That's a wing? I thought it was a shovel...

fredswain, you ever get to SA to play? I plan on getting out to Katy to try that track out one of these days. Sounds like a good time.

dont know about Fred but im down for a road trip soon! you got 2w or 4w buggy classes?

I found that after i balanced my springs at ride height(approx 1") that when filled with oil the ride height ended up lower because of the rebound dampening effect of the oil. I lost almost 1/4 " of ride height. I then had to adjust my spring preload again. Personally I would balance the springs with the ride height level front to rear, but a little higher than the ride height you want to end up at because it will settle down when you add your shock oil.

As far as figuring out what ride height to set at, it's really as low as you can get away with and still have adequate suspension travel for the track conditions you're running on. For indoor hard smooth tracks it will be lower than rough outdoor loose tracks. like everything else in this thread, it will take some trial and error. At least there is a proper order and place for each part of the chassis tune.

Since "roll centers" change with suspension compliance, a lower ride height will have a lower roll center than a higher ride height. I personally like my camber links and arms to be parallel with each other at an even ride height.

I get out to SA a couple of times a year. It's a favorite place for my wife and I to go to relax. I don't think she'll let me go play with rc cars while we're there though!

Ok it's time to get a bit farther into this. As we all know by now I hate the term "roll center". The very concept of the chassis rolling about a point in space is actually a useless idea. What we are concerned about is roll stiffness and this is when we use the term "roll center". A sway bar also adds roll stiffness but one thing it doesn't do is contribute to roll dampening which is what your shocks do. A higher roll center equals more roll stiffness. A lower roll center is less roll stiffness. Simple enough. Let's go a bit further.

Let's say we have a camber link that is exactly the same length as our arm. Let's also say that it is mounted exactly parallel and centered with the hing pins. The wheels will always stay parallel to the ground. This roll center is actually quite low. Now lets say we move the links outwards a spot. Our roll center has gone up very slightly over the entire range compared to the first position. If we were talking about sway bars, the outer position would be the equivalent of adding a slightly stiffer sway bar.

Now what happens if instead of moving the whole link outwards, we shorten in? Let's say we move the inside closer to the wheel. As the suspension gets compressed, the roll stiffness increases. Again, if this were a sway bar, instead of being larger, it would be the same as if it were getting larger and larger as the suspension compresses. Hopefully you can understand what I'm talking about. A shorter and shorter link will make this more and more pronounced.

Perhaps you wanted to take our original length link and move the inner mounting point down keeping the length the same. What you have now done is to move the roll centers down.

Every possible link position effects roll centers (roll stiffness) and each location affects in it various ways. Which way is right for you is going to be trial and error. As a general rule, the heavier end of the car is going to need more roll stiffness than the lighter end of the car. A rear motor 2WD buggy will need far more roll stiffness compared to the front than a mid motor buggy would. Of course the opposite way to look at it is that the front would need far less in relation to the rear.

In general a higher roll center will transfer more weight to the outside wheel generating more down force on it. A lower roll center will transfer less weight to the outside wheel with a more even split between the inner and outer wheels which is less downward force in the tires. A lower roll center is more likely to slide while a higher roll center is more likely to grip. However when a higher roll center lets go, it really lets go. A lower roll center will generally be more predictable and controllable in a slide. From this paragraph you are probably thinking that a low roll center is what you want as the car is more controllable. Not necessarily. Your cornering power may suffer. Drivability is irrelevant if you are sliding past your corner.

Why does the upper link location affect roll stiffness? In simple terms it is about leverage. The higher the roll center, the more of the chassis weight is transferred to the suspension in a roll. The lower the roll center, the more weight is transferred to the shocks in a roll. Basically. Think about the camber links. Look at where they are pointed at level ride height. Fairly flat. Now compress the suspension. The are pointed downwards on the inside. The more downwards they are pointed, the higher your roll center.

