BRDRACING, When it comes to anti-squat, anti-dive, instantaneous centers (Roll Center). We are talking about basically the same principles. When load transfers in a car, a proportion of that load is transferred through the springs and bars. However, at the same time, some of the load is also being transferred through the solid geometry of the car (this is the portion that we are discussing when it comes to anti-geometry and roll centers).

The total weight transfer is easily calculated by using the formula

lateral transfer=(CG_height*lat_acc)/track width
longitudinal transfer=(CG_height*long_acc)/wheelbase

The tricky part comes in how that total weight transfer is distributed across the front and rear of the car under lateral acceleration or across the left side or right side of the car under longitudinal weight transfer.

The easiest way I have found to explain this is through what is called the lateral-anti method of solving weight transfer. The amount of weight transferred across the solid geometry is considered first.

1. Take the lateral force at each tire. In cornering, lets say:

LF-10 oz, RF-30 oz, Rear-60oz (100 oz total all to the inside of the track. With a 40oz car with a track width of 6.25", . With these values, the car would be cornering at 100oz/40oz=2.5 g's)

2. Take the given geometry at each location. The pivot ball height at the rear geometry is say 3/8" off the ground in the center of the car, the LF instantaneous center is 5/8" high and 19" in to the right of the LF tire and lastly the RF instantaneous center is 1/2" high and 5" to the left of the RF tire.

3. From these geometric values we can calculate out their direction vector (basically the angle at which the tire’s lateral force is acting into the chassis)

LF=(5/8)/19=.033, RF=(1/2)/5=.1, Rear=(3/8)/3.125=.12

4. Using trigonometry, we can determine the amount of weight being transferred away or to a given tire by multiplying, the given lateral force value by the geometric ratio.

LF=10*.033= .33 oz (off of the LF tire)
RF=30*.1= 3 oz (on to the RF tire)
Rear=60*.12= 7.2 oz total across the rear

So, the total of this would be 3.33 oz across the front roll center (a combination of the two front instantaneous centers) and 7.2 oz across the rear pivot ball, a total of 10.53 oz through the geometry of the car.

5. Finally we can calculate out the total weight transfer of the car using the first formula. We'll call the CG height 1.5".

WT=CG_height*(lat_g*weight of the car)/(track width)
=1.5*(2.5*40)/(6.25)=24 oz

That would be 24 oz of total weight transfer. As we already know, 10.53 oz of this transfer has already occurred through the geometry of the car. So, there will be (24-10.53)=13.47oz of transfer that occurs through the springs and anti-roll bars of the car.

6. The total amount of roll in the car is determine by the total roll stiffness of the car. The calculation of how that remaining 13.47 oz is distributed (front and rear) is determined by the roll stiffness distribution of the car.

7. With out getting too specific, we'll say that the Roll stiffness= 1 deg of roll for 10 oz of transfer and that the RSD=(F/R)=70/30.

8. Therefore, the car will roll= 13.47/10= 1.347 degrees,
a. Front transfer through spring and bars= 70%*13.47=9.43 oz
b. Rear transfer through springs and bars= 30%*13.47=4.04 oz

9. Lastly we combine all of our totals.

Front transfer= 3.33+9.43=12.76 oz
Rear transfer= 7.2+4.04= 11.24

The next post I will make common sense out of this.

S & B

BRDRACING, When it comes to anti-squat, anti-dive, instantaneous centers (Roll Center). We are talking about basically the same principles. When load transfers in a car, a proportion of that load is transferred through the springs and bars. However, at the same time, some of the load is also being transferred through the solid geometry of the car (this is the portion that we are discussing when it comes to anti-geometry and roll centers).

The total weight transfer is easily calculated by using the formula

lateral transfer=(CG_height*lat_acc)/track width
longitudinal transfer=(CG_height*long_acc)/wheelbase

The tricky part comes in how that total weight transfer is distributed across the front and rear of the car under lateral acceleration or across the left side or right side of the car under longitudinal weight transfer.

The easiest way I have found to explain this is through what is called the lateral-anti method of solving weight transfer. The amount of weight transferred across the solid geometry is considered first.

