Hideeho
What is the difference in handling characteristics between having your instant roll centers ouside the wheels (top link angled up toward the chassis) vs. having instant roll center inside the wheels (top link angled down toward the chassis). I'm guessing the roll center can be goten to the same point, but the roll resistance (right term?) and camber gain will be different. what will the those differences be? which would be preferable & why?

If the top link and suspension arm are angled away from each other, big end of the triangle on the chassis, you should have some serious problems I would think. For the suspension to move, it would basically want to flip the hub/wheel over flat, and wouldn't have much suspension travel at all.

At the very least, just a slight amount of it, you would have camber loss, instead of camber gain. When the wheel leans into the car as the suspension compresses, with this set up, it would be leaning out. I can't imagine there is a scenario where that would be good, perhaps some extreme edge case.

I did the spring balancing to both my scte, one of the lightest ever built, and my sons tlr scte. Tho it took 4-5 hrs toget both set up and have a stiffer option for tuning, I went with the absolute softest I could get on mine and my sonsi just looked for balance on the lighter side of stock since his truck had about 8oz removed from stock . Both trucks r amazing to drive I will say I got my scte about a pound to lite cause it just wouldn't hook up but it could be fast if smooth . Only thing with the softer setups was big jumps . Having to keep oil thin enough to react to the bumpy areas u really, or I didn't want to go thicker to keep it from slapping on landings . So can I get a explanation of pack and order of importance for finding oil viscosity. I'm sure its within this thread but .... loving the thread lots of info

http://users.telenet.be/elvo/
Not sure if you have seen this site, but I found it a nice reference to the concepts discussed here. The site is mirrored on two urls I believe, one of them has a downloadable version. Under Suspension > Page 2 it discusses fluid dynamics, which explains pack, and how to achieve different levels of it.

A lower viscosity oil with smaller piston holes, vs higher viscosity with larger piston holes, will have the same static dampening. Which is the dampening when say you press the car down on your work bench. But when the suspension compresses very fast, like landing off a big jump, the turbulence caused by the high velocity of the oil going through the piston holes, creates pack. That is it takes more energy to compress the shock. This happens to a greater degree with the light oil and smaller piston holes, as the oil will be moving faster through the piston holes for a given speed of compression. Check the site out, it explains it in more detail along with a lot of other things.

I'm not an engineer but I have slept at a Holiday Inn Express so here is my 2 cents. What you have started out at sounds good. If you can build the car lighter than what the rule book calls for then you can always add weight front or rear to achieve the balance you want.

Something is telling me I'm about to lose half of you to the voices telling you that what I've written must have come from the mind of a complete idiot. Maybe it did! I've come to some very backwards sounding conclusions as of late but they all seem to make sense after really thinking about it. Studying the unique Nissan Deltawing race car project has confirmed many of them and made me think differently in regards to others.

The further rearward the center of gravity, the easier it is to turn the car. You've got tons of leverage over the bulk of the weight. Moving weight backwards favors oversteer while moving weight forwards favors understeer. Heresy! You're an idiot! Stop spreading such lies!!! I know it sounds strange so hear me out.

I know when people complain that they don't have enough steering or front end grip the usual advice is to add weight up front, shifting the cg forwards. The importance in this isn't in the fact that there is more weight up front but rather what is happening with the effective roll stiffness. I've found with 2wd buggies that when a balanced spring rate is used, the car will have a high tendency to oversteer under braking while understeering under corner exit acceleration. I believe some of this has to do with the excessively high amount of front end rake run on 2wd cars which has also led me to believe that we really don't need much of it.

The snap oversteer tendency during braking shows that the car definitely has no problem getting the front end to steer into the corner. The inside front tire may lift during acceleration coming out of a corner though. A greater amount of front end rake only makes this worse due to excessive weight transfer. However the real issue is the amount of roll stiffness front to rear. The front has too much of it and the rear too little. Remember I'm talking about a rwd car with about 70% of it's weight on the rear.

The solution many would say is to run more weight forwards. This actually isn't a bad piece of advice but not for the reason most think. What is really happening now is that the added weight on the front has more leverage over the suspension. It is effectively lessening the front roll stiffness. Taking that weight off of the rear is lessening the leverage on the suspension system effectively adding roll stiffness. The static weight increase up front isn't holding the front wheels down based purely on weight. It's what is happening leverage wise through the suspension and roll resistance that is important. What happens if you have a very high amount for front roll stiffness such as a thick sway bar up front? The car understeers. What happens when you reduce this? The understeer tendency decreases or goes away. When shifting weight forwards, we are effectively doing the same thing. The added mass more easily affects the roll of the vehicle. The car no longer understeers and we gain cornering power. It's simple to understand when you think of it that way. It's not just weight "holding the wheels down" that causes this.

