If anybody has any questions as to tuning on your car I am open to help. I can provide a wide array of both practical as well as theoretical answers to your questions.

S & B

thats great! only problem is..who in the heck are you? we have danny B and a few others offering advice..we know those guys..if you choose to remain a mystery some may not trust your info? :(

I choose to remain anonymous for now. I can assure you that all of my answers are based upon years of experience as well as a detailed level of knowledge, based in TRUE vehicular dynamics. If you do not want to trust my answers because you do not know who I am that is fine.

But, I assure you that just because somebody has a name in this industry; it doesn't mean that he knows what he is talking about. There are plenty of fast racers that claim boat loads of knowledge, yet 70 percent of what they explain is completely unfounded in any true understanding of vehicle dynamics. I do not argue that there are individuals that might help you out, giving out there opinions based upon their practical experience.

There is nothing wrong with that, pragmatic advice is as powerful as any advice. I wish to offer advice and help based more on applied theory. Specific practical advice may only work in one circumstance, only a true understanding of theoretical applied vehicle dynamics can extend to all cases at all times.

Oh,
As far as I am concerned I will take a Known Fast individuals Practical Experiance over anybodys theorys! :D
See Ya! Lee :cool:

Ok S&B, I have something that I need explained. The heavier the side skock the more on less rear bit will you get. I have heard this both ways and would welcom another answer. :thumbsup:

here is another mystery to me anyways..

last weekend we ran a snowbirds size track same carpet flat oval..

most of our cars came back on the scales with maybe 1 or even -1 ounces of wedge on the left rear..a few select cars that were realy fast came back on the scales and had -5 ounces of left rear weight..or 5 ounces of what i would call reverse tweak..

the theory i have always had blasted into my skull year after year was..the left rear tire is what drives the car up off the corner? scales dont lie? so what is the dealio with the current wedge theory in oval?

btw good avice is good advice..theories look awesome on paper and work great on the cad programs..they do not always transfer over to out little cars equaly as well as there full size counterparts.. but you are a expert so you know all this anyways,lol.

how can I fix a push from the center of the corner off. i am driving a TC3 running 19t

how many licks to the center of a tootsie pop? oops lol

FL Flash, I'm not disagreeing with you, practical advice is very valuable. To say I would take it anytime over theory is a little far fetched. Just remember, I am not downing practical advice, there is plenty of it anywhere you go. I am just trying to offer up something that more or less doesn't already exist.

Larry B, you pointed out one of the ever lasting mysteries, side shock springing. The answer is not a cut and dry one. One thing we do know is that R/C car tires do behave similar to conventional tires; Meaning that the property of load sensitivity does exist. How do we know that our tires behave as conventional tires? Without going into pure tire theory, I will say as practical example, if you put more wedge in our cars (more LR/RF weight), it will tighten a car up.

Load sensitivity in simple terms is that as a tire is more heavily loaded its traction coefficient drops. This is to say, as a generic example, if a given tire with 16 oz. of load makes 16 oz. of lateral grip (=16oz lat/16oz vert=coeff=1). Now if that same tire is loaded with 32 oz., it will now only make 30 oz. of grip. (=30oz lat/32oz vert=coeff=.937). This property is what allows us to tune our cars by changing the dynamic weight transfer.

So, by that simplified theory, more roll resistance across the rear would lead to a higher percentage of the roll stiffness distribution to be carried on the rear. With more roll stiffness distribution carried in the rear a higher percentage of the lateral load transfer, would be carried about the rear tires, the rear tires would be come more unevenly load resulting in the car being looser????? Right? Well not really.

As we already know, this does not work like this in reality. The question is why? Here is an example where a simplified theory yields the wrong answer.

The reason why softening the side springs actually works to free a car up is mostly a transient handling property. As the car initiates turn in, lateral forces are developed before a car takes it's full roll angle set. Therefore, the properties of the roll balance (front/rear) of the car(tight or loose), don't take there effect until car establishes its full roll set, which often never occurs on a short flat track.