A good analogy is the broom handle. Let's say we have a broom. Hold the end of the handle way down next to the ground. Slide the broom. If moves very easily. In some cases it may even just glide over an object rather than move it. Now let's try this again. Hold the broom more upright and again slide it. It's a bit tougher to move but is more effective at sweeping away objects. What if you try to slide the broom while holding it completely straight up? Good luck! This is a simple example of how roll center heights work. The lower broom handle example is a low roll center and so forth and so on. The same basic phenomenon is happening with your suspension through the upper links. The low broom handle is easier to slide and very predictable. The higher broom handle however has more traction but is harder to get moving.

Ok so how do I know how to tune this? I'll get to that next...

Alright so now you're wondering how to dial in the roll stiffness using your camber links based on the previous post. First off, by this point you should have your shocks and springs sorted out. The car should handle the bumps and landings well. If you changed any of your shock or spring settings based on it's cornering ability, change it back!

I prefer to start with a ride height where the arms are level. At this ride height I also like my camber links to be level. I generally set them for about as long as I can get them provided they aren't longer than the kingpin to kingpin distance on the arms. When you push down on the vehicle at each end, any camber gain (wheel lean) you get should be equal front to rear. At least at this point it should be. This is just a starting point. Things are going to change quite a bit before we are done.

Now go drive it. Try many things. Go fast into a corner and hit the brakes hard. Does the car plow through the corners or does the back end swing around? Accelerate hard out of the corners under power. Does the car have severe push where the front inside wheel comes off the ground or does it over steer?

Let's start with how it handles coming out of a corner. Let's say under hard throttle out of a corner the inside front wheel lifts off the ground and you get severe under steer. Most people would be tempted to stiffen the rear springs. Don't do this! You do need more roll stiffness though so start raising your roll centers. I prefer to keep the links level at level ride height so I'd start shortening the links. Keep testing out of a corner. Does the problem fix itself or does the wheel keep coming up? Can you lower the front roll center? Can you make the front link longer? This will reduce some front roll stiffness allowing the front to roll more. You want all 4 wheels on the ground in a corner!

Perhaps you can't get any lower with the roll center in front. Concentrate on raising the rear roll center. Again, the easiest visual way to see what is happening is how far inward the tire leans during suspension compression. If it leans in too far you'll end up scrubbing inside edge of the inside tire in a corner which means too little of your tire surface is on the track. Not only do we want all 4 tires on the track, we want as much surface area as possible on the track.

Let's say you just can't get enough rear roll stiffness but your rear tires are leaning way too hard. You need a rear roll bar. Changed thicknesses until the front wheels stay down coming out of the corner. Hopefully you see what we are doing with this example and can figure out how to transfer this theory into different scenarios. A roll bar may not always be needed. A 2wd rear motor buggy is very different than a 2wd mid motor buggy or a 4wd buggy, etc.

Now let's say you've got it steering well under power out of a corner. At least to a point where all 4 wheels are on the ground. What happens if you are going hard into the corner and slam on the brakes? Does the rear end fly around resulting in a spin? If it does you may need to compromise on some things. This is an area where the only car on the market that can help tune this out is the TLR 22. If this scenario takes place, too much weight is transferring forward which means less front end rake is required. The 22 is adjustable between 20 and 25 degrees.

No other car can tune this area out and you'll see really quickly how well your vehicle is truly designed. On my vintage RC10 the front end rake is 30 degrees. That's WAY too much and needs to be reduced! Fortunately the front end unbolts and due to it being made out of aluminum a vice can make everything better. The current car the B4 runs 25 degrees. When the JRX2 came out it had a 20 degree front rake. Later on they changed it to 30 degrees. The chassis also got longer when they did. Keep in mind you 22 guys, if you do change the rake, you'll need to go back to square 1 and make sure your spring rates are still balanced. It sucks I know. You'll also need to reverify your roll stiffness experiments. They may need some tweaks. Tuning isn't quick. It's a process.

So for the rest of the world who can't correct this issue, what can we do? Well one thing I didn't get into is the front caster blocks. Play with different types here as they each have a different effect on off throttle turn in vs on throttle turn exit. You may also need to dial out some of the rear roll stiffness again to get some inherent on power turn exit under steer back. You are going to have to adjust your driving style. You may have to go into and out of the corners a bit more gentle than the cars that can correct this issue.

