Automotive Race car suspension Class

[Ranger Mike]

Mustngthundr...thanks you..

question- is car pushing going in and loose coming off turns?

 

[mustngthundr]

Typically not loose on exit. From about mid- turn off its usually pretty decent unless I get held really tight to the inside, then it will get a little loose.

 

[Ranger Mike]

When we have Roll Center too far to the left of centerline, the car will not turn well. We have to load the right front tire with down force to assist the tire. See Post 251 on page 16 Body roll does not give enough leverage to stick the rt ft tire. It slides sideways thru mid corner. When we exit, there is not enough lift from the Lft Ft on to the RT Rear to add traction.
Your roll center is 10 inches to the left. You are right on with the suspension software as thsi is the tool to figure out the set up.
We must locate the RC to the right of centerline so at least half the left side mass sprung weight is rotating thru it to stick the Rt Ft. Unless you have Aero adding a lot of down force at the end of the chute, you need this to stick the rt. ft. So we run 3 to 4 inch offset to the right of centerline just for this purpose.
As a minimum relocate the RC to center...3 inch to the right is ideal. This means you will have a little more than 55% left side sprung weight wil rotate thru the RC ( on 66" track width car). This will make your set up consistant and you can fine tune from here.

 

[mustngthundr]

Ok that makes sense. I'll give it a shot. Thanks again!

 

[NaLLa8705]

Hey mike!

Finishing up my race car build, found a friend with chassis software, now wondering where to measure my upper control arm pivot points so i can determine roll center. The upper control arms on my car are angled so at what point do I pick to plug into my software? Dead center?

 

[Ranger Mike]

welcome and sounds like a good plan. On all the chassis software i use, i have to measure the height and location from center line of the top outer pivot point and top inner pivot point and the software calculates the angle. The better and more accurate you measure, the better. I had to make stop blocks to jam under the lower A-arm to maintain exact height and slipped off the front tires on occasion when running wide tires and big wheel offsets masking the outer pivot point. Eventaully I borrowed a portable cmm arm.

 

[NaLLa8705]

Perhaps my question wasn't clear enough, or maybe because I haven't I looked at the software I am confused, but what I am having trouble understanding is where on the pivot do I pick the point to put in. The arm is angled like I drew up in paint.

That is in a two dimensional plane...

 

[Ranger Mike]

on circle rack analyzer use attached..i use suspension analyzer which requires 3D input

 

[rohitsr987]

hi..i am building a groscope sysytem to balance two wheelrs..i need to know what is roll torque and how it can be countered?

 

[07superstreet]

Mike,
Hello, i am new to the discussion. I stumbled across this website and forum, luckily i might say, trying to find some information to help my race team. We have a stock snout, camaro frt. clip, tubular 2x3 tubing, chasis. It's been difficult getting the handling on this chasis. Before, we had a stock camaro chasis and we had figured out what it took to make that chasis work, but we were behind everyone else. They had swicthed to the chasis that we have now. With the old chasis, we would run 49-50% frt. and rear percentages. Only reason for that was that was all we could get. On this chasis, we run 55% rear percentage and 52-54% left side. The issue we are having is with ride height. We can not find anyone that can or will give us ride height numbers for this chasis. In reading all the information on this thread, i see that ride height and all related to that are very important. I know that if we can get the proper ride height, everything else will fall into place. Thank you so much for all the information you give. I have been glued to this thread since i found it.

 

[07superstreet]

Mike,
I failed to mention that this is a dirttrack car. Sorry for the omission.

 

[Ranger Mike]

welcome 07superstk and thanks for the kind words...I am not the only contributor here and we have a lot of racers on this post!.
my opinion for what its worth ...
Ride height – distance of track surface plane to four reference points of the bottom of the race car chassis. This Ride Height will allow the race car to go faster than any other height setting for a particular track. Typical ride height has 3 criteria.

