Larry Herman

It's not quite done yet, but I thought that I would throw this next article out for your edification and commentary.
Hopefully I will complete it on Sunday.

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What Shocks Do
By Larry Herman

Shock absorbers, or just plain shocks as they are colloquially known, are probably the least understood component of one’s car. And to that point, their American name is even a misnomer; they do not “absorb” shocks. The English refer to them more accurately as Dampers or Dampeners because that is what they do. They limit or dampen movement through hydraulic friction. The early shock absorbers like on the Model T were actually leather based disks that resisted movement through dry friction, and had to be tightened up as they wore. And though they quickly disappeared with the advent of the hydraulic based shock, some British cars continued to use them up through the 1940s. Today’s shocks are engineering marvels, with nitrogen pressurization, remote reservoirs, multiple velocity bleed disks, electronically adjustable valving, and even electro-magnetically altered (magneto rheological) fluid viscosity. But most of you are probably not as concerned with how they work as much as with what they do, and that is the goal of this article.

The shock absorber has a tough job to do. It has to limit the high speed (or high frequency) motions of the suspension as well as control the low speed (or low frequency) motions of the body. And it has to do this with no fixed anchoring point, because the shock is literally floating between 2 moving objects, the body and the suspension. In order to properly control the slow movements of the heavy body, the shock needs to have a lot of resistance, but if the shock is too stiff it will not allow the relatively light weight and quick moving suspension to properly follow the contours of the road. This is what makes shock design so challenging, and why they have become so complex. In order to accomplish proper control of both, the modern shock has special internal valves and bleed ports to allow a softer response to a quick movement generated by the suspension, and a harder response to a slow movement generated by the body. So far so good, right? The trick now is to understand how the dampening effects of the shock actually affect the loading of the suspension, which directly influences the grip and balance of one’s car.

While the springs are what suspend the car, and provide the overall resistance to body roll and suspension movement, shocks control those movements on an immediate basis. They also are what initially transfers load until the body has time to roll and transfer load to the springs. So shocks can be used as a tuning tool to affect grip and balance on initial movement of the suspension. It is that instant resistance to movement that causes the shocks to either load (on compression) or unload (on rebound) the suspension, and cause a resultant increase or decrease in grip. This is why racing shocks have evolved from a simple one way loose/tight adjustment to the 4 way control (low & high speed compression and low & high speed rebound) that can be found on top end racing units like Moton Motorsports, costing as much as $3,000 per shock. So what exactly happens when you turn your car into a corner?

As we slow, turn the steering wheel and bend the car into a corner, the body starts to roll on the suspension and the shocks are immediately in play. The outside front starts to compress and the inside rear extends. This causes an increase in load on the outside front tire, and a decrease in load on the inside rear. The immediate shift in balance is determined by the relative stiffness of the front compression as compared to the stiffness of the rear rebound. As we continue in the corner, the springs will compress (and unload) their respective amounts based upon their rates, and the balance of the car will now change to the relative stiffness of the springs (and sway bars). As we transition to the gas around mid-corner, the balance will shift back towards the shock bias, but this time it will be based on the rebound in the front and the compression in the back.

Land Jet

Love to read your articles Larry. Hope you include shock adjustment and how to tune dampers in the conclusion of this presentation.

winders

Larry,

Don't get upset here....I am commenting to help improve the text.

They are only called "dampeners" by mistake when people mean to use "dampers". Also, "They limit or damp movement", not dampen. It is "damping" effects", not "dampening effects".

Today's dampers do indeed absorb shock, or more correctly, bump. That is not the primary function, but they certainly do it none the less. That's how the compression circuits control high and low speed bump.

Scott

Larry Herman

Thanks for the input Scott. I will make the changes.

FredC

Keep on writing Larry. This is really interesting. Perhaps a little more on compression and rebound would help better understand the rest of the article. Excellent stuff!

Also, any good reference materials for the role adjustable sway bars play? Tx.

Veloce Raptor

Nice stuff, Larry









Professional Racing and Driving Coach

Brinkley

Larry,

Thank you for sharing. Like many, I am waiting on the edge of my seat for the next paragraph.

I hope you'll share further descriptions of how each corner is working as we transition from braking, turn in, back to throttle, and exit.

And while I know books are written on this subject, it would be interesting to read how you would summarize what adjustments would be done to correct common, generalized, track issues such as over steer at turn in. Or at what point do you stop adjusting compression and rebound and start adjusting sway bars.

