I too am in need of clarification

This was borrowed from the B4 tuning guide.

I also strongly encourage you both to head over to http://users.telenet.be/elvo/ now and start reading up on roll centers. This discussion will get a lot more abstract once we move on to that topic.

Think of pack like this: An MX bike going through a series of whoops-like in SX.
The bike hitting the 1st one will rebound fully and be ready for the next if it has little to no pack, but if it "packs" it wont rebound to full length fast enough, and will hit the next bump @ say 3/4 travel, and so on until it can't fully absorb the bump and usually donkey kicks your backside over the bars..
Great thread, and has been a fun read. I tried this method last weekend , and I unfortunately can see "it" with my eyes, unless my springs are that close already, I couldn't notice a difference front to rear..

I don't understand. Given the springs natural frequencies are matched, I thought the rear which is heavier needs more damping vs the front. In doing so, the chassis should settle evenly when hitting bumps or landing off jumps. However, using heavier oil in the front which weighs less doesn't make sense to me? When you do the drop test WITH these oils in your car, does the chassis still bounce evenly? The reason I ask, is because I have tested this extensively years ago and the front end was overdamped.

I had a similar setup when I tested matching f/r spring frequencies. I had to use a heavier oil than I would like to in the front. Otherwise the front end would dump in the middle of the corner. The heavier oil cured that, but I didn't like it because the front end was overdamped and didn't rebound fast enough. BTW no amount of adjusting camber links, tire selection corrected this so I HAD to run heavier oil like you do OR just increase the front spring rate slightly.

I realize I'm contradicting your preference in setup and I'm not saying it's wrong, it just didn't work best for me. As I said in my previous posts, I personally prefer a slightly stiffer front when compared to the back. This allowed me to run a lighter front oil, so when you do the drop test WITH oil the chassis settles evenly. It also allowed me to enter the corners without the front end dumping. Overall I got faster lap times and it was easier to drive at the limit.

top shotta: Yeah no joke. It's hard to talk about roll centers without being general in many areas leading to even more questions. The fact that there is (as with everything) no one right answer only makes things worse.

As far as watching the suspension moving up and down, you aren't watching to see if one end bottoms out or not. You aren't trying to make them bottom out at the same time. You are merely trying to make each end move up and down at the same rate. If they are off, such as the front end bouncing up and down at a faster rate than the rear, you've got an imbalance. The rate at which is bounces up and down is the suspension frequency and each end has one. We want them to be the same or nearly so.

To paint a mental picture, let's say we have a booming stereo system. Let's say we have 2 big 15" subs playing a 30 hz note. The actual frequency doesn't matter but the point is that we have each sub going back and forth. We can see this. If they are each playing 30 hz, they are the same, correct? Now what happens if we change the signal to one of them and now one is playing 30 hz and the other is playing 40 hz. Is it still the same? Of course not. The cones even move at different rates. One goes back and forth 30 times per second and the other 40. This is what we are balancing with springs. We want both to play the same frequency.

Now in regards to the rear of the car bouncing more than the front, from the above example we agree that each speaker playing the same frequency is balanced. It's obvious that it's the same. They are moving in and out at exactly the same rate. What if one speaker is playing 30 hz at 125 decibels but the other speaker is playing 30 hz at a much lower level, say 50 decibels? Are the still playing the same frequency? Of course they are. They are just doing it at a different intensity level. There is more energy going to one than the other. On the XXX video (that sounds bad!) there is far more weight in the rear of the car and hence more energy going back and forth. For all intents and purposes the rear is playing louder than the front but they are playing the same frequency.

Hopefully that example works and makes things a bit more clear and for god's sake please don't try to pick technical holes in the analogy. I'm just trying to get a mental picture going, not write a technical manual for an engineering college.

You aren't choosing your shocks oils on the bench. You are systematically determining what to use based on how the car drives. For me when I tune 2WD buggies, the fronts always end up with a heavier weight. Why? It's due to the front end rake. The more rake you have, the more oil weight you need. If we had no front end rake we'd probably end up with the same or near the same weight front to rear.