1. Chassis clearance –You need enough clearance to accommodate suspension travel ( 3 inch for stock car classes paved, 4 inch for dirt) yet keep the car as low as possible without bottoming the suspension components.

2. Front camber build. As the body rolls we build camber. For every 1 inch body roll we build 1 to 1 1/2 degree camber because the bottom A-arm is longer than the top A-arm. Set the ride height and check camber build over 3 inch travel ( paved). If the camber build is over 1 1/2 degree per inch the car is too low. If the change is less than 1 degree the car is too high and I do not believe this rule of thumb. More on this later.

3. Rear Steer- We want minimum to zero rear steer at desired ride height UNLESS WE INTENTIONAL DIAL IT IN. We want rear trail arms as level to the pavement as possible. Leaf springs will most likely be slightly down hill to counter anti squat.


My opinion – I think it best to change the Roll Center Height and location with the applicable suspension components. Drop the RC to at least 2.5 inch above track surface and 3 inch offset (paved, 4 inch dirt) to the right to help plant the RF tire, reduce camber build, and reduce weight jacking effect. If you can afford it get the spindles that will give your set up minimum camber loss due to King pin Inclination angle (KIA) on the right side and max positive camber build on the left side AS YOUR SET UP REQUIRES. I like Ackermann and zero bump steer. Once you got all this you should roll steer the car at the rear to see what is happening through your suspension travel and correct to zero. Then see where things set. Pick your 4 bench mark points and permanently mark them. A grease pen is not permanent and paint grinds off is you suffer an off track experience ( get into the marbles or out in the weeds). Weld a big washer at each point. Now you got a permanent bench mark at each corner. Finally, cut a piece of 2 x 4 board the proper height to slip under each bench mark and mark them RF,LF..etc... When at the track you can use a level concrete pad and check the established ride height should you crash and need to swap out suspension parts.

Personally, I am not a great believer in ride height as much as being aware of what is happening thru suspension travel.
Chassis Rake - not so much on door slammers as Formula Cars, Rake is a setting where the front is as low as possible and the rear is an inch higher to try to channel air properly under the car. With todays disfussers and belly pans, level is good and the hiked up rear is old school and can hurt aero.
If you need specs, here they are-

Typical ride height is LF – 4”, RF – 4.5”, LR - 5”, RR, 5.5”. paved
dirt needs a little higher to gain overturning moment
LF- "5, RF - 5.5", LR -5.5" , RR - 6"
One alternative to ride height blocks is to make clearence blocks that will fit between front A-arm to chassis points and trail arm to rear end tube points on the rear. Paint large arrows at these points so you can duplicate measurements at the track.

 

[07superstreet]

Thanks Mike. Can you give me some points to make the measurements from? The stock snout is connected to the tub chasis where the rear clip bolts would be bolted to the stock camaro chasis. That is what the snout is from. A 1979-81 camaro. The 2x3 tubing chasis is that from an older Dirt Late Model. The frt. suspension is stock lower A-arms, tube upper A-arms with the mounts relocated more forward and shorter racing springs with screw jacks on top of springs. We have racing shocks all around. The rear suspension is Chrysler style multi-leaf leaf springs attached to the chasis with Sliders. We just added the Sliders this off season, so we don't know what the car will act like with them. Any advise on the best/easiest way to make the RC measurements would be great. The car doesn't have the body on it, but it does have the engine and everything else in place. Thanks again for your help and time! If anyone else is reading this that might have some helpful information, that to would be greatlt appreciated. I am trying to get away from the"good ole boy" information from the locals.