Thanks again and can't wait.

swftiii

Larry,

This is great stuff and I love reading your articles - you have a tremendous amount of setup knowledge. I am an absolute ameteur with this stuff and in this off season want to learn more about how each of the tuning points of my Moton Club Sports affect the car's suspension. Please be gentle with me as I really don't fully understand beyond the basics. Specifically:

1. Canister pressures - what car dynamic does this affect when going up in pressure vs down in pressure
2. Rebound settings - what car dynamic does this affect when going stiffer vs softer
3. Compression settings - what car dynamic does this affect when going stiffer vs softer

More info: 92 964 C2 stock F class; RS sway bars set in the middle F/R, 500/700 lb H&R spring rates.

In other words when do I adjust which setting?

Thansk for continuing to share and help those of us that need helping...

Gary R.

Fred - I will send you the manuals to examine when I get my Motons...

FredC

Now that's what i am talking about. Larry's article is all the more interesting for you then.

Veloce Raptor

To augment Larry's discussion, this is from Neil Roberts:

Neil Roberts Article on Shock Tuning

For the purposes of this discussion, we will assume the racing surface to be perfectly flat, smooth, and uniform. So, all damper velocities will be relatively low, assuming a smooth driving technique. We will assume a simple road course setup, with no asymmetric adjustments. The damper velocities and travel directions resulting from each cornering phase affect the distribution of load among the four tires. This change in load distribution changes the cornering balance. We will focus primarily on the effects of diagonal weight transfer due to damper forces and the resultant change in cornering balance.

CORNERING PHASE DEFINITIONS

Phase 1: Increasing braking + increasing steering
This phase is the first part of a fast decreasing radius turn. This phase will not occur at all if maximum braking is achieved before turning in. Since weight is being transferred both forward and outboard, the outside front damper moves in the bump direction. Also, the inside rear damper moves in rebound. The other two dampers do not move as much or as rapidly, so their effects are minimal. For our purposes, we will consider the inside front and outside rear dampers to have a fixed position during phase 1.

Phase 2: Decreasing braking + increasing steering
This is the turn in phase of a slow corner. This phase may or may not occur depending on the type of turn and driving technique. Weight is being transferred outboard and aft, so the outboard rear damper moves in bump and the inside front damper moves in rebound. The other two dampers are considered to be stationary.

Phase 3A: Increasing steering at constant throttle
This phase can be a course correction, a slalom turn in, or a turn entry taken at full throttle. Weight is being transferred outboard, so both outside dampers travel in bump and both inside dampers travel in rebound.

Phase 3B: Decreasing steering at constant throttle
This is the opposite of phase 3A. During a slalom, this phase occurs while the steering is changing away from the current cornering direction. As soon as the lateral acceleration passes through zero, the car reverts to phase 3A. This is part of why so many spins occur in slaloms.

Phase 4: Decreasing steering + increasing throttle (or decreasing braking)
This is the apex-to-exit phase. Weight is being transferred inboard and aft, so the outside front moves in rebound and the inside rear moves in bump. The other two dampers are considered stationary.

EFFECTS OF DAMPER INDUCED WEIGHT TRANSFER

At all times, cornering balance is affected by the distribution of load between the two front tires. Because the efficiency of a tire decreases with increasing load, a larger difference in load between the two front tires increases understeer. Also, a smaller difference decreases understeer. The same concept applies to the two rear tires.

To illustrate the effect of damper adjustments, consider a phase 3A flat out turn entry. If the front dampers are adjusted to increase either bump or rebound damping, more weight will be transferred across the front tires during entry. The same result occurs if the rear dampers are adjusted to decrease either bump or rebound damping. This increased front load transfer increases understeer during turn in, just as a larger anti-roll bar increases understeer in steady state cornering.

The same increase in understeer results from diagonal weight transfer from the inside rear to the outside front. The fact that the two diagonally opposite dampers move in opposite directions allows us to modify cornering balance with damper adjustments.

Note that we are only considering longitudinal weight transfer if accompanied by steering change. Longitudinal weight transfer without steering change moves both front and both rear dampers in the same direction at the same speed, so damper adjustments cannot change the diagonal weight distribution. Obviously, longitudinal weight transfer affects cornering balance. But, since the dampers cannot affect balance unless accompanied by roll, we will ignore this effect for damper tuning.

The following table presents the damper adjustments available to modify the cornering balance in each phase. Each entry lists the phase, the damper travel directions, the desired change, and the damper adjustments available to produce that change.

