Suspension Encyclopedia - OEM Valving Specs
This page is the beginning of my promise to bring free to consumer, objective information about suspensions to the masses. Over the past few months i have written down the valving info for some of the shocks i've rebuilt or tuned.
I will also be posting tons of linked suspension data including measured COG heights, roll center, anti's, bump steer, etc. from many popular kits and OEM setups, look for that soon.
FJ Cruiser Fox 2.5" Front Coilover
These had 600 lb springs on them and 8 hole linear piston. Rebound holes were .25 and comp holes were .344". 1/16" bleed hole.
Rebound
.8 x .020
.8 x .020
.95 x .015
1.1 x .015
1.25 x .012
1.35 x .012
1.425 x .010
1.6 x .010
Piston
1.8 x .012
.8 x .008 - Flutter
1.6 x .010
1.425 x .010
1.35 x .012
1.1 x .012
0.95 x .012
0.8 x .020
3g4r Total Chaos long travel spec front king coilover
Came with 500s, customer swapped to 650s. I think 600s would be more appropriate or 550s with less bleed. Had 3 bleed holes open with no set screws in place on kings standard high flow piston.
Rebound
All .010s
Piston
.012
.012
.08 Flutter, 1" diameter
.015
.016
.016
.016 (i know there arent 16s but they all measured .016)
2nd Gen Tacoma front king 2.5
600 lb springs, rebound 3 holes at .328 each, comp 6 holes at .375. 3 bleed holes open with no set screws in place. I am too lazy to write the full specs, these are thousandths of an inch and its kings standard valving layout.
12
12
12
15
15
15
15
Piston
12
12
10 - flutter
20
20
20
20
Fox 14" Coilover w/ sas tune
This was from a popular tuner, it had 30/90 with a flutter and 2 large bleed holes. On a 14x2.5 with DSC. I did not ride in the vehicle to verify performance.
2nd gen tacoma rear king 2.5
2 bleed holes open, 1 set screw.
8
8
8
10
10
10
piston
12
8 - flutter
12
12
12
12
12
lx470 king 2.5 rear with adjusters
These have a 2.0 res on them which is odd, i see this on 5g4r versions as well but not sure why. 2 bleed holes open 1 set screw
All 12s
piston
12
12
10 - flutter
15
15
15
15
15
Customer was complaining about how soft it was all around, has a dirtbike hitch carrier and it pogo's bad with the bike on the back even with the comp adjuster all the way firm.
Upon opening the shock i found lots of air and nitrogen was leaking past the IFP. I ended up just closing 1 of the bleed holes and rebuilding it with no air in the shock although i did consider swapping the comp side to all 15s.
5g4r king front 2.5 coilover with adjusters
3 bleed holes open. Came in pressurized to 135 psi. Leaked in the normal spot for kings, very small hose fittings. Not sure if these have been revalved or not as they did not match with the valving from the next set i did.
All 20s
piston
10
10
10 - flutter
18
18
18
18
.615 washer
rate plate
Customer complained they weren't getting enough shaft speed at low speeds which is crazy with 3 bleed holes. I ended up swapping the rebound stack to 15s for the first 3 and the comp to 8s for the first 2. I also closed 1 of the bleed holes, in my opinion on a mechanical advantage like an IFS front end 3 bleed holes is alot.
5g4r king bypasses rear 2.5
1 tiny bleed hole, this is standard for bypasses industry wide.
All 12s
piston
All 12s
5g4r king front 2.5 coilover with adjusters
Not sure if these have been revalved or not. 2 bleed holes, 1 set screw.