 

[Ranger Mike]

Now is the time to do all the hard work on measuring the suspension. Taek out the front coils and unhook the ARB.
Use the easy acess to record bump steer, ackermann, camber build, rear steer and the like thru at least 3 inch travel, more for dirt. Suspension bind will kill you on handling. Pay close attention to shock travel and make sure they are not rubbing at max travel. And make sure you don't have shock that limits your required suspension travel. It happens. Same with ARB (swaybar). You don't need the body on thecar to get some good scale data but you should have weight added for fuel and driver. Once you set ride height go thru the drill of cranking on the wedge bolt to see how much cross weight you gain. Record it. Your penci lis your best friend during this time.

read page 19 post 290 and the rest on benchmarking the car.
Ifin you get the Roll Center height and location close and it does not migrate all over the place, and you get close on the spring rates, you can tune in the rest at the track.
But you must bench mark the car to get there.

 

[Ranger Mike]

Nascar Gen 6 car

Couple of things about Daytona this year. First up – You can thank Nascar for making as good and safe a race as possible in spite of the bad crash that saw an engine and various components end up in the stands. Dales death was a loss but we all gained from it by efforts made to make the sport safer.

Generation 6 Car - The Car of Tomorrow (COT) has been raced for 5 years and Nascar decided to try and make the actual race car look a lot closer to the production cars. One reason - Dodge dropped out of the series, another rumor is that GM threatened to leave if the cars did not resemble production cars.. NASCAR allowed the three manufacturers to develop unique versions of the Gen-6 car. That led to cars that closely resemble the Chevrolet SS, the Ford Fusion and the Toyota Camry. Grills and body lines are similar. Silhouettes are within millimeters of their showroom counterparts. Hence the new G6 car and you saw Ford, Chevy and Toyota all show case their Nascar entry in a show room with the production model during the race.

Last year they mandated ethanol and fuel injection and that gave the engine room boys a full load. This year they decide to cut 160 pounds off the car and re-engineer the rear end package. The hope is, with less weight, Goodyear will be able to build a softer tire that will provide more grip, create more tire wear and make the cars racier while using the same chassis from the current car.

One team crew chief said the center of gravity will be off from last years set up and all new bench marks have to be established. NASCAR is doing all it can with the new car to improve handling and reduce the aerodynamic push that makes it hard to pass with the current car. The center of gravity for all these cars will be off (too) because they (NASCAR) are taking weight out of the cars: 100 pounds off the right-sides, 60 more pounds off the left-sides. The intent was to ease the load on the right rear tire.


Another significant development with the Gen-6 is the attempt to do away with “crabbing” — where the rear of the car is skewed to the right.

Crabbing was achieved by altering several rear suspension components and it improved handling by increasing down force and side force.

“Everybody did it to some degree,” Germain Racing crew chief Bootie Barker said. “Instead of having moveable bushings, you don’t have those anymore, you’re limited on your truck-arm split and you cannot run a rear sway bar (except at the road courses). Elements that went into crabbing have been taken away. Crabbing' is the long-familiar chassis trick in which cars appear rather sideways down the straights, in order to have better cornering. That's part of the trick that Rick Hendrick's teams, particularly the Jimmie Johnson-Chad Knaus team, have used so successfully.

NASCAR changed, again, the 'skew' of the rear-ends of these cars and wants basically a 'straight-up' rear-end housing. 2012 cars run rear-ends with a half-inch of toe-in on the left and a half-inch of toe-out on the right. This year 'zero toe.' means the 'crabbing' around the race track will go away.

In addition, NASCAR will be allowing teams more 'camber' in the rear-end, four degrees instead of just two degrees in an attempt to get grip back in the car. And no rear sway bars. According to one crew chief , “The rear of your car will be more 'stuck' with four degrees." Here is the wrinkle- The COT was designed for aero grip but did not look like a stock car. Todays production cars do not have the same aero grip as the COT so the G6 rear spoiler is bigger to aid rear down force. Had to since you are taking aero-grip away from the car ( G6 vs COT) and putting mechanical-grip back in the car. That's good, though Goodyear may have to make some tweaks since the changes force teams to design new drive-plates and rear axles because when you start 'bending' rear tires further, things that want to run straight don't run very well.


