Intro

For those who don't know, In order to make your suspension absorb larger bumps, and to slow the rate of body roll, we use a thicker shock oil, with a higher viscosity ('thickness'). Or alternatively we use a shock piston with fewer or smaller holes in it.

Viscosity is like how thick a fluid is, for example water has a very low viscosity compared to honey that has been put in the fridge.

Lets compare Honey now with silicon shock fluid, with honey, if we heat it up it becomes very thin and has a much lower viscosity and when it is cooler it is much more viscous, silicon shock fluid will not do this whatsoever, for this reason, you cannot use motor oil or anything like it, as it does change thickness, silicon will not.



Now, to move onto using this knowledge to your advantage.

You never tune a stadium truck or buggy to absorb jumps, ever, they are designed such that the car will bottom out, and all of the force is absorbed by the chassis, NOT the suspension, this will not hurt your car, its how its designed.

The thicker you shock fluid is, the slower it will roll (body roll that is) and the less initial grip it will have. The stiffer the springs, the less total roll, and in theory less initial turn in.

The thinner and softer, the opposite.

If your car needs more grip at either end, you should try softening up the suspension at that end first (assuming the suspension has shock oil in it, cos shocks can be leaky, and if theres none, well use your imagination) by using softer springs , thinner oil, or larger/more holes in the shock piston.
Alternatively, we can use leverage instead. Think about a second order lever (a suspension arm levering a shock shaft), if we consider this, the closer the shock is to the chassis the less resistance it will offer to the suspension arm, if the shock absorber is mounted at the end of the arm, the tyre will have a force on it equal to the entire spring, but if it is mounted only half way up the arm, due to mechanical leverage, it will have only half of the force compared to mounting at the very end. Due to the suspension arm (when mounted half way down) having a 2:1 mechanical advantage over the shock.
So for minor changes (usually whats done at the track as the setup is probably right, we are just accounting for the conditions of the day) this can be used also.

Another thing to keep an eye on is that when the shock is mounted closer to the chassis, again due to leverage we can see that the car will have more suspension travel in both directions, particularly down.

If you have a good idea of geometry and the dreaded vector, we can quickly see that changing the angle of the shock also influences its resistance applied to the arm, if the shock is in a more 'layed down' position, the shock will also be in effect softer. There are a lot more complicated traits that each of these adjustments do also, like comparing traveled angle change for a more layed down shock (consider how the angle of the shock changes as the suspension compresses), but these are things only the hardcore racer needs to know and cares about. Not necessary to know here.

If the suspension at either end needs less grip, then all of the opposite above applies.

Now you ask why do you want less grip?

Consider this, the car ALWAYS has the exact same amount of friction applied to the road when it has the same tyres on it, because it weighs the same and has the same friction device (tyres), so changing suspension setup is all about balance, and applying that grip at speed, not getting more, so in order to get more grip in one end you can give the other end less comparatively.



For more minute changes, its possible to do this through weight balance very easily, simply lower the end that needs more grip a little, but again, this will change all handling characteristics, not just grip at one end.




Pack

Pack is the ability for a fluid to become turbulent.

Anyone who knows anything about aerodynamics will understand that turbulent flow travels much slower and with much more resistance that laminar flow (smooth flow).

And anyone who's been paying attention could see that we could theoretically get the exact same amount of dampening by using a large holed piston with thick oil, or a small piston with thin oil.

Where that comes into play is with whats called in the racing community as pack. Pack happens when the shock fluid hits a certain speed as it travels through the piston holes. When it reaches a high enough speed, it becomes turbulent, slows down, and therefor the rate at which the suspension can be compressed is slowed a lot too. so using a smaller piston and thinner oil will more easily achieve pack.

How is this useful you say?
When you do a series of jumps you don't want your chassis to slap, you want it to absorb your jump ready to accelerate towards the next jump. This is only really useful with a track that has successive sets of jumps, but achieving pack here allows the car to accelerate much quicker and smoother due to not well, bouncing :shock: .