"+" = stiffer damping; "-" = softer damping
“IF” = inside front, “OF” = outside front

Phase Directions More Understeer More Oversteer
Phase 1 entry OF bump F bump + F bump -
OR rebound R rebound - R rebound +
Phase 2 entry IF rebound F rebound + F rebound -
OR bump R bump - R bump +
Phase 3A entry OF&OR bump F bump + F bump -
IF&IR rebound F rebound + F rebound -
R bump - R bump +
R rebound - R rebound +
Phase 3B exit OF&OR rebound F bump - F bump +
IF&IR bump F rebound - F rebound +
R bump + R bump -
R rebound + R rebound -
Phase 4 exit OF rebound F rebound - F rebound +
IR bump R bump + R bump -


As you can see, none of the available adjustments affect only one cornering phase. This is where the balancing act begins. Notice that the same adjustments that increase phase 2 entry understeer also increase phase 4 exit oversteer. Compromise is necessary even in the case of a constant speed slalom.
It is worthwhile to spend some time studying the table to figure out how to fix more than one balance problem at the same time. For example, consider a car that has phase 1 oversteer, phase 2 understeer, and phase 4 understeer. Can this combination of problems be corrected by damper adjustments alone?
Careful, focused analysis of the behavior of the car during each phase is necessary to begin real damper tuning. Then, the correct decisions must be made concerning which phase(s) are most important and require damper adjustments to improve cornering balance. The adjustments made will alter performance in other phases, so the magnitudes of damper adjustments must be selected accordingly.
As you can imagine, it is rather difficult to accurately remember the balance of the car in each cornering phase for each corner of the track. This process can be assisted considerably by an in-car video camera and/or a data acquisition system.
A truly optimum damper setup is only possible with highly developed active dampers. The optimum compromise with conventional racing dampers is difficult to determine. This should not deter us from trying.
The restriction to symmetric damper adjustments is the source of many of the required compromises. If you have followed the discussion to this point, you can work out for yourself the amazing cornucopia of damper adjustments available to oval track tuners. If a particular road course features all or most of the important corners in the same direction, asymmetric adjustments can be used to fine tune the setup to that track.









Professional Racing and Driving Coach

95m3racer

There are entire series of books on this topic...unfortunately its not something that can be explained properly "in depth" easily. Obviously, it depends on who the reader is and what they are trying to get out of it. For the basic car enthusiast, the basic description from any source online is sufficient. For the race guy who wants to really understand...it will take some researching, learning, and applying basic engineering principles to the application. Because dampers live in a complex dynamic environment, there are MANY factors involved, all important. I also think its important to make sure readers realize there is no "proper" setup, it depends on many variables and nothing but testing and a good engineer can really get the car to be "better" from a certain setup. Some companies like Ohlins offer software to aid in this setup, and you might want to raise the $3k/shock price to $10k Obviously this is on the extreme end, but there are dampers that cost this much, less support lol

DaveConn

Skip -

A couple of thoughts:

Contact Lex Carson at Moton for a more in-depth (and from the horses mouth) discussion. He has been indespensible in me learning and developing my car (also a 964, using Club Sports).

motonusa@bellsouth.net

If you are racing, or at the higher end of the DE spectrum, you might consider a change to a slightly stiffer spring. I just swapped my springs from H&R 500/680 to H&R 600/800. An adjustment to rebound was made as well, but the change in the overall character of the car is astounding.

Feel free to PM me if you want more details.

Dave

Larry Herman

What Shocks Do
By Larry Herman

Shock absorbers, or just plain shocks as they are colloquially known, are probably the least understood component of one’s car. And to that point, even their American name is a misnomer; as part of their main function they do not “absorb” shocks. The English refer to them more accurately as Dampers because that is what they do. They limit or damp movement through hydraulic friction. The early shock absorbers like on the Model T were actually leather based disks that resisted rotational movement through dry friction, and had to be tightened up as they wore. Though they quickly disappeared with the advent of the hydraulic based shock, some British cars continued to use them up through the 1940s. Today’s shocks are engineering marvels, with nitrogen pressurization, remote reservoirs, multiple velocity bleed disks, electronically adjustable valving, and even electro-magnetically altered (magneto rheological) fluid viscosity. But most of you are probably not as concerned with how they work as much as with what they do, and that is the goal of this article.

First let’s start with a little nomenclature. The shock is made up of 3 basic parts, the body, the shock rod, and the internal piston and valves at the end of the shock rod. I have attached a picture of this. Movement which compresses the shock is called “Bump” or “Compression”. Movement which extends the shock is called “Rebound”. The rate that the shock compresses or extends is called the “speed” of the shock, and so high speed bump refers to quick compressions of the shock as would occur from suspension movement, and low speed bump would refer to slow compressions of the shock as would occur from body movement.



The shock absorber has a tough job to do. It has to limit the high speed (or high frequency) motions of the suspension as well as control the low speed (or low frequency) motions of the body. And it has to do this with no fixed anchoring point, because the shock is literally floating between 2 moving objects, the body and the suspension. In order to properly control the slow movements of the heavy body, the shock needs to have a lot of resistance, but if the shock is too stiff it will not allow the relatively light weight and quick moving suspension to properly follow the contours of the road. This is what makes shock design so challenging, and why they have become so complex. In order to accomplish proper control of both, the modern shock has special internal valves and bleed ports to allow a softer response to a quick movement generated by the suspension, and a harder response to a slow movement generated by the body. So far so good, right? The trick now is to understand how the dampening effects of the shock actually affect the loading of the suspension, which directly influences the grip and balance of one’s car.

