Race car suspension Class

[rick7343]

Can I get your opinion Mr. Mender? (others welcome too!)

The front geometry is really stable in my car, so I thought it would be advantageous to let the front dive in the corners... What do you think?

Not going to bump stops, just softer than traditioal springs... is it worth it or will it just make the car harder to set up and keep consistent?

Since it is a new car, I almost wonder if I should start with a conventional setup and play with the soft setup later...

What do you guys think should be in the car for springs and bar?

thanx!

 

[rick7343]

wow... did I ask the wrong question...?

 

[Ranger Mike]

design suspension from ground up


Conrad has asked me to help him design a car suspension from the ground up. We think this project has merit so follow along and please give your input..


I need advice as I write this from some real good Mech. engineers to make sure we don't go off into the weeds.

Please look at page one and page two of this post ..good review of what we are looking for..


Reading assignment ..for history and back ground of suspension..look at this link..

http://www.automotivearticles.com/123/Suspension_Design_Types_of_Suspensions.shtml


real good info on suspension design from ground up

http://www.rowleyrace.com/PDF/Chapter_6_Excerpt.pdf


watch the following hands on video

http://www.youtube.com/watch?v=6crOSs6LCTQ&feature=youtube_gdata_player


I am using "Tune to Win" by Carroll Smith as reference..excellent book.
Construct a 2D model of a 4 bar link suspension...

Conrad is getting me the specs on track width and wheel base but you can start by printing out the pic and start to play with the suspension links. Cut out the model and glue it to an old manila folder. Get a cheap protractor, some thumbtacks rulers straight edge) some string. Conrad has access to CAD so he is drawing along. Once you cut out the components of the " paper doll" you can use the thumb tacks to move the pivot mount points around to get a lay out that will get us close to a good set up.

 

[Ranger Mike]

Before we get into layout of the ideal suspension ( no such thing) ..lets look at the double wishbone layouts.
Equal length and parallel links - this is the hot set up- minimal camber change but..the track width changes. Note the change when using short lengths. The longer links still change the track width..though minimal..the whole draw back is the width of the race car and this set up is real hard ( if not impossible ) with front engine stock car...there is just no room. Note the Roll Center and location. The min camber, and the camber build and track width change during roll plus bump and RC location/ height is my reason for thinking that this is the hot set up. my opinion..

 

[Ranger Mike]

Unequal length parallel links - shorter top link means the top link has shorter radius and the camber build is greater. We still have some track width change in roll plus bump but the Roll Center behaves better than any other configuration This set up is not bad and I could live with it on a stock car.

Unequal and non parallel links - OK the camber build in figure 27 is dramatic but serves a purpose. RC is off set the track width is ugly in roll plus droop. In many stock classes of racing you got no choice.

 

[Ranger Mike]

Drawing the suspension
here as are the steps to design your suspension. Either draw a 1/4 scale model or use the cut outs to replicate the components.
Draw the Ground line, vehicle center line and center of the left and right front tire contact patch. It is assumed you have the tires mounted on the wheels you are going to use and you have the spindle attached to each one. If you are totally starting from scratch..follow along and you will need to work backwards from the end result. Determine where the outer lower ball joint centers ( could also be rod ends) are to the spindle by bolting them to the spindle. Mark the BJ centers on the drawing. ( note- you can input this data into the software package of your choice..I use circle track analyzer from performance trends)

Determine the Roll Center you want and mark it down.

we want the instant center of the left ft and rt. ft a-arms/control arms/wishbones to be 2 inches inside the opposite lower BJ. draw a vertical line from ground to each location and label as Instant Center vertical plane.
Find out the kingpin angle of the spindle and the amount of static camber you want to use. Most stock cars use 10 degree king pins and we normally run 3 degrees camber on the right front so draw a 13 degree angle from the rt. lower BJ vertically. Same with the left side.

Determine the location of the pivot center of each upper BJ. Measure the lower BJ center to the upper BJ center.
Draw a line from the center of the rt. ft. tire contact patch thur the RC to the Instant Center Vertical plane on the left side. The intersection point is the Instant Center (IC) of the right side suspension.
Draw a line from the Rt. ft. IC to the rt. ft lower BJ center.
Repeat the process to get the left ft. IC point.
Now that you have the lines from the IC to the upper and lower BJ centers, the point of convergence is the location of the lower inner pivot points for the lower control arms and this mounting point must fall along these lines.
The only thing left to do is connect the dots and figure the length of the upper and lower control arms. One wrinkle is the fact that the steering rack will impact on lower control arm length. The steering rack tie rods travel must straight in line with the lower a-arms so we don't run into bump steer. The inner tie rod ends of the steering rack must be in line with the lower a-arm inner pivot points to avoid this.

