Automotive Race car suspension Class

[fstock34]

Thanks guys for your quick responses it is greatly appreciated. For some reason the website won't allow me to link the rule book so i copy pasted it below. I am in a hurry right now but later tonight or tomorrow i will create another post with some other questions i would like to pick your brains about. Thanks again.

YEAR, MAKE, AND MODEL MUST BE DECLARED BEFORE CAR WILL BE ALLOWED TO COMPETE. IT IS THE DRIVER'S RESPONSIBILITY TO UPDATE THIS INFORMATION, AS NECESSARY. SUSPENSION AND STEERING COMPONENTS MUST BE IDENTICAL AND FUNCTION AS THOSE AVAILABLE ON STANDARD PRODUCTION VEHICLE OF THE SAME YEAR, MAKE AND MODEL. THE ONLY SUBSTITUTION AND MODIFICATIONS ARE THOSE MANDATED AND DETAILED IN THE FOLLOWING RULEBOOK. ABSOLUTELY NO SPECIAL OR NON-PRODUCTION OTHER SUSPENSION OR STEERING COMPONENTS EXCEPT FOR THOSE ALLOWED IN THE RULEBOOK.

BODIES

1. Must be 1955 to present American made cars with minimum wheelbase of 100”.

2. No trucks, sport utility vehicles, station wagons, or front wheel drives.

3. All bodies must utilize a full factory stock steel hood, steel roof, and steel trunk lid. All three pieces must be from the same year, make, and model vehicle. Internal support structure may be removed but all factory window channels and drip edges must remain intact on roof panels. Internal support structure only may be removed from hood and trunk lid. Perimeter edges on side of hood may not be removed. Factory front and rear roof pillars must remain stock to top of front fender and top of rear quarter panels.

4. Body sides including front fenders, doors, and rear quarter panels may be fabricated using minimum 22 gauge steel but must retain original factory appearance and body liner. Body sides may not be any lower than original rocker panels. Doors must be welded or bolted shut. All sheet metal must maintain 5 inch ground clearance.

5. Gutting of bodies allowed. All flammable material must be removed along with all glass, chrome, and plastic.

6. All cars must have full stock front firewall, in the original location of chassis being used. Stock floor pan must be maintained to rear of driver’s seat, across entire width of interior. All holes in front and rear firewall, and floor pan, must be covered with minimum 22 gauge steel. Rear firewall MUST be steel. Modified or sectioned firewalls will be subject to a 50 pound minimum weight penalty.

7. Aftermarket stock appearing rubber or plastic nose and tail pieces may be used, but must match body being used. All cars using such nose and tail pieces must have (2) tow hooks in both the front and rear for towing purposes. Hooks must be fabricated from solid steel or chain. Cables will not be allowed. Slits may be cut in nose and tail piece so that hooks or chains may be tucked in until needed, but must be accessible at all times without the need for hood or deck removal.

8. Cars must have complete wire screen or lexan windshield, supported inside at center by (3) vertical steel bars, minimum 1 inch by 1/8 inch, not less than 4 inches apart. No part of the front windshield opening or rear window opening may be obstructed. NO rear windshields.

9. Hood scoops allowed up to 4 inch maximum height, measured at any point. Hood scoops may be aftermarket or factory items. Single hood scoop only. Opening may face forward or be located at rear of hood.

10. Maximum 6 inch height, clear lexan spoilers allowed. No lettering on lexan spoilers. No side pieces allowed on lexan spoilers. May use factory OEM spoiler for body being used. Maximum 4 inch tall aluminum or steel spoilers with no side pieces are also permitted. One spoiler only allowed and must attach to rear of trunk lid.

FRAMES and SUSPENSION

1. All cars may replace frame rail from centerline of rear axle, to rear bumper mounts, utilizing 2 x 3 inch box tubing. All cars must retain unaltered front crossmember and spring mount location. Coil spring cars must retain original cross member and spring mount location. Uni-body cars must connect front and rear sub frames with minimum 2 x 3 inch box tubing. Uni-body leaf spring cars may replace rear frame rails entirely with 2 x 3 inch box tubing and may connect to rear of original unaltered front sub frame. Leaf spring mounting points on cars with fabricated rear frame sections must be in OEM location and must mirror one another from side to side. Any leaf spring lowering blocks used must be the same dimension on both sides. Rear crossmember on coil spring cars must be in stock location and must remain unaltered from stock except for upper control arm mounting brackets which may be improved. Frames on coil spring cars must remain stock from front bumper mounting surface to rear axle centerline except for additional bracing.