Under initial lateral force build up (the front tires forming slip angle as they are steered) the car begins to rotate or yaw, the amount based upon three major variables, front tire grip, CG location and aerodynamic side and downforce centers of pressure.

With softer side springs, these effects are more pronounced for reason that the car takes a longer time to get into it's steady state roll angle and therefore steady state balance set (which is a function of a number more variables but also including those listed before).

Our RC oval cars are heavily rear biased in weight (55-65% rear) so there natural transient handling tendency is to oversteer. The longer the delay for the car to achieve a "tighter" steady state set, the more the car will continue to rotate into a corner a quite possibly continue to rotate past center.

This is a common situation seen in modern Winston Cup racing situations. However the situation is found in reverse form. With Winston Cup cars, the majority of the roll stiffness distribution is handled by a large front anti-roll bar. As the front anti-roll bar stiffness is increased, often one will find that the car actually turns (rotates) better. This is based on the same transient handling concept, but on a different end of the car.

This is not the easiest thing to explain on paper, but one can see especially on a flat track, a car that is softly side sprung, seems to cut more aggressively into the corner and through the center, and if enough yaw momentum is built, the car will actually carry that yaw momentum all the way through the corner.

The best known example of this is a Rally car or dirt track car, the initial steering input creates enough of a yaw moment that the car builds yaw velocity quickly on entry and the rest of the corner is used trying to reduce the yaw velocity to get the car back strait.

Hence the reason why guys such as Ryan Newman and Tony Stewart (guys that are used to transient loose on entry set-ups) have been so successful as of recent in Cup. Getting a car rotated on entry allows one to run a tighter steady-state set-up, which assists in laying down power earlier and more efficiently off the corner.

A lot of these set-up factors are heavily influenced by driver preference. Drivers who prefer a tighter entry set-up give up a lot of speed middle and off of the corner and often complain that they are too loose in, too tight in the center and too loose off.

I can elaborate more on a lot of this stuff but I ought to stop and make sure the explanation up to this point makes any sense to you guys. To summarize in practical form: As a rule of thumb, the less traction that exist in the track the softer you want a car sprung in order to slow down the transients of the car (or to make the car more forgiving to drive). As bite comes up, one wants to stiffen a car as to avoid excessive roll angles and a sloppy handling car.

S & B

Remember, theory isn't wrong, theories are wrong.

ok,here's 2?'s
1-why are we having to run such softer side shock springs now with the new BSR cap tires?
2-leading the caster with the RF does what?
3-IYO,moving the left rear in WITHOUT moving the RR out does what?

katf1sh,

The consantacy that the numbers repeat on the scales before and after the race is a factor of tire wear. If the car comes back with less wedge than the car has worn more reverse stagger across the front than across the rear. This can be an indication, but not always, that the car is too tight.

I know that when one runs low wear rubber (pinks or purples) on the left front with standard wear RFs (black) that the RF will wear more, even if the car is neutral.

To further answer your question I would have to know what compounds everybody was running.

If everybody was running the same compounds, the better cars are wearing there tires more equally, one factor that could indicate a better handling car.

One other possibility, is that the better cars have less kinetic friction in their suspension, which allows the car to more easily maintain its wedge value on the scales.

Lastly you are correct, the LR on are cars have the closest distance to the cars center of gravity, thus the least amount of lateral moment about the car's CG. Thus, you are correct the LR tires primary roll(percentagewise) is produce longitudinal or foward traction.

S & B

davepull, I need more info, what does the car do on entry, most problem center off are aggravated by a corner entry condition, and are often caused by over driving a car on entry (not allowing it to rotate getting to center).

I am also asuming that your problem is occurring on power. On power pushes can be fixed with a variety of changes. But lets get the root cause of the problem figured out first and then we can formulate a better answer.

S & B

my eyes are bleeding..... :roll:

DK47, Without any experience with the new BSR caps, I can only venture a educated guess. My guess would be that the new BSR cap tires construction is different, which makes the traction build up (lat force/slip angle=cornering stiffness) of the tire slower. The slower build up in lateral forces make the tire behave more as if an old bias ply tire acted.

