Please explain shock packing...what is it etc...

This is a great thread and touches on things that are never mentioned in setup guides. I tried this method a few years ago and discovered a few problems that makes it hard to translate to real world. But it does have merit as a good starting point if your starting from absolute scratch. Here's my observations on spring matching w/o shock oil as a baseline setup.

Here's what I noticed: When you initially setup using just springs with no oil to find a matching natural frequency (NR) for the front and rear. After dialing in the correct shock oil, you end up having to play with the springs rates again anyway. You start out usually with a lighter spring rate in front vs rear so it's balanced with no shock oil. But end up with equal or heavier spring rate in the front after getting everything balanced with shock oil. If you take the oil out of your final setup and check the natural frequencies, you usually end up with the front NR much higher than the rear NR. My guess, and this is only a guess, is that a springs NR changes once you add friction. (ie dampening) Also, checking NR on the bench has nothing to do once the vehicle is in motion and weight transfer is added to the mix. especially front to rear weight transfer.

I do think someone who knows more about physics than I do can figure out an optimal spring rate (NF) front to rear taking into account weight distribution. This calculation has to take into account f/r weight distribution. Even though this method does work, I just don't think the result would be a balanced NF front to rear, I think it will tend to be a higher NF in front when compared to the rear. The problem is how do you do the calculations. In the end, I'm back to trial and error.

This does seem to work better on 4wd vehicles, and I'm thinking this is because the weight distribution is closer to 50f/50r when compared to a 2wd. I have an 8th scale buggy with close to 50/50 weight and have used this method of balancing spring NF with really good results. When I do use this method I noticed, I ended up with the same pistons and oil front/rear. The chassis tends to stay level when I hit bumps instead of having that porpoise/front end to rear end bounce. Setting up this way worked well for me on very rutted rough tracks, where corner speed was not the most important factor. Using this method on a smoother track ended up getting me slower lap times. The front end was just too soft.

This method did not work for me at all with a 2wd buggy. You end up with really light front springs in comparision to rear springs. Even with thicker front shock oil, you end up with a buggy that pushes entering the corner, and sometimes oversteers exiting.

The 2wd buggy really does soak up the bumps as long at you go straight. But when you turn and the weight transfers forward to the front springs, the springs are too soft and the buggy just dumps while entering the corner, and the rear end lifts and then spins out when you run out suspension travel in the front. Yes you can compensate for that by maybe playing with shock limiters, oil ect. But you end up with a car that doesn't land off jumps well because there's no downtravel, or the front is too stiff because you will need really thick oil to prevent the front from dumping.

That's my .02

If someone can figure out the math, I believe this method will work. I just don't think the f/r NF should be the same. At least from my experience.

Of course you end up with a lighter front end than the rear on a 2WD buggy. The front end is lighter. Typically over 70% of your vehicle weight is in the back. The front has to be lighter. It's all about balance. On a mid motor 4WD vehicle where more weight is centered, you'll have a more equal front and rear setup. The front end does typically get a thicker shock oil.

Once the springs are set, they are set. After you get your oil sorted out, you do not go back and adjust the springs UNLESS you adjust ALL of them! Springs need to be treated as one entity yet one separate from shock oil. If you change the front, the rear goes with it and vice versa. Balance must be maintained. You may need an overall higher or lower suspension frequency but you must always maintain balance. I can't stress this enough. Going back and changing the springs again after the fact is a huge mistake that too many people make.

This is not something that works on only 1/8 scale or only on 4WD or 2WD. It works on ALL cars regardless of vehicle design, weight distribution or scale. It is a universal method that is used to arrive at a solution.

If you are blaming cornering issues on shock or spring rates, you are ignoring a host of other things. Shocks and springs are ONLY used to determine how well the vehicle absorbs bumps. Cornering ability is adjusted through roll centers and tires. Front end rake plays a role with weight transfer when decelerating and you'll notice that the new 22 has a few different options in this area and the optimum rake even changes with weight distribution in the car. Do not use your shocks to tune your cornering ability. Roll stiffness is the number 1 thing used to determine cornering ability and the roll stiffness chosen needs to be based on how stiff your shocks are. It is all related yet separate. I haven't gotten to all of these issues yet but this is pointing out the problems with typical tuning methods. Shocks are not the be all end all tuning item for every problem! They are a part of a greater assembly and everything has it's own dedicated purpose.

Keep in mind I am not telling anyone what the best setup always is. Not at all. No one can do this. If you use these techniques, it is still up to YOU to get it right! You can use proper techniques but still get it wrong if you don't pay enough attention to what is happening. I can't give you the answers. I can only tell you a logical course to take in order to get there.

