GT car style suspension setup?
 

If you were to setup a twin to feel and act like a GT car, what if anything would you change from stock. Alignment, bushings, dampers, spring rates, ride height, wheel size, tire size, compound... Anything is on the table. I'm looking for something that can chew up highway miles with ease while also having rewarding grip and feel in a corner.

What I liked about my 2013 FRS's stock setup was that it was quiet and comfortable during most driving. What I didn't like was how easy it was to put it on the bump stops and thus how easy it was to get unsettled in a corner, even on the stock tires. I've made several changes since it was stock, and now I'm thinking it's time for a blank sheet approach. This time I'd like to add some science to the decision making process instead of just doing the same cliché things.

I'm thinking a simple set of slightly stiffer springs with dampers that allow more travel, some more caster to give more camber gain and feel, better tires that maintain composure when pushed, 17" rims as they're decently light and allow sufficient sidewall, and an assertive vice an aggressive alignment.

To this end I'm think the ever vaunted B6s for dampers.

I'm consider a couple of different spring setups. RCE yellows is an obvious choice as they increase the front spring rate a significant amount more than the rear. As the rear always seemed to behave well that seems logical. But I'm also considering a set of BRZ front springs mixed with FRS rear springs to keep as much travel as possible and as much comfort as possible.

Pedders strut mounts for the increased caster camber and better SAI, and whiteline control arm bushings for a little more caster without increasing NVH too much, and camber bolts for fine tuning.

Tires is a whole thread in and of itself, so I think I should leave that for now. But I'm wondering if tire width has any noticeable effect on NVH?

Stock or lighter rims.

For alignment settings I'm thinking ~Camber - 1.75 front - 1.25 rear, and toe set to zero everywhere.

Please critique any and everything here.

Kw v3 set to Max height
Toe in on rear for road stability
Conti ecs tires oe size
Leave everything else stock

The spring rates on those are 343 front and 400 rear. I'm questioning if 250 square will possibly be too stiff for my liking. I've read people say that damping can help ride a lot, but I'm having a hard time believing those would ride better than stock.

I also have very little interest in changing damper settings or ride height. If V3s is the best way to get what I want I can set them and then leave them, but I'd prefer to not pay for functionality I'm not using.

The pavement here causes significant NVH on my present setup, I can't see going to solid mounts helping anything with my goals.

Is my understanding incorrect?

going to have to raise the car so it's not hitting the bumpstops as much as it does in stock form for a softer ride.

TRD Rally springs + Sachs dampers seem to be worth looking into based on this glowing review. It raises the car 10mm so you're not hitting the bump stops as easily:

https://www.ft86club.com/forums/show...8&postcount=31

17×8 light wheels with 225×45 tyres for more sidewall and comfort. 2017 MY suspension for softer ride, sound deadening in cabin , doors , quarter panels and boot for a quiet Mile muncher! This will be my ideal GT set up

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I'm pursuing the same goal. Here's what I've done so far:

Chassis

Whiteline Poly Sway Bar bushings front and rear - Slightly better body roll control. Sway bar action is more immediate/linear. No noticeable increase in NVH.

Whiteline Poly Steering Rack Bushings - better feedback through the steering wheel and more immediate/linear response to steering inputs. No noticeable increase in NVH.

Whiteline Differential Mount Inserts - Tightened up shifting a bit and reduced driveline lash w/o noticeable increase in NVH.

Camber Bolts - Alignment set at -1.5 camber front and rear; OEM caster; 0 toe front and rear

Pretty extensive sound deadening in the trunk.

RaceSeng weighted shift knob

Conti 225-45/17 ECS tires on 17x8x40 Konig Ultraform wheels - about 2lbs lighter than oem at each corner.

Lighting:

Added OEM Fog Light Bezels - (the car's a Premium - no factory fogs

Installed Diode Dynamics SS3 - Pro Fog Lights wired to operate on command

LED Turn signal bulbs with DD flasher relay

Not much under the hood:

Sound tube delete
OEM Forester XT oil cooler/temp regulator

To Do:

Bilstein B6s - Unsure about springs at the moment. I may very well stick with the OEMs as I don't want to sacrifice bump travel or obstacle clearance.

I'm waiting to see what the RCE rally spring/B6 pairing has up its sleeve.

I've considered 949 Xidas - Dead sexy kit. But their development path seems to have taken them away from what I'm looking for - and they are probably way beyond my price range.

Edit: After I get the shocks sorted, I think I'll be finished. I do have a few more suspension/chassis bushings/inserts that I may play with, but I'm quite happy with the car as she sits and don't want to add unnecessary NVH.

I've considered and am still on the fence about flex fuel. A few more ponies would be fun to play with now and then, but ... I'll probably just keep procrastinating. :)

Kw v1 then
Kw uses oe mounts unless you get the clubsports
More about kws focus on gt ride quality then adjustability

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.

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)."

https://live.staticflickr.com/4834/4...12ebae5d_h.jpg
^ 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

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

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

For purely comfort goals 2017+ dampers or the entire spring/strut assembly as a takeoff if you can find them used. Cheap and will improve ride.

I am on B6+ yellows. Ride is firmer than stock but far from typical coil setups. My comparison is to 2017 suspension.
Strikes a happy medium of sportier feel without being racecar.

