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Car Tuning

Old 03-15-2007, 08:19 AM
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Doahh
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Default Car Tuning

Stadium Trucks
Contributor: Danthenitroman

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.
Old 03-15-2007, 10:56 AM
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2916jr
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Default RE: Car Tuning

thx doahh we needed one of these
Old 03-15-2007, 12:32 PM
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xenergyx
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Default RE: Car Tuning

So is this going to be a continuing thread with car tuning tips or is this just for Dan's post?

Either way [sm=thumbup.gif]
Old 03-15-2007, 06:53 PM
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dannthenitroman
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Default RE: Car Tuning

No idea, but THANKS

Ill add more as people ask okay.
Old 03-15-2007, 07:04 PM
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dannthenitroman
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Default RE: Car Tuning

Hang on, not to complain but wouldnt it have been wayyyy easier to just click sticky on my other thread, that way i can actually modify it and add more?
Old 03-15-2007, 07:19 PM
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xenergyx
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Default RE: Car Tuning

^^ yeah that makes a little more sense...

And also since this is sort of directed to ST it should be in that forum...



I dunno...

If I came here for the first time needing help with my car/truck not knowing anything about the site and the first place I went was the General forum and I clicked the thread "Car Tuning" and all it had was ST suspension tuning tips I would be a little dissapointed.



On the other hand.....

If the plan is to add everyone's personal tuning tips to this thread so that it is eventually a large compilation then I can understand the reasoning for the new thread/location.
Old 03-15-2007, 07:31 PM
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dannthenitroman
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Default RE: Car Tuning

But that wont work unless the posts are filtered. you cant really have a racing suspension tuning section written by more than one person, unless like added to that first post was a new section written by someone else entitles touring cars etc etc...
Old 03-15-2007, 10:26 PM
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Doahh
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Default RE: Car Tuning

Guys it will be added on to and it is way more practical to put it here so the ELECTRIC stadium trucks can also be applied to it too.
Old 03-16-2007, 01:12 AM
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dannthenitroman
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Default RE: Car Tuning

Actually hes very right. maybe put ST in the title and add ist suspension not engine.
Old 03-19-2007, 09:40 AM
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gam
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Default RE: Car Tuning

Doahh
Thanks for the info. Been racing for some time and I find you can allways learn something new in car set up.
My question is on Droop
Will it also apply to TripleXT? We have a group of guys that run evey Tuesday and Thursday night on an indoor club track. Due to building size we run on a short but fast carpeted track with only 1 jump. I'm temped to try droop but don't want to waste my time if the set up is not going to help handling with regards to the track conditions I have explained.
Please advise.
Old 03-19-2007, 11:54 AM
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Default RE: Car Tuning

Doahh
With regards to my last post question with the Triple xt. Wouldn't sway bars accomplish the same thing. In other words help keep the car flater in turns.
Old 03-19-2007, 02:11 PM
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mattnin
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Default RE: Car Tuning

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.
I disagree with this statement. It is more accurate to tune your truck or buggy to the majority of the track. If there are a lot of jumps, you need to tune your vehicle to it.

Also, the chassis may be designed to bottom out and not take severe damage, but this is a very inconsistent way to race. When the chassis bottoms out and slaps the ground, you lose traction and can cause a very unpredictable situation and spin outs. This can make the difference between winning or losing.

I am not advocating tuning your vehicle because of one big jump, but if you have many big jumps where your chassis bottoms out, tune your suspension to absorb them.
Old 03-19-2007, 05:49 PM
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gam
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Default RE: Car Tuning

I agree with the bottoming out issue. Even with one jump. My set up was wrong and I did bottom out, and lost a consider amount of time. Changed set up and really didn't lose any time on corners and inproved time without bottoming out.
Old 03-19-2007, 10:33 PM
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dannthenitroman
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Default RE: Car Tuning

Ok i agree, but you guys get it. This was written for noobs, and i have seen sooooo many just use heaps and heaps of shock collars to make it 'stiffer' and stop it bottoming out and they handled soooo badly. Its just terrible to watch and they WONT listen so sure their car will just shatter, and not realising that this 'stiffening' method is in fact not helping it land at all.

On the swaybars, yeah swaybars do a similar thing, but swaybars do not help the car to lower as it turns, yes adding droop limiters to your car should help its handling on a smooth surface and help it change directions quicker. Swaybars are a very good invention but if there are any bumps or ruts they will limit grip a lot.

i general though, if your ams already are limited in down travel in that they cannot go past level, then theres not MUCH point limiting droop anymore.

Any more questions or comments?
Old 03-19-2007, 10:43 PM
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mattnin
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Default RE: Car Tuning

Yea I get what you mean. I am not knocking you in any way, I admire that you took the time to write all this. Often noobs (I was one at one point) stiffen their springs to remedy chassis slap and end up making it worse for the rest of the race. This is wrong, chassis slap should be fixed by using thicker shock oil and/or removing droop limiters (i.e. increasing shock travel), not stiffer springs or tightly compressed springs.
Old 03-20-2007, 10:18 AM
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Default RE: Car Tuning

doahh
Thanks for the info. I really like that you took the time the do a thread on motors, gearing, brushes, etc, etc. Like I said you can allways learn something new, and if it were not for guys like yourself taking the time to post this info we wouldn't be able to learn.
Old 03-27-2007, 12:21 AM
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dannthenitroman
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Umm.. that was me actually... [8D]
Old 03-29-2007, 08:42 AM
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Default RE: Car Tuning

ORIGINAL: Doahh

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.
For the sake of accuracy, I must debate these points here too.