You've got to start somewhere. Where the factory sets it is as good as any.

So let say I got a 4wd with 50/50 I will start out same spring rate front and back? For 2wd with 30/70 I will start out 3lbs front and 7lbs back to begin with? Assuming both front and back have same suspension control arms and shock towers etc.

Theoretically that would be correct.

Ok, I made a quick little video of my XXX-CR. (1/10th 2WD buggy) Front springs are red (2.5 rate), rear springs are white (1.8 rate) Best I can tell the back has a much lower frequency rate and must be brought up to match the front since I have the softest springs available in the front for this car. What do you think? How far "mismatched" does this appear to be in your opinion?

http://www.youtube.com/watch?v=f20gDe6BeNc

Also, most drops were made from about 2-3" as anything above that would bottom out the rear chassis.

I agree with everything your saying except the front and rear natural frequency needs to be balanced. As I mentioned earlier, I end up with a front natural frequency slightly higher than the rear as the best working setup. (at least in a 2wd buggy)

I think this would hold true if the front kickup was the same as the rear antisquat angle. But it's not. Once you enter a corner the forces involved were never factored in for spring selection doing the bounce test.

Yes to get it more balanced you need to raise the rear spring rate.

One thing to keep in mind to make this test as accurate as possible is:

1. the suspension arm downtravel is close to equal front to back.
2. You do this test on the tires/foam you'll be running with. If you change to a totally different foam you may have to redo this test.
3. the chassis shouldn't bottom out and hit the table. If the chassis hits the table than the natural rate the spring will rebound changes. Select a drop height where the chassis doesn't bottom out.

I'm pretty aware of what happens on a 2WD buggy since that's what I run and what I tune the most. Camber links and roll centers are used to fine tune cornering. On a 2WD buggy you are going to end up running a heavier front oil than the rear anyways. On my vintage RC10 (the car I have been playing with the most lately), I run 40W in back and 60W in front with #2 pistons all around but the spring rates are still balanced. My front oil is 50% heavier yet the car has about 45% less weight up front than in back. A different piston could change that ratio though. If I were running 40W all around, the back end would pass the front everytime I get on the brakes.

One other thing to consider is to reduce total brake strength and learn to drive a bit differently. A 2WD rc car does not have front brakes. Try to drive a real car hard into a corner using only the emergency brake to see what happens! You need to drive a 2WD differently than a 4WD as a result.

I think you've pretty much got it figured out! I do a drop test from a few inches but I'll also push one end down at a time as well and watch how fast it rises. I'll also hold the entire car all the way down and let go and watch to see if one end rises faster. You can even just drive it around and observe how it moves but this is really only easy on a real car when you are inside it. There is no one way to do it. The goal is the same. You just need to be able to tell what is happening and it doesn't matter how you do this.

The back looks like it is bouncing off of its wheels so don't you need a softer spring in the back?

That actually doesn't look bad at all. In fact you might have it. I need to watch the slow motion shots a bit closer. It's hard to ignore the rear end bouncing but you need to try. The only thing we are looking for is on the rebound when the car is on it's way back up. Are the front and back rising at the same time? Will they go back down at the same time? The chassis will remain flat if they are and it appears that it does. On a 2WD buggy the rear end will continue to pulse for longer simply due to where the weight is concentrated so just ignore that. It's pulsing at a frequency that isn't changing. It's duration at the frequency is and that's ok.

The first and third slow motion shots seem to show good balance. You can see a bit of porpoise happening in the second slow motion sequence though but it may have been due to the way it was dropped. Overall I'd say that's a pretty nice combination. Once you get shock oils worked out, you won't have the bounce problems anymore. We are only looking for suspension frequency right now. Not how long it keeps bouncing or how badly it may bottom out.

Here's one thing to try. Figure out approximately where your center of gravity is. Just use a finger on each side of the chassis and try to pick the car up. Move your fingers farther back if the front end is rising first. You'll probably end up somewhere near the center of the battery in location. Once you find it, push down with 1 finger on this spot. The front and rear of the car should both go down at the same time if it is balanced. Do this on springs only as shock oil can change this a little bit.

The tracks are run on tend to be smooth but do not have large jumps. would I want to run thicker oil and less packing or vise versa? Can you explain packing?

so as long as the truck goes up/down at almost or the same rate the balancing is good? the bouncing will/can be solved once i add the oil? sorry if it sound repetive.. but i wanna try to get it right on my next shock built