Race car suspension Class

[Timaladd]

Ranger Mike,

I want to pick your brain on 2nd gen camaro leaf spring mounting for 3/8 medium banked dirt. Track usually goes slick.
1.-What are your thoughts on raising one or both of the front spring mounts to gain drive off? Any othe adverse affects of only altering the left front mount?
2.-Effects of splaying front mounts inward? Effect of splaying one side more than the other?
3.-Besides changing ride heighth, what other affects (sidebite) do lowering blocks resent. More focused on roll heigth changes than leaf spring wrap.
4.-How much rear steer do leaf spring provide? I have been successful on crate latemodel using rightside bars to reduce right side wheelbase as right rear bumps. Much better to reduce wheelbase in bump than put more angle in leftside bars which reduces leftside wheelbase.

Thanks so much for you help. I have learned a lot reading your posts.

 

[Ranger Mike]

i have just finished rebuilding the old Ford NAA jubilee tractor..got to mow 6 plus acres and the girl friend is blonde...no way am i going to get any help form that quarter..so i got behind in my posts and emails..should be caught up this week..folks

 

[Ranger Mike]

Timaladd..welcome,,good to have new racer.. i grew up on these set ups..even had torsion bar front end..

see post 116 on page 8 for roll steer explanation

Hotchkiss drive rear suspensions
NO rubber bushings belong in any race car chassis set up.Get nylon or urethane or brass bushings but get rid of the rubber stuff.

Been around since horse and buggy days but it is simple and it works. it was found that mounting one shock ahead of the axle and the other behind would reduce torque induced wheel hop during acceleration and braking.
Since the leaf spring is used to transmit acceleration and braking forces, their positioning and configuration is critical. These forces cause the axle to twist and tend to wrap up and distort. To counter this it is necessary to increase the number of spring leafs or thickness of the leaf to get enough force to counter spring wrap. You can add a full leaf or thicker leaf but this also increases spring rate. It was found that if only the front half of the spring leaf is added, axle wrap is decreased while not adding as much spring rate as a full leaf.

Spring eye height of the front spring eye primarily determines how much anti-squat the rear suspension will have. The higher the spring eye the more anti - squat. Generally height between 10 and 15 inch above ground give best results. If you run the spring eye too high you will get brake hop. The rear spring eye also effects anti-squat but not as much.

To work properly, mono leaf springs must be mounted straight and parallel to each other and perpendicular to the axle housing.

The rear Roll Center (RC) on mono leaf setup is located half way between the bottom of the rear end housing tube and the top of the leaf spring.The Rc can be changed slightly by using shorter or taller lowering blocks. Don't go over 2.5 inch because a taller block will create too much leverage on the leaf spring and really adds deformation under acceleration/braking.
Cars with monoleaf springs usually have rear RC at 8.5 to 11 inch. These leaf systems are not as tuneable as Coils/ coil over shock packages. The only way to change rear RC is to move ballast weight around. On a dry slick track mounting ballast higher in the chassis will create more overturning moment which creates more right rear side bite. Typical monoleafs come in .323, .291 and .262 inch thickness. Thinner springs work better on dry slick tracks because they deform and cushion wheel spin better. But this weakens the springs and you must monitor the leafs for deformation. Thicker leaf will last longer but not provide optimum hook up. The .291 inch leaf is best compromise but..you need to replace these at least once a season.
NOTE: The springs must always remain parallel to each other in the fore/aft plane. In other words.. Don't locate the right side spring eye in the top chassis spring eye hole and the left front spring eye in the bottom front spring eye hole. Move them the same and together.

Use slider boxes to mount the rear spring eyes. They eliminate spring bind cause by shackle distortion. The mounting angle determines the amount of roll steer you will have. The best way to amount a leaf spring is with slight downward angle, as viewed from the side, with the front eye of the spring slightly lower then the rear spring eye. The downward angle should be 2 to 4 degrees.

Arch of the leaf and amount of torque warp in the leaf determines the amount of rear roll steer. When cornering, the more arch in each spring will mean more roll steer. The right rear spring compresses and lengthens. The left rear unloads and shortens up. The right rear is lengthened creating rear over steer. The amount of roll oversteer depends on the spring arch and amount of body roll. Three inches of arch usually produce a fair amount of roll over steer. One inch is probably not enough.
When you nail it out of the turn, the torque wraps the front spring and shortens the front segment and pulls the axle tube forward. This depends on the arch and thickness. One last note; see the post # 298 on page 19, on eccentric for right side front spring eye. hope this helps.

 

[rick7343]

Time to order some springs...

How do I calculate what springs I need in the front of my chevelle clipped car? I hear some of the metric guys are as low as 600 lbs...

If there is a benefit to dropping the front end in the corner, I will do it...

Does 600 lf, 650 rf, and a 534lb bar sound crazy for a mid banked 1/3 mile ashalt oval?

Can the anti sway bar be too big?