Another thing affecting the roll stiffness is the track width at each end. Wheels further out have more suspension leverage. Moving the front wheels inwards for a narrower front track width would also have the same effect as decreasing roll stiffness and this is why the Deltawing works so well. With all of the weight on the rear, it has a very narrow front with nearly zero front roll stiffness. It corners wonderfully and would actually corner worse if it had a wider front end. The key to it is the fact that so much weight is at the back. If the center of gravity were farther forwards, that car would be a disaster with such a narrow front end. This is why 3 wheeler offroaders and most other 3 wheeled vehicles (where the single wheel is doing the steering) have historically been so unstable. It's not the fact that there are 3 wheels but rather where the weight was centered.

The problem for us in off road is that we need our wheels pushed all the way outwards towards the corners since we need the stability over bumps and jumps. Narrowing the front on a heavily rear biased car may be fine for on road but for off road it's benefits are going to be more than offset on anything but the absolute smoothest of tracks.

So then you may gather that since we have wheels all the way out as far as legally possible, the best option is to run a near 50/50 weight balance. That may be fine for a 4wd car but on a 2wd we need weight on the rear wheels for traction. This is a problem for mid motor cars and the reason why many mid motor 2wd cars don't hook up well on slippery tracks. Also, if a true 50/50 balance were achieved, I'd personally argue in favor of all 4 tires being the same size rather than narrower up front.

What then can we gather from all of this? 2wd, no matter what, is full of a high amount of compromise. 4wd is far more optimal. Basically with 2wd the weight goal should be not so much any particular static number but rather only as much rear weight bias as is necessary to get rear traction for your track. If you are running max rear antisquat then it really tells me that you've got too much rear weight bias and could benefit from shifting weight forwards, re-balancing, and running less antisquat. If you can't get enough rear traction then shift weight rearwards. If you can find a way to play with front end rake, I'd highly encourage it. I am no longer a believer in 25* rake and I'm definitely no longer a believer in high amounts of steering caster. It's not doing what you think it is. More on that later.

For now, think about it all and either come to the conclusion that things happen for different reasons than most think they do or that I'm just a complete rambling idiot. Either way is fine!

I have always thought that the lighter the front the.more responsive initially thus having more steering feel. And a heavier front would make it lazy and less responsive lacking it feel like it has less steering . Is their any truth to this? Now this thinking came from my on road rc racing logistics. Off road I see how heavier makes a lil more grip but it takes a sec for it to "catch"

I'm no expert, just hear to learn, so take it as you will, but here are some thoughts based on what I've gathered so far.

This reminded me of a rickshaw, with all the weight over the rear wheels making it easier for someone to pull. Also, if you've ever driven a Ford Bronco, to me, when turning, they always seemed to pivot around the rear wheels, instead of somewhere towards the middle. Which imo made them a bit scary to drive, felt easy to tip over, in a 3wheeler sort of way, and too sensitive to steering input or twitchy.

Would agree here, the rake promotes front end dive, opposite of anti-squat. One concern would be lowering it, with the inherent lightness of the 2wd, it might bring up issues with approaching bumps and jumps. With out the added weight, like in a 4wd, and the decreased angle on the suspension, it could have more of a jarring effect. Basically the side effect, less dive, vs ability to handle bumps would be my concern.

Not sure the as wide front would be needed. Since the front tire is only dealing with turning. The rear tire is dealing with side grip and forward grip. A tire only has so much grip, the rear tire has more traction needs, than the front, during acceleration while turning at least. Toss in more unsprung weight, and rolling resistance, and I would think the compromise would outweigh the gain. In 4wd its a bit flipped on this perhaps, has more to do with the front needing less steering traction, since they are driven wheels compounded with the added weight over them?

Thanks again for this thread, it's been very interesting and informative.

