How do you figure?

The variable relationship between spindle height and the distance between your lower arm and upper camber link pivot. If the spindle height (from the lower pivot to the upper camber link mount) is greater than the inner pivot's dimension, than raising the inner ballstud will raise the roll center and lowering the ballstud will lower it. However if the inner dimension is greater than the opposite will be true. Generally in off road the spindle is taller, but not always. I have read vehicle specific tunin guides where they had contradicting advice for achieving the same goal simply because the suspension geometries between the vehicles were different and required different adjustments from the other vehicle.

I see what you mean. Why would anyone do that though? I don't know of any r/c cars that do that and as such really doesn't make this setup relevant to the discussion. It would only serve to confuse people.

Its important to note because someone is going to read this and then be reading a book like the Hudy or XXX Main setup books and they may be contradictory to what you are saying here.

The problem I think many people run into is not sticking with a particular tuning theory. There are many of them out there, and each can be fast and handle well, but using bits and pieces of many different approaches can get you into big trouble. As an example, when we were racing full size SC trucks the differences in truck setups varied greatly, yet lap times among the top trucks were minuscule. There really is no single correct way to do it, but if you are going to subscribe to someone else's theory than stick to it. Don't worry if the local fast guy has these springs or this oil- use your system, whichever one you have chosen, and tune your vehicle to you.

If someone is trying to learn and they hear, "it works that way sometimes but opposite to that other times" yet one of those ways never applies to r/c cars, that way shouldn't be discussed. This is not a masters class in mechanical engineering. We are trying to help people learn how to tune r/c cars and as such should stick to things that are only relevant to them. In the end, when they learn all of this, they'll probably figure out what to do should they encounter that situation. I won't mention that which doesn't apply. If someone reads something contrary somewhere else and has a question, they can ask about it.

Again, I'm not telling people what tune they should be running. I'm telling them how to systematically arrive at a tune. The end result may be very different for 2 cars tuned by 2 different people.

I have been eagerly waiting for the geometry part of this discussion. There is alot of good info here instead of the usual " changing this or that gives more traction" without explaining whats actually happening.

There is one part that has not been mentioned yet that I feel is just as important if not more important that roll center. Nothing ever gets said much about camber gain. The reason for camber gain is to try to keep the tire upright as the chassis rolls over in a corner. I have been an alignment technician for 18 years and raced stock cars for 15 of those. To me I wouldnt say I ignore where the roll center is, but I put more importance on camber change through suspension travel. If you think about in the end the goal is to get as much traction as possible out of the car and still have it drivable. Managing camber change along with caster and suspension travel are all interrelated. And as you stated earlier its all a balancing act. everything affects other areas. some just more than others. Hopefully I didnt step on anyones toes by throwing that in there.

With that in mind going to a longer or shorter upper link will affect how quick or slow camber change will occur. If the lower arm and upper link are the same length and same angle to eachother, there will be practially no camber change through the suspension travel. A shorter upper link will have more change than a longer one obviously. It also works hand in hand with the upper angle. With a shorter upper than lower and both even with each other camber change will be minimal on initial travel but will gain negative travel as compresses farther. A longer link will have a slower more gradual change while a shorter link will have a faster rater more aggressive rate of change. Adding angle to the upper link with the outer end higher will advance the process and start camber change sooner.

Another thing to Keep in mind. Running a shorter upper link with no angle will have some disadvantages also. As that upper link tips in under compression to help the outside tire stay upright it will also cause it to tip in as the suspension extends. That will cause the inside tire to lean in and not be as affective.

This brings be to the question part of my rambling. Why is it that alot of the buggies and trucks that I see have no angle in the upper links or have the inner upper mount higher than the outer. It would effectively lower the roll center and make the front end softer but at the same time camber change goes completely haywire as it rolls over. As long as I can remember that seems to be the standard setup.

Nick

Nice thread about setup with interesting take from Fred.

I liked how practical Freds solution was to balancing with springs.
For those of you that have read the setup guide writen by Elvo, in the suspension section he has the mathmatical version of what Fred has described. ( I have tried it and works well to balance the spring front to rear, without having to try so many options on the buggy, takes less time )

In my humble opinion, roll center can be handled in the same practical way Fred had started. Have the front and the rear roll the same amount to maintain balance.
As the front and rear suspension are seperate, but forced to work toghether by the chassis linking them. What I mean is that the front and rear will roll to the avarage of both ends.
Sit at the bench and measure camber gain front and then rear at the same chassis side compression, adjust camber link positions untill front and rear measure the same.