All 15s
piston
12
12
10 - flutter
15
15
15
15
15
1500 truck fox 2.5 w/ dsc rear smoothies
All 12s
piston - digressive style
bleed shim (sorry didnt measure total area)
1.8 x .008
0.8 x .015 flutter, probably to accomodate the DSC
all 8s
2nd gen tacoma +2" total chaos long travel spec coilover w/ dsc
2 large bleed holes on linear style piston
15
15
15
10
10
10
piston- photos below
8
6 - same 1.6" dia
.8 x .010 flutter
8 - same 1.6" dia
.8 x .010 flutter
10 - same 1.6" dia
10
12
10
10
20
2nd gen tacoma fox 2.5 2 tube bypass, valved for spring under kit
1 small bleed hole
All 12s
piston
Dual .015 x 1.8 shims
all 15s
1G Tacoma IFP King
12
12
12
15
15
15
15
3 open bleed holes
12
12
10 - flutter x 1.15
20
20
20
20
5g4r King 2.5 smooth bodies with comp adjusters
All 12s
2 bleed holes open
12
12
10 - flutter
15
15
15
15
15
2.0 resi. Comp side seems high considering it has adjusters.
5g4r king coilovers 2.5 with comp adjusters
Not sure why these were valved differently from the ones above
all 20s
3 bleed holes
8
8
10- flutter
15s
2nd gen tundra king 2.5 long travel with comp adjusters
12s
3 bleed holes
12
12
20s
No flutter, which is typical for long travel coilovers due to the increased motion ratio. These are not valved to work with the bypasses they are paired with, adding in a flutter would help alot with that especially with the comp adjuster.
2nd gen tundra fox 2.5
15s
12
2 large bleed holes
8
8
8
8 - flutter
12s
fox 2.5 f150 front w/ dsc for dirt king kit
all 12s
2 3/32 bleed holes
8
8
10
12
12
12
king 2.5 carli kit for newer f250
This truck was really nice but came in complaining of ride quality issues. After pulling it apart i learned that carli specs king pistons to have stepoff shims. My best guess is the goal is to have directional bleed. First thing i did was rebuild the shocks to have a good baseline, which helped alot. The stepoff shims make low velocity stuff really weird and jittery/unmetered feeling. I ordered standard pistons to swap it to. My best guess is that the stepoff shim area that is cutout of hte piston is 8 thousandths thick, so in theory a 12 thousandths shim will give you 4 thou stepoff for the face shim.
Front smooth bodies:
12
12
12
10
10
12 preload shim
piston
8 preload shim
12
12
10
10
8
8
Rear smooth bodies:
12
10s
10 preload
piston
9 preload
8s
1983 Ford bronco solo motorsports ttb kit king 2.5 coilover
12x2.5 coilovers. Rode insanely stiff before revalve
12s
3 bleed holes in piston
20
15
15
15
ended up adding a flutter after the 1st 15 on the comp side, the 20 takes so much force to initially lift off, this is likely to compensate for it being dual rate springs (think 300/500?) on an IFS setup which vastly reduces your spring rate.
Lexus gx470 icon 2.5 front coilovers
15
15
15
15
18
30
15
(2) 18s
15 preload
3 bleed holes open (out of 4) in piston
15 preload
15 face shim
15 x .925 flutter
all 15s
ADS 2.5 with adjusters for 1st gen tundra with camper setup
I've only taken a few ADS shocks apart but these were a bit different than the others. Similar to the King carli kit which is trying to have directional bleed with step off shims, these had a 8 thou face shim and flutter underneath the normal shims which also sort of gives it directional bleed before engaging the stack.
Rear 2.5 smooth bodies with adjusters:
10s
8
8 flutter
8
Piston with 1 tiny bleed hole
8
8 flutter
8
10
10
12s
Front:
15s
Piston with 1 tiny bleed hole
8
10 flutter
8
10
10
12
15
15
Again the comp side face shim and the shim after the flutter are the same size. This setup was much too soft for all the weight and was a bit floaty and uncontrolled. The front had a jounce/rebound zone spring section which is cool, but there were a lot of aluminum shavings inside the shock from the spring rubbing its guides.
Shock Value 2005-2023 Tacoma 2.5 shocks test:
Last year we tested 5 different shocks back to back on a new tacoma. Here are the valving specs for every single shock and also a bit of subjective feedback on how each one performed.
Fox 2.5 race series coilover
Looks like a low flow linear style piston but is also possibly dished in the center.