See why some claim the 22 can corner harder than other cars if setup well? Keep in mind mid motor makes everything even better as balance is better. Basically a rear motor car is always going to suffer a bit compared to a mid motor car, 2wd or 4wd. When setup well a well balanced car can hold far more corner speed. You really only need to worry about tons and tons of forward traction if you are constantly slowing way down and that usually comes at the expense of straight line speed and cornering ability which only further slows you down even more.

What if we have a nice handling car but don't know if our roll centers are optimal. You've got balance at this point. If you want to try a lower roll center, do it evenly all around. Adjustments from this point on are small. Whatever you do at one end must also be done at the other. When you get balance you never unbalance it by making changes only at one end. If you need to only change one end, you don't have overall balance.

If you've gotten to this point you can see that if you need a stiffer spring, you need to do it at all corners. If you need a higher roll center, you need to do it at all corners. The hardest part about tuning is to get a balanced car. From there it's tweaking little things and each thing is done to address one problem at a time. I suspect this part is going to get lots of questions but it's not the easiest thing to understand until you see it.

Umm.. no. this is 100% backwards.

Nope try again.

Not here to debate ya, just letting you know.

You don't have to debate me. You're wrong. Instead of laughing about it. Go study. Pay particular attention to jacking forces.

Im not jumping on the argue with fred bandwagon but there are a few things I would like to point out.
In the first part of the quote, the tires will only stay vertical to the ground under straight line movement. with both upper and lower even and parralell you have 0 camber gain through travel. Any body roll at all and the tires will lean to the outside.

Lowering the inner upper point will raise the roll center. Similar affect as raising the outer upper.
Still alot of good info though Fred.

Nick

That's correct. I can't list every possible scenario.


I drew a very simple and very crude picture to demonstrate what is happening to vertical loads at the wheels based on roll center. Obviously it's a huge exaggeration and there is no suspension compliance shown but hopefully the point is clear that a higher roll center results in more load at the outside wheel in relation to the inside wheel. A lower roll center results in each wheel sharing the load more. If you somehow threw the roll center down a mile, each wheel would basically have the same effective load being exerted at the contact patch. Again this is a huge exaggeration. Sorry about the quality and color. It was quick.

In the high roll center diagram when the tire hits it's traction limit, and it lets go, the loads aren't evenly divided between it and the inside tire which means less usable tread to catch it. The car goes around faster. Since there is lots more vertical load being exerted on that tire, it will try to release that energy much more abruptly. In the lower roll center scenario, since there are more equal loads on each tire, they will let go more gradually and a slide will be more controllable since we have more usable tread area being used. That isn't always desirable. It's all about compromise and balance.

Now keep in mind the other end of the car plays a huge role. If one end of the car has such a stiff roll rate that a wheel comes off the ground at the other end in a corner, there could be varying levels of roll center change introduced into the end of the car coming off the ground that would still have little effect. This is why I don't like using the term "roll center". The only thing that really matters is roll rate stiffness at each end, or more appropriately the force application points, and this can somewhat be adjusted through the camber links.

EDIT: I redid the diagram in black so it can be seen better. I also added a dimension at the top. It represents the horizontal load which is trying to make the wheels slide. You can clearly see that with a lower roll center for the same amount of chassis roll there is more weight transferred into horizontal load. With a higher roll center more weight transfer is going into vertical loading of the outside tire increasing it's grip. It does this through increasing roll resistance. A sway bar increases roll resistance which transfers weight to the outside tire. Sway bars do not transfer weight to the inside tire.

I’m not sure what you do for a living I could guess. I’m been studying what you have been saying and I have learned a lot. I don’t know your money situation but you could write a book on what you have talked about. I’m sure all of us on here and many other would buy it.

I have been one of those guys that would copy pro setup sheets but that is now in the past . I wish you would have talked about this sooner you could have saved me some money on mag. subscriptions. Thanks!!

Can I ask a basic question that I have gotten different answers for? If it has been answered I apologize. Been bugging me for months since I started in this hobby.

How tight/loose should sway bars be? Should they move freely side to side, or be locked down tight and if they should move freely...how freely? Or is it that important?