 

[rick7343]

Reasons for having low Roll Centers ( RC) - I can not say this too often...Racing is about Tires, Tires , Tires. All efforts are to provide the best tire contact patch for the longest period of time and making sure the car finishes. To this end, it s all about planting the tire with enough downforce to permit the fastest corner turn entry, fastest mid turn time and fastest turn exit traction. Tire compound is a critical factor. I could write a book on this but let us assume we are stuck with a hard compound tire..Duometer reading around 85 hardness. Let us also assume we can not manipulate Mass placement in the race car ( can not offset the engine, and rules dictate minimum engine height, percent left side weight, percent front to rear weight. The most critical element is to have the best balance between Mass placement and RC location so that the car turns in the middle of the corners. Sufficient weight must be transferred to the outside tires to create vertical downforce.
Jacking Effect- This is the reaction of the outside tire force transmitted to the RC pushing it up ward during the turn. Imagine a poll vaulter going up over the bar. the poll vaulter is the RC. The pole is planted at the outside of the outer tire patch. The pole vaulters forward motion in comparable to the centrifugal force acting on the cars body during cornering. The greater the forward motion of the pole vaulter, the greater the height attained..comparably the greater the centrifugal force cornering, the more JACKING EFFECT and the higher the RC is raised. the lower the RC, the less jacking effect. RC located at ground level have zero jacking effect.
If this is not enough to make your head explode..there is one more major thing to consider. The distance between the Center of Gravity (CG) and the RC will effect the handling. This is best covered in Spring selection since the springs counter body roll as well as the anti roll bar ( sway bar). Suffice it to say the closer the distance between the CG and RC requires stiffer springs.
Bottom line is that cars with high CG have more body roll. Harder compound tires require lower RC combined with softer springs to create vertical downforce so lower RC creates more body roll and provides the traction and side bite that hard tires require.

So am I reading this right? We want body roll to get the outside tires to bite? Doesn't the SSBB theory work against this as it limits body roll?

 

[Ranger Mike]

Rick..you are pretty close to correct on the " soft" springs..I recommend every one re-read post 17 on page 2 _Spring rate vs Wheel rate and post 19 on page 2 - how to calculate front spring rate required for your car. And I can see I got to finish the sway bar/ARB post cause you are all asking for more info on this. I'll do her now!

 

[Ranger Mike]

Anti Roll Bar (ARB) - sway bar - stabilizer bar

Back in the 1960s passenger cars did not have ARB until the end of the decade. I was a kid going to the local asphalt track and none of the hot dog late model cars had these. This was in the day when you could stick a 1200 # railroad car spring in the right front of the car as the hot set up in hobby stock class. Meanwhile the NASCAR boys were going faster and faster on the high speed ovals and found out that low was good ( regarding body to pavement clearance). In fact back then you only had to pass ride height inspection at pre-race tech inspection. Some crew chiefs fabricated chassis stops that would break off during the race and ZHAZAMMM..the car would drop an inch in the front to channel air better and grab some aero advantage. About this time it was found that if you added the ARB, you could run softer front end springs and still corner the same. The softer springs got the car even lower once air started to push the nose down at higher speed. Naturally, everyone started copy catting the set up and after that, every one was running ARB but most did not have a clue as to why.

The same thing was going on in the open wheel formula car world. When the Fc cars went from skinny tall tires to short wide gummy rines the suspension designers didn't keep up. The shorter tires dropped the roll center which added to roll. The idea that soft springs were needed to maintain the tire contact patch so in came the pencil thin ARB used on the front and rear of the FC cars. When the chassis mounted WINGS became effective, the Fc boys had to up the spring rate or replace the belly pans pretty frequently. The wing thing got ridiculous to the point the spring rates were way past 1000# to the point that aero down force was the only game in town. Everyone forgot about the contribution the ARB made to the set up. This insanity continued until the tire was the only spring thing on the car .(See solid axle conversion kit later on in the post.). eventually the ground effects stuff was banned and reason returned to the racing world..for a time and the ARB was back in vogue. What people do not appreciate is that within reason, springs and ARB are interchangeable so far as roll resistance is concerned. We can reduce roll resistance of the ARB if we up the spring rate on the springs, the same amount at the end of the car that is effected.Chassis Engineering by Herb Adams - One excellent source and got a lot of this post from his fine book.

Roll Angle
When a car corners the body rolls to the outside and we have BODY ROLL. The amount it rolls is ROLL ANGLE. When we have this condition many bad things can happen and only one good thing. It is all about tires, tires, TIRES. A tire has max traction when n it is perpendicular to the track surface. During body roll, the camber changes and once we have over 3/4 degree camber gain per degree body roll the geometry is not there to maintain proper contact. Now we can dial in static negative camber of 2 to 3 degrees and this helps keep the outside tire square to the track surface but there are draw backs to this set up. We have to control the body roll, more specifically, the Roll Angle (RA).

We can reduce RA by lowering the Center of Gravity but in most cases this is already done. We can change the Roll Center height and location but this is a tough thing to do on the front end due to all the related suspension components. We can increase the track width with wheel offset but we can only gain a minute amount with this tuning. You can reduce the cornering force that generate roll angle (slow down)..NOT! Or we can increase Roll Stiffness.

Roll Stiffness- One way to reduce roll stiffness is to increase the spring rate. If the spring rate is high enough to limit roll to the maximum, the wheel rate in ride inevitably would be too high for tire compliance.

Anti Roll Bar - These are traversally mounted torsion bar springs, adding spring rate to the chassis during cornering.As the chassis goes into roll, the outside arm of the bar moves up while the inside arm moves down, crating twist in the bar. The resistance to twist is the bars spring rate and this adds to the total spring rate required to handle the weight transfer during cornering. Stiffness of the ARB increases very quickly as itsdiameter increases. Stiffness is a function of diameter to the 4th power, stiffness = D4.The effectiveness of the ARB depends on the length of the swing arm. The longer the arm the less force applied relative movement at its ends. Short arms are "stiffer" , long arms are" softer" , since you have a longer lever.

 

[Ranger Mike]

Calculation of proper ARB rate.

See post 19 on page 2 for the calculation of the correct spring rate. Of the total front spring rate ( left front, rt. front and ARB) the ARB should be 30 to 50% of this. Over 50% and see "solid axle conversion kit" note below. Flat asphalt track requires the most ARB higher bank tracks go to the minimum ARB rate %.

