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Old 06-17-2014, 02:45 PM   #1
RaceComp Engineering
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Default 2015 WRX and STI suspension TECH thread.

Wanted to start a FIFTEEN suspension tech thread to keep all of the misinformation to a minimum.

I will start with some basics and write a review impression piece later. ( had the privilege to do a back to back and I mean back to back comparison a few months ago and I found it very interesting.


STOCK SHOCK DYNO COMPARISON




motion ratio rear 0.78


STI fronts are mono tube

WRX front is twin tube

BOTH REARS are TWIN TUBE. (notice graphs look almost the same)
---------------------------

measurements below are for WRX

bump front 48.1 mm (1.89 inch)
droop front 88.9 mm (3.5 inch)

44.5 mm front bumpstop

bump rear 51mm (2 inch)
droop rear 66 mm (2.6 inch)

55 mm rear bumpstop

_____________________________________


STI front spring rates 5.8K
STI rear spring rates 5.3k

WRX front spring rates 5.8K
WRX rear spring ratees 5.2K



STI front sway bar 24mm
STI rear sway bar 20mm

WRX front bar 24mm (23mm measured on press car FEB 2014)
WRX rear bar 20mm
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Last edited by RaceComp Engineering; 11-19-2014 at 03:37 PM.
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Old 06-17-2014, 02:46 PM   #2
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Old 06-17-2014, 02:46 PM   #3
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Old 06-17-2014, 03:51 PM   #4
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can you confirm that the WRX and STi are also the same fitment as far as the knuckles go?

as in:
the 2015 STi front shocks will now fit on the 2015 WRX
the 2008+ STi front shocks will now fit on the 2015 STi
the 2008+ STi front shocks will now fit on the 2015 WRX

i know the WRX is now the 5x114.3 bolth pattern, and wasnt sure if that translated to the knuckles and bearing sizes too.
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Old 06-17-2014, 07:57 PM   #5
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Subscribed for the RCE Yellow drop springs !
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Old 06-17-2014, 07:57 PM   #6
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Quote:
Originally Posted by gsrcrxsi View Post
can you confirm that the WRX and STi are also the same fitment as far as the knuckles go?

as in:
the 2015 STi front shocks will now fit on the 2015 WRX
the 2008+ STi front shocks will now fit on the 2015 STi
the 2008+ STi front shocks will now fit on the 2015 WRX

i know the WRX is now the 5x114.3 bolth pattern, and wasnt sure if that translated to the knuckles and bearing sizes too.
Yes. 3 local dealers looked it up and they use the same part numbers for front and rear hubs etc. So yes you could install take off STI brakes on a WRX ( FIFTEEN TO FIFTEEN). Or 2008+ front and rear STI brakes onto a 2015 WRX.

Myles
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Old 06-18-2014, 08:52 AM   #7
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A couple of thoughts from Andy @ RCE:

1. The shocks are pretty good. Lots of damping available and it's a quality curve, especially STI.
2. Spring rates are the highest ever for STI and WRX in the USA. And both cars still ride relatively well. See note 1.
3. I'm not convinced all coilovers will be an "upgrade." See note 1 and 2.
4. Less than 5mm of travel before engaging the bumpstops up front (on the WRX). I'm not convinced all lowering springs will be an "upgrade" either.
5. Softer rear spring rate is interesting with the lower motion ratio in the rear. You'd expect more understeer from that (and there is some) but it's not as bad as you'd think.
6. Swaybars are BIG. Those are serious bars from the factory.

All in all, damn good job Subaru! Yes there is room for improvement for those looking to get a little more serious but you can tell Subaru has been focusing on handling the past few years and it's paying off.