With the slower build up in lateral force it gives the feel as if the tire has less grip (or what we refer to as grip, which is called the cornering stiffness of the tire by SAE definition ('Milikan and Milikan, Cha. 2')). This increased time it takes for the tire to build grip makes one have to slow down the transients of the car to make the car feel as if it is more "into the track" and less as if it were driving on ice.

If I could get more information as to what the compound or construction changes were with the new caps I could probably give a more refined answer.

S & B

benifit of larger spur off corner?
is 120/36 better or 108/32 both are 3.3

thanks TJ

toytowne, The biggest effect of the the gear size has very little to do with the inertias of the gear and or reduced friction of meshing larger gears. I agree with Cliff Lett's fundemental philoshpy that a gear ratio is a gear ratio.

It is my opinion, but not easily provable, that the largest effect, is the position of the motor in the car. A larger gear would push the motor foward in the pod and foward in the car which in a general sense is a positve effect in two ways.

First it reduces the car's polar moment of inertia by placing the motor closer the the CG. Secondly, it decreases the pods inertia which allows the rear unspung inertial weight to better soak up the bumps in the race track.

As always, there is always a place and time and a specific example where you would want more rearward weight distribution with a higher polar moment of inertia and/or a more inertialy heavy rear pod.

There are no absolutes in racing, so there are never absolute answers. This might be left in the same realm as what pinion angle does in a stock car or a dragster. No real solid theoretical answer as to whay it gives more foward bite, but it always seems to give more foward bite???

I would be curious as to what others thoughts and experiences are with different gear sets.

S & B

WOW, You can lay down a explanation to anything Dude. I have to agree with pancartom, my eyes are bleeding also.

S + B = Switchblade??

Are you coming to the 'BIRDS???

Mike,

S & B, Switchblade, no. Skull & Bones. Like the secret society, except with a K. Not sure yet, depends upon that other track's race in Florida about the same time.

S & B

Friggin' excellent!!!!

DAYTONA??

:cool:

S&B,
Didnt say practical advice! BTW,Experience is PROVEN theory :) But getting everyone thinking is a good thing.
Later, Lee

davepull, I need more info, what does the car do on entry, most problem center off are aggravated by a corner entry condition, and are often caused by over driving a car on entry (not allowing it to rotate getting to center).

I am also asuming that your problem is occurring on power. On power pushes can be fixed with a variety of changes. But lets get the root cause of the problem figured out first and then we can formulate a better answer.

S & B


So what are some things you recommend for one to do/try to their car setup for it to rotate more freely on corner entry?

VB

S & B
What effect would a front roll bar have on tuning the chassis of a pan car? Is there a benifit to running one?

wildman

thanks for the info. J!!! :wave:

DK47, by leading caster in the right front, I am assuming you mean running caster split to the right front (more RF than LF caster).

In an RC car Caster does two major things, the third isn't applicable, because you are not in the car feeling the steering forces.

1. It creates dynamic camber in both front tire as the wheels are turned. Which would create more dynamic camber at the point at which the tires are turned the most. Which on short tracks and road courses helps one run more conservatively (less) on the bump camber gain in the unladen tire. The typical detrainment in running less bump camber gain on the unladen wheel is you inherent loose more LF camber in roll. The added camber on a road course set-up gets back some of the camber loss on the unladen tire in roll (of course max roll usually occurs in about the same place as max steering. For that matter more caster in general usually will help a car turn more in the center of the corner.

2. The other effect is the jacking effect. More caster in the LF (with left hand steering) raises the left hand corner of the car. More caster on the RF (with left hand steering) lowers the right hand corner of the car. So equal caster in both fronts with naturally jack the car into a dewedged state, by inducing roll. The amount that this occurs is dependent upon the stiffness of the suspension.