2013 changes include new Windshield package. The windshield frame is oriented to position the test windshields at 37° from horizontal. Both the monolithic and laminate windshields were tested. All test windshields had a single layer of Mylar tear-off applied. A steel projectile passed through the monolithic windshield but did not pass through the laminate windshield. Analysis of the high-speed video reveals that the steel projectile was traveling at 110 fps after passing through the monolithic windshield. This equates to 161.6 ft·lb (219.1 J) of kinetic energy. While the monolithic windshield allowed the projectile to pass through it, the projectile kinetic energy was reduced by more than seven times. As a result of testing, the laminate windshield is being implemented for 2013 NASCAR vehicles. FYI - Simply increasing the thickness of a single-layer monolithic polycarbonate windshield is feasible only to a point. Acceptable optical clarity becomes increasingly more difficult to achieve as material thickness increases. Secondly, as the windshield weight increases, more emphasis must be placed on windshield retention.

Other changes include a redundant Halo bar and backwards Petty bar to stiffen the roll cage.

While the wheelbase remains at 110 inches, the length of the car was reduced by 6.3 inches—from 198.5 inches to 192.2. The width also was increased by three inches—from 74 inches to 77. There were no significant changes to the height (54.2 inches) or ground clearance (3.5 inches).


http://www.nascar.com/en_us/2013-car.html

 

[sierra76]

A Arms

Hi Have not been on forum for some time. Thanks for the 3 link advice Ranger Mike your set up worked really good with our car winning 7 Features in a row.
Just working on front arms and was wondering is there a ratio to the length of top to bottom. Also ideal front roll centre height for space frame 4 cylinder dirt track car . Any help would be a appreciated.

 

[Ranger Mike]

changing front RC and cheating the scales

Thanks much for the kind words but we have a lot of contributors here and the credit goes to them too,,
I would not change a thing..until,,,I measured your front end setting and found out exactly where you are now with the RC height and location...
ifin it aint't broke , don't fix it...and you got 7 checkers...i really recommend you find out where you are before changing a thing..then get the software and figure out what the Roll Center migration is and where it is moving within your suspension travel...there is no ratio on upper to lower A-Arm length in a purpose built car as they all are different and unique..hence the need to benchmark a winning set up so you can come back to a base line after a crash or going off in the weeds regarding new " trick" hot set ups...

one more thing..I got a private message asking if a race car can be too light...in my opinion..no...you can never go too light ..as long as safety is maintained..in my early days we ran a roll cage set up where only the main hoop was to the required wall thickness..the other bars were “ exhaust tubing” wall thickness...dumb dumb dumb...this action was when I was always seen at tech inspection at the scales with my clip board. I would lay it on the right side of the car when we pushed it on the scales...surprising what you can do with a acetylene torch and a bunch of old wheel balance weights on a winter night...ask me about the 50 pound helmet that was an exact copy of the one our driver wore in the race and ALWAYS hung on a hook on the right side of the cockpit..left side weight rule, huh! ...takes practice to swap out things on the way to the scales after the feature...but that would be cheating...

 

[Ranger Mike]

200,000 views

200,000 views of this " race car suspension class"...wow!

Thank you for the support over the last few years...what ever small contribution I have made here is due to the books and references I have tried to note along the way. Credit goes to those authors as well as various software programs related to chassis set up. Like I have always said..You can set up a winning race car your self..all I did was shorten the time a little...
RM

 

[NaLLa8705]

Thank you so much for the picture, it helped immensely.



Here is a theoretical question for you. On a small 1/4 mile track with a 7-10 degrees of banking, which car would be more successful.

Car A) 52% Left side weight, 2300 pounds total
Car B) 55% Left side weight, 2450 pounds total

Assuming all other things similar (rc/cross/ect), fwd chassis, stock everything

 

[Ranger Mike]

lighter is faster

thank you...in my opinion, lighter is faster and what you said. this is a bone stock class...which means power to weight ratio is everything...if bot hcrs have same engine..i.e .power out put...go with the light one.