Think of it this way. A shock that is mounted straight up and down and is getting a purely vertical load exerted on it will be utilized 100%. You are fully using the spring rate and dampening rate. Now let's say we lean that shock over 45 degrees yet keep the vertical load. Suddenly the shock is only 50% effective. Our effective spring rate and dampening rate has decreased. How do we get the effective rate back? We stiffen the spring and increase the oil weight. Remember that the front of a 2WD buggy is laid back anywhere from 20 to 30 degrees thereby lessing the effective dampening ability.

We have 2 things to understand and those are the static dampening and the effective dampening. The static dampening/spring rate is what the shock is sitting on a bench. A 4 lb spring is a 4 lb spring. 30W oil is 30W oil. The effective dampening/spring rate is what it ends up being in the real world. Let's say we install that shock directly in the middle of the a-arm. Let's say the a-arm is 2" long. With the shock being at the mid point suddenly our 4 lb spring behaves like a 2 lb spring due to the leverage the arm has on it. Our 30W oil acts like 15W. What if we lean the top of the shock over 45 degrees? Suddenly our effectively 2 lb spring acts like a 1 lb spring and our effectively 15W oil is now 7.5W. See how this works? Again, please no one get too picky about the examples. They are there to get a point across without getting overly complicated. A 2WD has far more rake than a 4WD and will have stiffer oil as a consequence.

When you drop the car on a bench, hopefully it won't bounce at all! It should just absorb the impact.

So, as I understand it -- "Shock pack" will consist of less resistence internally within the shock. In other words --- Shock pack goes up as pistons with larger, or more holes are installed making the flow of shock oil faster through the piston. This is increased shock pack, yes?

And increased shock pack is recommended for big air applications.

Yet, if this is true... I can't see why it works. If you have less resistence internally with the flow of shock fluid from one side to the other in a quicker manner from pistons with bigger or more holes allowing such, would this cause the car to simply bottom out a lot more fierce than if you had less resistence within the shock (smaller piston holes / less) so the fluid could not as quickly travel from one side to the next?

Confused...

Increased pack is when the piston holes either get fewer in number or smaller in size (or both). Pack goes up when available area in the piston for oil to flow through goes down so basically you've got it backwards.

Now that makes sense to me. This article right here:

With more hole surface area (three hole piston) there is more "Shearing" as the oil passes through the holes. This gives the shock more pack

That specific statement is what threw me off.

I understand pack now. Thank you.

Thanks for the explanation on effective wheel rates. I am aware of those variables. But you didn't answer my question. So your saying that your setup settles evenly when you drop it on the bench, and the front end is not overdamped on the track?

Let's just agree that we can have different opinions and move on.

Of course it settles evenly. The effective spring and dampening rates front to rear are balanced. Ignore the static dampening numbers.

Thanks for the help guys.

anything on camber yet?

pack is the same as compression stroke when hitting a jump face or a landing.

http://users.telenet.be/elvo/3/2_content.html

Last night I ran a few laps with this new set up. (balanced).

Car handled very well for the most part.

On the tripple, major problems. I was bouncing off the ground on landing. The height of take off wasn't very much either.

I began to think "ok.. shock packing... ok.. more dense shock oil..."

then my buddy grabbed my car... and took my front suspension collars down 7threads.. and rear a couple.

I got 2 more feet of air and landed smooth as butter. Every time.

I had problems in the "S" turn... I begin thinking "hmmm... perhaps stuff we haven't gone over yet with camber, toe, roll centers, etc...".

then my friend wanted a try at it.

I watched him drift turn #2 like a pro and come out on a perfect line. He hands it back to me and says, "It's goood."

I said, "Where did you learn how to dial in set ups like this?"

He says... "I drove it."

I love the science behind all of this set up stuff... but man.......... I'm wondering if there comes a point > you just have to DRIVE baby drive...