Rate in pounds per inch of arm deflection of solid ARB
1,125,000 x D4 / L x A2note: D4 and d4 is to the 4th power..it did not copy over from my word document so multiply it 4 times

Where

D= bar outside diameter

L= effective bar length

A= effective arm length

For tube or hollow bars use

1,125,000 x (D4 – d4) / L x A2

D= bar outside diameter

d= bar inside diameter

1,200,000 is base number for 4130 C34-C38 material

ARB must be mounted square to the lower control arms. The bar must be perpendicular to the vehicle center line. You have to mount it as close to the lower ball joint as practical. Just as we had to calculate the motion rate of the springs on post 19 page 2
we have to go through the same drill with the ARB. Effective wheel rate is found by multiplying the motion ratio squared by the ARB spring rate. The motion ratio is the arm mounting position length on the control arm (A) divided by the lower control arm length (B).
Then this motion rate is squared.

Too stiff ARB - The ARB has to be balanced with the front end spring package. The less work we get out of the springs, the more the ARB has to do. There is no dampening effect on the ARB by the shocks (dampers) Shocks only work on the springs when compressed or in rebound. We can run into '' rock roll back" where we get oscillation. When we run into a stiff ARB condition, and one wheel goes into BUMP, the two wheels are no longer independent and the load will transfer laterally by the ARB itself. This makes for a very darty car. When we reach the point that the ARB is far stiffer than the springs we get to the point the car is very slidy due to roll resistance of the set up. Avoid making the ARB so stiff that we have a "solid axle conversion kit" going on.

Misc. stuff on ARB - Never drill a sway bar ( ARB ) to soften the rate..it will snap. Never weld on the ARB..even tack weld. Beware of nicks and dings as it will weaken it and may even snap.
Paint a stripe the full length of the effective part of the bar and if you see some twist, replace it. ARB can go on you and you will never know it. One hard to find problem is when handling suddenly goes away.Beware - ARB can yield without breaking. Handling will diminish subtly and you can not spot it unless you pull the bar and measure its effectiveness. When you first scale the car, stick a bottle jack under the right control arm and jack it up and inch. Note the scale reading on the left ft. Write it down.
We used a sway bar loader that had a hydraulic jack and the driver could dial in load on the ARB. Worked great. If you have a left side weight rule this is one thing to get you 50 extra pounds but remember to dial it back to zero before you post race scale the car. Recommended only for the team that has radios to "remind" the driver about this.
No one uses solid ARB any more as you are only adding weight.
If your race class dictates a stock sway bar..look at
http://www.hotchkis.net/_uploaded_files/hollow_vs_solidinstructions162file.pdf
stock looking sway bar but is mucho lighter on the front end.

 

[mender]

Too stiff ARB - The ARB has to be balanced with the front end spring package. The less work we get out of the springs, the more the ARB has to do. There is no dampening effect on the ARB by the shocks (dampers) Shocks only work on the springs when compressed or in rebound.

Not strictly true; the shocks dampen suspension movement, which the ARBs (and springs) are connected to.

ARBs effectively add (or subtract) spring rate due to body roll non-linearly and require a different valving split on the shock. Going too far with BBSS can lead either to oscillations (duckwalk) or overdampened reaction to bumps; harder to get the right mix.

 

[rick7343]

So is the soft spring route worth pursuing? Seems a lot have opinions against it..

 

[Ranger Mike]

mender..this is why i value your participation...i'll give you that..shocks do dampen the weight transfer..the point i was trying to make is when the nose it totally down and the the car hits a bump, we got no damping and if you have a very hairy ARB you will run into skatey action..you are correct that shocks do in fact dampen the ARB roll action since we need to plant the right front tire, we need to use some roll to do this.

thank you
rm

 

[Ranger Mike]

rick look this over and decidehttp://www.longacreracing.com/articles/art.asp?ARTID=30

the following is summary of this article from Longacre

Articles : Front End / Chassis Setup


Big Bar Soft Spring Set Up Secrets

Should you be jumping into the latest soft set up craze for late model asphalt cars? Maybe you will find more speed or maybe you won’t, but either way understanding the dynamics will help to improve your corner speeds.

The soft set up is designed to take advantage of spec tires that are now commonplace. New age tires put up with more abuse and resist blistering as compared to those from the tire war era. Taking advantage of aerodynamic benefits created by body designs that are sleeker is part of the soft set up as well. Maximum stability is created through less side body movement. By understanding the goals of the big bar soft spring set up you can find ways to improve your lap speeds.

The new soft set up buzz involves a big sway bar to control roll and the softest front springs possible that are just big enough to keep the nose from bottoming out. Ironically, the new buzz has been referred to as the “soft set up” when in actuality there is much more spring rate added by the sway bar verses the reductions in the front spring rates.

Higher shock rebound rates are needed to control the added spring rate introduced by the bigger front bars. Added rebound helps to tie the body in the lowest nose position possible. Typically, the package is coupled with rear springs that are stiffer than traditional set ups. The stiffer rear springs can be vital to the so called soft set up for a variety of reasons which we will analyze.

Why soft front springs? A big benefit is getting the nose down on the ground. Air that gets under the car creates lift which is just about always bad. Getting the nose down creates more airflow over the entire body creating more down force literally pushing the entire car into the track promoting more corner grip. While the front springs are softer, the big sway bars are adding a large amount of overall spring rate to the car. As you go up in bar diameter the rates increase exponentially.