2. All cars must retain minimum of 5 inch ride height at all times, with driver buckled in seat.

3. Front spring pockets must remain stock and in stock location. Front crossmember must not be altered in any way.

4. The rear shackle attaching points must be within factory tolerances of stock location.

5. Wheelbase may not be shortened.

6. No rod ends allowed on any suspension part, except for shocks and sway bar links.

7. Aftermarket sway bar and sway bar links allowed. Sway bar must fasten to lower control arm.

8. Front lower control arms and steering components must be from make and model of chassis being used. All suspension components must remain stock unaltered. Stock steel OEM passenger car spindles only. NO corvette spindles. All casting numbers and other identification marks must remain on spindles.

9. All suspension components (except otherwise noted) must mount in stock location for year, make, and model of chassis being used. Front upper and lower control arm mounting points on frame, may NOT be altered or relocated in any way. Gussets may be added to suspension pieces for strengthening purposes only.

10. Shocks may be mounted in any location. Only steel shocks permitted, one per wheel.

11. Stock type ball joints only. Screw in lower ball joints are permitted. Ball joint and tie rod ends with interchangeable studs are not permitted. No Howe precision ball joints or tie rod ends permitted.

12. Stock type steel springs only although spring rates may be altered. Springs must be in stock location.

13. Aftermarket steel tubular upper control arms are permitted but they must mount to stock frame mounts without modifications. Control arms must bolt directly to factory mounting holes and retain factory type ball joint. Strut cars may use aftermarket strut mounting plate, but must mount in stock location utilizing stock holes.

14. Urethane, rubber, or metal suspension bushings, may be used.

15. Rear suspension upper control arm or torque arm mounting holes, may be moved on frame only.

16. Lower control arm mounting holes, may be moved on rear end housing only.

17. One external weight jacking device allowed per wheel.

18. Rear upper control arms or torque arms must be for year, make, and model of chassis being used. These parts must not be altered in any way except for bushings. Lower control arms may be fabricated from rectangular or round tubing, but must be dimensionally identical to stock components that they are replacing with respect to center to center distance of mounting holes. NO tolerance will be given from stock dimensions.

19. No aluminum suspension components.

20. No panhard bars allowed except for factory torque arm cars. No rear sway bars allowed.

21. Suspension must be stock configuration and design for year, make, and model of vehicle being used.

ROLL BARS

1. Minimum 1 ½” x .120” or 1 ¾” x .095” round steel seamless (or DOM) tubing mandatory.

2. All cars are required to have a rear vertical hoop behind and above the drivers’ head connected to left and right front roll bar legs by a roof hoop.

3. The front roll bar legs must follow the contour of the windshield post and cowl.

4.. Maximum distance from the windshield to the rear of roll bar should be no more than 4 inches.

5. A diagonal bar from the top left to the bottom right must support the rear vertical hoop. 6. A roll bar must connect the left and right of the rear vertical hoop at seat height and across the floor pan at the bottom.

7. An additional bar must be installed at dashboard level, extended from the left front roll bar leg to the right front roll bar leg.

8. A minimum of three door bars on the left side and 2 door bars on the right side must be used. Door bars must be convex in shape and extend into the door panels. Door bars must be attached to each other and the frame with vertical bars.

9. Minimum 1/8” x 1 ½” gussets must be welded into all main cage joints and driver’s door bars.

10. Racing seat MANDATORY.

11. Minimum 1” diameter steel tubing welded directly into the cage must support driver’s seat. 3” lap belts and 3” shoulder harnesses are mandatory. Crotch belts are recommended. All belts and harnesses must be securely fastened to the cage (harnesses must be attached below shoulder level).

12. All belts must be dated and no more than 5 years old. All belts must be un-frayed and in good appearance. Roll bars in the drivers’ area must be padded.

13. Headrests and drop-down window nets are mandatory.

14. A radiator hoop may be utilized in front of the cage with a maximum of 2 upright supports.

15. Rear cage supports may extend to the rear of the frame, no uprights allowed. All main hoops must attach to the original frame.

16. Plating of driver side door bars HIGHLY RECOMMENDED.

RUB RAILS/ BUMPERS

1. Rub rails allowed.

2. The top of the rub rail is to be no higher than the top of the tires, and no lower than hub center height.

3. Rub rails must be made of tubing maximum 1 ¾” O.D. and will be 2” maximum to the inside of the rail to body.

4. One single rub rail per side.

5. Ends must not be exposed to the outside of the body skin.

6. Bumpers must be securely safety chained to each frame rail to prevent them from dropping onto the raceway.

7. A flat piece of metal must be welded or bolted from the outside edge of bumper flush to rear quarter panel and front fender if not using rubber nose.

8. Tow hooks required on both frame rails, front and rear.

9. No sharp edges or cut-off ends.

10. Front and rear bumpers may be fabricated but must not extend any further from body than stock bumper and must fit under stock or replacement nose and tail pieces. Fabricated bumpers may not be any wider than sheet metal in front and rear, and must be capped to eliminate any sharp edges.