 

[Ranger Mike]

light is right

We all know the saying “ opinions are like A------s, every one has one”

Let us look at the above post and put some numbers to it.
Given the race car has a ultra stock restriction..we assume the tires are hard, tall and narrow.
If we assume the engine is stock as well and may put out maximum of 150 horsepower
we need to look at the power to weight ratio.
150 / 2300 = .065
150/2450 = .061
looking at the attached table we see that the lighter car will make 3 mph more speed over 1/4 mile.

Lets look at the weight transferred ( see post 19 on page 2) -
2300 x .35 = 805 pounds transferred to the front and right side
2450 x .35 = 857 pounds transferred to the front and right side
remember that right front tire has a pretty small footprint to begin with and we don’t need an
additional 30 to 40 pounds overloading it. Don’t forget that additional left rear weight is going right over to the right front going into a turn.
The McPherson strut situation has bad camber build to begin with.

To summarize, for the same horsepower, light is faster, light is easier on the spec tires, light means slightly more acceleration off the turns.

 

[Ranger Mike]

Polar Moment

Many private messages on this weight question-
Let us look at weight (mass) and how it effect a race car-

UNSPRUNG Weight -Everyone parrots “ Unstrung weight is bad”..but why? Because we can not control it. This is why we go with light weight wheels, tires, turn shock absorbers upside down. Sprung weight must be placed where we can have maximum control of it. Ballast is the biggest problem so we minimize its height and mount it at the polar moment to minimize its effect during cornering.

Sprung weight – Weight we can “ control” as far as that thinking goes. During this discussion we focus on Ballast or weight we need to meat the governing rules of the race track for minimum weight and percent left side weight and percent rear weight. So where do we place this ballast weight?

Simple moment of inertia is used to estimate resistance to rotation.. It is analog to inertial mass, but for rotation instead of linear displacement. Moment of inertia: Kg*m2

The area moment of inertia or second moment of inertia, is used to estimate resistance to bending. Think of a beam when you want to know how much will it distort under load. It’s a measure of the resistance of a section of a solid to perpendicular loads. Area moment of inertia: m4

Polar Moment of inertia is a quantity you use to estimate resistance to angular torsion. It’s a measure of how much resistance to twisting around an axis has a section.
Polar moment of inertia: m4

Polar Moment is the center of all forces in a race car. This is the Point about which the car pivots during weight transfer ( cornering). This point will move the least amount during this action. Indy cars have low polar moment of inertia. Sportsman Saturday Night special have HIGH Polar Moment of Inertia. Look at the attached illustration. Indy car has Low Polar Moment of Inertia as all the Mass is concentrated as close to the CG as possible. The door slammer has a V 8 mounted up high ( usually with minimum height requirement), has a big old battery mounted up high and a fuel cell mounted past the axel ( outside the wheel base). High Polar Moment does not have to do with height. High means it takes a lot of force to change the DIRECTION of Mass. Think of a 50 pound fly wheel vs. a 10 pound flywheel. Once the Mass rotates ( as going into a corner) it wants to keep rotating. Think of a bowling ball and a volleyball . The volleyball is easy to get rolling and easy to change directions..not so with the bowling ball.

So why is it important to know about the Polar Moment? We want to build the car with the desired percent of left side weight, front to rear weight. Only when we achieve this do we want to add weight to meet the minimum weight requirement when we scale. We want to add this Mass or weight at the Polar Moment as this is the point where it will move “ the least” when cornering.

Think of the old teeter totter at the local school. If two people of equal weight sit on it at the same position from the middle pivot, no teetering or movement. The center pivot is the polar moment. Now bounce up and down and the teeter totter moves but notice the center pivot has the “ least movement” relative to the rest of the board.