The thicker the shock oil, it will have the same turn in as it would with softer oil, but then immediately after the truck will plow. So heavier oil affects mid-turn, not turn in. Also heavier springs will cause your truck to have more turn in as well. Softer springs will cause the roll rate to increase so the truck reaches mid-turn quicker but at a trade-off at initial turn in.

Also, if your truck needs more grip at one end, it isn't always wise to just soften it up. It is important to look at the handling properties of the entire truck. If your truck is already soft and one end does not have grip, that means the other end has too much grip, so the other end is too soft, so stiffen the opposite end to bring the truck to neutral steer and achieve balance.
Old 04-04-2007, 09:56 AM
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Default RE: Car Tuning

Also it would be a good idea to add on how to tune pack for a race.

Pack is adjusted by changing out shock pistons. There are different pistons that give different hole sizes. A larger holed piston will give less pack, a smaller holed piston will give more pack.

So how do I know what piston to use? Well, it depends on the track of course. Obviously, you will need more pack if you are having huge jumps with no landing slope. This means your truck is just landing on the ground hard. Use smaller holed pistons here. If the track is for the most part, smooth and good jumps where you are landing on a slope, no real chassis slapping anywhere, use larger holed pistons.

So basically if you are using large holed pistons with 35Wt oil but find out you need more pack. Try using smaller holed pistons and 30-32.5 wt oil. Or lets say you are using small holed pistons and 30 wt oil, but you are racing at a smooth race track, go up in piston hole size and drop oil weight a bit.

And remember to tune your pack to the majority of the track. If you have just one awful jump but 95% of the track is smooth, use larger holed pistons. If the entire track is crappy jumps, use smaller holed pistons.

More pack can be detrimental to the handling of your truck. High pack can cause your truck to skate around on the straights or through washboard/hazards. This is because the truck tires are never allowed to fully rebound to get the best grip.
Old 04-13-2007, 07:18 AM
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MarkHocky
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Default RE: Car Tuning

Top article on one of the most difficult topics. I think a lot of the info is relevant for all types of racing not just ST's.

I am new to RC, but know a little about cars, and wanted to add some more about the notes on camber:

The comment about wanting negative camber is spot on, but it is not just about chassis roll. If you think about the lateral (sideways) load on the tire during cornering, it sort of wants to peel the tire away from the wheel. This lateral load causes uneven loading on the contact patch of the tire by biasing the load towards the outside (with respect to the corner) of the tire. By adding negative camber, when going straight the load on the tire contact patch is biased, but as the lateral load increases during cornering the tire deforms causing the load to be spread more evenly, and hence increasing the cornering performance of the tire. In a full size car having high levels of negative camber limits braking performance in a straight line, but this shouldn't be an issue in the RC world (provided you don't have front brakes!).

Chassis roll and suspension geometry is important because as the chassis rolls and the suspension compresses, the orientation of the wheel with respect to the road changes usually tending towards positive camber (as described in the original post). So what you want is the tire to lean in slightly (negative camber) during cornering, and this can be achieved via camber gain (depends on the suspension geometry, in particular the length of the upper control arm versus the length of the lower), or static camber (what we're interested in).

One last point of interest:

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.
A beam axle behaves like this because the wheels never move with respect to the road, but they aren't ideal because they don't handle single wheel bump very well. Ideally the suspension would provide the perfect amount of camber at each different cornering speed/body roll condition. The problem is knowing what the ideal amount of camber is, because it is highly dependant on the tire characteristics, which are probably the most complicated thing on the car!

Sorry didn't mean to get so nerdy, but i find this stuff interesting. Once again top article, suspension tuning is so confusing because everything is inter-related.

Cheers all, hope you found this interesting/informative.
Old 05-13-2007, 07:18 AM
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M3IZD
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Default RE: Car Tuning

Can some one help me? I have a HPI Savage with the 4.6 big block engine and using 20% nitro fuel. I keep burning out glow plugs after about 10mins runing? I know this is not correct, please if any one knows why can they give a posible solution to fixing this?
Old 05-25-2007, 07:41 PM
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_Lucas
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Default RE: Car Tuning

yer probly starting youre own thread would be much more helpful than asking for help in a stadium truck suspension tunign thread.....
Old 06-17-2007, 06:40 AM
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Default RE: Car Tuning

That's a good point I agree with you. At a course with a load of jumps I tried my suspension soft.
My chassis got bashed around heaps.
Old 07-27-2007, 11:46 PM
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Default RE: Car Tuning

Old 08-04-2007, 04:10 PM
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Default RE: Car Tuning

if the car is running to hot will it burn the exhaust off if not what will cause it to melt the exhaust

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