Rebound vs Compression

[jtwoods4]

So I am experimenting with my Viking Double adjustable shocks. I have spent the night reading about rebound and compression rates. I am trying to learn what the most common setups are for street use vs road course use.

For example, for road courses is it common to see the compression set softer than the rebound setting ( Faster compression with a slower rebound rate)

I am just looking for a general understanding of the ratio between shock compression and rebound. From what I have read it seems that the compression can be set soft so the "bump" is absorbed and then the rebound set a little stiffer so the suspension spring expands back out a little slower.

[jtwoods4]

Wow 58 views with no response. This may be a more complicated question that I thought.

[UMI Tech]

For corner carving or road racing we tend to use the rebound setting to tune. Many shock companies include rebound adjustment with their single adjustables (i.e. rebound is pretty useful for tuning).

https://www.pro-touring.com/threads/87409-idiots-guide-to-shocks

[jtwoods4]

Great! Thank you!

[jtwoods4]

Shock research led me to this article. Excellent place to start

http://farnorthracing.com/autocross_secrets6.html

Recommended "general" knob settings for Viking Double adjustable B Series Shocks. This is straight from Viking Support

FC - Front Compression
FR - Front Rebound
RC - Rear Compression
RR - Rear Rebound


For general cruising:

FC - 3
FR - 5
RC - 2
RR - 6

For autocross:

FC - 10
FR - 8
RC - 8
RR - 12

For road race, I will soften up the autocross setting a little.

For drag race (weight transfer):

FC - 14
FR - 2
RC - 2
RR - 14

[RecceDG]

Here's the problem though:

You might assume that the shocks work like this: 1 Click = (Force Full Hard - Force Full Soft) / 14

Assuming 14 clicks of range.

I promise you that they almost certainly DO NOT do that. A linear range like that is something of a Holy Grail amongst shock manufacturers and is really, really hard to get.

Far more likely is 1-7 do nothing, 8 makes a little bit, 9, 10, 11 are mostly linear, then 12 is double 11, 13 is double 12, and 14 locks the shock solid.

Also VERY likely is that two shocks, same part number, same setting - different forces.

Unless you have the shocks dynoed and know for a fact what they are doing, twiddling knobs gets you nowhere.

The website goes into this in exhaustive detail.

DG

[jtwoods4]

Here's the problem though:

You might assume that the shocks work like this: 1 Click = (Force Full Hard - Force Full Soft) / 14

Assuming 14 clicks of range.

I promise you that they almost certainly DO NOT do that. A linear range like that is something of a Holy Grail amongst shock manufacturers and is really, really hard to get.

Far more likely is 1-7 do nothing, 8 makes a little bit, 9, 10, 11 are mostly linear, then 12 is double 11, 13 is double 12, and 14 locks the shock solid.

Also VERY likely is that two shocks, same part number, same setting - different forces.

Unless you have the shocks dynoed and know for a fact what they are doing, twiddling knobs gets you nowhere.

The website goes into this in exhaustive detail.

DG

Yes, I understand what you are saying. However, your statement "twiddling knobs gets you nowhere" is incorrect. The knobs on these shocks do work and do change the compression and rebound settings very drastically. The settings I posted are a good starting point for the Viking Double Adjustable. If you have these shocks start with those settings. If you do not adjust the knobs then your shocks will be set to the minimum resistant for compression and rebound, and this is a bad idea. The knobs do work and the settings I posted will get you a decent ride in the scenarios I stated.

[alocker]

I recently purchased a set of the Vikings and here are my thoughts. I have zero automotive shock tuning experience, but some motorcycle. I would say at a minumum I understand what each knob is doing :).

The Vikings seem to stiffen up pretty good early in the clicker range. My first test drive was baselined at 4 comp, 6 reb and I was a bit worried at first because it rode like a dump truck. I backed the comp all the way out and left the rebound and found it to have a really compliant ride that gave me that modern car feel.