WEIGHTS and PERCENTAGES

1. All coil spring cars must weigh 3000 pounds, with driver-after the race.

2. All leaf spring cars with stock rear frame sections must weigh 3100 pounds, with driver-after the race. This type of car is one using frame connectors to join front and rear stock frame sections and may not have any other fabricated frame rail except for rearward of rear axle centerline.

3. All leaf spring cars with fabricated frame rails from front clip back, or cars with altered wheelbase, must weigh 3200 pounds, with driver-after the race.

4. Coil spring cars may have a maximum of 57% left side weight. Leaf spring cars may have a maximum of 56% left side weight.

5. Leaf spring cars may have a maximum of 48% rear weight. No rear percentage limit on any coil spring cars.

6. All cars with engines having 10:1 compression ratio must add 100 pounds to base weight and have 1% less left side weight. 10:1 coil spring cars are allowed 56% left side weight. 10:1 leaf spring leaf spring cars are allowed 55% left side weight.

7. All cars with fiberglass or aluminum aftermarket bodies, must add 100 pounds.

8. All weights and percentages will be measured with driver buckled in seat.

9. Riverhead Charger cars are allowed to compete, but must maintain 5 inch frame height, weight a minimum of 3350 pounds and have a maximum of 54% left side weight. Riverhead Charger cars must adhere to all other Charger rules, with the exception of rear windshields-which will be allowed.

10. Frame height will be measured at lowest part of frame, including any bolt on lead.

BRAKES

1. Four wheel stock hydraulic brakes in working order mandatory.

2. No brake adjusting devices within driver's reach. No adjustable proportioning valves allowed.

3. Aftermarket master cylinders permitted.

4. No aluminum brake rotors allowed. OEM calipers only for year, make, and model of chassis being used.

5. May install rear disc brakes utilizing stock parts and an aftermarket bracket.

ENGINE

All engines must be sealed within 3 races from start of season. Cubic inches, compression, carburetor, and engine components will be checked and verified. Seal will not guarantee that engine will not be rechecked additionally, at anytime during season. It is the driver's responsibility to have engine sealed. Tech sessions will be scheduled before the season begins and during the season, as necessary. All seals will be installed at track or at scheduled sessions only. A small fee for seals and drilled bolts will apply.

1. Any overhead valve V-8 American manufactured production engine permitted.

2. Stock stroke and stock bore (+0.60 max.)

3. Engine must be in stock location, with solid type motor mounts utilizing stock holes in both block and frame. Engine must be centered in chassis and may not be lowered in chassis, tilted, or moved toward firewall.

4. Engine must be of same manufacture as car used. GM in GM, Ford in Ford, Mopar in Mopar.

5. Maximum compression ratio of 9.0:1.

6. No porting, polishing, or alterations of any kind permitted.

7. Chevy engines must have a maximum stroke of 3.480 and a maximum bore of 4.060.

8. Maximum displacement of 360 cubic inches (+.030 overbore on Mopar) on all engines. 9. Edelbrock Performer PN# 2101 or 2116 and unaltered Holley R4412, 500 cfm, carburetor mounted on a 1” adapter plate. *Check with tech inspector for part # of intake manifold for different manufactured engines*

10. Mechanical throttle linkage with toe strap and double throttle return springs required.

11. Stock production, cast iron heads (no bow tie or bowtie vortec heads). World Product #4266 and #4267, Engine Quest: CH 350C, CC 170BA, CC 170 BA2, CC 167 CS2, CC 167 CS, CC 167 ES2, CC 167 ES and Dart: 100-210-70, 100-210-10, 100-242-66, 100-243-65, 100-263-64, 100-243-70, Pro topline 2236494906, and World Products #5303B for Fords are allowed (part numbers must be visible).

12. Dish or flat top pistons only.

13. Any flat tappet or hydraulic roller camshaft allowed.

14. Stock dimension magnetic flat tappet lifters or hydraulic roller lifters for engine used mandatory. If hydraulic roller lifters are being used, the valve springs may not exceed 1.300 inches in diameter. Retro-fit hydraulic roller lifters are permitted. No modification or shimming of hydraulic roller lifters is allowed.

15. Roller rockers allowed, no shaft style rockers (unless factory issued) or stud girdles.

16. Stock single point distributor or stock electronic ignition only.

17. No MSD boxes.

18. Stock unaltered standard or automatic transmissions mandatory.

19. Stock type steel flywheel, clutch, and pressure plate ONLY. Minimum weight of flywheel will be 15 pounds. Minimum weight of pressure plate will be 13 pounds. Minimum weight of clutch disc will be 3 pounds.

