Topic: Shock Tuning

[jrock]

Is there a list of good threads that delve into the details of shock tuning? If not, let's start one here.

Ride conditions and what to change in the valving and pressure. General valving to start with.

[TacoRunner]

Okay. I've never seen or heard of a shock manufacturer sending anything other then .010" compression stacks out the door unless the user specifically requested something else.  So just start there and spend and extra $40 and get a couple of extra shim stacks so you can play around with stuff.

Compression:
Valve stacks are very much like leaf springs. The longer ones flex easier than the short ones and of course the thicker they are the stiffer. But the similarity doesn't end there. On leaf springs the top leaves are typically used during normal drive or street conditions where the bumps are small and the heavy leaves are there for when you load up the vehicle. The same is true for valving. Top shims for little bumps, lower portion of the stack is there for big bumps. If the little bumps are nice and soft but the big ones are blowing through the shocks, then you need thicker shims at the bottom of the stack.

[TacoRunner]

Most shock manufacturer's us the following thicknesses of shims, while diameter varies between companies and diameter of shocks.

.006
.008
.010
.012
.015

[jrock [OP]]

On the valve stack, which side is compression and which side is recoil? Then, in the valving stack, the bottom of the stack (against the plunger) is the larger diameter shim and the top is the smaller diameter shim?

[TacoRunner]

Shims on the bottom of the piston are the comression. You are correct on the rest.

[jrock [OP]]

So in the valving stack, do you always have 5 shims? And then of the 5 shims you change the thicknesses and diameters?

[TacoRunner]

You can have more than that if you want. Think I've got six.

[jrock [OP]]

What makes the valving number? And which number means comp. and recoil?

[jrock [OP]]

Cool. Found some pictures and a writeup on King Shocks website.
http://www.off-roadweb.com/tech/0906or_off_road_race_shocks_explained/index.html

[Nimyad]

Watching

[TacoRunner]

What makes the valving number? And which number means comp. and recoil?

[jrock [OP]]

Okay, so when valving a shock you use a stack of one #. So all #30, #40, #90....

I've heard of "flutter stacking" which involves putting a small shim over the the large bottom shim. This is to soften the shock over light bumps but it keeps the rest of the valving for harder bumps. I read it as a way to get progressive valving out of coil overs before bypass shocks. Pretty cool

[TacoRunner]

Okay, so when valving a shock you use a stack of one #. So all #30, #40, #90....

I've heard of "flutter stacking" which involves putting a small shim over the the large bottom shim. This is to soften the shock over light bumps but it keeps the rest of the valving for harder bumps. I read it as a way to get progressive valving out of coil overs before bypass shocks. Pretty cool

Yes a flutter stack does just that. But as to how thick the shims are and how many you put in is part of the tuning process. Both on the flutter and the rest of the stack.

Most of the time, when using a bypass shock, the coilover becomes a coil carrier. i.e. the guts are ripped out and the shock just holds the coils while the bypass does the work. You are correct that flutter stacks were used more before bypasses existed.

Think of shocks like this, the harder you push them the harder they fight back. They are Dynamic pieces of equipment. Springs compress at a certain rate no matter how fast or slow you go, they compress in a predicatable manner. They are Linear.

Stiff springs need softer compression valving in the shock to ride smoothly. However because stiff springs typically do the work of the suspension they are bad at soaking up larger bumps at high speed because they dont fight back the harder you hit them.

Softer springs need stiffer compression valving to maintain vehicle control otherwise you end up driving a sloppy slinky P.O.S. Because shocks are dynamic and can soak up larger bumps with easy, the stiffer the compression is the faster you can go. But you have to match that stiff compression with a soft spring or you're back to riding a brick.

Coilovers were designed from conception to run springs soft enough to net you 50% or more of compression of the spring at ride height. I like about 60% for crawlers.

[OldGold3VZE]

Like anything else, shock tuning can get quite complicated really fast.  I would recommend purchasing a damper manual if you plan on getting involved in learning about the many variables involved in shock tuning.  The numbered stacks that Fox gives are so basic it's not even funny, and all the numbers are for is nothing more than an identification of their given shim stack.   Check out www.shimrestacker.com for a basic start.  Also, get yourself familiar with multi-stage valving to really boost the performance in basic emulsion dampers like the Fox 2.0, it makes a huge difference.

[jrock [OP]]

This is awesome, thank you for the replies

Taco, coils on coilovers aren't progressive, as you said but leafs are somewhat progressive. Correct?

OldGold, is there a damper manual you would recommend? That link is cool, thanks.