So if I go get the neighbors fat kid and put him on the right side of the teeter totter opposite me, the teeter totter will tilt in my favor. I have to scoot toward the center pivot point to “ equal up” the weight distribution. In fact, an observer looking at this mess from the side would see my weight was shifted 10% bias toward the center pivot point. If we were to measure the distance between the seat positions ( think track width) and measure the center pivot point from my seat position we would see a 60% left side weight bias.
If we then try the same drill but at 90 degrees ( think wheel base ) and the center pivot point – we have front to rear weight bias.

All polar moment is the intersection of these two points AT CENTER OF GRAVITY HEIGHT.

By the way, most door slammers run 18 inch CG Height and super late model cars with dry sump oil pans and aluminum heads get as low as 16” CG Height. There is a method you can use to measure exact CG on your car with wheel scales and a floor jack,

You can run up to 70% left side weight on asphalt cars but 55% is max on dirt, and 52% rear is good for asphalt and 55% max rear wt. on dirt..
see good article on this at

http://content.yudu.com/Library/A1vgq2/RacecarEngineeringFe/resources/33.htm

 

[Ranger Mike]

Center of Gravity Height explained

Ok I been getting a lot of PM about finding Center of Gravity.

If you do not have access to a set of wheel scales you can rough estimate the CG by measuring the distance form the pavement to the center line of the cam shaft on the typical V8 door slammer or V6 for that matter..even OHC 4 cylinder will get you close.

Use your local Landmark or Farmer s Coop grain elevator scale. Measure your wheel base. Mark the mid point of the wheel base on your car with a piece of masking tape. Drive on the scale so the front tires are on the scale and the tape is aligned over the entrance edge of the scale. Record the weight. Drive off the scales to the point the masking tape is over the exit edge of the scales and only the rear tires are on the scales. Take a reading. You now have the Front vs. Rear weight. Simply divide the front weight by the total to get % front weight. Then multiply the wheel base by this percentage.
Say we have 3000 pound door slammer with 104” wheel base. we scale it as noted above and get 1590 front weight, 1410 rear weight. 1590 / 3000 = .53 or 53%.
104 inches x .53 = 55.12 inch so the COG is located 55 and 1/8 inch forward of the REAR axle.

This will give you COG in one axis or 1 dimension...front to rear.



If you have wheel scales you will be able to measure this a lot more accurately but the same math is involved.
With the wheel scales you can calculate the COG in two dimensions. We get Front to Rear as noted above and we can calculate left to right % by substitution Track width for wheel base.
Same 3000 # car that has 60 inch track width. Our wheel scales show 55% left side weight. This means COG is .55 x 60 = 33 inch to the left or 3 inch toward the left side from the center point of the track width and 55 1/8 inch forward of the rear axel. Better but his does not give us the true COG which is a 3 dimensional point.

To measure the COG most accurately, we need to prepare the car as race ready..tires properly inflated, full fuel load, driver ( or substitute weight of driver PROPERLY DISTRIBUTED). Don’t just throw in a few sacks corn that total the drivers weight, you need to replicate the weight of torso , helmet and legs as close as possible.
Note: You must replace the shock absorbers ( dampers) with solid links to replicate the race ready ride height. These solid bars will permit the car to be raised without collapsing as the shock would do under load.

the following is from Longacre who make a fine series of wheel scales. http://www.longacreracing.com/articles/art.asp?ARTID=22

To find the 3-D COG height we need to use a little trig. Specifically, we are using the Law of Tangents, and the Pythagorean Theorem. We use the wheelbase in place of the Hypotenuse and we will use 10 inches for the short leg of the right triangle since we intend to raise the car 10 inches.
a2 + b2 = c2