1. Take the lateral force at each tire. In cornering, lets say:

LF-10 oz, RF-30 oz, Rear-60oz (100 oz total all to the inside of the track. With a 40oz car with a track width of 6.25", . With these values, the car would be cornering at 100oz/40oz=2.5 g's)

2. Take the given geometry at each location. The pivot ball height at the rear geometry is say 3/8" off the ground in the center of the car, the LF instantaneous center is 5/8" high and 19" in to the right of the LF tire and lastly the RF instantaneous center is 1/2" high and 5" to the left of the RF tire.

3. From these geometric values we can calculate out their direction vector (basically the angle at which the tire’s lateral force is acting into the chassis)

LF=(5/8)/19=.033, RF=(1/2)/5=.1, Rear=(3/8)/3.125=.12

4. Using trigonometry, we can determine the amount of weight being transferred away or to a given tire by multiplying, the given lateral force value by the geometric ratio.

LF=10*.033= .33 oz (off of the LF tire)
RF=30*.1= 3 oz (on to the RF tire)
Rear=60*.12= 7.2 oz total across the rear

So, the total of this would be 3.33 oz across the front roll center (a combination of the two front instantaneous centers) and 7.2 oz across the rear pivot ball, a total of 10.53 oz through the geometry of the car.

5. Finally we can calculate out the total weight transfer of the car using the first formula. We'll call the CG height 1.5".

WT=CG_height*(lat_g*weight of the car)/(track width)
=1.5*(2.5*40)/(6.25)=24 oz

That would be 24 oz of total weight transfer. As we already know, 10.53 oz of this transfer has already occurred through the geometry of the car. So, there will be (24-10.53)=13.47oz of transfer that occurs through the springs and anti-roll bars of the car.

6. The total amount of roll in the car is determine by the total roll stiffness of the car. The calculation of how that remaining 13.47 oz is distributed (front and rear) is determined by the roll stiffness distribution of the car.

7. With out getting too specific, we'll say that the Roll stiffness= 1 deg of roll for 10 oz of transfer and that the RSD=(F/R)=70/30.

8. Therefore, the car will roll= 13.47/10= 1.347 degrees,
a. Front transfer through spring and bars= 70%*13.47=9.43 oz
b. Rear transfer through springs and bars= 30%*13.47=4.04 oz

9. Lastly we combine all of our totals.

Front transfer= 3.33+9.43=12.76 oz
Rear transfer= 7.2+4.04= 11.24

The next post I will make common sense out of this.

S & B


So how can we from this understand what roll centers and anti-squat mean out of this mathematical explanation? First off, the roll centers are basically "anti-squat" for the car in roll.

Or, anti-squat is the "geometric holding-up" of the rear of the car under longitudinal acceleration.

The thing we must first understand is that the weight transfer that occurs through the geometry of the car occurs instantaneously. Where the weight transfer of the car in roll takes time to occur. Basically, the time for the car to establish its roll angle.

As for anti-squat, this transfers a percentage of the weight to the rear tire instantaneously.

So to answer the question as to what increasing anti-squat will do. It can assist in incautiously creating forward bite. But just for an instant, and then will go away. This might seem like it will help rear grip, and is some specific cases it will. However, this instantaneous transfer (geometric stiffening) comes at a cost of decreasing the rear compliance of the car which in the long run , can often hurt rear bite.

The same principles can be used and considered in the roll center heights front and rear. The roll centers will favor their effect on the initial conditions of the car(corner entry and late exit), where as the springs and bars effect car after the car takes its roll set (middle of the corner).

I hope this helps a little bit in understanding most of your questions regarding front end geometry and anti-geometry. These effects are used very extensively in WC cars, but to a much more complicated degree, by using anti-squat and anti-dive splits (LR to RR or LF to RF) to control instantaneous changes in wedge under longitudinal acceleration. And by changing t-bar rake angle and front I.C. position splits to instantaneously change wedge under lateral acceleration. The changes are also used to control body attitude.

S & B

vwal, yes you are correct, we use the soft springs and big bars to control the body into ideal aerodynamic conditions. In terms of R/C cars, body attitude is still important, but to a lesser degree. I haven't seen many good cars that have their nose mounted 1/2" off the carpet. Now whether it is better to have and 1/8" of body gap vs. 1/32", I am looking to explore this further in the future.