[OldGold3VZE]

http://books.sae.org/book-r-381

[TacoRunner]

Taco, coils on coilovers aren't progressive, as you said but leafs are somewhat progressive. Correct?

Yes leaf springs have a progressive rate, but there are progressive coil springs too. What Im trying to say in the above statement is that springs are crap for soaking up bumps.

When you apply X amount of weight they compress a certain amount no matter what.

While a shock doesnt. It does not dampen X for a certain weight, it dampens depending on hard hard you hit a bump. How hard you hit a bump depends on what speed you were going. Yes we can say the same for springs but only to a point. Sorry Im having a hard time explainning this. But they just aren't the same. Springs get softer the harder you hit them while shocks get harder the harder you hit them. Thats their job, to absorb shock. This is why its pointless to use springs to dampen the vehicle over tough terrian.

OEM's use high spring rates and soft shocks because its much easier to get a good on road ride with much less R&D. Once you start going down the road of soft springs and quality tuned shocks you increase the cost of the vehicle development. On the other hand, a stiffer spring costs just the same as a soft one and cheap crappy shocks are a dime a dozen. This is also why stock sprung vehicles typically ride horrible offroad.

Leaf springs have to be stiffer otherwise they will compress to much at ride height, wear quickly and most notibly have tons of axle wrap. If you intend to run leaf springs, the absolute best shock to buy is a bypass. This is because of the progressive spring design of leaves. With coils or coilovers it isnt needed as much because of the linear rate. I am in no way saying bypasses aren't needed with coilovers. I think for racing they are.

[SolidAxle]

Staying tuned in to this thread. Great info about shock tuning and from a solid axle toyota truck perspective.
Its great to see the technology and knowlege from desert racing trickling down to 4wd truck entusiasts.

I've got some bilstein 7100's for my truck that I would like to play around with once i get some decent spring packs built for my truck.

Taco, in terms of stiff and soft spring rates on a leaf sprung toyota truck. what would you consider stiff and what would you consider soft, in general. say we are dealing with a regular built toyota truck. to make it simple lets say Marlins truck.

[TacoRunner]

The All Pro springs that Marlin used to sell were 220lb rate and about 240 or so in the back. With a leaf spring if you go softer you induce additional axle wrap and then you need a torque arm or axle wrap arm to control it. 220 on a leaf is soft but on a coil 220 (for a toyota mini and spring on the axle) is super stiff. Im at about 75lbs in the front of mine and about 80 in the rear.

[jrock [OP]]

I was noticing that Bilstien's shocks on the MC site are valved 255/70 where most of the stuff I've read for valving goes up to 90, my Fox 2.0 are 60/30. Are there different numbering systems for different companies?

[TacoRunner]

Bistiens are measued in Newton force. Fox has designated coding for valve stack combos that varry from 30-90 on 2.0" shocks and 30-120 on 2.5" shocks. An example is a 30 stock consists of all .008 shims while a 70 stack is .010 on top and .012 on bottom.

Others like King and SAW call out a stack based on each shims thickness, such as a 10 stack or 15 stack which is a stack of .010 shims or .015. Sometimes they will use an F in front of the number to tell you its a Flutter stack.

[SolidAxle]

The All Pro springs that Marlin used to sell were 220lb rate and about 240 or so in the back. With a leaf spring if you go softer you induce additional axle wrap and then you need a torque arm or axle wrap arm to control it. 220 on a leaf is soft but on a coil 220 (for a toyota mini and spring on the axle) is super stiff. Im at about 75lbs in the front of mine and about 80 in the rear.

So if I understand correctly, because leaf springs have a fairly stiff spring rate, A flutter stack is desirable and almost necessary in the sense of keeping the compression valving soft (to go with a stiff spring rate of leaf springs) in the low speed sections for good ride quality on smoother surfaces ans well as on pavement. while still being hard enough on those big hits or unanticipated bumps. does the progressive rate of a leaf spring mean that the compression valving could be slightly more soft or maybe less progressive then a coil spring?

Also, i've read that leaf sprung trucks work well with very minimal rebound dampening because of the interleaf friction. how little is too little.

One more haha. With spring rates that soft on your truck I assume you get some severe body roll, is somehow the shock valveing taking care of it, what about when you are sidehilling when wheeling. say you were at a dead stop on a side hill. dosen't your truck want to tip over? Maybe there is some link suspension black majic going on with the panhard/roll center height. sway bars?


Learning LOTS here. keeps my mind busy.