20. Blow proof steel bell housing mandatory for standard transmissions.

21. Automatic transmissions must use working stock torque converter only. Must be minimum of 12 inches in diameter, measured at the main body of converter, not at mounting flange. Absolutely no lock up or direct drive automatic transmissions.

22. All cars must be able to move under their own power, and be self-starting.

23. Headers allowed.

24. All cars must have 2 Dynomax #24222 mufflers. System must be securely fastened and leak free.

25. One radiator in front of engine only.

26. All cars must carry a securely fastened and leak-proof 1-gallon overflow tank. NO ANTI-FREEZE!

27. GM #602 Crate engine will be permitted with box stock #4412 2 barrel Holley carb. Crate motors are subject to tech inspection, regardless of seals.

REARS

1. Stock rears for year, make, and model. Mounting brackets may be moved on rear end housing.

2. May use Ford 9 inch rear (non-floater).

3. All rears must be locked.

4. Magnetic steel spool, mini-spool, or welded spiders only.

5. No lockers or ratchet type rears allowed.

6. No fabricated rear end housings. Center section and housing must be OEM production items.

WHEELS AND TIRES

1. 8” steel racing wheels mandatory.

2. 1-inch steel lug nuts with proper taper are mandatory.

3. Different offsets allowed.

4. ¼” spacers permitted.

5. Track tire only.

GAS TANKS

1. Encased fuel cell mandatory. 22 gallon maximum capacity.

2. Fuel cell must be securely fastened to rear frame.

3. Fuel shut off valve must be in plain view and within drivers reach, painted fluorescent red or orange and clearly marked “ON” and “OFF”.

4. Stock mechanical fuel pumps only, no electric fuel pumps.

5. Bottom of fuel cell may not be lower than 10” to the ground with driver.

6. Must have a minimum of a 1-inch by 1 inch X-brace under fuel cell.

7. Tip over valve is mandatory, Flapper under gas cap is recommended.

BATTERY

1. Battery may be located in the drivers’ compartment and enclosed in a spill-proof container securely fastened to the floor.

2. All batteries must have a spill or splash cover.

3. Battery shut off switch is mandatory. MUST BE IN PLAIN VIEW, painted fluorescent yellow or orange and clearly marked “ON” and “OFF”.

DRIVESHAFT

1. Magnetic steel drive shafts only.

2. Drive shaft should be painted white or yellow for visibility if lost on racetrack.

3. All cars must use a steel retaining hoop at the front and the rear of drive shaft.

GENERAL

1. No rear view mirrors, radios, or any other form of driver/crew communication.

2. Driver MUST monitor one way track scanner and obey and respond to race director’s instructions.

 

[Ranger Mike]

excellent...as crew chiefs dream...ok, i think we have some room to improve the chassis set up dramatically..and LEGALLY- let's start with the front..you can run aftermarket sway bar and this is a plus..
you can run screw in lower ball joints, you can run tube upper A-arms and as long as you got a " stock " spindle, you can run a different spindle..all of which can adjust the roll center and greatly assist the camber curve which is pretty bad.
If you have the time and the determination. you need to send me the details of your set=up but this will require you to measure many things on the car..reply back if you have a mind to do this..

 

[fstock34]

Ranger mike i definitely have the time and determination to do anything that will help. The factory stock i had was built by me from the ground up and we were protested throughout my last full season in 2009. Reason being while everyone else was buying tires every 2-3 races we bought three tires all season long the left front was 3 season's old and pulled out of a scrap tire pile. We couldn't afford tires that often so every week we cleaned the tires with a heat gun and wire wheeled them with mineral spirits (that what hoosier told us to do). Then based on what the car was doing during the last say 5 laps of the feature we adjusted the set-up to compensate for the tire-wear. Instead of tires we changed shocks we changed springs we made sway bar adjustments stuff like that so i don't mind doing work at all. We had an engine detonate during practice of race two so we missed a few weeks that year which probibly cost us a championship but of all the races we ran that year we finished no worse than third and no worse than second throughout the last 7 events and also received the trophy for fastest lap of the season furthuring baffling furious drivers who couldn't understand tires arent everything. We also ran the same tires the following season for the first three events and won another feature before we sold the car. Most basic things i understand its just the things that you couldn't do in the factory stock were allowed to do now and these new things I am lost on lol. Ranger mike in reference to the things you asked about i have these items so far.