In terms of the big car shocks, I am talking about single tube shocks. The base valve separates the main body of the shock from the gas resovoir on top. Base valve operation is a complicated subject.

S & B

mel , Adjusting the fore/aft weight distribution is the most fundamental way of adjusting the mechanical and overall handling balance of any race car. Moving the weight back, moves the cars CG back. The CG location F/A effects the leverage which the front tire pair or rear tire pair has on the mass of the car. Moving the weight backwards effectively gives the front tires more leverage, hence make the car go more to the oversteer side.

With our oval cars we usually use wide soft compounded rear tires to assist in making forward traction. So in a pure lateral cornering force situation, in order to have a balanced car, it is necessary to have our CG more to the rear of the car.

What combination of F/A weight distribution and wedge distribution you will want for ideal handling conditions depends greatly on the type of track, amount of grip and your preference in terms of driving style.

S & B

Cool, thanks for the info and keep it coming. So with the big car stuff and base valves, is that similar to seperator pistons and the gas chambers at the tops of most high dollor racing shocks?? On the body heights on our little cars, I would be interested to see what you find out. I have always just figured that no one had there bodies that way because it looked bad, but maybe there is more of an effect than I have thought there was?

katf1sh, I don't know, I just bite right into the pop, I don't have to patience to lick :tongue:

rckfracing, In big car racing, we put the cars onto steering plates to measure Ackerman. We also have bump steer gauges to measure bump steer. It might be a good market for someone to make some trick products for RC cars.

A four link, there probably would be 10 guys in the country who could understand how to set one up. Most people I see have trouble putting a t-plate car together correctly :)

Tres, I think JPHRacer basically answered your question. To be honest, I'd like to see an oval car that the rear roll center could actually be lowered.

S & B

The base valve controls oil flow between the main body of the shock and where the separator piston is. It can be adjusted to create an instantaneous high pressure above the main piston under large velocity spikes, therefore warding off cavitation during those spikes. Yet still allows one to run a lower gas pressure (better for grip) around the rest of the track.

S & B

"The roll centers will favor their effect on the initial conditions of the car(corner entry and late exit)"

When you say this is there a rule of thumb as far as setting up front to rear roll centers to make the car turn better out of the corner? I was allways under the impression that having a lower front roll center then the rear will help the car during corner entry, but decrease the front tires ability to make grip on corner exit, is that a true statement? If so then would it be correct to assume that if I raised the front roll center to be higher then the rear roll center that I would get more steering on corner exit?

I also have been wondering what your opinion on skewed roll centers is, i.e. having the front roll center offset to the right of the rear roll center, or vise versa. Does it have the same effect as offsetting the whole front end to the right, or to the left?

Thanks

David
Maverick Oval Chassis
Silva Concepts
KC Racing

Skull and Bones.........Please send me an email....I have something in the works as well........maybe they can be tied together.
Thanks.!!

By placing a shim under the front pivot ball of the t-plate affect the car,also by running a support between the castor blocks will this tighten up the car or allow the front suspension work better without allowing side flex?
Phillip

S&B or anyone else for that matter,

I just returned to RC racing after 15+ years, back when the RC10 Gold tubs first came out. Its therefore my first experience with pan cars. I have crewed on the big cars (more specifically GM/tube IMCA style cars and PRo-stock i.e. Howe 94 designs).

One of the areas of interogation was why use t-plates and not a trailing arm/upper link/panhard bar/conventional shock/ design? Maybe it used to exist (while I was not in the sport) and it was just re-engineered into what is out there today...

M.P.

VWAL, what type of BIG car do you work on or run?
As far as a four-link rear I wouldn't mind giving it a shot. They are actually pretty simple.

We have been running a late model sportsman locally but we are going to run some ASA races this year as well, I am the crew "everything" man and my brother is the driver. I have seen a few three link deals around these parts; most never have worked very well. I messed with one a little and well it didn't work either, something was wrong with geometry.

That's odd for a three link not to work. I had a Lefthander with a three link and it worked awesome. Also crewed on a NASCAR Featherlight MOD that used a four-link that ran well also. Oh both cars ran with BILSTEINS and HYPERCOILS only.

Hey skull and bones a couple quick questions for ya..

i was wondering i their was a way to measure bump steer and how it can help or be a disadvatage, same thing as ankerman is their a way to measure and how to use it..

jbm, I meant three links on RC cars!!!!! Our ASA car is a lefty and we run Pro's shocks.