I have a few decent roads in my area that make a nice test route to evaluate both comfort and handling. I started cranking up the comp to 6 and left the reb at 6. Car obviously became much stiffer, not as comfortable, but also stayed much flatter and much more controlled through the test "chicane" I go through.

Unless you are racing at a high level, here are some things to consider.

Experiment with what feels good to you. Confidence in your set up will take you further than using "magical suggested settings".

Don't be afraid to make large adjustments just to see if you are going in the right direction. Make sure you note your baselines before.

[RecceDG]

However, your statement "twiddling knobs gets you nowhere" is incorrect.

You're missing the point - not that that's particularly surprising; many who have made an investment find ways to self-delude. Me included. It's human nature.

The issue here is that building shocks is dirt stupid simple. A couple of hours in any reasonably well equipped machine shop and *anyone* can build a hydraulic shock with an adjuster knob on it that does indeed change the amount of force the shock puts out at a given velocity. It really isn't all that tough.

But building a hydraulic shock that produces the kinds of curve that maximizes grip - and provides the correct level of authority, predictability, and repeatability required to actually get the tune where it needs to be? That's a horse of an *entirely* different colour. To do it really right requires the kind of manufacturing ability, to hold impossibly tight tolerances, complex curve shapes, and exact surface finishes, that you just can't get without special knowledge and equipment. There's a reason why Penskes are so expensive - they can do it. And even they have gone through several iterations of "a little bit better" over the past couple of decades.

But lots - and I do mean LOTS - of other manufacturers have tried to make affordable (and not so affordable) adjustable shocks using off the shelf parts and control strategies. These parts suffer from the problems that all early-game adjustables have (including early Penskes) because it is a question of understanding fluid flow at a much higher level of resolution than you can get in a basic hydraulic textbook. A hydraulic cylinder in a front end loader just doesn't need the kind of fine control that a racing shock does, so the off the shelf parts and the textbooks don't talk about it.

So every would-be shock manufacturer winds up learning this on its own - or more usually, DOESN'T. They either don't use shock dynos in their development, or they rely on the fact that their customer base just doesn't use them very often. (Usually, almost never)

Aftermarket shocks is one of the few places where you can still hide ****ty work, because as long as the damn thing doesn't actually explode, people naturally want to believe that they got some value for their dollar.

I've seen this over and over and over again. I experienced it myself (I didn't spring into being a shock expert; I had to learn the hard way like everybody else) and I saw it myself with my own customers.

I sold, at one point, Penske shocks for C5 Corvettes. These were $2000 per corner shocks (you got coilover springs with them too) and because they were Penskes, you got the really good adjusters with them. They weren't perfect (Penske has been through at least one new iteration of the rebound bleed since then) but they worked very well. Lots of control authority, decent linearity except at the very extremes of the adjustment range, and once you clocked the adjuster window properly, very repeatable. Great shock.

Part of the deal you got from buying them from me was that every shock was fully dynoed, the adjusters got clocked on the dyno, and I verified that left and right shocks on the same axle matched (sometimes even Penske's tolerances meant that shock 1 would match shock 2 when shock 1 was on "rebound 15" and shock 2 was on "rebound 12") But I also had to set them to some initial value, right? So the last step was matching the shocks to my reference shock - an 04 C5 ZO6.

So let's be clear - I shipped those shocks so that, out of the box, they matched a BONE STOCK Z06 shock. And I didn't hide it either. I put the dyno printout in the box, along with the full sweep.