1. As of right now we have a 1 and 1/4 stock monte carlo sway bar.
2. stock ball joints in the lower a arms. (in the thriller we experimented with taller lowers it made the car terrible however we changed back to stock lower's and reamed the upper ball joint hole about 1/4 inch to seat the upper joint farther down into the spindle and the car was 2 tenths faster and stuck amazingly in the corner.)
3.We have tubular upper a frames from left hander. We have a set where the ball joint is in stock location and stock mounting holes and also a set where the ball joint is relocated for caster purposes (left hander is only company that makes this a-arm to my knowledge) and the mounting holes are slotted for further caster adjustment.
4. 86 monte carlo spindles however we also have a set of impala spindles on the shelf.
5. also for rear "control arms" if you read the rule book about it references the rear trailing arms as "control arms" and the rule book clearly states you can have tubular "upper control arms" so we purchased these as well.

I am definitely willing to do anything that will help ill message you anything you need or if you want private message me a number and a time when your not busy and available to talk racing i could probibly explain clearer about the car. Any information is greatly appreciated its so hard to find racers willing to share it. When i had the thriller if a driver or crew member who was running around in the back getting lapped came up to me and asked me to look at their notes or what they could do to improve their cars i always tried to help them out a little bit so I am glad to see there are still people out there like me and I am not totally nuts for doing it lol. thanks again in advance for your help

 

[mender]

Let's start with a question: why are the Impala spindles still on the shelf? Get 'em on the car!

You've already proven that the car wants a better camber curve. It'll take some work but once you get the front end geometry fixed you'll be faster and go through even fewer tires. You'll find you can back down on the spring, shock and bar rates which will also add stick. It may take a bit to get used to a softer set-up but it will be faster.

Measure your present camber curve for a baseline then switch and remeasure. You'll have to redo the bumpsteer as well.

I haven't read these articles but you might find something of worth:
http://www.ansearch.co.nz/search?search=metric+chassis+setup&cc=com

 

[fstock34]

lol the impala spindles are still on the shelf because were building the car now and were starting by putting the rear end in so we can roll it across the shop and get it on the lift lol. I def agree with the soft springs in the factory stock we ran lf-800 rf-900 lr 225-175 rr-200-125 depending on what the car wanted which was much much softer than everyone else. But as far as the front end is concerned I've heard that at some point you can go to low and that's bad as well...but how low is that?

 

[mender]

It's too low when the suspension bottoms, the geometry starts to go away or the driver can't keep up with the car - soft requires a smoother driver that plans his/her driving a little in advance.

With bad geometry, high spring/bar rates are needed to keep the car in its very narrow sweet spot. Once the front end is sorted, the rates can be lower and the car is much less fussy about set-up.

What's your track shape? Length? How much banking are you running on? Dirt or asphalt?

 

[Ranger Mike]

good points, Mender...for those who are reading along with us, stock cars have tall ride height clearance to clear road hazards we find dead in the middle of the road..or road conditions. We want to reduce ride height to lower center of gravity, and reduce amount of air going under the car. Early Nascar racers went to soft springs to lower the car as low as possible ..they added stiffer sway bars ( anti roll bar) to assist the softer springs during corner weight transfer) ..it all goes back to the round track axiom - Low, Left and Light.
Ref- change out the spindles- this should lower the front Roll Center and you have just proved the benefit of lowering the ft RC when you lowered the top ball joints by 1/4 inch.

I attached the set up sheet so please fill in A thru L and email the data to me. I will input and send it back to you via email.
When we benchmark a race car we do this to record vital data that may be lost when we get in a wreck. I always taped poster boards togeather to make a huge sheet of white cardboard that was placed under the cars front wheels on the garage floor. You have to use plumb bobs to get some readings. Try to measure as accurate as possible.



I have a more advanced software program that has a third dimension but this program will be the easiest to use and give us the biggest bang for the dollar.




One more thing to consider - Buy a set of digital wheel scales( or borrow a set) We always used an old set of tires and wheels for the set up procedure. We painted these red. stored them and we made sure to air them up to proper Psi each time we used them. We also got a set of weights ( tractor weights in our case, but bags of salt, grain , the fat girl friend ( make sure to scale her if she looks like she been watching too much TV eating candy). These are common sense steps to keep measurement consistent. Make sure tires are at proper setting, full tank of fuel, driver weight in car, all chassis setting proper.

 

[mender]

Just have to mention that the tire pressures should be the same as when hot, and you should know how much weight difference different tire stagger makes and how much to adjust the weight jack to compensate. This can save your day when you end up cutting some tires and have to use odd sizes.