More caster split (0-LF,4-RF) The left front wouldn’t move vertically and the RF jack downwards, so there would be less caster jack than equal caster. In general more caster jack dewedges the car entry to middle(looser), and rewedges the car on exit(tighter). With equal caster the ride height of the car doesn’t change the car just rolls. With more caster split the car’s ride height drops and the car rolls.

There is some contention on what the effects are of caster on an RC car, because once again practical knowledge may vary from theory. Possible explanations of this are the fact that with a sliding kingpin front suspension, the longitudinal forces that are developed at the front wheels due to slip angle induced drag acts (a whole other topic of discussion) through the SVSA (anti-dive) of the front suspension, which I ?believe? is effected by the caster. This something I really am not sure about right now. Also, caster changes the dynamic wheelbase and somewhat the front spring bind on our cars, which adds yet another complicating factor into the analysis.

I am not positive myself on how to form a solid theory when it comes to caster. I would start out with 1-2 on the LF and 3-4 on the RF. Your best bet as always when it comes to these things is trial and error. It comes down to what you prefer as a driver. Drivers in Cup are all over the map when it comes to their caster settings.

On the third question, moving the LR in moves the LR closer to the CG of the car on the width axis of the car. Therefore, its longitudinal (forward traction vector would have less leverage. If you were to think about the forward force acting on the LR tire patch, it would have the tendency to rotate the car to the right or the tight side. Anytime more traction or more leverage is given to the LR tire, the more the car will be tight on power (that goes for putting a softer tire on that corner as well). The opposite is true for corner entry when the braking forces (in general small on an RC car) are applying rearward forces at the rear tires. So in general moving the LR tire <edit> out <edit> will give the car more off power rotation and less on-power rotation.

S & B

Skull & Bones could you email me. If you are who I think you are I'd like to get in contact with you. steved@msn.com


Steve Downs

I don't think I am, who you are thinking, but, I'll e-mail you anyway.

Hey guys
Your eyes may bleed, But I think I would like to have this guy pit with me anytime.

:D

Well I screwed up something as simple as a email addy! Sorry Its steved211@msn.com. Well I could post my asumption of your identity on here but I figured I would repect your wish to remain anonimous(sp?) just in case I was correct.

Steve Downs

Skull & Bones, I don't know who you are, but you obviously have a superior understanding of race cars and I'll read anything you want to write and I agree that you could certainly spend time in my pit anytime you wanted to.

Thanks for the information.

:thumbsup: :thumbsup: :thumbsup:

don't get me wrong, while my eyes might be bleeding, i am reading and digesting all of this! thanks, skull

Okay What I Want To Know Is How Do You Figure Roll Center On A Pan Car.

Thanks
Jason

Scul and Bones has a program that does it in his laptop ...... SDOWNS you are correct ...


Sand B great thread talk to ya SRM :thumbsup:

Where Do You Get This Program At Smrocket :(

If all this info is coming from a program I want it too!

S&B - It's great to finally have some theory discussed. Most racers don't understand the 'how's and why's' of the things we do to our cars. I would like to hear your opinion on the torque/lift effect transmitted through the t-bar from the rotation of the pod under acceleration. Will the car see this as a 'torque arm/lift bar' effect and does varying the wheelbase via the front end only make the car 'think' it has a longer/shorter torque arm.

Wow... this guy/guys/woman/women... is my kind of poster... Even so... Wow, I can't stop the eyes from bleeding at this point...


I like it alot.

I'll up-load the geometry calculator. It is a sample of what the final version will be and is based on the asumption of a STD. associated front suspension with the ability to adjust several common factors. I'll e-mail to Hank, so that he can post it.

S & B

Cool deal! Maybe it will give me a better understanding of how the front end works!

If hank has any trouble putting your stuff up, let me know. I've got a web host that I pay for, and can put up virtualy unlimited amounts of stuff. The guy told me as long as I don't put up any porno, I can put pretty much as much as I want in terms of space... so let me know if you need some place to put anything...