- Andy
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Old 06-18-2014, 09:35 AM   #8
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point 4.

are the bump stops that long? is subaru moving to a setup where the bumpstop is supplementing the spring rate, and not just for shock protection? dont some other car manufacturers do somthing like this? i thought i recalled some german/european cars did this pretty often.
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Old 06-18-2014, 09:57 AM   #9
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point 4.

are the bump stops that long? is subaru moving to a setup where the bumpstop is supplementing the spring rate, and not just for shock protection? dont some other car manufacturers do somthing like this? i thought i recalled some german/european cars did this pretty often.
Yup. It's not entirely unexpected (Subaru has done this before) BUT I am a little surprised since the actual springs are fairly stiff and don't really need the extra rate from the bumpers. The initial progression isn't super stiff but it does ramp up for a progressive feeling. It does add to some at the limit understeer while making things feel more "tossable" and neutral before that limit. That was possibly their goal.

I have other theories as to why they've moved in this direction but would love to talk to one of their engineers. Subarus over the last decade have been bumpstop active but generally don't run such high main spring rates, so in that sense it's new. The BRZ relies on the bumpstops but is sprung super soft. It does make the valving of the dampers a little more interesting for both cars.

- Andy
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Old 06-18-2014, 10:02 AM   #10
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Quote:
Originally Posted by RaceComp Engineering View Post
A couple of thoughts from Andy @ RCE:

1. The shocks are pretty good. Lots of damping available and it's a quality curve, especially STI.
2. Spring rates are the highest ever for STI and WRX in the USA. And both cars still ride relatively well. See note 1.
3. I'm not convinced all coilovers will be an "upgrade." See note 1 and 2.
4. Less than 5mm of travel before engaging the bumpstops up front (on the WRX). I'm not convinced all lowering springs will be an "upgrade" either.
5. Softer rear spring rate is interesting with the lower motion ratio in the rear. You'd expect more understeer from that (and there is some) but it's not as bad as you'd think.
6. Swaybars are BIG. Those are serious bars from the factory.

All in all, damn good job Subaru! Yes there is room for improvement for those looking to get a little more serious but you can tell Subaru has been focusing on handling the past few years and it's paying off.

- Andy
Wow, good news. More spring, more frt bar and better damping sounds like a much improved setup. It would appear that the only change that might help more aggressive DD use would be a 6k rear spring.
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Old 06-18-2014, 10:15 AM   #11
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Yeah, and a solid alignment will get you far on it's own too!

But a solid alignment + some good MILD drop springs with a little more rate...

Really though, these dampers can support a lot more spring rate easily. Not a ton of headroom in the rear, but tons up front.

- Andy
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Old 06-18-2014, 12:38 PM   #12
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Have you guys thought about (or tried) throwing on your STi yellows (5mm drop IIRC) on the 2015 WRX/STi? they should fit right?
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Old 06-18-2014, 01:29 PM   #13
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Previous gen springs may physically fit, but I don't think that you would get the ride heights you'd expect. I'm not entirely sure...Myles might have a better idea of this.

- Andy
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Old 06-18-2014, 02:01 PM   #14
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I have had BOTH GR STI shocks next to 2015 STI shocks and if you put 15 shocks on your 2008 + you would be lowered by about 25mm ! We haven't tried it, but with the new dampers being significantly better than the previous generation, if the lowering was even front to rear you would have a SOLID set up.

EDIT: 2015 SHOCKS are a FULL INCH SHORTER assembled on the bench than 2008-2014 STI.

With that said it goes without saying that putting 08+ on the 2015 would result in raising the front at least and possibly the rear.

I found that from an "all around " stand point the 2015 WRX shocks felt the best. A decent amount of damping WITHOUT the overly active mono tube feeling that some might not like about the STI at speeds below 30mph.

So yes you could actually install WRX shocks on your STI ( both 2015's) and our soon to be released "Functional Lowering springs" and have a solid performer without the typical low speed feeling the STi has. Let me be clear, I dont mind this feeling but some have already complained about the STI feeling super stiff at low speeds( mph).

THe other thing we will test next week is installing our GTWORX BILSTEIN rear shocks ( mono tube with cir clips for height adjustment) on the rear of a 2015 and testing it with our new springs. Could be a way to REALLY bump up the stock 2015's with some SOLID spring rates and for not too much money.
The GTWORX BILSTEINS have +10 up or down range of adjustment on height so this could work. We are working on this already.