 

[Ranger Mike]

mender has good points..this is for the"advanced chassis setup " course..ha ha ..this is prob way to much detailed info but here goes,,,

once you have bench marked the car, you should scale it and measure impact of adding air pressure to the applicable tire relative to scale weight. Also find out how much weight change happens when you turn the jack bolt, or sway bar link. Ackerman will effect this too. Once you have it bench marked, place the car on level floor and cut ride height blocks for each corner and make sure you paint set up marks on the frame at each location. this is a good pit side shortcut when you have to make major component swaps after a wreck and this will get you close to the original set up when you do not have scales available.
(btw - we use roll off ramps which are simple wood platforms of same height as the scales. the car is rolled off the scales and you can jump on t he car to work the suspension until it " settles" and roll the car back on the scales). Other scale tips are to disconnect the sway bars during the process.

 

[mender]

Mike, I think we could fill quite a few pages just with tips!

 

[Ranger Mike]

Mender..i hear you..only prob is this forum would not appreciate it unless...we could state the tip relative to physics and application there of..we " old timers" got a wealth of info that will disappear when we take the ultimate dirt nap...maybe..ifin there is enuff interest, and we had some formal schooling help from the advisors..we could document these speed secrets relative to the particular principle of physics that it applies to?

 

[mender]

Good points; I agree with you regarding the intent to keep things "sciency".

Maybe we could get an indication from one of the admins?

 

[mender]

No comments?

Well, since this thread has a rather remarkable 245 views per post, one might assume that it's in the right place and the people who frequent this forum are interested in the topic and that it's safe to proceed!

 

[Ranger Mike]

fstock34 and the Dr. ...would you like to share your chassis set up information with the public? I will contact ADMIN regarding recommendation on this subject..mean time, can all those racers, Engineers, old hands that have contributed to this thread, please give us input.

Prankster16a ..want to help?
My thought is that we have two project cars available - fstock34 and the Dr. One is a dirt car and the other is an asphalt car. I think the folks at the software program I use would be receptive to assisting with the tech data regarding the math used. The purpose of this endeavor would be to demonstrate the use of Physics when applied to race car set up.
xxChrisxx please let us know..Dr. Dodge? Turbo-1? Brewnog? Input?

 

[Ranger Mike]

ok guys
step up and give me yer opinion

 

[Ranger Mike]

This thread has been viewed by quite a few and was intended to discuss the design of various suspension components. It has started to turn into a set up help line and general racing tips thread. I just received a PM from the PF Mentor Russ Watters and Kevin Gertgen from Performance Trends software. Both encouraged me to start a new Thread to discuss Race Car Set- UP. Russ thinks the Mech Engineering forum is best place so will start to work on a new thread.
RM

 

[rwstevens59]

I'm new here so, hello all.

A question that I keep asking myself and many others, seems to have many answers, so I thought I would consult this group.

Spring rate and wheel rate for an independent front suspension was covered very well at the beginning of this thread and is covered in many references the same way.

Now my question is from wheel rate we can calculate the roll resistance of that independent front suspension (as well as an independent rear suspension) and we can compare roll resistance front to rear. The problem comes in when I ask or try to research what the roll resistance is for a car running solid axles front and rear with spring split, and with the chassis offset to the left for oval racing. There are many simple explanations of solid axle cars as long as a. The spring rates are equal left to right and b. The car is symmetrical about the average track center line. Does anyone have a reasonable answer or method for figuring this out?

Thanks,
Ralph

 

[Ranger Mike]

Welcome Ralph
maybe I'm missing something but you said " Now my question is from wheel rate we can calculate the roll resistance of that independent front suspension"...the only roll resistance i know of is regarding tires..are you talkin about the amount of weight transferred when cornering?

 

[rwstevens59]

Sorry, Mike,
Terms and being very specific about what you mean always seem to get us in trouble in this complicated business.

I am referring to the amount of roll resistance provided by the spring pair at one end of the car. In a steady state corner when the inertia force acting at the CG rolls the car right in a left hand turn the spring pairs front and rear produce a resisting couple (torque) to counter that roll. My use for that is, that in load transfer calculations, the resisting moment produced by the spring pairs front and rear is considered the elastic portion of the sprung weight transfer. The other portions of weight transfer are the sprung geometric weight transfer transmitted through the suspension links, this governed by roll center heights. And the unsprung weight transfer, which is basically uncontrolled, except for tire spring rate, caused by the rolling of the unsprung components such as a solid rear axle housing.

The quick and dirty formula for this is: K(angular)= 1/2 Kroll * Spring track width^2/57.3 which yields an angular roll resistance for the spring pair in lb.in./ deg. The kicker is what is the value for Kroll which should be in lb./in. for a spring pair on a solid axle with split and an asymmetric layout. For simplicity let's assume the springs just sit on top of the axle with no linkage to add a further motion ratio to the mix.

All I really want to know is how stiff is my elastic (spring) resistance relatively speaking front to rear. The stiff end gets the weight transfer and therefore the more unequal tire loading left to right and therefore less grip. If you stiffen the front springs relative to the rear at some point it's going to push.