I had dozens of customers tell me that those shocks were perfect right out of the box and they had never touched the adjusters (or had tried other settings and went back to the factory setting) DOZENS. $8000 on shocks, and they produced the exact same forces as a $300 set of OEM shocks. (Mind you, that 04 OEM tune was *really* good - GM knows what it is doing)

I bet that if you actually dyno those shocks, you'll discover that they do not do what you think they do. Oh, in broad terms, it's probably safe to say that "full stiff" will be stiffer than "full soft". Two identical shocks *might* make the same forces at "full soft" and "full stiff". And you *might* get changes in rebound that don't cross over onto compression (or vice versa) But two identical shocks making identical forces at the same midrange settings? Probably not. Linear adjustment steps across the whole range? Almost certainly not. And there could be other surprises, like changes in compression changing the rebound adjustment range (seen that) or changes in rebound changing compression more than they changed rebound (seen that too) or entire adjustment ranges entirely dead (very common, especially with shocks that use a lot of clicks)

Until you dyno the shocks, you just don't know. And your butt dyno LIES LIES LIES (I've got dozens of examples of that too)

It's your choice dude. You can choose to live in ignorance and hope for the best, or you can pay the money to make the test and learn if you got something flawed but workable (like a Koni Yellow) or something that's just junk.

[RecceDG]

[quote] Car obviously became much stiffer, not as comfortable, but also stayed much flatter and much more controlled through the test "chicane" I go through. [quote]

Here is part of the problem: drivers, left to their own devices, like a lot of rebound. Rebound slows down roll - it doesn't change the *amount* of roll, that's a spring/bar change - but rebound slows down how fast you get to max roll angle. If the element is sufficiently transient, you can be in and out of the transition before the car makes it to max roll.

If the car is softly sprung, and within reason, this can be an acceptable way to pick up a little transient response without hurting ride comfort. Some of the electronic suspensions out there work this way - they have a servo on a rebound knob, and g-sensors and steering angle sensors and whatnot, and when the computer figures you're in a high-g maneuver, it jacks the rebound for a bit. It's a little crude, but it works (my Stealth does this)

But much beyond the level of acceptable tradeoff on transient roll control, extra rebound starts hurting grip. But it's subtle stuff - and it is largely masked by the feeling that the car is more "planted". Drivers like lots of rebound. But that feeling is totally illusionary. In car after car (including my own) we forced the driver to pull out rebound - and the car got faster. It took a little more trust from the driver, because the car was rolling around more... but faster is faster.

[Rod]

Wow 58 views with no response. This may be a more complicated question that I thought.

I think they were looking for answers, not trying to give you one :rolleyes:

[Cobra 498]

You're missing the point - not that that's particularly surprising; many who have made an investment find ways to self-delude. Me included. It's human nature.

The issue here is that building shocks is dirt stupid simple. A couple of hours in any reasonably well equipped machine shop and *anyone* can build a hydraulic shock with an adjuster knob on it that does indeed change the amount of force the shock puts out at a given velocity. It really isn't all that tough.

But building a hydraulic shock that produces the kinds of curve that maximizes grip - and provides the correct level of authority, predictability, and repeatability required to actually get the tune where it needs to be? That's a horse of an *entirely* different colour. To do it really right requires the kind of manufacturing ability, to hold impossibly tight tolerances, complex curve shapes, and exact surface finishes, that you just can't get without special knowledge and equipment. There's a reason why Penskes are so expensive - they can do it. And even they have gone through several iterations of "a little bit better" over the past couple of decades.

But lots - and I do mean LOTS - of other manufacturers have tried to make affordable (and not so affordable) adjustable shocks using off the shelf parts and control strategies. These parts suffer from the problems that all early-game adjustables have (including early Penskes) because it is a question of understanding fluid flow at a much higher level of resolution than you can get in a basic hydraulic textbook. A hydraulic cylinder in a front end loader just doesn't need the kind of fine control that a racing shock does, so the off the shelf parts and the textbooks don't talk about it.

So every would-be shock manufacturer winds up learning this on its own - or more usually, DOESN'T. They either don't use shock dynos in their development, or they rely on the fact that their customer base just doesn't use them very often. (Usually, almost never)

Aftermarket shocks is one of the few places where you can still hide ****ty work, because as long as the damn thing doesn't actually explode, people naturally want to believe that they got some value for their dollar.