Why a big bar? Since the soft front springs let the nose settle down to the pavement we then need to keep the body position low throughout the turn. A big sway bar is utilized to resist roll and it adds spring rate as the car enters the turn. We are trading roll rate from the front springs and moving that work to the sway bar. We are also adding overall spring rate and taking advantage of the aero grip created by modern day body designs. The benefit of the big bar is that it helps to hold the left front down as you roll through the turn and on acceleration. With the sway bar holding the nose piece low throughout the turn more air flows over the entire body surface creating additional down force and grip. The car being held down low allows for less overall side travel through the turn, hopefully resulting in more overall stability and consistency. With the suspension linkages traveling less after corner entry, the dynamic changes are controlled and the car becomes more predicable throughout the turn. Minimizing travel in the center of the turn is a big piece of the new package and the added bar rate enhances driver confidence. In addition, the center of gravity is lower in time with when the corner loading is at its maximum point. The big bar creates a quicker responding car that feels more stable due to the elimination of nosing over on the RF.

To enhance less lift at the left front tire additional rebound is utilized in the shock package. Shocks with more rebound and less compression are a common practice when utilizing the soft set up. Once the nose settles during braking, keeping it down there becomes the goal. The added rebound helps to keep the car flat and added rebound controls the spring oscillations as well. Shocks need to control the spring rate included both in the springs and in the sway bar. As always, the teams that best match up the shock package will go faster for a longer period of time. In fact, matching the shocks to the overall set up package, track, temperature, and driver style is still a critical piece of the puzzle. Remember, there is generally more spring rate to control and these forces need to be considered when matching your shock package to the new concepts.

Controlling the body angles in the turns helps to create consistency. You can imagine that if the nose piece were low on entry and then lifted on exit that you are introducing variables resulting from the continually changing body position. Constantly changing linkage angle changes have an affect on the handling as well. Lift at the nose and squatting in the rear reduce down force at a varying rate throughout the turn. Nose raise creates additional front lift and rear squat moves the spoiler out of the air for less rear down force. With traditional set ups, the front aero lift and the rear spoiler moving down occur at the worst possible times. Obviously more rear spoiler on corner exit would be good for forward bite and a lower nose piece throughout the turn is going to create more speed. These two gains are included in the Big Bar Soft Set Up. A more constant body position allows the driver to chase the car less as the aero change throughout the corner is more consistent.

With the soft front springs, big front sway bars, and additional rebound the front end is now doing its part. Big rear springs pitch into keep the rear spoiler up in the wind for more exit grip and forward bite. Added right rear spring rate holds up the right rear corner helping to keep the left front low promoting more air flow over the body for more overall down force. The big bar soft spring set up gets the front and rear to work together for maximum aero balance and grip.

So now that our soft set up has the body flat, the nose low, the rear spoiler held up in the wind and body movements controlled promoting consistency, this now brings new chassis parameters into the process.

We can look at each corner of the car and think about new dynamics created by the soft set up as compared to traditional set ups. Each corner is affected differently and we can think about the new challenges and consider the adjustments required to make the big bar soft spring set up work best. All adjustments must work together. A complete package is the goal and you must tune the entire car to achieve improvements. A traditional set up that is completely dialed in would be much better than a big bar soft spring set up that did not address all of the variables.

LF
The left front starts out at the tech approved minimum ride height. The soft front springs allow the front end to drop under braking and the big bar, big right rear spring, and added rebound hold the left front suspension for maximum nose drop on entry and throughout the turn. You can see that the added downward travel will have an affect on the camber patterns and adjustments need to be made. With the LF A-arm being shorter than the LF lower control arm your car will lose camber under the left front suspension compression created by the big bar soft spring set up. The shorter upper A-arm decreases in length faster then the lower control arm causing camber loss. This camber loss is opposite of traditional set ups that promote camber gain during upward body movement.

The soft set up usually requires high amounts of LF static camber as compared to traditional set ups. Top crew chiefs check the camber at ride height and then recheck the camber at the anticipated corner ride height. The camber in the center of the corner is most important and static settings need to be adjusted for optimal camber at the center of the turn. The new approach creates static camber settings that seem radical as compared to traditional set ups.

RF
The right front starts out at the approved minimum ride height and drops during braking and moves down even more when the body rolls. Our soft set up with a big bar and high rebound actually allows for more RF drop from static ride height to the middle of the turn. The additional amount of travel created allows for more camber gain as the RF A-Arm is shorter than the lower. Our new big bar soft spring set up will require dramatically less static camber allowing for more optimal camber in the center of the turn. You can see that experimenting with the camber curves and static adjustments require a change in thinking from past ideals.

LR & RR
Bigger springs in the rear create new thought processes as well. More spring keeps the spoiler in the air allowing for more down force and less downward movement of the body. With less movement you may experience the need to vary anti-squat adjustments. Again, our thought processes are different with the new set up. You may find that you need to run more split in the panhard bar to get an equal amount of rear steer as the stiffer springs coupled with the stiffer sway bar create less roll. You might want to experiment with more trailing arm angle as well to help rear steer the car through the center of the turn. The whole mind set relating to the rear linkages needs to be based on less travel. It is very common that you will run considerably more RR spring rate than LR with this set up.

The soft set up should really be reserved for those that already are consistently fast and have a handle on traditional adjustments. In order to achieve improvement it really helps to understand the dynamics behind all adjustments from springs to shocks to weight adjustments before experimenting with the unknown.

Once the decision is made to experiment with soft set ups experience has shown that it is an all or nothing proposition. The soft set up is an entire package versus just a spring adjustment. Moving up one sway bar size and changing 25 lbs. of spring rate is not really embracing the concept. The new bar rates and spring choices are eye popping as compared to traditional set ups, an open mind to these ideas is truly required.