Hyperdrive Man , There are two major effects of bump steer and one major effect of Ackerman steering. Just to be more specific Ackerman steering is defined as the amount of dynamic toe change per steering angle change. The last steering issue that you didn't mention is the hardest to fully control, that is steering compliance. One last thing to consider, is the toe split caused by the fact the LF tire and the RF tire are traveling different radiuses of about 6 1/2 inches with our R/C cars. This can be significant at small corner radiuses, up to a degree split with a corner radius of 5 ft. So, if one were to have no compliance, no static toe, no bump steer and no Ackerman steering with a 5 ft. corner radius, you could think of the cars as having a degree of toe in.

Nevertheless, the steering effects all determine the dynamic toe. Dynamic toe is the split in slip angles of the two front tires. The more dynamic toe, the more left front slip angle is higher than right front. With dynamic toe-in, there is more RF S.A. than LF S.A. Later, I will try to go into more detail as to when one would want dynamic toe-in or toe-out.

As for the second effect of bump steer. Bump steer can also be used to control corner entry or exit understeer/oversteer. The more the RF bumps in or the LF bumps out, the more of a transient oversteering effect you will get on corner entry (assuming you are getting downward front travel on entry). Just the opposite for the exit of the corner or for reversing the bump steering directions.

In general, I would avoid using this effect to control the handling of a race car. But, in some cases it can be beneficial. In general, you want to determine what your final amount of dynamic toe by the center of the corner.

Going back to the effect of dynamic toe on the handling of a car, the first thing one must consider, the direction of steering compliance. With a rear steer car (car where the steering linkage is behind the front axle, like our RC cars). Steering compliance goes in the direction of toe in.

With that in mind, if you are running zero static toe, no Ackerman and no bump steer with a significantly large corner radius there would be natural toe in.

So what do you want, dynamic toe in or dynamic toe out. This is not as easy of a question. It is especially hard to determine without specifically knowing what our tires properties are, specifically what the slip angle vs. lateral grip curves are for each type of tire we run.

From this, we need to apply good common sense reasoning and rules to determine what might be best. In some cases, our best solution might come from plain trial and error methods. Here are some general rules.

1. The more load that is on a tire, the higher the slip angle at which peak grip is made for that tire.

2. The stiffer the construction or the lateral stiffness of a tire, the lower the slip angle that a tire makes its peak grip at.

3. Ideally we would like to make maximum front tire grip in the center or apex of the corner.

So from this we can begin to think of circumstances where on would want either more dynamic toe-in or toe-out. I'll try to give you a couple cases of this.

On a flat tracks, where there is tremendous amounts of load transfer from the inside tire to the outside tire. This would suggest with equal compound tires on the front of the car, that the outside tire would need more slip angle than the inside tire or dynamic toe-in. On banked tracks where front tire loading is more equal, one would need less dynamic toe-in.

A second example is when one has a tire compound split across the front. If one were to say have a soft compounded white left front with a hard compounded purple on the RF, the left front would more than likely make its peak grip at a higher slip angle than the harder purple RF, this would make one want more dynamic toe-out.

Once again this is something I haven't played with enough yet to give you a guys more practically based information. I do, however, think that there is something to be gained in experimenting with. Your thoughts and experiences are greatly appreciated.

S & B

S + B did you attend the Norrca nats at classic last month???

I recently raced on a very short oval for the first time.The entire track measured roughly 50' long by about 15' wide.I noticed when I let completely off the gas to turn the car woul bite really hard and jerk.If I stayed about 1/4 to 1/2 way on the gas the car would turn smoothly thru the radius.It was difficult to maintain the proper throttle to drive smooth consistant lines.What was my car doing?I think by letting off the gas I was upsetting the balance and causing the jerky turning, but I don't know how to adjust this.What do I do to make the car more forgiving?I am looking to give myself a little more room for error and still drive smooth lines.Thanks...

Oh yeah I run a TC3 in pro stock.thanks!!