Center of Gravity Height Formula

COH = WB x FWc
TW x Tan q

Center of Gravity Height Formula

Definition of Variables

CGH - Center of Gravity Height
WB - Wheelbase (inches)
TW - Total weight
FW1 - Front weight LEVEL
FW2 - Front weight RAISED
FWc - FW2 - FW1 (change in weights)
HT - Height raised (inches)
Adj - Adjacent side (see below)
Tan q - Tangent of angle (see below)
CLF - Left Front tire circumference
CRF - Right Front tire circumference
C - (CLF + CRF) / 2 (average circumference)
r - Axle Height


The center of gravity height is found using the rules of trigonometry and right triangles. Specifically, we are using the Law of Tangents, and the Pythagorean Theorem. The following diagrams are greatly exaggerated for illustration purposes.
Tan q = opposite / adjacent

Tan q = HT / Adj


Pythagorean Theorem


So, in our exercise, when we raise the car 10" we are creating a right triangle with the following properties:
Hypotenuse = Wheelbase = c
Opposite = Height = b
Adjacent = a
C = 2 p r ( r is axle height of 10 inches)
Therefore using the Pythagorean Theorem:

Adj = square root of (WB2-HT2)


Once we know the value of the adjacent side of our triangle we solve for the tangent of q using:
Tan q = HT / Adj

Ok, now that we know the tangent of the angle we can calculate the center of gravity height based on our weight measurements using the following formula:

COH = WB x FWc
TW x Tan q
WB is the wheelbase
FWc is the change in front wheel weights
TW is the total weight
Tan q is the tangent calculated above
This calculates the Center of Gravity Height from the axle height.

To find the CGH from the ground, you must add your axle height to the above calculation. You can measure your axle height or calculate it using the average of your two front tire sizes and the formula for the circumference of a circle.

C = 2 p r ( r is axle height of 10 inches)

C is the average circumference found by adding the LF and RF sizes and dividing by 2.
p approximately equals 3.1416
r is your axle height
For example: Your LF is 85.5" and your RF is 87". Your average circumference is (85.5 + 87) / 2 = 86.25". Your axle height is (86.25 / 2) / 3.1416 = 13.727". Add this number to the CGH to find the center of gravity height in relation to the ground.



Now you have your true 3-D COG.

 

[Ranger Mike]

I apologize for many " errors' in the above formulas used in calculating 3D COG...I wrote the post in Windows messanger because of spell check..when i copied and pasted it some symbols translated to what ever software is used on this forum and the letters changed to th edefault format...i recommend you click on

http://www.longacreracing.com/articles/art.asp?ARTID=22

for details

 

[Rahul jeta]

although all your methods was on the mark,but since i am learner,i do have difficulty in understanding this second point.
2. draw the ground line ,vehicle center line and center of the left and right tire contact patches. Determine where the outer lower control arm ball joints (BJ) are located by bolting the upper and lower control arms to the spindle and bolting the spindle on the wheel to be used...some round track cars have different wheel offsets so be careful. mark these BJ centers on the drawing.

my question is..how will we determine the outer lower ball joints..?
i want to design a suspensiom system,and i wann know where to start from?
and how will we locate the pivot joints and how will we determine the lenth and angle of the arm..?
I am using double wishbone

 

[Ranger Mike]

starting chassis from scratch

Welcome and great questions...
Please note on Page on page 6 of this post..shows typical ball joint. To do a good job you can contact the manufacturers (Moog) being one), and have them send you diagram of exact pivot point. Another alternative is to find and old ball joint of same type you intend to use and cut it to determine the center of the ball stud.
You have a huge question that has many possible answers.
Will your suspension be:
Front wheel drive, front engine
rear wheel drive rear engine
rear wheel drive front engine
front wheel drive rear engine...??
What will vehicle weight be?
What is wheel base and wheel track width?
Where are the heavy components like fuel cell, transmission, differential, battery, driver going to be located?
What size tires will be used and what are wheel specs?
What is desired ride height to be?
Do we have a roll cage ? is the vehicle a hard top of convertible?