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.

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.

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?

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.

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

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

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.

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.

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

- Andrew

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.

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.

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.

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.

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:

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.

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

Wow, great point among several good points. Maybe I should just throw the frs springs I have on to B6 dampers and call it a day. And if I end up on the bump stops in corners upgrade the sway bars slightly.

Thanks for this.

@itschris Thanks for posting the link to the article. Looking at the parent site there is a wealth if information there. Wow. A lot of reading material - a lot of food for thought. Thanks again.

If looking for a plug-and-play option for the GT feel on a daily driver. Both of these DFV style setups will do the trick.

Ohlins Road and Track
https://www.ohlins.com/product/road-...2012-2017-zn6/

Showa Tuning Evolution (non-U.S.)
https://showa-tuning.com/line-up/toyota-86/

OptimumG is good stuff!

We did a very basic primer on suspension frequencies on our instagram here:
https://www.instagram.com/p/B6TKG6Un..._web_copy_link

Stock springs do work nicely with Bilstein B6 and actually BRZ front with FRS rear is pretty good. That would indeed ride better than Bilstein + Yellows (performance was important when designing those springs).

IMO if you're designing from the ground up (which means you're also starting from scratch on the dampers and bumpstops and swaybars etc) then flat ride is the ticket for comfort. But as an example, a BRZ with 200 lbs/in springs front and rear will likely be more comfortable than a car with 200 lbs/in springs front and 250 lbs/in springs rear, (with the same dampers and/or same damping ratio). I encourage you to think about the bumps you encounter, which are most noticeable, and if/when flat ride would help.

One note since it sort of came up...don't go above recommend ride heights with a coilover like KW V3, SS1, or Bilstein B16 for comfort reasons. You do get tons of bump travel which is nice but you also limit your extension/droop travel. I've gone beyond in testing and it isn't great. There are a lot of "drop off" type bumps where I drive and they become a little annoying.

- Andrew

Thanks Andrew. My reading and arithmetic so far had suggested just that. B6s - BRZ front/rear or BRZ front - FRS rear.

Edit: quick question. How does the motion ration built in to the rear affect the calculations?

I saw the math and my mind went a little numb, but then I remembered there's smart people put there that's done the math already. So it's just a matter of understanding the concept and using it to help me try to pick parts. So yeah. I found their tech tips and read through all of them, despite having no need or ability to add a third spring to my inboard suspension...

I actually found your Instagram post last night while digging around for more info. [emoji106]

Yeah, I'm pretty set on trying the B6 with what I have now and then playing with factory springs to tune as required. Maybe I'll play with ARBs later as well.

Talk to me about the MCA traction mod, please. It looks fantastic and like something I would really benefit from as I've encountered oversteer several times when I didn't intend to. Surprisingly, that is a large part of why I started down the road of modifying my suspension. I started by trying to gain feedback from the rear, then to increasing spring rate to increase ride frequency, then to coilovers for better damping... When I started I'd be feeding a little throttle into the car to maintain a corner line, nothing intended to accelerate, just maintaining balance front and rear at what should have been about 8/10s, and then I'd hit a bump and would end up thanking the traction control programmers. It seems like the MCA kit would help with the predictability there. Is there any down side? Aside from possibly increased wear on the trailing arm bushings I can't see where a down side would be.

Comfort is a priority, but predictability and competence in a corner are still priorities as well and unless I'm misunderstanding something, this shouldn't negatively effect any of those.

If your in SoCal I have 2017 dampers, yellows, and peddler top hats for camber I am selling

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I had been debating about this for sometime. I tried the white line subframe inserts and didnt like the noise it generated ( there was no vibration or harshness).

And the car would under steer a lot and this change in character of the car didnt make it fun anymore.
Then i removed them and fitted STI subframe stoppers coupled with STI subframe bolts. ( Any restriction of subframe movement in form of bushings or braces will give the feel of the rear being very planted)

The amount of play you decrease in the rear subframe determines the degree of under/over steer you induce at the limit of grip.

This, in my opinion, is a much better compromise in keeping the subframe in check, not promoting under steer, giving predictable/controllable oversteer at the limit and with very minimal noise ( I have sensitive ears, lol).

As for the GT suspension set up, the B6 with the yellows seem to be a very good compromise. I have not heard any negative reviews yet from anyone considering them from a DD perspective.

Will be following this thread. I like the discussion so far. :)

Pardon my ignorance, my education on this is only read and not practical experience, but what is the general opinion on air suspension? It sounds like the thing modern GT cars often do from the factory for comfort.

General opinion on air suspension on twins is that for money it costs, better return is from high end classic coilovers for same money. I guess, only "use" for air suspension on twins is for those very few/rare that are into overdone lowering/hardpark and so on, to at least have it somewhat driveable at all via onthefly height adjustment. For 100x more owners that don't do that, paying half the cost for comparable suspension performance/comfort or getting higher performance for same money, is better choice.

The MCA traction mod doesn't do anything to subframe, it has nothing at all do with the controlling movement of the subframe. They move the position of the trailing arms body side mount. They don't even reduce compliance of the trailing arms bushings.