Subframe/Swaybar GR86 vs BRZ

[Lelandjt]

So which is the better system? Have any owners swapped?

[dragoontwo]

It isn't exactly easy to swap mounting systems. One is part of the subframe, and we don't know(highly unlikely) if you can have both installed together.

[Lelandjt]

Has it been decided which system is theoretically best?

[bradsm87]

Originally Posted by Lelandjt

Has it been decided which system is theoretically best?

The BRZ system is. Bodyroll would not pull on the subframe from the swaybar links, making it move, which isn't desirable.

If you fit solid subframe bushes to a GR86, it's effectively the same as a BRZ. I plan to solid mount and lift the subframe with Parts Shop Max solid bushes once 2nd gen compatibility is confirmed.

[LRNAD90]

Originally Posted by Lelandjt

Has it been decided which system is theoretically best?

Are you asking a Subaru Engineer, or a Toyota Engineer?

Same questions exist regarding the choice of aluminum front knuckle vs the nodular iron one. Was it just an accounting decision, or did the engineers feel it was the better choice (for whatever reason)..

[CincyJohn]

Originally Posted by Lelandjt

Has it been decided which system is theoretically best?

Both. Neither. Did you watch the video? The answer is they are different...

Having said that, we do know that the GR86 was quicker on a certain track, on a certain day, under certain circumstances.

I think it is also safe to say that the BRZ system is not as harsh for daily driving.

[Spektyr]

Originally Posted by LRNAD90

Are you asking a Subaru Engineer, or a Toyota Engineer?

Same questions exist regarding the choice of aluminum front knuckle vs the nodular iron one. Was it just an accounting decision, or did the engineers feel it was the better choice (for whatever reason)..

This. Different drivers like different setups. The two setups pull nearly identical numbers on the skid pad, but the way the cars react at the limit is just enough different that some drivers significantly prefer one over the other.

The GR86 is more willing to get the tail out earlier. The BRZ stays tucked in longer. For me, I'd rather have some tail slip before all four tires hit the limit because A: it appeals to my inner 12 year-old and B: a rapid transition from grip to drift brings a significant chance of losing control.

The BRZ also (from what I've read - haven't driven one) has a slightly less harsh ride in daily driving conditions. The GR86 isn't going to rattle your fillings, but if you drive home with a case of carbonated beverage in the trunk you might not want to open it right away.

[Stonehorsw]

To properly compare the rear sway bars, would need to have same spring/damper/tire configuration.
@ZDan and @Racecomp; Any of you 2 analyzed the differences on the sway bars? Anything that can be understood from FBD or any kinematics?

[raisingAnarchy]

Weren't the primary differences in design covered in this video featured in this thread?
https://www.ft86club.com/forums/showthread.php?t=150324


The 86's bracing of the subframe mount provides more rigidity, as well as making the sway bar easier to remove/change. Swapping would require at least changing out subframes, but I would need to spend more time with the above video to see if it might require swapping rear hubs too

[Stonehorsw]

Checking with an experienced suspension engineer (40+ yrs of experience), based on a quick look on the video (no car on lift, no slalom or any vehicle testing), his comments were:

1. Seems like Subaru priority was ride while Toyota was handling.
2. Toyota bracket seems to have a stronger rigidity, as Subaru’s is attached to a bolt.
3. Expects for the GR to have a quicker response on the rear.
4. Expects for a improved roll control on GR
5. Expects Subaru to have better response to irregularities and bumps.

[ZDan]

I dunno, if Toyota bar is braced to the subframe, which is attached to the mainframe with bushings, that adds compliance, the bar is less firmly grounded to the chassis.

I have to say, from what I've seen with the aluminum front knuckles vs. steel, and the different mounting of the rear sway bar, these differences look so minor as to pretty much be negligible. Handling differences are likely more down to spring rates and possibly bump stops giving the Toyo more outside rear loading in cornering. I'm leaning towards the Subie for the aluminum knuckles just because even ~6-7 lb. off the nose of the car is a positive when it's so dang front-biased (55.5/44.5 ), and I like the Subie Pleiades badge aesthetically over the 2 ellipses within an ellipse Toyo badge (also working in the astrophysics biz at the moment, so...)

[DarkSunrise]

Yeah it almost seems like he got the two mixed up. I don’t see how the sway bar that’s attached directly to the chassis/body could be slower or more compliant than the one that’s mounted to the subframe.

Someone else answered this question on a Reddit page and the answer made sense to me, at least in theory:

The thinking behind mounting the sway bar to the unibody is that you’ll get more work out of a smaller bar and the bar will act faster in reducing roll because the subframe moves around while cornering and that movement delays the operation of the bar. Now if you took out the stock subframe bushings and replaced them with solid bushings then there would be zero difference between the operation of the sway bar in either car.

https://www.reddit.com/r/ft86/commen..._on_2022_cars/

[bradsm87]

Originally Posted by Stonehorsw

To properly compare the rear sway bars, would need to have same spring/damper/tire configuration.

Exactly!

People are chiming in stating the differences between the COMPLETE vehicles but that wasn't the question. The question is solely regarding the swaybar setup.

[Racecomp Engineering]

Originally Posted by Stonehorsw

To properly compare the rear sway bars, would need to have same spring/damper/tire configuration.
@ZDan and @Racecomp; Any of you 2 analyzed the differences on the sway bars? Anything that can be understood from FBD or any kinematics?

The swaybars themselves?

The 2022 GR86 uses the 2017-2020 set up, 18mm front and 15mm rear.
The 2022 BRZ uses a new 18.3mm hollow front bar and a 14mm rear.

The equations for figuring out spring rate from swaybar dimensions aren't too hard and there are numbers posted on this forum somewhere. Have to remember the motion ratio for the swaybars as well (which can be different than the main spring motion ratios).

That new hollow BRZ front bar has been quoted as a mild 2.3% stiffer than the standard 18mm solid front bar. That's not very much but it is probably a little lighter which is nice. As with the aluminum front hubs you can see Subaru made effort (at extra cost) to reduce unsprung weight. Which is good.

With both springs and swaybars you have more front roll resistance and less rear roll resistance with the BRZ vs the GR86.

The rear swaybar mounting method is a related but different question. Like others said the new BRZ takes the subframe and subframe bushings out of the equation, meaning it acts without compliance from the subframe bushings. The subframe on standard bushings moves more than you think. Yes you can add subframe bushing inserts but something like a solid bushing insert or full replacement adds noise and is not great on a daily driver.

Does that make the 14mm BRZ rear act like a stiffer rear bar? Not really, but it's a more linear and direct action. Which is good IMO.

All the discussion about the playful nature of the GR86 vs the stability of a BRZ is largely the spring and swaybar rates, not the front hubs or rear swaybar mounts.

This is just my opinion but the GR86 using the old style front hubs and the rear swaybar mounts was simply cost savings. Arguably the solid vs hollow front bar too (2.3% difference in stiffness isn't much).

So why is the GR86 sometimes faster around a track? Well the new BRZ components are better but not a huge change. Meanwhile, off the factory floor these cars desperately need more front camber. Without that, more rear roll stiffness from the GR86 helps a lot to get the car to turn.

With the aluminum front hubs and new rear swaybar mount, the GR86 would be largely similar and still have the "playful" character.

The best handling 2022 would be a BRZ with GR86 rear springs and the OEM crash bolts for a tiny bit more camber. Maybe the GR86 rear 15mm bar too.

- Andrew