FAQ: JDM OEM suspension
JDM OEM suspension FAQ (updated 12/12/11)
What is OEM suspension on JDM BP/BL Legacy?
JDM Legacy GT, GT SpecB, 3.0R SpecB use Bilstein struts and shocks. The fronts are inverted monotube struts. Other trims use lesser KYB shocks, similar to what USDM 2.5i and GT have. The difference in handling is amazing; the car on Bilsteins drives infinitely better than stock. In fact the car is more comfortable, too - while impact hitting a road imperfection can be felt more, the dampening so much better and quick so it goes away instantly, while stock will float and bounce much longer.
What is the difference between JDM GT Bilsteins and JDM SpecB Bilsteins?
JDM GT Bilsteins try to balance ride comfort and performance. They are much sportier and provide far more controlled ride than stock USDM GT dampeners (KYB). JDM SpecB Bilsteins are geared more towards performance at some sacrifice in ride comfort.
What the heck are these confusing revisions?
Revision is actually a misnomer. The lettered "revisions" refer to model years in JDM. A is MY2004, B is MY2005, C is MY2006 and so on. Indeed, the suspension actually was revised several times that resulted in differences in dampening and springs. Generally each subsequent revision got softer due to the complaints that these cars ride too stiff.
Note, there was no "original revision" or "revisionless" Bilsteins. Some posts, including the "Part numbers" thread in turbo section contain incorrect information.
JDM GT Rev.A
Original GT setup. Great balance of performance and ride comfort. I currently use this setup as my winter suspension. It is firmer, but not too firm. Closer to JDM SpecB Rev.B than to JDM GT Rev.C (had both setups earleir). Everyone who has this setup seems to praise it, especially with Pinks.
Part numbers: 20310AG060 (front right), 20310AG070 (front left), 20365AG040 (rear)
JDM GT Rev.B
This one is bit of a mystery. Does not really feel softer than JDM GT Rev.A. Interestingly rear shocks are the same as on JDM SpecB Rev.B, front struts are different. I just drove a car with these on Pinks and indeed the setup seemed more complaint than JDM SpecB Rev.B, but the difference is not big. Note, there is an old post quoting someone from Bilstein Japan saying this setup is for SpecB and tuned for 18 inch wheels - that is incorrect, I verified this against JDM parts database.
Part numbers: 20310AG140 (front right), 20310AG150 (front left), 20365AG120 (rear)
JDM GT Rev.C
This is the current JDM GT and JDM 3.0R setup, present on Rev.D cars as well. Also used on 2006-2007 USDM SpecB (not sure about 2008 yet). These are noticeably softer than any other revisions. Give nice and controlled and oscillation free ride, but they are more on the comfort than performance side. There were complaints that these do not handle stiffer springs (Pinks) very well and feel bit underdampened. I can believe this as in certain high speed situations these did not feel as secure as other revisions.
Part numbers: 20310AG400 (front right), 20310AG410 (front left), 20365AG260 (rear)
JDM SpecB Rev.A
The original SpecB setup, stiffest of the bunch. I rode in a car with supposedly this revision (not 100% sure, not confirmed by part numbers) - it felt marginally stiffer than SpecB Rev.B. Opinions about this setup range from "great ride" to "too stiff for daily driver". I guess this is very subjective plus it depends on the road conditions, wheel size, tires, etc.
Part numbers: 20310AG100 (front right), 20310AG110 (front left), 20365AG050 (rear)
JDM SpecB Rev.B
Supposedly softer than Rev.A. I had it on my car with Pinks for few months and liked it very much. Excellent performance, yet still great ride. However, can be too harsh on really bad roads if paired with stiff tires like RE070.
Part numbers: 20310AG180 (front right), 20310AG190 (front left), 20365AG120 (rear)
JDM SpecB Rev.C
This is the current JDM 2.0 SpecB and JDM 3.0R SpecB, present on Rev.D cars. Bit less aggressive than Rev.B, yet still excellent handling and great ride. This is my favorite Bilstein setup so far for a street car - I think they really got this one "perfect".