While the springs are what suspend the car, and provide the overall resistance to body roll and suspension movement, shocks control those movements on an immediate basis. They also are what initially transfers load until the body has time to roll and transfer load to the springs. So shocks can be used as a tuning tool to affect grip and balance on initial movement of the suspension. It is that instant resistance to movement that causes the shocks to either load (on compression) or unload (on rebound) the suspension, and cause a resultant increase or decrease in grip. This is why racing shocks have evolved from a simple one way loose/tight adjustment to the 4 way control (low & high speed compression and low & high speed rebound) that can be found on top end racing units like Moton Motorsports, easily costing over $3,000 per shock. So what exactly happens when you turn your car into a corner?

As we slow, turn the steering wheel and bend the car into a corner, the body starts to roll on the suspension and the shocks are immediately in play. The outside front starts to compress and the inside rear extends. This causes an increase in load on the outside front tire, and a decrease in load on the inside rear. The immediate shift in balance is determined by the relative stiffness of the front compression as compared to the stiffness of the rear rebound. As we continue in the corner, the springs will compress (and unload) their respective amounts based upon their rates, and the balance of the car will now change to the relative stiffness of the springs (and sway- bars). As we transition to the gas around mid-corner, the balance will shift back towards the shock bias, but this time it will be based on the rebound in the front and the compression in the back. Remember that shocks exert the most control on initial movement, and over time (measured in tenths to full seconds) the load transfers back to the springs and sway-bars.

Proper shock settings can be difficult to get right. If the shocks are too soft for the spring rates, the suspension will oscillate over bumps and the body will roll and wallow. Everyone has seen what a car looks like bouncing up and down when the shocks are worn out. The shocks have to be set stiff enough to control the quick movements of the springs as well as the large movements of the body. However, if the compression is set very stiff to limit initial body roll and keep the tires on the road over bumps, major impacts can raise the body and actually reduce the amount of grip until the suspension recovers. If the rebound is set very stiff to try and keep the body from wallowing and feeling floaty, then the suspension may not be able to extend quickly enough to maintain grip when the road drops away. This could occur over undulations or after initial contact with a bump. As spring rates are increased, the time and actual distance that a shock moves is decreased, so proper adjustment becomes even more critical. This is why racing suspensions typically require the use of externally adjustable shocks.

The last item that I want to touch on is how shock adjustments can actually affect car handling. It is probably one of the hardest concepts to understand because it is so complex and inter-related with the rest of the suspension (springs, sway-bars, etc.). There is also a lot of disagreement on the subject due to that. Using the basics, you can dissect what is happening and apply that to further your understanding. As previously discussed, the shock is floating between the body and suspension with no fixed point of attachment. This means that what affects the tire is transferred through the shock to the body, and what affects the body is transferred through to the tire. This occurs much like what happens with springs, except the effect is much quicker, and temporary. If you tighten the bump in order to reduce the amount of initial body roll, you do so at the risk of displacing the body over large bumps, reducing load and hence the grip on that tire. If you tighten the rebound to “clamp the body down” you do so at the expense of grip, because preventing the suspension from extending will again reduce load and hence the grip on that tire. Also realize that body roll will unload the tires more quickly with higher amounts of rebound. To some extent, however, this can be used to your benefit. If you are trying to reduce understeer on initial turn-in for example, a little more rebound in the back will cause a slight unload of the inside rear, and so can help the car turn-in better. Conversely, as you pick up the throttle in the turn and the car rolls back on the rear suspension, increasing the bump in the rear will cause the body to more quickly put pressure on the rear tires and create grip faster, reducing the tendency to oversteer.

Knowing whether or not you have too much overall bump or rebound is very much a trial and error process. If the car chatters too much over little bumps, and you lose grip after impact with big bumps, you may be over damped on the compression. If the car feels really tight, but seems to lose grip over undulations, and after dips or where the road falls away, you may have too much rebound. With remote reservoir shocks, canister pressure can play a part too. With most canister shocks, increasing the pressure will increase the force on the piston, adding to your spring rate and increasing the compression damping. Since every manufacturer is different, it is best to check directly with them concerning the effects of increased pressure on your particular brand.

For some of you, I am sure that your heads are quite full right now, and I hope that I have provided you with a little enlightenment on what can be a very dark subject. For others, I am sorry if I have left you wanting but this was Shocks 101, and the like I said, many books have been written on shock absorber technology and adjustments. Hopefully as you dig a little deeper, things will be a little clearer for you.
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Hey guys, let me know what you think before this evening as I have to submit it. Thanks.

Land Jet

Very well done. Thanks.