I too and super excited about the "New Twins". Subaru REALLY did us a solid on the shocks and spring rates. Just adding T2's to my WRX and I have 6.9 caster !

Myles
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Old 06-18-2014, 02:45 PM   #15
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And here is a comparison we did a while back between the REARS ONLY on the WRX and the PREVIOUS WRX models. MASSIVE difference.

You can't tell me Subaru project engineers weren't following the aftermarket on rates and what needed to be done chassis wise.

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Old 06-18-2014, 05:11 PM   #16
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Some good data gathered here! Subaru have definitely stepped up their suspension game for this model year. I think from a performance road car standpoint, the stock stuff is looking pretty damn impressive.

A bit more rear bar maybe to help with rotation in slower turns, but other then that, damn fine. What sort of alignment specs are we seeing with the factory stuff for this MY? You would think Subaru would run a bit more aggressive specs, given all the other improvements. My Fiat Abarth stock runs -1.5* up front from the factory haha. You'd think on the STi at least they might run a bit more aggressive. Especially considering the difference it makes in feel

-Anthony

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Old 06-19-2014, 12:04 AM   #17
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I Was able to get -1.8 front camber ..BUT…thats lowered only .50".

Thats also with 6.9 caster too. So that feels REALLY good.

Myles
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Old 06-25-2014, 02:15 PM   #18
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The 2015 STI struts with all that front low speed rebound are going to be AWESOME in transitions/slaloms for auto-x.

- Andy
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Old 06-29-2014, 08:53 AM   #19
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Great information!
Question, would the 15 sti springs lower the 15 wrx a little while maintaining an (almost) stock spring rate? I ask since it seems the sti body sits a tiny bit lower to the ground than the wrx yet with a slightly taller tire from the factory and also less wheel gap. Lower spring being negated by a taller tire? A small drop like 0.5" seems to cosmetically make quite a nice difference if this is the case.
Interested to find out more about your "functional lowering springs" though. Thanks for the shock dynos, they look great!
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Old 06-30-2014, 02:41 PM   #20
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Quote:
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Great information!
Question, would the 15 sti springs lower the 15 wrx a little while maintaining an (almost) stock spring rate? I ask since it seems the sti body sits a tiny bit lower to the ground than the wrx yet with a slightly taller tire from the factory and also less wheel gap. Lower spring being negated by a taller tire? A small drop like 0.5" seems to cosmetically make quite a nice difference if this is the case.
Interested to find out more about your "functional lowering springs" though. Thanks for the shock dynos, they look great!
Well as soon as we can take STI springs and put on the WRX we will know that they have the same free length between the perches. The WRX front is twin tube and NON inverted and the STI is inverted and mono tube.

Myles
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Old 07-03-2014, 02:52 AM   #21
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When are you guys planning on releasing lowering springs (yellow and black) for 15 WRX? Late Summer?
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Old 07-03-2014, 03:35 PM   #22
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When are you guys planning on releasing lowering springs (yellow and black) for 15 WRX? Late Summer?
Very late summer. Testing now. This car is already good. We want to improve it which takes some doing. Subaru raised the game a good amount this time!

Myles
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Old 07-03-2014, 04:04 PM   #23
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Very late summer. Testing now. This car is already good. We want to improve it which takes some doing. Subaru raised the game a good amount this time!

Myles
Would be nice if understeer gone.
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Old 07-03-2014, 04:21 PM   #24
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Quote:
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Would be nice if understeer gone.
I asking this when I hear people talk about that………what are your alignment specs?

The new car does push stock, but adding a little bit of camber goes a long way. The new car has more caster than the outgoing model.

Myles
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Old 07-03-2014, 05:32 PM   #25
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Quote:
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I asking this when I hear people talk about that………what are your alignment specs?

The new car does push stock, but adding a little bit of camber goes a long way. The new car has more caster than the outgoing model.

Myles
Bone stock. I haven't done anything to the car yet, but I probably look into that option you suggest. I try to fit 18x9.5 +38 in there, but that's probably a lot of work vs +45. If camber is more adjustable than out going model, that's a good thing.
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