Part numbers: 20310AG420 (front right), 20310AG430 (front left), 20365AG270 (rear)
Are Bilsteins the same for sedan and wagon?
Yes there are no differences in struts/shocks between sedan and wagon.
Are springs the same for sedan and wagon?
No, rear springs on wagons are a little bit longer to compensate for extra weight. Note the extra weight is minimal (60 lbs. for non-limited wagon vs. non-limited sedan).
Do Bilsteins work on 2.5i as well?
Yes. Since all suspension parts except front sway bars are fully compatible between both GT and 2.5i.
How USDM SpecB Bilsteins compare to JDM Bilsteins?
USDM SpecB Bilsteins are identical to JDM GT Rev.C Bilsteins, see above.
What are the JDM tophats?
JDM cars use different front top hats (mounts). The USDM top hats cannot be used on JDM OEM Bilsteins (or other struts like Ohlins, Tokicos, Bilsteis HDs) - the USDM top hat has taller bearing and the threaded portion of the strut rod is too short and will not allow for safe installation. Pictures that compare JDM and USDM top hats are located here.
By the way, JDM top hats are beefier, the bearing in them is huge compared to USDM one. Thet are much stiffer, help steering response and contribute and to the "road feel" - there is much less play in the top hat. USDM top hat is very rubbery and clearly designed for comfy ride.
The JDM and USDM names are customary - JDM top hats refer to top hats used on Bilsteins, including Bilsteins on USDM Legacy SpecB. USDM top hats are used on some JDM cars, not sure which but are used on some Outbacks. Note, interestingly AusDM 2.0i or 2.5i cars seem to use JDM top hats on KYB struts.
Do JDM tophats raise the front of the car?
I compared these top hats side by side and they seem to locate bottom of the bearing at the same height with respect to the chassis, so the top hat should not affect ride height. This is moot question since the top hats are not interchangeable, with the exception of KW Variant 2 coilovers.
I installed Bilsteins and my rear sits lower wrt front than I would like! Why?
There might be few things which contribute to this. First, our cars from the factory seem to have "saggy butts" - the rear wheel gap is smaller than front, this gets accentuated when the car is lowered. Second reason might be use of AT specific front springs on MT car.
It can be addressed with "saggy butt shims" that go between the rear shock top hat and the chassis. See this thread. They can be bought here.
You should use longer top hat studs with them. Perfect replacemnt is a Geo metro wheel stud, Dorman part #5090B. Available from rockauto or AutoZone. Fits well up to 3/8" thick shim (my recommended thinkness for JDM suspension setups, that's what I run with my JDM GT Rev.A wagons setup).
Other alternative is to double up the top rear spring seat.
Finally there are springs that by design drop front more than rear - like Swift, Wangan, Prova, or TN Guts. Most are rare JDM only items unfortunately.
Can I use JDM springs on USDM stock dampeners?
Yes. However they will drop the car more in front compared to JDM suspension. The reason is that lower spring perch on the front struts is actually located lower compared to Bilsteins. Ascetically this is good as it results in more even stance, however I do not believe USDM struts/shocks can handle stiffer lowering springs.
Can I use USDM stock springs on Bilsteins?
No. USDM stock springs are longer and while probably you could cram them on Bilstein, the car won't ride or look good. Other USDM specific springs like USDM-specific Ions on Cobbs might fit but again would be seriously mismatched.
I want to install Bilsteins, what parts do I need?
For the front you need JDM top hats, corresponding dust caps (seals) and front spring upper perch/seats. Some people used stock USDM GT front perch/seat, but since they look bit different and have different part number I recommend using the Bilstein specific one. Also, the dust boots are different in front. For the rear you can use the stock top hat and spring seat.
Of course you also need some sort of JDM GT/SpecB specific springs like STI Pinks, Swifts, R-SR, Wangans, Teins or Provas, etc.
Part numbers (available from US dealers):
20320AG000 - front top hat (strut mount), 2 needed -
20326AG000 - front top hat dust cap (dust seal), 2 needed
20323AG000 - front spring seat/perch, 2 needed.