Suspension design over the past twenty years is virtually the same from Nextel Cup to Saturday night. If that is the case then why is this big bar soft spring set up gaining popularity? There are several things that have changed during that time allowing the concepts of the new set up ideal to be possible. First off the new bodies are very sleek as compared to old body designs. Aero grip is something that has increased steadily over the years. In addition, most people are running tires that run longer. Harder longer wearing tires that do not fall off much have become common. The aero advantages really help to create grip in harder tires. While the aero advantages are vivid, the new era tires are the main reason that the new set up concepts are to be considered. Further, big bars speed the loading to the contact patch and the new harder tires are up to the challenge. We also have more horsepower and more RPM as compared to twenty years ago and more forward bite makes that horsepower more effective. Shock technology has improved and better shock control reduces tire temperature increasing tire wear. Current shock adjustability allows for more grip by keeping the tire on the ground.

If you ran super soft tires it makes sense that the big bar soft spring set up would be fast for qualifying but the tires would fall off or blister on a long run. Blistering tires were common in the tire war days but for now it seems that most divisions are currently being supplied harder, longer wearing tires that easily go the distance allowing more stress to be placed on the contact patch. It makes sense that bigger front bars and more rear spring rate transfer load to the tires more quickly. The point is that sleeker bodies and better, harder tires have made the bigger bars and soft front springs possible. In addition, radial tires create a lot of grip through superior side wall design further enhancing the big bar soft spring concepts.

The big bar soft spring set up does seem to work better, at least to date, on tracks with less banking. Why? Banked tracks compress the suspension due to the higher speed and additional travel. Banked tracks keep the nose piece close to the ground throughout the turn. Sway bars simply do less work on banked tracks as cars compress into the banking where as on flat tracks the roll is much more evident. The aero advantage is created by the banking. Certainly the big bar soft spring setups can still work with banking but you can see that the banking creates some of the benefits naturally. Thinking out the dynamic movements on flat and banked tracks will help you take advantage of the positives on all track types.



Big Bar Soft Spring Benefits:

* The car reacts quicker
* Roll centers and move less in the turn creating stability
* More grip due to Aero advantage
* Lower center of gravity throughout the turn
* More forward bite
* The added front sway bar rate enhances entry confidence

Drawbacks:

* More stress on the tires
* Lots of trial and error testing to identify new baselines
* Sway bar neutral setting and preload becomes critical
* Camber settings become more critical
* Your old set up book will be junk!

Where the big bar soft spring set up works better:

* Experienced drivers and successful teams
* Flat tracks seem more conducive to the principles but it can help anywhere
* On tracks with reasonable grip
* With tires that can take some punishment

 

[rick7343]

How come every time I look for answers, I only find more questions...

 

[mender]

It's always darkest before the dawn.

 

[Ranger Mike]

ifin it were easy everyone would win.

 

[rick7343]

SO what do you guys think?

My plan would be to run soft, but not soft enough to need bump stops or coil bind...

Would that bar be big enough?

 

[Ranger Mike]

i would go with the light spring package and sway bar can deal with the softer package..did you figure out total weight transfer yet? what is your front motion rate?

 

[mender]

Used to be that you set it up as soft as you could, then went one step softer and learned to drive it like that. Soft is fast but don't get behind the car or it'll be driving you.

 

[rick7343]

Ok, here is how we determine the proper springs for each corner of the race car. you asked about loads on each wheel..well here is an example of our old door slammer running on a medium banked asphalt track.
Stock suspension with solid rear axle.
We calculated that it is under 1.3 Gs in the turn. " F= ( m*v^2 ) / R " is correct formula
one more piece to ponder..

from our cone killing days in SCCA Autocross..skid pad testing ,,go to parking lot, airport,,what ever, set up circle 200 to 300 feet in diameter, drive around the cirle as fast as you can without spinning out..
G = 1.225 x R / T squared
R= Radius of the turn in feet
T = Time in seconds to complete a 360 degree turn

typical Corvette corners at .84gs
road race sedan like Tran Am 1.15 Gs


if you know the tire performance curve from the manufacturer charts weight (vertical load in static pound) vs Traction (lateral load in lbs) you can calculate the Cornering efficiency.

This particular car weighs 2800 lbs. of 35% of weight will transfer under 1.3 G
and 75% will be on front end due to engine weight and corner loading

2800 lbs. X .35% = 980 lbs. transferring or loading tires

75% of 980 lbs. = 720 front end weight
divided by three to determine wheel rate ( two front springs and sway bar )
so we need wheel rate of 240

Wheel rate = (Length of A-arm divided into inside frame mount point to center of spring mounting point) squared

times spring rate


now the hard part
get out the tape measure and measure bottom front A-arm length
1. inside frame mount point to center of outside ball joint
2. distance from inside frame mount point to center of spring mounting point

stock Chevy A-arm is
16.5 inch inside frame mount point to BJ and 9 inch from inside frame mount point to center of spring pocket
assume you have a 800 lbs. spring
wheel rate = 9 / 16.5 = .54


.54 x .54 x 800 = 233 lbs. spring required to handle weight transferred

run a little stiffer sway bar and tune from here..
Chances are the Gs are off a little but we need a baseline t ostart andthis is as good as any.

A little clarification on this measuring process??

I would assume that because the control mounts are angled on the stock chev frame and arm that I would have to project a line between the 2 mounts and then "draw" a line thru the center of the balljoint and spring pocket and then measure from wher those 2 lines intersect?

The ball joint is almost in line with the front control arm mount on the chevelle, both upper and lower arms are offset...

Performance trends looks like maybe it assumes the ball joints are located in the center of the arms... on the upper anyway... I have been spending all my car time on physically finishing the build, and haven't spent much time on the computer program yet... feel free to correct me. I can access this forum while at break at work, but not the preformance trends program...

Thanx for the time!

 

[Ranger Mike]

Rick, the performance trend software Circle Track package assumes 2D and assumes everything is "in Line". the Perf Trend Suspension Analyzer is true 3D and you must measure depth distance as well as length and height, It takes a whole lot of work, Depends upon what you are after. i use the 2D if I am trying to get Roll Centers located properly. The 3D package is what I use on Formula Car as the Circle Track package can not accommodate the dual wishbone set up.

