This is probably going to be a wall of text but hopefully some of you learn something new and it helps in some way in the future. These are things that I’ve found tinkering on my own and others vehicles over the past 10ish years.
Shims adjust how the piston travels through the oil of the shock. Thicker the shim, the more dampening you get. Thinner the shim, the less. Pretty simple. Oil weights also play a large factor in this but I’ve only ever ran one type of fluid in an off-road truck shock. It’s all about limiting the flow of oil through the piston.
It’ll probably be helpful if you know the terms before I start explaining what little I know, most of these can be found by googling if you don’t understand it.
Compression dampening is what keeps you from smashing into your bump stops. Stiffer valving is better for go fast, but you need to tune it to be comfortable. It’s great if you can speed through dips and whoops but not if it comes at the cost of your back.
Free bleeds for the most part should be left alone from what I’ve read and experienced. On my rears I only have 1 of 4 bleed holes open, by doing this you restrict fluid flow a lot. Restricting fluid flow causes cavitation on hard hits and the oil to move a lot more in the resi and can cause a lot of damage to your shocks(this is why resi ifp depth is very important for all shocks, top mounted resi most importantly). Can be combatted by adding nitrogen to your resi cans, but it isn’t always the best option. My first revalving I did of my 4runner when it was completely stock other than the shocks and tires was to try and make it quick and comfy on Fox 2.0rr shocks. 6.5” travel shocks in front and 10” travel shocks in rear. I ended up having to run 350psi of nitrogen to combat the cavitation and shock fade after a few miles, but it rode awesome. Could skip across stuff in Barstow and Lucerne almost as fast and guys with LT. only drawback was all that valving in the tiny shock caused a lot of cavitation even with 350psi of nitrogen and would cook the seals out of the shocks every long trip. After years of this I finally said fuck it I wanna go fast so that’s when LT happened.
The small shocks are fine if your vehicle isn’t heavy and you’re not trying to haul ass. A Toyota 2wd pickup can be incredibly fast on 2.5 shocks if it’s built with weight in mind and valved appropriately. Hell even on 2.0s if it’s light enough. The heavier the vehicle the more shock you need because you need dampening to combat the weight of the vehicle pushing down. Not necessarily spring rate, but shock valving. Springs should be picked for weight of the vehicle, shocks for type of terrain.
Let’s get back into compression valving.
If you have a standard .015 stack on your compression side of the piston that’s probably really good. Might be a little stiff in the shorter quicker bumps, so you combat that with a flutter stack or a mixed stack. Let’s use fox standard shim sizes for 2.0 shocks cause that’s what I know off the top of my head.
Compression side
•Rate plate
-.800” diameter
—.950
—-1.100
——1.350
——-1.425
———1.600
-piston
———1.425
——-1.350
——1.100
—-.950
—.800
-.750 “backup” washer
Rebound side*
Between the 1.350 and the 1.100 shim on the comp side id insert a .020”x.800” shim to create a flutter, this will allow those larger base shims to open up sooner and allow fluid flow on the short quick hits like washboard, small rocks, potholes and such. If .020 is too much and I felt like that was also making it blow through travel, I’d go with .015 or .010” thick. You can also shorten shim stacks from but ALWAYS use the larger base shims. You can add more base shims to have a stiffer “zone” before the shims flex past the flutter and engage the rest of the stack. That’s what’s so fun about tuning shocks, there’s nearly endless ways to adjust the shims. You can create two or three zones using flutter stacks, at one point in the front of my 4runner when it has stock length arms I had a double flutter and it rode really great, but I had to ditch that when I put the longer arms on it.
Flexible rate plates are something I’ve fooled around with only a little bit. From my understanding it makes the shock not hit it’s harshest “zone” so violently. Instead it hits and flexes the rate plate to allow a smoother feeling of hard hits. The hard part it making it flex enough to accomplish this and not blow through your travel and bump so hard you piss blood.
There’s fulcrum shims that allow freebleeding. It’s when you put a .800” shim of whatever thickness you desire between the comp side of the piston and the largest shim. This allows the fluid to flow past the fulcrum and not engage the stack for smaller bumps like washboard and small rocks. I liked .010 fulcrum with a .015 compression stack for trail driving. The fulcrum shim method works well, but increases the overall fluid flow when hitting hard because it increases distance between the piston and it’s largest shim. Flutters just allow the base of the stack to open a little easier to allow the smaller hits to not engage the entire stack.
Mixed stacks work well too. You can have a .020/.015 mixed stack to allow the stack to be more progressive.
Rebound valving is something that I haven’t spent a whole shit ton of time on. I usually just valve it around what I see is needed for the spring rate I have. Usually .012 or so shim stack and it works fine, if you’re on leaf springs you need much less, probably .008 shims. You want your wheels to stay in contact with the ground as much as possible to maintain speed and not load/unload your drivetrain constantly, keeping you from ruining axels and driveshafts and transmission parts. You want it quick enough to maintain a good amount of contact, not so quick you get the classic pogo stick esque donkey kick that sends your rear end up and over the front. This is caused usually by too heavy of rebound allowing the suspension to “pack” and not droop enough to have enough compression travel to dampen the next hit. This happens a lot, most of the time it’ll be okay if your shocks are tuned right, also has to do with comp valving to make sure you’re not bottoming so fast that you’re hitting bump stops constantly anyway.
A lot of people have their own methods and may differ completely from what I’ve done and what I like. I personally like light rebound in the front to keep the front from diving and packing, almost making it feel like it’s growing through whoops. The rear I like to be controlled but light to keep the rear tires planted, but again no so light that the springs can push the shocks open so quickly that the rear will pogo.
Bypasses are something that I’ve messed with only a few times, the more tubes the better. They allow different dampening zones at different dampening rates which is awesome, you don’t have to pull the shocks apart all the time. You set your baseline valving for your trucks weight and driving style and you then adjust the bypass valves in or out to make it handle better. I’ve played with fox’s internal bypass that utilizes holes covered by different thickness reeds. These are the ones that come on raptors. IMO they’re cool but overall I’d go with an external bypass because why open the shocks to tune if you can leave them closed.
Hydro Bump stops are truly one of the best things to ever happen to off-road. I haven’t spent a lot of time on tuning them because it’s not really needed. It’s a tiny shock that’s valved to hell. I put the appropriate amount of fluid and fill them to 200psi of nitrogen and call it good.
To end id like to say it’s not all about wheel travel numbers, it’s about how you set your truck up and how to tune your shocks. There are guys that have 9 inches of travel and can haul absolute ass. With stock arms I was making I think 8” up front and 13” in the rear. Everyone I took for a ride said it was ridiculously smooth *for a stock truck*. Yeah, it was a little rough till it got up to speed, but I could cruise through washes of Barstow at a good speed and my back never hurt after the trip.
I think I covered most of what I know, if anyone has any questions feel free to ask.
Also I’d like to add I’m selling a set of 2.0x6.5” fox remote reservoir shocks, if you’re interested let me know. Fit perfect in stock length arm trucks and 4runners 86-95.