A rickshaw has a very high center of gravity directly over the rear axle. The whole point of it's design is to take the weight off of the person pulling it. A Ford Bronco too has a pretty high center of gravity. Add a short wheelbase to it with a soft suspension and it will get a bit unstable. The thing that nearly all unstable 3 wheelers have in common is a high center of gravity. Obviously in offroad we prefer to have 4 wheels and I'm not condoning removing one of ours. The point is that what makes a 3 wheeler inherently unstable is not the fact that it has 3 wheels but rather where the center of gravity is placed. Not only front to rear but also vertically.

That's not heresy, that's standard vehicle dynamics.

When you move the cg forward, yes the vertical load on the front tires increases but the coefficient of friction for a tire actually DECREASES. For example:

Say a tire with a 1 pound vertical load has a friction coefficient of 1. Increase the load to 2 pounds, it might drop to .9. Lets see the effects of this:

A 4 pound car with the above tire on all four corners and equal static weight distribution would have a 1 pound vertical load on all four corners. 1 pound vertical load times 1.0 friction coefficient times 4 tires means the car has a maximum potential lateral acceleration (cornering force) of 4 pounds. So this car should corner at 1g (4 pound car). Of course, weight transfer and other factors means the car will never reach that maximum but let's ignore all that for now.

Now let's increase the car's weight to 8 pounds. Now each tire has a vertical load of 2 pounds, times a .9 coefficient of friction means each tire now can generate 1.8 pounds of cornering force times 4 tires equals 7.2 pounds total. So as you can see, the total grip has gone up but it has NOT gone up as much as the weight has since this car now weighs 8 pounds. 7.2 divided by 8 yields a maximum potential cornering ability of .9g. This is why lighter cars can corner harder than heavier cars, all else being equal.

So what about moving weight instead of increasing it? Well, if you move weight forward, yes you are increasing the vertical load on the front tires and therefore the grip of the front tires. But, you are also moving the cg forward, meaning the front tires will be "pushed outward" with more force. The amount of grip the front tires gain is not as much as the increase in outward lateral force. In addition, the rears are losing grip but not as much as the lateral force on them decreases. Therefore, the car gains understeer.

Now I can hear many people screaming, "but that's opposite from my experience." Well, there are circumstances that can cause opposite results, especially in offroad dirt racing. For instance, moving weight rearward can improve forward grip, reducing wheelspin and thus reducing understeer when on power.

Also, all those funny spikes, knobs, treads and whatnot in our tires combined with soft dirt can result in a tire's coefficient of friction increasing instead of decreasing with increased vertical load due to the spike being driven into the dirt more. This is actually pretty rare since most tracks are quite hard but in mud or sand, it can happen.

There is another situation that can cause reversal of the effect but I don't feel like mentioning it since it will only start an argument and it's only masking another problem rather than being an actual solution.

I totally agree, also that the weight over the rear wheels makes them easier to turn. Like the barbell analogy. With the weights at the end, its harder to get moving, if you are rotating it, but if the weight is in the middle, it is fairly easy. Reminds me of a zero turning radius reel mower I used to use, though the 3rd turning wheel was in the back, all the weight was down low near the 2 wheels. You could spin circles no problem, and never get the feeling the mower was going to tip, it would throw you off long before that.

f1 teams were exploiting the rear bias for years, peaking in the mid-2000's. now, their balance is fixed by the rules - 45.5-46.7 percent front, 53.3-54.5 rear.

when you say "rake" are you referring to the front kick-up, not the front-to-rear rake of the floor?

Saw the thread "Tune with camber links" and thought maybe I can learn something. I thought I would sit down and read a couple pages, stopped at page 41. Hope to finish the rest of the thread after I finish this post.

Thank you Fred for enlightening me with some great information. I started with my Serpent 811T e-conversion. Got balanced and now I am working with the links to pick up a little more steering getting into the corners. The truggy drives fantastic and is very stable. Next comes my RC8BE.

Thanks again Fred and everyone else for all the great information.

Neil

I've read a lot about shock angle changes that are perpendicular to the chassis but what would be the effect of parallel changes?

In the case of the 'coming soon' B4.1 big bore shocks the bottom mount will not change but the top will be spaced out making the front shock lean backwards. The rear tower will likely require similar spacing.

Just thinking about it logically it seems like the shock pistons will have increased friction inside the shock body because the angle between the arm and the shock shaft are farther from perpendicular. I'm not sure how far off the angle is on the stock buggy, I was just curious about the setup guru's thoughts on this.

There may some difference but it won't be nearly as much as the orientation changes during normal suspension travel.