[TacoRunner]

Actually its because of the leaves progressive rate that flutter stacks aren't used. Typically they are soft at first and ramp up quickly on larger hits. But because of their stiffer rates, higher speeds aren't handeled so well. As for little rebound, I've found the opposite. The Bilstein numbers are deceptive because they use Newtons, 255/70 sounds like it would be lite but rebound forces are up to 5x's less then compression forces. So 70 may be heavy.

[SolidAxle]

I don't want to sound rude, But you're saying a progressive spring dosen't quite work well with the progressive valving of a flutter stack? and that a leaf spring with much slower rebound characteristics then a coil spring works well with lots of rebound dampening? is this for rock crawling only?

[TacoRunner]

I don't want to sound rude, But you're saying a progressive spring dosen't quite work well with the progressive valving of a flutter stack? and that a leaf spring with much slower rebound characteristics then a coil spring works well with lots of rebound dampening? is this for rock crawling only?

Ok so maybe what I said wasen't so clear. A proressive spring like a leaf that is soft in the beginning and stiff in the end doesnt work well with a flutter, which is also soft in the beinging and stiff at the end. Because typically when the spring gets stiffer you dont want to also get stiffer on compression valving. That makes for a harsh ride. Stiffer spring requirer softer compression stacks and vise a versa.

Leaf springs typically have higher rebound rates than a coils not lower. If the typical leaf spring is sprung at 220lbs per inch and at least my typicall coil is 94lbs which is higher.

Softer compression rates of the spring require stiffer compression valving. Stiffer rebound rates require stiffer rebound valving. In the end a spring with high compression rates also has high rebound rates. Ramping up in spring rate "IS NOT" beneficial for high speed racing. You need to keep the spring the same and progessively stiffen the shocks compression rates to handle better.

[OldGold3VZE]

This is why the web site posted above, www.shimrestackor.com, is so important.  You need to familiarize yourself with multi-stage valving to optimize things like inexpensive leaf springs and their somewhat harsh ride at speed.  Running a particular stack, usually all the same shim diameter, for low speed (cornering and braking) forces, then a separated 2nd stack, this is your pyramid stack, for high speed (bump impacts) is going to blow your mind.  Don't limit your dampers to just what Fox or whatever the brand recommends, the possibilities are endless, and I'm only talking about basic emulsion or IFP style dampers here.

[TacoRunner]

Your only real limitation on shim combinations is wether or not there is enough room on the inside of the shock to allow for what ever stack you come up with. So for you guys that have never taken a shock apart, at some point the shaft ends and you cant stick any more shims on because you run out of room and have no thread left to put a nut on.

[SolidAxle]

Ok so maybe what I said wasen't so clear. A proressive spring like a leaf that is soft in the beginning and stiff in the end doesnt work well with a flutter, which is also soft in the beinging and stiff at the end. Because typically when the spring gets stiffer you dont want to also get stiffer on compression valving. That makes for a harsh ride. Stiffer spring requirer softer compression stacks and vise a versa.

Leaf springs typically have higher rebound rates than a coils not lower. If the typical leaf spring is sprung at 220lbs per inch and at least my typicall coil is 94lbs which is higher.

Softer compression rates of the spring require stiffer compression valving. Stiffer rebound rates require stiffer rebound valving. In the end a spring with high compression rates also has high rebound rates. Ramping up in spring rate "IS NOT" beneficial for high speed racing. You need to keep the spring the same and progessively stiffen the shocks compression rates to handle better.

Okay I getcha that makes sense. since the coil spring rate is soo soft it needs quite high compression and quite low rebound compared to a leaf spring which has a much higher rate.
IF the leaf spring were the same rate it would need a bit less compression because its going to be progressive and the rebound will need to be less due to interleaf friction correct?

this is very general I just want to make sure i'm understanding.

[TacoRunner]

Friction on the leaves will slow the compression and rebound of the spring. But overall yes, a really soft leaf will do the same as soft coil. Its just that leaves that soft have all kinds of problems. Because a leaf springs also controls the lateral movment and rotational movement of the axle, control arms would then be needed. Then you'd have to buy some nice shocks to tune up the suspension and by that point you're pretty much at a 3link with coilvovers.

[TacoRunner]

This is why the web site posted above, www.shimrestackor.com, is so important.  You need to familiarize yourself with multi-stage valving to optimize things like inexpensive leaf springs and their somewhat harsh ride at speed.  Running a particular stack, usually all the same shim diameter, for low speed (cornering and braking) forces, then a separated 2nd stack, this is your pyramid stack, for high speed (bump impacts) is going to blow your mind.  Don't limit your dampers to just what Fox or whatever the brand recommends, the possibilities are endless, and I'm only talking about basic emulsion or IFP style dampers here.

Agreed!!!