Wow! Is anyone out there printing all this info besides me? Keep it coming.My other eye isn't bleeding yet :freak: :confused:

SCULL AND BONES ,,, do you really want to post this before SNOWBIRDS ....... :eek:

Seems like a bad idea to me to give it away !!!!!!!!!!!!!!!!!!!!!!!!!!!!

No need to print for me , I have all this at my fingertips ....heheheh

SRM :devil:

S & B,The sky just opened,it seems there is no better place to get cutting edge info.than here,its like reading a Bob Bolles article in circle track mag.on a assoc. rear pod the rear axel is spaced a certain distance from rear t-plate srew there are a few other chassis that have there rear axel about almost 1/2 inch. further back would you say one would be better for carpet or asphalt.also if you are going to talk about roll-centers could you put into actual procedures like place both pins in stock positions does this or that. DOM-19

All I can say is WOW !!!!!!!

It's no wonder I am so slow, I didn't have a clue what I was doing or why.

I can tell now I have a lot of information to digest and hopefully be able to apply it.

Thanks Again. :thumbsup: :thumbsup: :thumbsup:

DOM-19, Anti-squat it is an interesting topic of set-up that is rarely talked about or knowingly changed on a RC car rear suspension. Anti-squat is defined as the ratio (height of rear suspension pivot/longitudinal distance from the center of the tires contact patch the rear suspension pivot). This is .375/2=.187 (rough) on our cars. One thing that nobody has ever offered up a good explanation for, is why a t-plate car handles differently from a pivot ball car. The reason for this is that the location at which the rear pod pivots at.

For a pivot ball car, this location is at the pivot. But, is more like in the center of the t-plate for a t-plate car. This of course adjust two things:

1. The anti-squat of the rear suspension
2. The motion ratio for the center shock

So as a rule of thumb (I wish I had a car with me here) a pivot ball car has more anti-squat, say .375/1.5=.25 or 25 % anti-squat, where as a t-plate maybe more like .375/2.5=.15 or 15% anti-squat.

As for the motion/leverage ratio of the rear shock. This is defined as the amount of movement of the rear tires for a given movement of the center shocks shaft. This also changes based on where the rear pod is pivoting about. I can't really figure exact values with out a car, but it might be a good experiment for someone to measure and to see how it changes with various types and shapes of t-plates???

S & B

S&B
Not to be nit-picky, but I didn't completely follow the answer on moving the LR in. I think it may be that I'm over simplifying the case (if there's one thing you learn in college engineering, its how to simplify conditions down to a bare minimum).
You start by saying that:
-->"moving the LR in moves the LR closer to the CG of the car on the width axis of the car. Therefore, its longitudinal forward traction vector would have less leverage."
This I follow, as you're reducing the lever arm.
But to me it seems that this would reduce the moment to rotate the car clockwise. This would then yield oversteer on power.

But then what you say kind of confused me a bit...
-->"Anytime more traction or more leverage is given to the LR tire, the more the car will be tight on power (that goes for putting a softer tire on that corner as well)." Sounds good...

-->"So in general moving the LR tire in will give the car more off power rotation and less on-power rotation."

Doesn't that contradict the first two things you said? Could easily be a case of being so caught up in the question that you forget where you started, or me reading/analyzing it incorrectly.

Other than that, I think I'm following everything pretty well (although I have to go back and re-read it to fully absorb it not to mention apply it) and appreciate the technical discussion and the help you're giving. Thanks a ton for subjecting yourself to our questions.
Chuck

You are correct CBear3, i stated that backwards, moving the LR out will give the car more off power rotation and less on power rotation. Thank you for the correction. If anybody else sees an error please point it out.

I'll go back an fix that. That serves me right for making a post at 12:30 in the morning.

S & B

Thanks, I just didn't want anybody who was getting lost in the technical side to look at the summary and get crossed up.
On the plus side, I'm glad to know 5 years to get a BSME was worth something :)

Who needs theory? Stewart and Newman are fast becuase there not panzzies and use this simple theory: They put the petal to the metal!!!
So in RC terms just grip it and rip it, or drive it like you stole and you will be fine! :thumbsup: