idiots guide to shocks

[john55blaze]

In my search for shocks for the front of my 69 camaro wanna be p-t/autox budget build I had to admit that I know a lot less about them than I would like to admit as a life long "car guy". The proof coming from to me from the fact that they can be $20 or $2000 for a single shock (possibly more), they even have dyno's for shocks! My hope from this thread is a "sticky worth" compilation of information on shocks, both coilover and not, single adjustable, double adjustable, triple adjustable, price, advantages/disadvantages, who makes what, etc.

I see that single adj. shocks adjust only the rebound? I would have thought compression would have been more important but I guess thats the springs job? While the double adj. have comp/rebound, and triple have 1-rebound/2 compression?



And aside from ride height adjustment with coil over shocks are there any other advantages or disadvantages? To put "true" coilovers on my 69 it looks like I have to buy a kit like DSE or ridetech chicane (although I plan on asking about this in another post).

Is rebuildable important? how long should a shock or coilover last and what are the signs they might be going out? Anyways I think you get the point, and I am hoping that some of you will chime in and help me (and hopefully a lot of others) out

[exwestracer]

In my search for shocks for the front of my 69 camaro wanna be p-t/autox budget build I had to admit that I know a lot less about them than I would like to admit as a life long "car guy". The proof coming from to me from the fact that they can be $20 or $2000 for a single shock (possibly more), they even have dyno's for shocks! My hope from this thread is a "sticky worth" compilation of information on shocks, both coilover and not, single adjustable, double adjustable, triple adjustable, price, advantages/disadvantages, who makes what, etc.

I see that single adj. shocks adjust only the rebound? I would have thought compression would have been more important but I guess thats the springs job? While the double adj. have comp/rebound, and triple have 1-rebound/2 compression?

And aside from ride height adjustment with coil over shocks are there any other advantages or disadvantages? To put "true" coilovers on my 69 it looks like I have to buy a kit like DSE or ridetech chicane (although I plan on asking about this in another post).

Is rebuildable important? how long should a shock or coilover last and what are the signs they might be going out? Anyways I think you get the point, and I am hoping that some of you will chime in and help me (and hopefully a lot of others) out

Single adjustable shocks can either adjust rebound and compression equally, or one or the other (typically rebound as you pointed out). The adjustments are nowhere near as important as the main damping curve. That still has to be right for the corner weight, spring rate and wheel motion ratio.

[UMI Tech]

I have some QA1 damping curves I'll post. This thread could get huge.

ramey

[marolf101x]

I can go on and on regarding the aspects of shock absorber design and application, but it will take forever.

If you want a really well written, in depth look at everything I suggest reading this (it's focused on off road, but the basics still apply):
http://www.pirate4x4.com/tech/billav...lovers/Part_1/

Here's a quick summation:

What is a shock absorber?
-The main purpose of the shock is to control and slow down or stop the oscillation of the spring. This keeps the tire in contact with the road.
-A shock is a timing device. . .it controls how quickly or slowly the wheel and tire move into the body (compression) or back to the pavement (rebound).
-Typically the spring does most of the compression "work" while the shock slows down the rebound (or the spring wanting to return to free height).
-A shock is a radiator. . .it turns suspension motion into heat and must be able to keep the oil at a proper temperature. If the oil becomes too hot the viscosity changes and the damping effect is lessened.

How does a shock work?
-A piston moves through a column of oil. The oil forces valves open. This force is controlled by the design of the piston/valve. The motion is transferred into heat through the oil.
-As the piston moves into the shock (compression) the volume of the shock rod must be displaced (remember, the oil is a "solid" and cannot be compressed) so the oil has to move to accommodate the volume of the rod.

There are basically two types of shock designs used today, twin tube and monotube.
Twin Tube:
Twin tube shocks have two tubes. One is the larger outer tube you can see which holds oil (and typically a plastic bag filled with nitrogen). The inner tube is smaller and is where the piston resides, which actually does the damping.
As the shock is compressed the rod moves into the shock and the oil is moved through a base valve at the bottom of the shock where it turns 180-degrees and moves up the outer tube.
Pros:
-inexpensive (though they use more parts 50 years of cost reduction by OEM suppliers has dramatically lowered the overall cost)
-short packaging (extra oil and the nitrogen are stored around the inner tube)
-rebound and compression knobs can be located on the bottom of the shock.
Cons:
-smaller piston means less surface area and therefor less damping capability
-captures heat (heat is created as the piston travels through the oil. Since the piston is enclosed by a second tube with oil around it the heat cannot be dissipated as efficiently as a single tube)

Monotube:
Monotube shocks have a single tube. The piston rides on the inside of the tube you can see, and is therefor much larger than that of a twin tube. There is a separating piston close to the bottom of the shock, which separates the shock oil from the nitrogen. The nitrogen keeps pressure against the oil so the piston is always travelling through oil, not an oil and air mixture. As the shock is compressed the rod moves into the shock and the oil column forces the dividing piston to move down the shock tube. The oil does not really "flow", it just moves the same volume as the shock rod.
Pros:
-larger piston for more control area
-cooler operation (the oil is contacting the tube which is directly touching airflow, and will therefor not get as hot and has the ability to cool quicker than the twin tube)
Cons:
-longer packaging (since the nitrogen has to go under the oil column the shock must be longer. . .unless you use an external reservoir)
-rebound adjustment is through the shock shaft, while the compression adjustment must be put on a reservoir
-damage to outer tube could potentially destroy the shock as the piston or dividing piston is no longer allowed to move on the ID of the tube

This is some VERY basic information about shocks in general. I'm sure we'll get much more in depth in this discussion, so we can address the more technical questions later.

