17 BRZ performance package lowering springs

[Yoshoobaroo]

The 2017+ spring rates are even front to back, they’re around 3kg/mm.

[gpvecchi]

I have the JDM STi pinks on my PP 86. I'm very happy with them! Nengun says that they are 4 kg/mm front and 5 kg/mm rear, but, meh, IDK...

[timurrrr]

Originally Posted by Yoshoobaroo

The 2017+ spring rates are even front to back, they’re around 3kg/mm.

Oh, that's interesting. Where did you find that information?

[Yoshoobaroo]

Originally Posted by timurrrr

Oh, that's interesting. Where did you find that information?

Taking the old spring coefficients and the claimed stiffness %changes from the facelift literature lead me to that number. There’s a thread out there that has a pdf off all the changes.

[Racecomp Engineering]

Softer springs in the front may make you think the car will have less understeer, but keep in mind you will end up cornering on the bumpstops....

More initial roll in the front followed by a steep ramp in spring rate from the bumpstop tends not to be the best thing for handling and stability on the track.

Also, a large proportion of your handling balance comes down to alignment. Even spring rates have been proven to work well by us and other suspension shops. Rear biased spring rates can also work well, but either way you need to look at the complete set-up.

- Andrew

[timurrrr]

Originally Posted by Racecomp Engineering

Softer springs in the front may make you think the car will have less understeer, but keep in mind you will end up cornering on the bumpstops....

More initial roll in the front followed by a steep ramp in spring rate from the bumpstop tends not to be the best thing for handling and stability on the track.

Also, a large proportion of your handling balance comes down to alignment. Even spring rates have been proven to work well by us and other suspension shops. Rear biased spring rates can also work well, but either way you need to look at the complete set-up.

- Andrew

Thanks for the reply!

Do you mean that Eibach Pro-Kit front springs (3.6k rate, 1.0" lowering) will be compressing all the way to bumpstops frequently, but RCE Yellows (4.0k rate, 0.8" lowering) will generally have no such issues?

Can you please also comment on how well do RCE Yellows work with stock PP Sachs dampers? As far as I understand, making spring rates significantly stiffer also requires making dampers tighter too, which doesn't happen when swapping just the springs. To the best of my knowledge, RCE Yellows were also originally developed before PP came out, and the rates didn't change since then, which makes me wonder how much they were tested with PP Sachs.

[Shizuka]

To be honest, I don't think I'd run any kind of lowering spring on the PP Sachs (just my two cents). In my opinion the ride is already overly stiff/crashy for the street, and shorter & stiffer springs will only make it bouncier. I guess it wouldn't matter if the car is a track tool, but for a DD I avoided going that route.

FWIW I got HKS Hipermax IV GTs on my 2018 PP, been on them for about 1k miles. The ride harshness is essentially the same as stock (smoother over small bumps but worse on big stuff), but I'm also a little over an inch lower. Cornering is possibly even flatter than it already was before, but with the camber adjustment and alignment the turn-in is much sharper, even with 255 wide tires. Overall handling is more neutral, and I have mine set up for DD and canyon use-- I'm sure you could go much more aggressive.

RCE and CSG also have great coilover options, and they're very active on the forum as well! I went with the HKSs because my build is JDM themed/inspired so basically just a superficial reason. The freedom to adjust coilovers to your desired spec is a huge benefit over springs, especially since our PP cars are already tightly wound. I've used springs on cars with softer setups and love them on adaptive dampers, but on the BRZ I'm not sure. I've only ridden in one BRZ with lowering springs though, and that was definitely a rough ride-- small sample size though for sure!

TL;DR Stiff car & adding stiffer springs = bounce city. Stiff car + coilovers = controllable bounce.

[Racecomp Engineering]

Originally Posted by timurrrr

Thanks for the reply!

Do you mean that Eibach Pro-Kit front springs (3.6k rate, 1.0" lowering) will be compressing all the way to bumpstops frequently, but RCE Yellows (4.0k rate, 0.8" lowering) will generally have no such issues?

I would say that the Eibach's are more likely to use the bumpstops in a corner than the RCE Yellows. With sticky tires (and a few other variables), both will still use the bumpstops...as will stock or some coilovers. With RCE Yellows, we just wanted to minimize how bumpstops active and how reliant the car is on bumpstops. It's not just a question of if the car hits the bumpstops...the way the two work together (or don't!) is really important too for both grip and driver confidence.

Originally Posted by timurrrr

Can you please also comment on how well do RCE Yellows work with stock PP Sachs dampers? As far as I understand, making spring rates significantly stiffer also requires making dampers tighter too, which doesn't happen when swapping just the springs. To the best of my knowledge, RCE Yellows were also originally developed before PP came out, and the rates didn't change since then, which makes me wonder how much they were tested with PP Sachs.

The OEM dampers (of all model years) are actually overdamped when looking strictly at how they work with the OEM main spring. In terms of main spring rate alone, most lowering springs are a reasonable match for the dampers (or "better" than stock by the numbers). Some years more so than others. The damper of course is also working with the bumpstop. A lowering spring that puts the car deep into the bumpstop (at rest or in cornering) may end up underdamped in certain cornering or ride conditions. Remember that our RCE Yellows include replacement shorter bumpstops, as do the Eibachs to their credit.

Yes the RCE Yellows work quite well with the later model year OEM shocks including the PP shocks and they're on a lot of street and track driven cars. We determined that we did not need to change the specs on the springs as they are still well within range of what the valving can handle, and just as importantly they don't dump you into the bumpstops at rest, potentially taxing the dampers even more.

Available travel and mismatched valving are the main reason for poor ride with lowering springs...in our case we wanted to look at both together as connected issues to make the best springs we could for this platform.

- Andrew

[timurrrr]

Originally Posted by Racecomp Engineering

...

Thanks a lot for the detailed answer, I'm sure it will be appreciated by others too!

[Racecomp Engineering]

Anytime.

Also, good coilovers are indeed a significant step up from good springs. But crap coilovers OR good coilovers that have not been set up well are not better. You don't necessarily have to spend a lot of money but you do have to do it right.

- Andrew