20322AG010 - front dust boots, 2 needed.
Any tips on the install?
Not really. Make sure to properly position front seats/perches - the drain holes need to be oriented outside. Do not use stock dome washer/spacer between spring seat and top hat. Other than that universal precautions apply, do not over torque stuff, top hats bolts and piston rod can be easily broken.
Links to useful install threads: here and here.
Where to get OEM Bilsteins?
JDM GT Rev.C / USDM SpecB Bilsteins can be bought from any US dealer. JDM only revisions need to be imported from Japan.
What about aftermarket Bilstein HDs?
Bit of a mystery here. They look pretty much the same as OEM Bilsteins and also share monotube inverted construction. Originally a Bilstein dealer claimed they have less travel than OEMs in front (108mm vs. 130mm) making them not well suited for lowering springs. Recent findings are that they have the same travel as OEM Bilsteins, plus few members are using them successfully with Pinks so it seems these concerns are unfounded.
They supposedly ride bit stiffer then OEM USDM Bilsteins. Dealers claim 20% stiffer. Can't say, never rode in a car equipped with them.
The bigger mystery is the difference in price - OEM Bilsteins cost more than $1200 new from the dealer (in the US or Japan), while HDs seem to cost around $500. I don't know where the difference comes from. OEM markup?
What are Pinks?
Pinks are lowering springs designed and sold by STI branch of Subaru. Compared to stock JDM cars lower the car all around 15mm. Pinks are not designed for stock struts and result in crappy ride. If mated to stokers they lower more like 25mm.
Which Pinks should I get?
There are few variants of spring: for MT, AT, sedan, wagon, SpecB, 3.0R. They are different to account for difference in weight between these cars (not damping rates or ride height, if it would be so SpecB application would not share springs with anything else).
Due to the "saggy butt" being pronounced with Pinks, I recommend getting regular GT MT wagon Pinks for all applications. They will keep the rear of the car little higher lessening the saggy butt effect, and possibly drop the front a hair more, further evening the wheel gap.
Note, JDM SpecB has 5mm higher ground clearance than JDM GT, which given 12.5mm longer radius of tire means the stock suspension must be lowered ~7.5mm vs normal GT suspension. It does not seem to be true for Pinks. A car with SpecB wheel setup will ride higher.
In the table below B4 indicates sedan, TW indicates wagon. The 4th column has part #s of the front springs, the 5th of the rear springs.
Ok, finally ;) I am receiving many pm and see lots of questions related to these so I thought I should finally post this...
This is unlikely since the ride height should be determined solely by the knuckle/strut. The LCA should only locate it on a horizontal plane.
I can't find the post now, but a member spoke to a Subaru insider who claimed alu LCAs have "different geometry" - whatever this means...
Nice! Thanks for that, um.
Thanks for posting this, it makes a lot more sense than what I've divined from reading threads.
The aftermarket Bilsteins likely have different damping rates and spec ranges than factory, but same quality control (different quality control systems would be unusual in manufacturing).
I wonder if they fit the USDM top hats?
just my $.02,
Nice summary unclemat! :)
Nice Information. Are sti pink springs, the springs that come stock on the Tuned by STi in Japan and Aus?
nice write up
So I wonder if the USDM and JDM knuckles are different. In other words, would JDM knuckles lower the front of a USDM car?
same between USDM SpecB and GT, so I guess it won't be any different in JDM.
On second thought, sgt is right, it's the sturt/spring/top hat plus the knuckle should determine the ride height in front.... so, yeah, what I said doesn't make sense. So it's a mystery then... perhaps the front is correct, it's the rear which is lower? If the hole in the trailing arm where the rear shock was attached was placed at different height in KYB equipped cars, then it would explain it. Although a unscientific look at SpecB alu trailing arms idicates the location is the same... :confused:
The knuckle is part A in the diagram.
Its bolted to the strut and also holds the ball joint.
That Boss, should basically be a steel insert so that the aluminum doesnt get destroyed.
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