[ace_xp2]

And if you want to go down the rabbit hole, here's a good thread on shock tuning ideas, shock dyno curves, etc:
http://forums.corner-carvers.com/showthread.php?t=41374

[exwestracer]

Twin tube shocks have two tubes. One is the larger outer tube you can see which holds oil (and typically a plastic bag filled with nitrogen). The inner tube is smaller and is where the piston resides, which actually does the damping.
As the shock is compressed the rod moves into the shock and the oil is moved through a base valve at the bottom of the shock where it turns 180-degrees and moves up the outer tube.
Pros:
-inexpensive (though they use more parts 50 years of cost reduction by OEM suppliers has dramatically lowered the overall cost)
-short packaging (extra oil and the nitrogen are stored around the inner tube)
-rebound and compression knobs can be located on the bottom of the shock.
Cons:
-smaller piston means less surface area and therefor less damping capability
-captures heat (heat is created as the piston travels through the oil. Since the piston is enclosed by a second tube with oil around it the heat cannot be dissipated as efficiently as a single tube)

Monotube:
Monotube shocks have a single tube. The piston rides on the inside of the tube you can see, and is therefor much larger than that of a twin tube. There is a separating piston close to the bottom of the shock, which separates the shock oil from the nitrogen. The nitrogen keeps pressure against the oil so the piston is always travelling through oil, not an oil and air mixture. As the shock is compressed the rod moves into the shock and the oil column forces the dividing piston to move down the shock tube. The oil does not really "flow", it just moves the same volume as the shock rod.
Pros:
-larger piston for more control area
-cooler operation (the oil is contacting the tube which is directly touching airflow, and will therefor not get as hot and has the ability to cool quicker than the twin tube)
Cons:
-longer packaging (since the nitrogen has to go under the oil column the shock must be longer. . .unless you use an external reservoir)
-rebound adjustment is through the shock shaft, while the compression adjustment must be put on a reservoir.

This is some VERY basic information about shocks in general. I'm sure we'll get much more in depth in this discussion, so we can address the more technical questions later.

Another potential problem with monotube shocks... ANY damage to the outer shock body will usually ruin the shock, as there is no insulating layer between the outer body and the piston.

[marolf101x]

Ray,

Good point. I added it to the "cons" of the monotube design.

[exwestracer]

To add a little to the "adjustments" mentioned earlier...

"High" and "low" speed refers to the speed of the shock shaft during a given suspension motion. High speed is typically 3"/second or faster. Low speed is less than 3"/second shaft speed. "Progressive" and "Digressive" damping refers to the change in resistance above 3"/sec.

Single adjustable: Compression/rebound adjust together (may or may not have external knob), OR only rebound is externally adjustable.
Double adjustable: Compression and rebound stiffnesses adjust separately but across entire shaft speed range.
Triple adjustable: Has separate high and low speed compression or rebound, but single (full range) adjuster for the opposite motion.
4 way adjustable: Separate high and low speed adjusters for both compression and rebound.

Some manufacturers include ride height or spring preload adjuster (coilover) as one of the adjustments, but the industry standard refers only to the damping adjustments of the shock absorber itself.

[bret]

Another potential problem with monotube shocks... ANY damage to the outer shock body will usually ruin the shock, as there is no insulating layer between the outer body and the piston.

True...but in reality the material thickness of MOST monotube bodies would prevent internal damage unless it was a severe impact. Normal, and even heavy, road trash would not damage the shock. You would have to be in an accident of the magnitude that would likely damage a twin tube as well.

[Bryce]

Bret,

Can you supply a shock dyno sheet with each shock?

[marolf101x]

Sorry, I missed this thread (thought I was subscribed). I'll get some Dyno sheets up Monday when i'm back in the office.

[marolf101x]

As promised, here are the graphs for the NA, SA, and TA shocks.
3.6_NA_large.pdf
3.6_SA_large.pdf
3.6_TA_large.pdf
***Edit Note: I decreased the range of the graph so they are easier to see.***

[SSLT1KID]

I have been hoping something like this would come up. Subscribed! Anyone have any input or a good link for selecting coilover length?

[marolf101x]

ridetech.com, perhaps

[UMI Tech]

Double 0-18 every other click SD.pdf
NA SD.pdf
R series 0-18 every 3rd click SD.pdf
Single 0-18 every 3rd click SD.pdf

Here are the QA1 Dyno curves.

ramey

ps not sure why one is a jpg and the rest are inline but there you go

[exwestracer]

^^^Good Stuff! ^^^

For shock newbies, "up" from 0 on the graph is compression motion, "down" is rebound (extension). The descending force curve (as shaft velocity increases) is called "digressive" damping.

[tlillard23]

Don't your shocks have a lot to do with what you are doing with the car? A big fat pig car in autocross usually wants to squat and stick for acceleration out of the corner, I don't know about drag race... Road race is a little different, street is different again...?

[marolf101x]

that's why we have lots of knobs on the shocks! ;)
Shocks are just a timing device. . .they do not control how the car moves. . .they only control how quickly or slowly the car moves in a certain direction (the car is going to move where it wants, all you can do is control that movement).