S+B
I was woundering about your opinion on longer upper a arms, do they give more grip? longer a arm was achieved by adding shims between caster block and lower arm. I believe that longer rf upper arm gives more bite on entery, not like a softer tire fell but just sticks more aggresivley.......wanting to know facts WHY

TJ

It seems to me that when you put shims between the castor mount and bottom A frame it would increase your camber adjustment but I do not see any other affect in doing this JMO

It does more than that...

TJ

It will make the roll center raise less during corner entry, how it effects the car can be very dependent on the track that you are running on, is what I have found.


S+B do you have an awnser to my question on the last page about roll centers?

S&B here is a question i have....


currently i run a new prot type car.. and on this car it has a very simple feature for offsetting the pod....
all we have to do is move the motor plate over, and nothing else. I have talked to a few people already on the subject, and they say it is different than if u move the whole pod over like the traditional offset pods. though they say it is different no one can explain why it would be different..

so for our car u just mive the motor plate over , and throw on a wide hub everything else stays the same.

and for the traditional cars u move the whole pod over one step by changing the t plate holes, ball studs on the toplate, wide diff hub, and a narow left hub..

so i guess my question is will just moving the motor plate and motor weight over have the same effect as moving the whole pod. and what do u think the difference is between the two options. thanks

MIKE BURBEY
KGB FACTORY DRIVER
TM RACING TIRES TEAM DRIVER
INTEGY TEAM DRIVER
BRC TEAM DRIVER

SCULL AN BONES IS ON A RACING TRIP ...HE WILL RETURN IN A FEW DAYS ......srm :thumbsup:

Hey Rocket,, I sent you a PM..........

thanks
dbr

SFM, it is hard for me to give you such general practical advice. Your best bet is to find somebody at your track who is fast.

toytowne, longer upper a-frames will slow down camber gain and lower the front roll center. Consult my past post about geometry to find out more of what that does.

burbs, I'll think about your question and get back to you later.

S & B

so for our car u just mive the motor plate over , and throw on a wide hub everything else stays the same.



If the cars you are talking about as 'traditional' cars being the KSG or the 10L4, I'd say it doesn't matter.

There is so little weight in the pod outside the motor, moving the motor plate over OR installing the offset pod will hardly change static weight one way or another.

Does it matter? If the pod was as heavy as the motor, I'd say yes. If you can get a pod to weight as much as the motor, you must be running a state of the art - 1987 car. And working on it.

:drunk:

how about this....

Why, all of a sudden, are and going much faster than before (at least it seems). No matter if they transfer the setup, or work on a new one. Is it the flex?

S + B

were you at the nats? (norrca)

There are a lot of choices as far as chassis designs go. From what I've seen there is a wide variety in stiffness. For running a flat oval would there be an advantage to running a stiff chassis over running one with more flex?

I have found chassis with more flex to run better than stiffer chassis on flat tracks.

That was what I would have thought but was unsure.

S&B: Why is chassis flex an adantage (or seems to be) on flat tracks?

S&B... your needed in the oval section of Hobbytalk... :)

I'll definitely get back to you tomorrow.

S & B

hey skull did u ever hget a chance to think about my qustion... u said u would think about it.. i was just wondering if u did later thanks

what differences dous these have on a car pro2 to be exact

Skull - Cool hanging with ya this weekend "Wise Guy"! LOL email me at mclin@rc-oval.com.

burbs, In thinking about it, I don't think it would make any difference, except for the difference in offsetting the whole pods mass versus just the motor's mass.

Carpet Assasin , Yes I was at Norrca Nats.

To a few of you, Chassis flex is not an easy subject and even in racing ranks all the way up to F1, the effect of chassis flex is still not fully understood. In the basic theoretical way of looking at things, one would think you want an infinitely stiff, infinitely light chassis. How ever in the real world this is impossible. Not only is it impossible, but time and time we find that pure simple theories always let us down.

I will break it down like this:

A stiffer chassis will:

1. Allows a more ridged structure for the body and suspension to mount on.

2. Will allow chassis set-up changes to be more effective in their changes to the car.

3. Will make a car more warp stiff, which will reduce grip on tracks with a lot of bumps or abrupt banking changes.

A softer chassis:

1. Will tend to make adjustments feel more dead.

2. Will be more forgiving to drive and to potentially set-up (this is not always true).

3. Make the car more warp soft, which will increase grip on tracks with a lot of bumps or abrupt banking changes.

Note: Warp stiffness is the last and least looked at mode of a car’s motions. Everybody knows pitch, roll and bump. Warp is the twisting stiffness. Warp stiffness is influenced by roll stiffness and chassis flex. High roll centered cars such as Sprint Cars require very little roll stiffness and therefore are very warp soft. However R/C cars have relatively low roll centers and need higher roll stiffness, there for warp stiffness is largely controlled by chassis flex.