Hope that makes some sense.

Thanks,
Ralph

 

[Ranger Mike]

as you said at the start - The problem comes in when I ask or try to research what the roll resistance is for a car running solid axles front and rear with spring split, and with the chassis offset to the left for oval racing. There are many simple explanations of solid axle cars as long as a. The spring rates are equal left to right and b. The car is symmetrical about the average track center line...
As I posted earlier in this post, we can calculate the total weight being transferred during cornering if we know the G force in the corner. The left side weight of the car will not change this total. Regarding the equal spring rates- these are ok if you are running a road course but not optimum if your racing left hand turn only. Cross weight or diagonal weight transfer from left rear to right front must be in the mix as well. This is why the right front spring has higher spring rate than the left front spring..rear springs are also not equal rate.
question - what kind of front spring set up do you have?

 

[rwstevens59]

The cars I am referring to here are Northeastern DIRT Modifieds if you are familiar with this 'breed' of car. The solid front axle has coil over front springs mounted just behind the front axle on the radius rod brackets, think of a T-bucket roadster hotrod only without the dropped axle. The cars are 2500 lbs and the average setup calls for a 250 lb/in LF spring and a 150 lb/in RF spring. The rear is a solid tube Winters quick change (not live) with a spool. The rear is suspended on a pair of torsion bars (sorry don't have my setup notebook with me and I forget the exact calculated spring rates at the axle). The rear torsion arms rest on rollers below the axle centerline, so unlike a sprint car they are a spring only and do not play a role in longitudinal location of the axle.

There is a one line mention of calculating spring split roll resistance in Milliken in the chapter on Ride and Roll Rates can't remember the page. And quite a bit in Warren Rowley's book on race car engineering dealing with solid rear axles. Both of these sources state that a pair of springs (or wheel rates on a front independent) provide a roll resisting torque equal to: K(left)*K(right)/(K(left) + K (right)) with K(left) and K(right) being the respective spring rates in lbs./in. This produces an offset spring center located somewhere closer to the stiffer spring. If you plug this value in for K(roll) you get an awfully low roll resisting moment in lb.in./deg. Now springs on any beam axle produce a much lower roll resisting moment than their respective ride rate just because the springs are inboard of the wheels with a spring track that is quite a bit less than the track width. All of the above (spring center calcs) I can prove from first principles just using a simple beam supported by two different rate springs as my model as well as just placing a bar over two small springs with different rates, shim the soft side up to level on a surface plate and find the point where the beam rotates evenly with dial indicators. All well and good, but is that how the car behaves and when you start adding in the asymetries of the car CG centerline being offset 4 inches to the left, I'm starting to get lost in the woods without a compass.
Ralph

 

[Ranger Mike]

I admire all the work you did on the calculations..more than I ever did.

About all I can offer is from all my notes on Dirt modified using metric GM chassis days, I can only reply with the following:
We ran 100 lbs stiffer spring on the right front vs left front...was 3 link rear suspension.
55% left side wt. 56% rear wt. 51% cross weight. if my notes are right we used 200 lb springs on both rears..
why are you using a higher rate left front spring? This is a "reverse Split" and can be used to keep the car flat at tracks with large amounts of banking or for when you want the car to lean over on the right rear...right?

Are you running a big wing on top?

 

[rwstevens59]

That is the chassis builders recommended setup and brings us to why I am scratching my head. The bodies of these cars don't have a big wing on top but do create a fair amount rear down force which leads to an aero push almost always. The rules really don't allow for a proper aero balance. The tracks we run are flat, less than 10 deg. at 5/8 mi. and semi-banked bull ring at 1/4 mile. I am questioning the spring choices and trying to decide which way to go and by about how much. I don't just want to take a WAG at it because the car is close. The overriding complaint by the driver is drive off the corner. Now, I have never believed you can calculate your way out of these situations because it is just too dynamic. But, calculations will give you clues as to whether you are fine tuning or making major changes. The other problems as always are money and time. We are now into the season, hot laps are just that and only tell you nothing fell off the car and the engine is running OK. The first opportunity to see what you have is in the heat race, experiment too much, and you don't qualify well. Doesn't offer a lot of space for test and tune. But if we stick to the 'Golden Rule' and change one thing at a time and only one thing at a time we will improve if for no other reason than finding out what doesn't work.

I have asked this question concerning roll resistance of spring pairs on solid axles several times in different engineering circles and am finding out that it really isn't simple and it is actually easier to calculate on an independent suspension. The seemingly simple beam axle becomes quite complex when viewed dynamically.

Ralph

 

[Ranger Mike]

i would equal up the front springs as change one.
when is the driver needing bite off the turn..on wet track/ tacky track? dry hard packed track?
can you adjust rear wheel track. i forget ..are you running a panhard bar?