4 washers
(4) 20 x.8"
12x.95"
12x1.1"
12x1.35"
12x1.42"
12x1.6"
low flow piston, one .171 bleed hole
8x1.8"
20x0.8" flutter
8s from here
and a 20x.8 at the end
Note: I drilled the bleed hole larger to see if that would help.
The foxes were the worst handling/performance of the bunch. I really genuinely like fox as a company, haft hardness is great, oil is awesome, seals work well, body coatings last a long time, and the dual comp adjuster is the best of all the aftermarket adjusters.
Now that all that is out of the way, this particular tune was pretty much worse than stock, i could not believe how firm it was. This was also the only shock of the bunch that had all the same size shims on the comp/rebound stacks.
This shock will make another appearance in our upcoming series where we will test it fully revalved and tuned to my specs, but still blind.
King 2.5
All 15s, or possibly 14s honestly, supposedly they dont have 15s but i swear i find alot of 15s
3 bleed holes
8
8
10 - flutter
15s
This shock was really impressive, although one of the fronts and one of the rears was already leaking after only a few hours. To be totally up front i dont sell much king shocks but they are the most common shock i rebuild by a large margin. After this test i've added a bunch of their stuff to the website.
On road handling was great on these and they were really good offroad but did top out hard. King doesnt have an internal bumper for the rebound stroke so that could be a cause. Overall id say these shocks were about as good as a normal shock absorber could be for a stock travel tacoma, although the leaking was a bit alarming, all the shocks were wiped down before install and this was the only set of the entire test with oil on the shafts after their run.
Icon - coming soon
Bilstein - Coming soon
Elka - coming soon
Bilstein Valving Specs
Bilsteins valving is notoriously complicated but also deceptively simple, here are the available stacks for various products.
All Bilstein valve stacks are listed by newtons of force at 0.52 m/s (around 20 in/s). Therefore 170/60 means it takes 1,700 newtons of force to move the shock on the rebound stroke at 0.52 m/s, and 600 on comp. Bilstein lists valving as rebound/compression, most brands will list compression over rebound.
7100 series valving
170/60
255/70
360/80
180/75
345/135
275/78
220/115
8125 valving
Unfortunately Bilsteins 60mm 8125s come valved at 370/110 which is possibly the worst universal valve spec of any brand. For solid axle swaps i suggest starting at 275/78 and slightly increasing the preload shim size (for less preload) and running much larger bleed disc, something around 18 mm squared total bleed area, for example 8 on rebound and 10 on comp.
9200 series coilovers come valved at 255/100 with a linear piston which is a really good starting point for solid axle swap front ends... although they only have 1 tiny bleed hole which could push it closer to digressive. Typically i will drill out the initial bleed hole and drill a second to around 1/16" or a bit more.
General Valving advice
Ultimately, valving is subjective...
It's important to keep in mind that whatever a customer thinks feels good, is good. Despite having a finely tuned butt-dyno i still run into some situations where i prefer a different valving profile than a customer, which is totally fine.
To get shaft speed up over razr burn and nuissance rocks, bleed plays a huge role. Bilsteins digressive piston really struggles with shaft speed over stuff like that and requires large bleed discs to not rattle you apart on washboard. Alternatively many companies just valve the shocks firmly and rely on you airing down to eat up that sort of stuff. Unfortunately the same valving that gives you shaft speed over razr burn will also ruin on road handling.
A flutter on the compression side will also help with things like nuissance rocks and washboard as it reduces the initial lift-off force of the face shims. I typically dont like to use flutters on rebound since piston bleed acts more on rebound than compression.
There are plenty of general guides online about what adjustments to make when... my best advice is to go out and just do it for yourself, you will never learn it by only reading and even 1 or 2 revalves will teach you alot. That being said an important thing to keep in mind is you cannot revalve a shock that needs rebuilt... you will not get a clear indication of the actual ride quality of the damper if it was in perfect operating conditions, so it will likely feel too soft because of air in the body. The damper must be in perfect working condition before you decide to change things around, often times folks request a revalve and find what they actually need is a shock that isnt full of air.