 

[rick7343]

So how do we alter the formula to use a bigger bar?

 

[Ranger Mike]

these are STARTER set ups from many sources...asphalt medium bank track
for car with hard spec tires conventional coils on traditional A-Arm suspension..
2800 to 3200 pound
LF 1000 RF 1050 ARB 220#

2400 to 2700 pound car
LF 950 RF 975 ARB 220#

With the above formula let's say we got 3000 pound car
3000 x .35 = 1050 wt transfer with 788 # coming forward
theoretically we need 262 " to be controlled by 2 springs and on ARB
since we know the wheel rate is .54 and we know the spring rate is a product of this -

.54 x .54 x 950 = 277
.54 x .54 x 900 = 262
.54 x .54 x 850 = 248

Rick, from your previous post, and I still don't know your car weight

.54 x .54 x 650 = 190
.54 x .54 x 600 = 175

total wt coming to front is 788
788 - 190 = 598
598 - 175 = 423 that has to be dealt with by ARB

In the real race world we are going to have 25 to 50 pound higher on the RF
a universal ARB 45 1/2" long ( arm to arm) with 31 1/2" to start of radius
will have following spring rate depending upon length of the arm
1 " diameter 176 to 264 #
1 1/8" Diameter 266 to 400 #
400 # is a BIG BAR.I would up the spring rate a little

 

[rick7343]

Thanx Mike... car is 3250, and the bar I had in mind is 540lbs... stock configuration..

 

[Ranger Mike]

Rick
i sent you private message

 

[Ranger Mike]

3250 # car weight means about 1138 # weight will transfer...
3250 x .35 = 1138
75% will come forward in the turn 1138 x .75 = 853 #s
853 / 3 = 284# to be handled by two springs and a sway bar..now the fun begins..
you can have different motion rates depending upon the A-arm used
figuring a typical motion rate .54 to .60

so .60 x .60 x 800 pound spring = 288 ..close to what we want

if we really want to go trick , a 600 pound spring will yield 216 pounds
216 + 216 = 432 pounds
853 - 432 = 421 pound ARB or one big sway bar..but...

when you dump 284 pounds of motion rate weight on a 600 pound spring, that spring will compress about 1/2 inch more than the 800 # spring so you have to compensate relative to camber build..and you have to have enough right front weight to plant the right front tire to turn it...
and..these numbers are ball park only..tires may not have that high of a traction, your Gs may be more or less, depending upon the track banking, roll center and Center of Gravity is all over the place..but...this method gives you a logical base line to start to tune in the chassis.

 

[rick7343]

So are we concerned about the location of the roll center when at ride height or in dive?

I have been told not to go too low with a cast iron head engine and harder tires...(3.5-4.5" range)

How is roll center location requirements changed by going to a big bar?

I assume the chassis won't roll as much, so does the outside tire still get loaded?

Need to move the roll center more to the right ?

 

[Ranger Mike]

Rick..am in Detroit on business...but..ifin I remember right..the standard reason for not going low on RC is to keep the lever arm ( moment) short..too long an arm means more spring rate to handle the extra leverage. With iron heads 3.5 inch is about max length. This whole theory assumes we have centered RC.
I never put much stock in this and I only looked at camber gain...Low RC means minimal camber gain. get the RC height and location right then tune in with springs and ARB...don't change Rc to accomdate a stiff ARb..it is the tail wagging the dog...same with springs


We need some body roll to plant the right front tire. we do not want ogo over board on roll though. I would look at roll center at ride height and location after one inch compersion..1 1/2 inch max..the RC migration is important. If you can start out at 3.5 inch RC height and 3 to 3.5 inch offset to right and end up between 2 and 3.5 offset to right...and the RC under where you started...you should be close. the reason we have the right side off set is to get enough weight to plant the rt ft tire andsince we have 55 to 60 % of car weight " rolling thru " the RC with this location...we get enough weight without going wild with body roll. If you run too stiff a roll bar and get zero body roll the springs have to do all the work and you are getting into the solid axle converion kit mode.
One more thing..beware of too much dive..you should have 1 1/2 to 2 inch dive max. Most super late models are running +/- 1.5 inch travel...if you think about it, 3 inch travel on a 600 pound spring means the spring is 1800 pounds with 3 inch compression...no way..

thats about all i can post not having my notes..

 

[rick7343]

So the reason for the question is that I am aiming for a lot of dive, so since the center of gravity and RC go down at the same time, the lever does not get longer...

But, since the dive will likely occur before cornering, should the "dive" roll center be looked at more than the static one?

Crank height is 13.5" so C of G will be around 19 "...

 

[Ranger Mike]

Rick..again I apologize for note having my notes..I think we use the camshaft location for the CG as it is pretty good average relative to the heads...
the CG will dive a bit but the RC will migrate and I have seen the RC acting like a wild weasel..all over the place and yes..the distance can vary a whole bunch. That is why the computer program is so important..plus you can see camber build at each segment of front end dive and roll. This situation is made more difficult if you use two differing lengths of upper control arms.

So you pretty much have to know RC ht and offset at ride ht and at max dive..I think the first inch is critical as this is when things happen..after that the transferred weight has done the deed and other factors are key.

I would concetrate on keeping the nose down on the straights ..that will pick up some aero and thus speed...and not doing so much dive in corners..what is the point of a lot of dive??

 

[rick7343]

A lot of dive... just to get the center of gravity down, I suppose... Isn't that why the BBSS craze is on?