I can remember that bumpy low bite track like King SS, used to really like a soft chassis. But I would say that a high bite smooth as glass track would probably favor a stiffer chassis.

S & B

well i would guess u run an adx car, according to there thread.... so we need to see who ran adx at norrca.. then we can see who u are lol

You still don't know who he is burbs?? I do, thanks to a friend.

nope V i still dont.. i thought it was someone, but it was washed out by others.. so i dunno :freak:

You still don't know who he is burbs?? I do, thanks to a friend.

yay!!

i hear all this hype about hpi shocks being better i was wondering what you would use for a shock piston and oil setup in one on a snowbirds type track. it has a few minor bumps but nothing major. currently i am using an associated threaded shock with a #1 or 2 piston i'm not even sure and 70 wt. oil and a green spring. any help would be appreciated. thanks in advance. Brad Sousa

Hey KGB, can I get a free car?????

Weights and cross weights???????????What are some of you running

S & B. If you had to weigh all the factors of racing in three categories: car setup, driver skill, wallet size. In what order and percentage of the overall picture would you give each. Thanks in advance.

shawnleary, I'll separate this by class.

Stock,

35 percent car
35 percent driver
20 percent batteries
10 percent motor

19T,

30 percent car
30 percent driver
20 percent batteries
20 percent motor

Mod,

25 perecnt car
25 percent driver
20 percent batteries
30 percent motor

I will postscipt this by saying that if you cannot drive forget about ever being at the top level of fast. You could give a savage driver, G. Honey's car, motor and batt. at Sandhills and he'd be 4 laps of the pace. I will also say that I have seen less than stellar cars, batteries and motors run up front. But if you have less than stellar all of the above, even if can wheel you'll be slow.

Final answer, it takes the total package at the highest level of racing.

S & B

the HPI shock thing is getting old.. i'm not sure where the "it works better" thing came from?

it's a shock with oil and a spring on it! it should in theory work as well as any other well built and designed shock!

the only thing better about the HPI shock is the fact that it's easier to build and it has a variety of pistons for it..other than that it should work like the other shocks for touring cars or oval cars! what i dont undestand is why some guys keep posting on how it works like the associated shock..of course it does! do you have to have one to go fast? hell no! do you want to be a sheep? hell yes..lol i have 2 HPI shocks..i never built the associated shock..if i saw one on your car i'm not going to tell you to throw it away..the new silva shocks dont work any better..they are just easier to build and dont leak half as bad as the kit shocks..will your car go around without them? YES! ok i feel better now!

skull i think shawn is looking for a $$$$ amount on what you think it takes to go fast in oval..you mentioned everything but cost,lol..

someone bought my old ADX car for 150.00 came with everyting but electronics..so for 150.00 plus there electronics they bought the current track record holding car in 4 cell stock in jacksonville..fact is that car never finished second up there ever! i posted my set up gear ratio and roll out 5 different times...i just dont think you can put a number on what it takes to win...LUCK has a roll in all of this as well as knowledge of both car set-up and track..i have been playing with these cars since 1986 and every time i go race i learn 5 new things! go to the snowbirds and hang out for a week and you will learn 1000 new things.. the best car threads and the best speedo threads and best tire threads and all those best threads kill me...i have sat back and watched some guys hand over there car..complete how it cam e off the track and watch the other guy bang walls and drive a wack line around the track...i think sometimes the racer himself cant admit he may not obtain the skill required to go fast sometimes? we all know at least one guy who spends 1000.00 of dollars on his stuff and still he is in the C main ..go look at mike boylans car and equipment..he whoops us all every sunday..he has maybe 20% the money we all do in his car..yet he wins week in and week out...i'll take skill,luck and knowledge over money ,motor and batteries all day long... phew blood pressure shot up 100 points,lol...skull will you be at the birds? peace out! :thumbsup: