I look at things in extremes. If we were to rake the front end back 90 degrees we'd have no suspension movement at all. We'd have a spring loaded front bumper. It stands to reason then that there must be some effect from front kick between 0 and 90 degrees. Incidentally, the more front kick you have, the less on power steering potential you have.

I am glad to see some people are starting to try to mathematically calculate their setups along with using Fred’s practical bounce method. I have a spreadsheet that I personally have been using for a long time based on the equations in “Race Car Vehicle Dynamics”. I have found that the easiest way to account for the spring motion ratio is to clamp the chassis to a stand with the shocks hooked up but no springs installed. Measure the exposed shock length at full droop, then measure the distance you can bump the wheel until the shock bottoms out. The ratio of those two numbers is your average motion ratio for the entire range of travel. I make a table of all the motion ratios available for each shock mounting configuration so when I want to make a setup change, I can easily look up the new motion ratio and enter that into my spreadsheet. I can get into more of the details of the spreadsheet and how I use it to tune based on roll rates and ride frequency if there is interest, but I don’t want to hijack this thread. I am impressed at how well most of you are able to balanced setups using Fred’s method, I just prefer a more analytical approach.

Interested! I don't think you would be hi-jacking at all. You will be adding to the knowledge base - which is always welcome!

Another mistake I made,I didn't measured kickup and you are right.
Heading to the track,I'll be testing rear shock positions.

Maybe I'm not understanding totally,are you basically measuring shock travel within different shock positions?

Anybody have a quick explanation on what happens if you raise or lower both camberlinks on outside and inside at same time? Like say 2/2 washers vs 1/1 or 3/2 vs 2/1? More or less grip?
Anyone?

Motion ratio is usually defined as change in shock travel divided by change in wheel travel. The ratio changes throught the travel since the shocks are angled and the links all move on an arc so to simplify things you need to find one value that represents the entire travel. The change in shock travel for the entire travel is equal to the extended exposed shock shaft assuming the shock bottoming out limits travel. The change in wheel travel can be measured by measuring the difference in wheel travel when the shock is fully extended and when the shock is fully compressed. So if the shock is able to travel 1" and the wheel is able to travel 2" the motion ratio would be .50.

thanks for the explanation,I mixed MR with wheel rate...My head still hurts from all the thinking but I see what you are trying to accomplish.

Dirtracing58 Just curious what is the source of your definition of motion ratio? Its the inverse of what is published in Tune to Win.

My equations come from "Racecar Vehicle Dynamics" by Bill and Doug Milliken, they refer to it as installation ratio on P595. You can define it as the inverse as some books do, however you need to change your wheel rate equation to match. WR=SR*(MR)^2 if MR is less than 1 like Milliken defines it, WR=SR/(MR)^2 if MR is greater than 1 like Carroll Smith defines it. An easy way to check to make sure you have it right is to make sure your wheel rate calc is less than your spring rate.

Can anyone please help me with pack/spring stiffness? I run on an indoor clay high bite medium size track. Most of it is fairly smooth, some shallow rippley patches. I was out for the first time with my Losi 8ight E 3.0, I had it set up per manual for a starting point. My buggy is pretty light, only 200g over lower roar limit, my balance is 50/50 L to R and just slightly off to the rear. Maybe 52/48. The buggies Losi used for the basic setup are even lighter I was told. A local fast guy at my track has the same buggy and suggested a better setup for our track. Im pretty sure his buggy is heavier than mine. I tried it and got better/more steering but a looser rear, which he likes to be able to throw the rear around entering a corner. I personally like a predictable rear, I feel more confident that way. I didn't adjust shocks any, and I noticed from a video my 14yr old took. In slow motion on the front straight after a long sloping back side of a jump. The track has sharper bumps, and my wheels seem to be bouncing off the bumps rather than the shocks working and keeping the buggy from getting unsettled. It was worse if you over jump and dont land the back side of the jump before the straight. Theres only 3 different spring rates for this buggy, I'm at the stiffest in front with 5x1.4mm pistons 37.5 wt oil. Rear is next spring rate down 5x1.5mm pistons 35wt oil. I saw a you tube video of the track they used to get kit setup, it is smooth all around. So maybe this combo is too stiff or are the shocks packing early? Everywhere else on the track the buggy seemed good, should I just adjust my driving for this section? Not much chassis slappping, bottom still looks new. Just a few times I heard from over jumping. Also going into the right hander after that straight my rear inner wheel comes off the ground, I agree with Fred 4 wheels on the track is better than 3. I cant remember if it did that with kit setup, im thinking softening the front and leaving rear stiff isnt helping. I've read this thread twice also have had the rc car handling site read a few times and keep a print out in my pit box for reference. Any help will be greatly appreciated.

I was playing around with suspension geometry in CAD today to test a suspicion that I've had for a while in regards to shock orientation, standing them up vs laying them over more. I created a simple reference suspension with a set travel distance and then created 6 instances of it on screen. Then I started with a shock that was 90 degrees to the arm when fully compressed and started laying it over from there. The first 3 models were in this setup. The next 3 moved the shock position outward to the outer hinge pin with these 3 orientations showing a shock laying further and further down. I took angle measurements on the fully extended and fully compressed locations of each setup. Then I subtracted the lower number from the higher to show how many total degrees the shock changed in reference to the arm.

What I found on screen confirmed what I've always suspected but never bothered to verify until now. The most vertical setup gave me a 26 degree total orientation change between the arm and the shock. As I laid the shock over, this range got smaller and smaller. The most extreme example showed a mere 4 degree total change in relation to the arm. It is hard to describe all of this without a picture but basically the more vertical the shock is mounted, the more progressive the spring and dampening rate are with suspension compression. The more laid over the shock is, the less progressive they are.

Edit: Yeah I'll throw a picture in here. Keep in mind this is just for illustrative purposes to display a concept.

If the wheels are bouncing, your shock oil is too light. If the chassis is bouncing, its too thick.

Get one end right, then do the other.

Thanks for the source. I always find it confusing when different authoritative sources use different definitions for the same term. Certainly makes for some interesting conversations until people realize they are really talking about two different things.

Me too 4 is better than 3. From your handle I assume you have a lot of experience racing on carpet. Whatever you would do on carpet (especially if you ran touring car) to fix the tire lifting problem should work with your buggy. What sway bars are you using and make sure the droop is the same on both sides of the rear (also check the front droop too).

The sway bar is picking the inside tire up. Before you mess with trying to change the rear roll
stiffness make sure you cant move the endlinks up or down the bar a little to try and take it
out of such a bind. Your asking for an awful lot of travel from them on a 1/8 scale and they
will bind up at full droop/compression.