet traction, but I very rarely drive this car in the rain anyway.

I'm thinking they'd be a decent pairing with factory BRZ spring or maybe something like the RS-R Down Sus with 177 front and 203 rear spring rates at on a 10-15mm drop.

I'm going to dig into the concept of flat ride further. But how critical is it that the front and rear frequencies match exactly? Is it all or nothing where if they aren't matched it doesn't work, or is it a situation where the closer the better?

[itschris]

Originally Posted by Calum

Ok, I just spent close to an hour going down a rabbit hole of reviews on b16, which also lead to a lot of discussion on KW V3s. Here's what I learned along the way, with regard to me directly.

B16 with progressive rate springs likely aren't for me. I didn't say it in the OP, but predictability is likely the absolute top priority. So those are out. I need to predictability to help mask my poor driving skills on this bad pavement.

V3 would be too low. We have "speed humps" (I need to steel one of these signs. That they actually put that on a street sign is hilarious to me) in my neighbourhood that are huge and I'd be bottoming out if not high centering at their highest setting.

That said, it looks like the factory BRZ springs 151 front/195 rear) from the 13-16 model years give very close to a flat ride setup. Maybe I should just look for a set of those.

At this point my intention is to run Pirelli P Zero All Season Plus tires. The reviews show them to be plenty sticky, but also very comfortable. They give up wet traction, but I very rarely drive this car in the rain anyway.

I'm thinking they'd be a decent pairing with factory BRZ spring or maybe something like the RS-R Down Sus with 177 front and 203 rear spring rates at on a 10-15mm drop.

I'm going to dig into the concept of flat ride further. But how critical is it that the front and rear frequencies match exactly? Is it all or nothing where if they aren't matched it doesn't work, or is it a situation where the closer the better?

The front and rear frequencies shouldn't match exactly - the rear should be ~10-15% higher. Not an exact science, suspension geometry, rwd, average speeds, and damping all contribute. The FRS springs have a ~15% split, 86 is ~8%. Your BRZ front and FRS rear spring idea is a similar split to the 86 but slightly stiffer overall.

Here's a short OptimumG paper on choosing ride frequencies, it's easier to visualize what's happening in combination with damping in figures 3 and 4. I like to think of the vertical difference between each line as the overall pitch. Figure 3 starts with negative pitch before switching to positive pitch and finally returns to neutral around ~5 seconds. Figure 4 starts the same, but is essentially neutral from 1 second on, meaning the front and rear settle together.
http://downloads.optimumg.com/Techni...Tech_Tip_1.pdf

Also, not sure if you came across this in your rabbit hole, but the B16s progressive springs aren't quite as progressive as they look on paper. The front is more like a helper + linear rate, and the rear is progressive but starts at ~360lb/in at ride height. I made a mistake in this post, but if you follow the thread ZDan helped correct me. The ride frequencies might be a little high for a GT car, regardless.
https://www.ft86club.com/forums/show...52#post3387452