But under normal conditions (aka not landing a jump) the suspension behaves perfectly as tuned, right up to the moment the suspension is compressed quickly and stiffens up. get it?

Anyways, if anyone wants clarification here, or another section on say, camber, and suspension geometry, just say here.


Simple geometry

Camber Angle
This is the angle of the tyres as opposed to the vertical angle, this is the top of the tyre leaning either towards (negative camber) or away from (positive camber; never used) the chassis.
It is necessary for a well handling car to have somewhere from about 2* to 5* and even upwards to 8 or 10* or negative camber on both the front and rear. Consider the car cornering and thus, the chassis leaning, the outside suspension is compressed and the inside extended, most weight is on the outside tyre and without any camber it, like the chassis is leaning over, now if we add some camber the tyre will be standing straight when we corner, giving much better grip when cornering.

Of course the ideal situation would be for the car to have reactive suspension meaning the tyre can be vertical all of the time, but it hasn't yet been invented.

Castor Angle
This is the angle at which the arms are kicked back (most importantly the steering but this is very hard to explain here). Look at the front arms of your stadium truck and note how there is a large angle there, now put it on a flat surface and turn the steering, note how the tyres lean (they give extra camber to the outside tyre) as you steer the car. They do as i just mentioned give extra camber, and this is part of the reason cars have this. You can change your castor angle using castor blocks, but if you actually are good enough to know when theres no point in me explaining what handling traits this effects. ;-)

Toe angle
Toe angle is the angle at which the tyres point in comparison to direction to the car is pointing, in other words the tyres do not point forward, on the rear the front of the tyres points a little towards the chassis and the front could be either way or straight.
In the rear, the more negative castor (points inwards towards the front) the more forward traction you have and the less the rear end wants to pivot around the front (aka sliding under throttle).
In the front, the more negative toe angle used the more high speed straight line stability and the more exit steering there will be.
As it gets straighter, and then gets to positive toe, the less stability the car has as the steering becomes more responsive with a lot more initial turn in.

Shock Angle
This has most to do with the hole on the shocktower you choose to use, weather it be a wider hole (less angle) or one closer to centre(more angle).
If you think about it and apply some basic trigonometry along with some vectors, you can see that a shock closer to perpendicular than another that is not, will be stiffer, but you will also see that as the suspension compresses, the shock gets closer to perpendicular by itself, try it, compress your shocks and watch them.
So with this in mind it only takes some common sense (or trig. if you'd prefer) to see that a shock thats more vertical will be harder sooner, so therefor be very reactive (good for bumpy and technical tracks) and a more layed down one, will get stiffer over a longer period of time as the car rolls, so this is smoother and better for smooth non technical type tracks.

Roll centre
This is a very difficult to explain thing so for now i will just explain how to adjust it and what this does.
The camber links on most cars can not only be changed in length but position, this change in position can help in a few ways but for roll centre, the important change is the height of the link at the bulkhead, if you lower this position, It actually raises the roll centre, thereby giving it more aggressive feeling suspension and a lot more initial bite from whatever end you did this too, the opposite is also true.

Droop
This i find is extremely important when setting up a traxxas stadium truck to race. Droop is how far the arms extend out when the car is lifted from the ground as opposed the extension when static on the ground. This is hard to explain but i will try.
Consider that with a lot of droop, when cornering, the chassis rolls, the outside arms are pushed up as the suspension is compressed, and the inner arm is extended as it decompresses. If you add droop limiters to your shocks, this inside arm cannot lower, meaning that that side of the chassis can not roll to a higher point it must lower and the outside wheel does. Try this, go to your car and twist the car so the suspension is how it would be when cornering, now, push the car down, while still holding it twisted, until the inside arm (the higher side) it parallel with the chassis, as if the arms droop were limited to parallel. You will see the whole car is lower, and the car has now rolled less than before.
Therefor we have a lower CG and more tyre surface area on the ground.
With a Traxxas, it is very important to limit the droop when racing, this stops the car from raising (particularly in the rear) as it corners, and stops that dreaded spinning traxxas ST's do.