 

[Ranger Mike]

Big Bar Soft Spring set up

Stock Car Suspension Guide - Big Bar Soft Spring Setups
How To Convert To The Popular BBSS Setups
From the March, 2009 issue of Circle Track
By Bob Bolles

read this from Bob at circle track

http://www.circletrack.com/chassistech/ctrp_0903_big_bar_soft_spring_setups/viewall.html#ixzz1rvKJHIqB




http://www.circletrack.com/chassistech/ctrp_0903_big_bar_soft_spring_setups/viewall.html

summarized below
The very first thing to know is that the BBSS setups are not going to be right for all racetracks. There are some tracks where the gains are significant and others where there is either no gain at all or where the more conventional setups are just plain faster.

Most ill-handling cars are traditionally tight and will not turn well. The BBSS setups do help the car to turn better by forcing additional load onto the Left Front (LF) tire.

Handling balance can be accomplished with adjustments to the weight distribution meaning a change in crossweight percent. So, making the car neutral once we have gone to the BBSS setup is usually not a problem.

Aero efficiency is improved, sometimes greatly improved, on longer tracks due to the front valance being lower and the rear spoiler being higher. The soft front springs compress more and the stiffer RR spring forces the LF corner down to where the front of the car is low and parallel to the track in the turns.


There are some interesting results that come from the transition. First of all, if the car is setup "right", meaning all of the way to BBSS as it is applied in most cases, and we'll explain what that means later, the dynamic balance could be way off. The front wants to roll to say 1 to 1.5 degrees and the rear wants to achieve a negative roll angle of from 0.5 to 1.0 degree.

This difference in desires means that a lot of extra load is being put on the RR tire. In older traditional setups that were unbalanced, the rear out-rolled the front and a lot of extra load ended up on the RF tire. That tire soon began to overheat and loose grip. The car either pushed badly or the driver could overcome the tight condition with extra steering input until the car went to a tight-loose condition.

The final result was either a worn out RF tire or a burned out RR tire. One of the two was sure to go. So, the big question is, why doesn't the RR tire give up on the BBSS setups similar to the RF tire that was overloaded with an unbalanced conventional setup?

When the car is unbalanced with the rear out-rolling the front, the RF tire has to not only carry a lot of extra load to keep the car on the track through the turns, but it also works to make the car change direction and turn the car. It's the extra duty of turning the car that overloads the RF tire and causes it to give up so quickly on a conventional setup.


Contrary to the conventional unbalanced situation, with the BBSS unbalanced syndrome, the RR tire does not have to turn the car. It only needs to resist the centripetal loads and keep the rear of the car on the track. It carries a heavier load to help it do that. But, the RR tire will be working harder in the acceleration phase because it will carry most of the rear loading of the car.

Since the BBSS setup is unbalanced with the front tires being more equally loaded side to side than the rear, the front develops more grip. So, there is a need to increase the crossweight percent to tighten the car to a more neutral handling condition. And that is exactly what we find when we do a back-to-back test.

Keeping in mind that there are many variations of the BBSS setups, let's take a look at a common configuration for the straight rail Late Model cars that usually run the touring series. We will offer general directions, so don't run out and put this in your car. Every car is a little different and a slow approach to the transition will keep you from getting in trouble.


The sway bar size runs from a low of 1.375 inch diameter medium wall thickness through a 1.50 inch bar and all of the way to 2.0 inches and more. For most Late Model cars, 1.50 to 1.75 is more common. Some very successful teams have backed off the very large bars and are now running a 1.375 inch bar with either medium or thick walls.

Front spring rates for the BBSS setups vary from a low range of 125 lb/in springs up to 225 and 250 lb/in springs. Again, if you're in the 200 lb/in range, you're leaning more to the soft conventional setup configuration, which is gaining popularity. The RR spring rate is usually increased over conventional rates from 100 to 300 lb/in. This means you would run a minimum of a 250 lb/in spring all of the way up to and beyond a 400 lb/in spring.

The crossweight must be increased along with these changes. Typical increases are from 2 to 4 percent of total weight. It's often better to begin with the lower crossweight range (for a 50 percent front percent car, it's around 51.5 percent cross with a conventional setup) normally used with stiffer springs and smaller sway bars and then add 3 percent or so until the car is neutral in handling.


Since the rear roll angle is a lot less than the front, we also want to lower the Panhard/J-bar about as low as it will go. With most chassis designs, we are limited to going down to 8-9 inches off the ground. Go there!

The RR shock will travel about half as much or less with the BBSS stiff spring in the car, so you need to adjust your RR trailing arm angle so that there won't be any rear steer to the right in the turns. With normal travel of 3.5 to 4 inches for the conventional setups, we usually use around 1.5-2 degrees of trailing arm angle in the right trailing arm. When installing the larger spring in the RR on the BBSS setups, reduce that to half, or 0.75 to 1 degree of angle-front high, of course.

One of the biggest changes that must accompany the BBSS setups is to your shock rates, both compression and rebound. The compression settings generally go up at the RF with the LF compression going down.

The RR will need a little more rebound to control that stiff spring. It's very helpful in the tuning stages of the conversion to BBSS that you use adjustable shocks, preferably double adjustable.


The rebound settings in both front shocks will need to be increased with the LF rebound needing the most increase. Some teams feel the need to run very high rebound rates at the LF corner. We don't agree with that concept and this trend has caused a lot of cars to develop a mid-corner push that can't be corrected with crossweight adjustment.

The amount of increase and decrease in rebound and compression varies as to the track size. Long, smooth, and flatter tracks can use much more rebound control than on shorter tracks that might be rough. Rough tracks also have a negative effect on the RR when using a very stiff spring. The car tends to bounce at that corner instead of negotiating the bumps smoothly. A reduction in the RR spring rate along with changes to the crossweight percent to bring the car back to neutral handling is necessary.