Hope I did not jump the gun Fred on your explanation of how you do it ?

* Will try to tag Elvo on this thread and hear his 5c *

W.

Sarinexia,

Sorry I do not mean to change the subject but I see you live in Abany NY. I will be moving to Malta NY at the end of the month and I was wondering what track you race at?

Thanks
Hugh

I bought the optional Losi springs for my slash. I am running 4.1 on the front and 3.7 on the rear. I have 40 wt shock oil in the front and 35 in the rear. My problem is I am still bottoming out on the jumps including the single. I am thinking of running lighter springs and 1 hole pistons in the rear and maybe the front. My other problem is my track is farely smooth with the majority of the bumps being pot holes in the corners. I noticed it seemed to bounce a little over the potholes. On the straights the bumps are real small and I can hardly tell the truck is bouncing. I am thinking I should not worry much about the smaller bumps. My slash is handling really well with this set up however. I am wondering if I am over thinking this.

Well, I got through the spring tuning on my B4 and was just moving into tuning the damping with 30 wt (I know you are supposed to start with 20 wt but I apparently have a hard time listening to instructions). The car felt better than it ever has on my track, even with the damping untuned. Unfortunately, I sheared the drive axle pin on my B4's CVD and didn't have a replacement. Either way, this obviously works and I can't wait to continue on with my testing/tuning.

You aren't supposed to start with 20W. It's just the lightest oil I have. You can start anywhere you want. I just advise that people start light and move their way up. Start anywhere you want. If you are pretty sure that a certain weight is too light for your track, don't start there.

IOP: Are the spring rates you are running considered fairly soft or fairly stiff for your truck?

They are the 2 stiffest rates that Losi makes I believe.

Thanks a lot Fred...I have more crap to try! Going to give it a shot on the SC-R this week. K only has 3 springs for it front and rear I can work with shock locations as well.

I thought I'd throw some lof my recent tuning experiences with the vintage car out there. I had been driving it around at home so no track and lots of concrete. Obviously a good setup here does not translate to a good setup at the track. It is an old RC10. I had blue springs in back and greens in front withe their mounting locations such that I had achieved balance. It was running 40W oil in rear and 50W in front. The car felt very nice and easy to drive. That is until...

At the track I got the car out there. My driving needs some improvement but the car was wrong. It was way too soft. You could tell the balance was good but it was bottoming like crazy. I was also getting a very bad push in the corners. There were other reasons for that though. Clearly changes needed to be made.

I did several things at once since I know the effects of each thing. First off I increased the spring rate by 15% all around which ended up with red springs in back and silvers in front. Just simply swapping them didn't quite give me balance. I had to move the top of the front shocks inward 1 hole to correct it. The interesting thing was that the drop test appeared to show balance. However when I pushed both ends of the car all the way down and then let go to watch the car rise, that's when I could see that the front rose slightly faster. Not a problem.

I discovered that I have the softest pack that I can get and sadly I don't have any other pistons right now. I need more pack so I am soon going to get some different pistons. For now I'll have to deal with the issue.

At the advice of my friend Marcus, I added weight to the car. I bought some digital scales to weigh all 4 corners at once and found the right side of the car to be heavier. It needed a quarter ounce more weight on the left side across from the receiver. I also strategically added weight in other areas as well. Yes the car is heavier than it was. It is also more balanced.

I finally ended up with 50W oil all around. Keep in mind that when I get a different shock piston, it'll end up lower.

I changed 2 other things. I was running a 30 degree caster block in front. The only other one I currently have is 15 degrees so I changed to it.

The rear roll center I changed a little bit. I moved the inner end of the tie rod up a hole to slightly lower the rear roll center.

My front tires are some hard compound rtr tires from Thunder Tiger so I'm suffering in the traction department in corners and will change those out next.

So how does it drive? MUCH better! It is so balanced over the bumps and turns much nicer but within the limitations of the front tires. It will still bottom over the big jumps but remember I am needed more pack. The added weight has helped quite a bit. This car is getting better and better everyday and I'm not done with it yet. Balance is always the goal and must always be maintained. In the end the weight I added was near the center of the chassis and a bit forward. Adding weight to a race car seems counterintuitive and obviously if adding a little bit is good, adding lots isn't necessarily better. Probably the contrary. Next up is a faster motor. I'd also love to get some big bore shocks. I'm pretty convinced that these are a must for anyone serious about performance. This old car is going to hold it's own with the modern stuff when I'm done. Of that I have no doubt.

Can I ask where you found your scales?