How to adjust droop in your ST
Seeing as how Stadium trucks do not have droop limiters standard, the easiest way to adjust droop is by using fuel tube underneath the shock piston, inside the shock.
Seeing as how droop is how far the shock shaft extends multiplied by the ratio at which the shock is attached on the arm (if it is 1/2 of the way up the arm, travel will be shock travel times 2, if it were a thrid of the way, it would be shock travel times 3), the easiest way is to physically limit how far the piston can go down the shock body and therefor how far the shock shaft may extend out of it.
You must take the cap off the shock, take the piston out and slip the fuel tube ove the shaft, pushing it down and reattaching the piston over the top, reassemble the piston and then pull on the suspension arm to ensure the tube is at the very top of the shaft. Remember to use the limiting calculation above, if the shock is mounted a third of the way down the arm (that is, with one third of the arm in between the shock and the chassis and two thirds on the other side, between the shock and the wheel) and we use 5mm of tube in the shock, we must multiply it by three to get our total droop limit, 15mm.



Cheers,
Dann

I was hoping for maybe a sticky here?

No?

And yeah I did write this myself.

Cheers,
Dann

WoW, most cool[sm=thumbup.gif],, whats a good set up 4 skateboard park bashing

Well you'll want a lot of pack, but also a stiff package anyway, if you use full downtravel you can still have a lot ride height without breaking your car as the suspension will extend to full length in the air anyway, so don't worry about having to have it high.

Go maybe a bit smaller pistons than stock and 50 weight oil. This should result in good handling and the pack required for the skatepark jumps. if it isnt stiff enough for you still use smaller pistons not thicker oil. then you have more pack.

Very nice. I second this to be a sticky, maybe the camber and the suspension geometry will get you that sticky.

Yeah ok.

Ill do that and then ill repost the WHOLE thing in another thread when i've done it
this one was a bit of work im not in the mood for another part atm.

Any mods here that can actually say?

changed my mind, i updated.
So anyway, is there a chance of a sticky mods?

thanks 4 the good info, very informive, gives me a better understanding of how shocks work, see,,,u can learn something new every day,, not sure what a sticky is but it sounds positive, good luck

great post filled with info...

one thing i am confused about in your post is this:


the parts that are Bold sound contradictory...
please explain...

sorry ill rewrite it, I'm saying that if the shock absorber is mounted at the end of the arm, the tyre will have a force on it equal to the entire spring, but if it is mounted only half way up the arm, due to mechanical leverage, it will have only half of the force compared to mounting at the very end. Due to having a 2:1 mechanical advantage over the shock.

Hope that explains it better for you.

It wasnt contradictory, just badly written :P
hahaha

Dann

come on there has to be one mod whos read this and can give me feedback as to the sticky.

Great post. Very informative. I always wanted to know how you adjust droop on a S/T like a GT or a XXX Etc?

Stadium truck droop limiting was added to the end there, sorry for not adding it in the first place.

Cheers,
Dann

Hey Dan i am going to link this to your other thread and show this to the that one dude...
BTW AWSOME POST! Looks like my "choosing you first R/C" one. Just add some pictures here and there where you can!

good point, i dont have a digital cam. But ill add some when i have access.

sticky bump

Wow thanks. [8D]

How do i get in contact with a mod through email or whatever anyway?

Just PM one..

A lot of good info here it's very helpful i'm going to try some of the stuff you talked about.

Seconded, sticky bump! Very informative, should keep me busy playing with the settings this weekend.

Thankyou guys, but i cannot PM. i dont have the priveleges, maybe thats telling me something why i cant get stickied...

I will do it for you then

Thanks man. :-)

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