Most of the high-end racing shock companies make shocks that are double adjustable. We've been using the hlins double adjustable shocks on our Late Model project cars with a lot of success. We can make changes to the overall spring stiffness and still have enough range of adjustment to make each work.

Yes, there have been a lot of problems associated with trying to run the BBSS setups, usually because of incorrect application. There are other areas where we need to make changes to accommodate the BBSS setups. The front geometry must be redesigned in order to properly gain the advantages of the BBSS setups. Moment center location is still very important, and camber change characteristics are totally different with these setups.


The BBSS car will dive more and roll less. That means our camber changes at the front are entirely different than what we saw with the conventional setups. Both front tires will loose lots of camber due to the high dive numbers, 3 to 4 inches in most cases and low roll angles that normally would counter camber loss in more conventional setups.

The bottom line is that the upper control arm angles will need to be reduced. If you had say 18 to 24 degrees of upper control arm angle with your conventional setup, you will now need to reduce those to 10 to 14 degrees, all the while maintaining a decent moment center location.

The static cambers themselves must be altered with the transition. The RF must be reduced from the normal (-) 3.5 to (-) 4.0 degrees to under (-) 1.5 degrees or less in most cases depending on the type of tire you run.

The LF tire camber must be increased from a normal 2.5 to 3.0 degrees positive to 5.0 degrees or more. This tire will loose around 4 degrees of camber in the turns.

Ackermann effect is very detrimental to the BBSS setups. If you are used to using some amount of Ackermann in your conventional setups, you can't run it with the BBSS setups. The reasoning is this, with the BBSS setup, the LF corner is forced down and a lot of the front load is carried by that tire. Since it is doing a lot of work, it will compete with the RF tire.

These two tires must track along their proper arcs, tangent to the curve and perpendicular to the radius. We have computed and proven that a car running on a short 1/4-mile track only needs around 0.100 inch of added toe, or about 0.2 (1/5) degree of additional steering angle in the LF wheel. On half-mile tracks, that number goes down to 0.040 inch of added toe or less than 0.10 (1/10) degree of increased LF steering angle.


We have made the statement in the past that we don't see track records falling from the use of the BBSS setups. OK, some have, but there aren't any cars out there going a half a second faster with the BBSS setups. And that doesn't mean it works everywhere.

We have proven that the BBSS setups are not meant for all racetracks. In general, the higher the banking at the track, above 10 degrees or so, the less effective the BBSS setups will be. If your track is above 12 degrees of banking don't even think about it.

Tracks with a rough surface and/or large transitions in banking angle from the straight-aways to the turns are hard to manage with the BBSS setups and you might be better off, and more consistent, running more conventional.

The tracks where these setups shine are the flatter and smoother tracks and the long "super" speedways like Kentucky or Nashville Super Speedway (not the Fairgrounds). Gateway International Raceway is another good one and I'm sure similar setups have been used successfully at the now defunct track in Lakeland, FL.

Out west, we might see the BBSS setups at tracks like Phoenix or Evergreen Speedway. The longer and faster tracks will benefit from the added aero effect to provide more overall grip adhesion for faster turn speeds. On 3/4- to 1-mile tracks, that added speed can add up to several tenths lower lap times.


I recently heard from a team that had won the last two year's championships with a more conventional setup. The team now wants to go to the BBSS setups for next year. I can't understand that reasoning, other than the fact that racers just can't stand still. I preach the idea that you can never just maintain, but at the same time, don't shoot yourself in the foot either.

The choice of setup is entirely yours, so chose your setup based on need. If you're winning a lot with conventional setups, you can experiment during a test session like we did, but not once the season starts. There's not enough time to properly evaluate the difference.

Watch your shock travels at the RF when using very soft springs. If the spring binds and/or the frame contacts the track, the car will move quickly toward the wall. Make spring changes in a progression rather than a one-step change. Adjust the shocks to control the transition. Add a little crossweight with each change to maintain the neutral handling.

Once the car is neutral, get good lap times up to 15 to 20 laps and then immediately switch back to the conventional setup and make another run. See which one feels better to the driver and which one is faster, especially for longer runs. Compare those times with the usual lap times everyone else runs. Make a choice and go with it.

If you decide to go with the BBSS setup, go all the way. Do the very soft front springs, install a larger sway bar, increase the RR spring rate by at least 200 pounds and adjust your shocks to complement the setup.

 

[rick7343]

Not a bad article ...Bob Bowles is usually an opponent of the whole BBSS movement...

 

[rick7343]

SO I wondered if we could discuss how to determine correct roll center height and location, conventional versus SSBB setups, tire hardness etc...

As usual, I have stumbled on a lot of different theories... The latest suggests moving the roll center to the left to help the car steer(I believe it makes the front softer to try to keep the it, especially left side down in the corner)

Feedback??

 

[Ranger Mike]

Rick,,,the numbers you sent me look pretty darn good and i would run them and concentrate on tuning in the spring shock package. They have good initial settings and migrate the right direction.

BBSS - I am not a fan of this set up unless you race a mile or longer FLAT track. This setup means chassis roll is severely restricted ( hence BIG BAR) and because of this the front roll center does not come into play " as much as" in the unbalanced set up where the RC is offset to plant the Right front. In BBSS set up cross weight is used to plant the rt. ft. It focus is to keep the nose down to increase speed by reducing aero drag. The left bias RC may in fact be to put some weight on the lft front tire even though minimum roll happens..but it does happen.
Question - what is the longest track you race and what is the degree banking?

 

[mender]

Watch your shock travels at the RF when using very soft springs. If the spring binds and/or the frame contacts the track, the car will move quickly toward the wall.

Of the two, spring bind is the one to stay away from: spring rate goes infinite as it binds and will cause the car to lose more traction and more abruptly than a slight unloading of the tire caused by frame contact.