I've seen this over and over and over again. I experienced it myself (I didn't spring into being a shock expert; I had to learn the hard way like everybody else) and I saw it myself with my own customers.

I sold, at one point, Penske shocks for C5 Corvettes. These were $2000 per corner shocks (you got coilover springs with them too) and because they were Penskes, you got the really good adjusters with them. They weren't perfect (Penske has been through at least one new iteration of the rebound bleed since then) but they worked very well. Lots of control authority, decent linearity except at the very extremes of the adjustment range, and once you clocked the adjuster window properly, very repeatable. Great shock.

Part of the deal you got from buying them from me was that every shock was fully dynoed, the adjusters got clocked on the dyno, and I verified that left and right shocks on the same axle matched (sometimes even Penske's tolerances meant that shock 1 would match shock 2 when shock 1 was on "rebound 15" and shock 2 was on "rebound 12") But I also had to set them to some initial value, right? So the last step was matching the shocks to my reference shock - an 04 C5 ZO6.

So let's be clear - I shipped those shocks so that, out of the box, they matched a BONE STOCK Z06 shock. And I didn't hide it either. I put the dyno printout in the box, along with the full sweep.

I had dozens of customers tell me that those shocks were perfect right out of the box and they had never touched the adjusters (or had tried other settings and went back to the factory setting) DOZENS. $8000 on shocks, and they produced the exact same forces as a $300 set of OEM shocks. (Mind you, that 04 OEM tune was *really* good - GM knows what it is doing)

I bet that if you actually dyno those shocks, you'll discover that they do not do what you think they do. Oh, in broad terms, it's probably safe to say that "full stiff" will be stiffer than "full soft". Two identical shocks *might* make the same forces at "full soft" and "full stiff". And you *might* get changes in rebound that don't cross over onto compression (or vice versa) But two identical shocks making identical forces at the same midrange settings? Probably not. Linear adjustment steps across the whole range? Almost certainly not. And there could be other surprises, like changes in compression changing the rebound adjustment range (seen that) or changes in rebound changing compression more than they changed rebound (seen that too) or entire adjustment ranges entirely dead (very common, especially with shocks that use a lot of clicks)

Until you dyno the shocks, you just don't know. And your butt dyno LIES LIES LIES (I've got dozens of examples of that too)

It's your choice dude. You can choose to live in ignorance and hope for the best, or you can pay the money to make the test and learn if you got something flawed but workable (like a Koni Yellow) or something that's just junk.

Great post and on the money, in shocks you do get what you pay for. The rebound comments are also very accurate.

[alocker]

RecceDG, I appreciate the info but I don't think anyone here would argue that a Penske makes a great shock. I can't help but think all you are trying to say is all other shocks are crap except for Penske. That being said, most of us here do not have an $8000 shock budget. The reason I switched is my generic parts store "made in the USA" shocks were completely shot in just a few years.

Have you had the shocks in question on a dyno to prove that they are indeed junk?

[funcars]

I didn't read that all other shocks are crap or that yours are junk - I read that tolerances need to be incredibly tight to match shocks to each other, linearity of adjustments is tough to achieve and dyno sheets show data and not sales claims. You can get shocks dynoed at many different circle track shops for low cost if you are interested. By the way - Penske now has a double adjustable 7500 series coilover shock for just over $500 ea if you call around. Good shocks for reasonable money.

[Rod]

Me, I, I've, I, I, I, I, I sold, Me, I verified, I, I, I, I had dozens of customers, I .

who are you?

[alocker]

It's your choice dude. You can choose to live in ignorance and hope for the best, or you can pay the money to make the test and learn if you got something flawed but workable (like a Koni Yellow) or something that's just junk.


I didn't read that all other shocks are crap or that yours are junk -

There is a possibility of that statement being out of context but we won't know until he replies. Either way the only ones we know aren't complete junk are the Penske and Koni Yellow shocks.

I actually would like to dyno my shocks just to see where they are. Anyone know of a reasonably priced shock dyno in the Chicagoland area?