The short answer is once you figure out where the 4 tires will be you can start to connect them to the chassis and locate the engine, transmission etc..
finally, after the heavy bits mounting locations are finalized we work backwards to tweak the wishbones and mount points to get the roll centers we want.
very short answer...

 

[Rahul jeta]

Thanks for the reply..:)
Currently I am working on a hybrid trike,it doesn't have any engine.
its a tadpole having rear wheel drive.the track width is 45" and the wheelbase is 90.

 

[latemodel18]

Big Bar Soft Spring Setup

Ranger Mike I have been going thru this whole forum trying to learn about this kind of setup and I am enjoying it very much. I was hoping you might be able to look at some of my numbers and setup and be able to give me a few pointers. We are running a template body tubular chassis on a hosier 970r 9" tire on an 8" rim, Our springs are 175 across the front and Lr-200, RR-350 with a medium rubber and 1.375 sway bar, panhard bar is 8.875 left side axle and 10.125 right side chassis. 2736lbs without driver, left side is 59.9- cross 54.4 before preloading the bar and rear 51.2 wheel weights are lf-673, rf-689, lr 918, rr-456, trailing arms are at 3 degrees uphill on the left and 1 degree on the right, top link is centered and a lot of downhill angle,{sorry forgot to write that down before I left the shop} and 2-7/8 stagger with a Detroit locker on a medium banked 3/8 mile asphalt. At the track last weekend we ended up starting off with 6 rounds of bar in the car to try even out the nose but as testing continued the driver said he was tight thru the corner and loose off so we bumped the RR up to a 375 with medium rubber took 1-1/2 out of the bar and put 1 round of cross in evenly and he liked the car much better but still was not able to pull it to the bottom at the apex when he needed to, still a little snug. I might be wrong but I think I could be crutching the car with to much bar and maybe need to up the rr more. I done some measurements today and plugged them into my roll center program and I tried to attach it for you to see but no luck. It shows RCH-1.7 and RCL-2.9 at static and 2" dive it moves to RCH-4 and RCL-7. Not real sure where the roll center should be with this setup as I am only into this 3 weeks as a first timer working on race car setups. I am sure I am still off on understanding all this but what I have learned has pretty much been from reading on this site. Thanks again and really enjoy it.
Rod

 

[Ranger Mike]

Thanks you fro the kind words and welcome. You have a good grasp of what is going on with the set up.

I had to re-read the part about springs...350 right rear...whoa...
just from what you tell me I think you have really twisted the car to make it work half way..
When you preload the ARB you take away the purpose of the bar...go as light as you can on front springs to keep the nose as low as possible until you hit the corner where the ARB will contribute to roll control. When you preload the bar you are really stiffening up the total front spring rate. I much prefer going up on the front spring rate and keeping the bar neutral.

no way would I run that much preload on the ARB and have my rear springs stiffer than the fronts.

you have a good initial set up regarding weight percentages..almost ideal in fact.
without knowing the A-Arm motion rates and the like a ball park setup on coil overs
350 # on lf and rf, 225 on lr, rr, and 220# ARB

My main question is the Detroit locker situation. Is the driver using a lot of trail braking on turn entry?
If he is, the locker outside ratchet will not sense the power off and will stay locked up, the differential will not work and the car will push.
Did you remove the holdout ring on each side to provide instant lock up of the cogs on the driven assembly.
Sounds like you are running about the same stagger as the folks running a spool and this is not letting the differential do what it is supposed to do.
can you calculate the ARB spring rate.

Please confirm the Roll Center static location.. it is to the left in static...correct?
Also where does the RC end up on dive..to the left?
Looks like you have classic push going in loose off caused by RC being too much located to the left , not providing enough leverage to stick the right front going in...the current twisted chassis setup is a result of band-aids applied at the track to fix the car...

 

[latemodel18]

yes Mike the RC is 2.9 to the left at static and goes to 7 left at 2" of dive and the RC height is 1.7 at static and then goes to 4
Thanks
Rod