 

[rwstevens59]

The car exhibits push in all phases of the corner when wet and sloppy early in hot laps depending on the group you go out in. As all tracks in the northeast the track does not stay wet and sloppy for long. The complaint of lack of drive off on late corner exit occurs when the track is dry. The 1/4 mile track transitions to an interesting condition when it dries out. I would say the clay sand content must be quite high as the track does not get hard packed and shiny but rather drys out and continues to abrade into powder which blows off and it almost never takes rubber.

The baseline setup starts with a 2 inch spacer in both the left rear and right rear, so yes, there is some ability to adjust rear track. The rear currently runs a 14 inch wide rim with a 5 inch back set. Three inch back set rims are also available.

The rear suspension is a torque arm with two lower links and a short panhard bar mounted to the frame on the right side (rear view) and the center section at the rear end on the left side of the pinion (rear view) in front of the axle centerline. Yes, this is the total opposite of what you would see in a current super dirt late model, but that is how all three current chassis builders construct these cars. To best picture the lay out think of the old GM 'F' body cars like the Camaro, the layout is similar but not the same.

 

[Ranger Mike]

now we are getting some where
have you measured the rear track under compression/rebound?
I am trying to determine if there is rear roll steer in play?
is the wheel base on one side growing or shrinking when in bump?
what is angle of third link? what is angles of both trail arms?
i am not too worried about panhard bar mount as much as angle

 

[rwstevens59]

Attached is one of my sons pictures to give you a better idea of what the heck we are talking about here.

The rear suspension on these cars would technically be considered a two link with panhard. The torque arm consists of two plates bolted to the quick change using the side bell through bolts either side of the drive-shaft. The plates go forward about 28 inches and attach to a large heim which attached to a slider plate mounted on two shafts attached to the chassis. The heim is mounted to the plate with a rubber biscuit to cushion rear end wrap up on throttle.
The two lower links are mounted on clamp on brackets at the outer end of the axle tubes below axle centerline. The forward end of the lower links have three mounting holes on the chassis to adjust link angle and therefore anti-squat, which also effects the amount of roll steer. This is kind of hard to picture if you have never seen the design, but it follows all the principles of a torque arm two link with panhard. When I say torque arm do not automatically envision a typical late model torque arm with fifth coil. These cars are laid out like an over grown sprint car with the driver centrally located with the driveline and torque arm between his legs and under the seat.

This rear linkage design has inherent roll oversteer in all lower link mounting positions. This is crutched (in my opinion) by using a spring rod for the right rear link to induce power on axle steer to the left to counter the roll induced oversteer.

The panhard angle is cockpit adjustable for angle, which to me just adds or subtracts a jacking force more than moving the roll center height. If I want to move the roll center I move the bar up or down equally at both ends while maintaining the angle.

Hope this all makes some sense.

Thanks, Ralph

 

[HowlerMonkey]

We're using the aim evo4 with smarty cam on our twin turbo ford GT.

That said, reducing the data from runs or laps is tough because of even tire width and where the contact patch (if not flat and perfect) will affect "spring rate" as seen by the car.

It makes reducing any useful date require a lot more figuring.

That said, look for our current 252.9mph standing mile record to be pushed past 270 in a few weeks.

 

[Ranger Mike]

pushing going in - rt front spring too stiff
too much cross weight
too much rt front tire pressure
not enough stagger
too much panhard bar angle
my opinion

 

[mender]

Sounds like an interesting set-up. You're right, figuring the roll centre when the springs are essentially the suspension pivots can get messy. I don't do dirt, so take my questions with a pound of salt!

What little I know seems to indicate that most of the action is at the back, and your description of the suspension seems to confirm that. The roll oversteer to get the car to point, then power-on understeer to transition into a set for the rest of the corner means that the rear changes position noticably when power is applied, right? Could it be moving too much and unsettling the tires, giving the poor drive off the corners? I'd be tempted to set everything closer to neutral in a test session, then move towards the recommended set-up and see if the car really needs that and if so, how much is helpful before going over the line. Does the car feel unsettled with on-off throttle adjustments mid-corner?

Having the reverse front spring split would seem to be an attempt to help traction off the corner by partially compensating for the torque reaction in the diff when throttle is applied; with a narrow rear track, that effect is amplified, so playing with the track might indicate how much that is affecting things. Again, I'd consider reducing the amount of things happening at the back end of the car, then adding them back in as you get a handle on what each adjustment does. Again, finding the range of front spring split for your car might require a test session. From what I understand not a lot of people scale their cars after baselining for the season; do you?

Have you talked to the chassis builder about how his design is supposed to work? Has the car been wrecked? Have you tried alternate set-ups?