The upper inner a-arm pivot points are located where you want your camber curve to be. By this I mean you have to find the location of the upper and lower BJs move 3 inch in Bump travel. Draw a horizontal line 3 inch above the lower BJ center. Use a compass and stick the point into the lower inner pivot point and place the pencil in lower bj center. swing the arc up to the 3 inch line. Now you know the location of the lower Bj in 3 inch of bump.
The inner upper pivot point for the upper a-arm is found by trial and error. The correct inner upper a-arm location is found by swinging arcs about different locations on the upper a-arm instant center line until the correct angular change is found. The correct angle will connect the static upper BJ center wit the intersection of the 3 inch horizontal bump travel line. the software program makes all of this a lot easier and is worth the $ 100 cost ..in sanity and cost of beer consumed drawing this stuff..

 

[Ranger Mike]

Pit tip on damaged threads

So there I am under the car at 4 in the morning changing ball joints. I pressed the new one in but manager to ding up the threads so the nut will not properly follow the threads. Ok, out comes the tap and die kit..to my horror its a metric thread.

Even worse, it is a relatively rare thread as it is M 14 - 1.5 which is the fine thread. No where in 30 miles will I find a metric die to re-thread the stud and I don't want to remove the ball joint and replace it. I can't use a small file to chase the damaged threads..

solution

I hack sawed a slot in a good M14 - 1.5 nut, spread the slot apart with a chisel (careful not to mess up the treads at the bottom of the nut). I opened the slot enough to be able to slip it over the damaged thread until it fitted over the good undamaged threads. I used a pair of Vise Grips to tighten the nut just enough and rotated the nut off the ball joint stud thus chasing the damaged threads. I did not clamp the nut totally tight as I did not want to ruin the threads on the nut. I did this four or five times, each time closing the slot gap a little more until the threads were repaired enough to run a good M14 - 1.5 nut up to the good threads and permitted me to tighten the nut to spec.
just thought I would pass this on.

 

[WN9Y]

How many beers does it take to come up with such ideas?

 

[Ranger Mike]

4 to 12??

necessity is the mother of invention

 

[British Menac]

Hehe ... nice humour as well as interesting thread Mike.
When finnished with your project I do have an interesting question for you.
For now, I would like to follow this project if I may.
BM

 

[Ranger Mike]

Welcome...always like input from our Brit connections..Pardon me..project?

 

[British Menac]

Yes Mike ... Your present project here on Designing a suspention set up from scratch.

My question involves a design which would not involve accomodating a driver ... :-)

Very good information here.

British Menace

 

[Ranger Mike]

some of the drivers I had to work with could in fact fulfill this requirment...i.e. the guy behind the wheel could not be considered a driver..

 

[British Menac]

Hehe ... funny Mike. I trust they are not the sort to read threads like this?
BM

 

[chriswh86]

Hi everyone,

Chris here from BC-Canada! Just had a look over a few of the pages in this thread. Amazing information. I don't have much of a background in racing as I just got into asphalt dwarf racing 2-3 years ago; A bit of time spent in the drivers seat, more time spent tinkering in the shop, reading books, using a computerized suspension program and going to race nights with my friend to help pit/tune/work on his car on race and practice nights.

I find dwarf cars to be quite interesting considering a coil over independant front suspension and solid axle, 3 link rear suspension. ~1210pound cars and the ability to try some wild suspension setups/ideas/parts/motors and so on

Anyways, just wanted to start out by saying hi and I will definantly be looking at having some questions answered in the near future. I am just 25 and I've got a lot of learning ahead of me. I still have a lot of learning to do on setting up a car before race day. I am not yet consistant on taking a LOT of notes and doing the same very involved overview and setup of his car before race day.

My friend is the type of, if it aint broke, don't fix it, and if the car is resonably fast leave it, and just put a round in here or out of there. So its hard for me to try any changes that i want to try.

Anyways, I would like to see if I can get a couple questions answered without jumpin in on the threads above on designing a suspension system from scratch. I am looking to see if you all have some good information on string lining a car, i can't afford lasers so what is my best bet on string lining the car, what should I look for and so on and how should I do it. Also, is it best to use the string line setup to check/adjust toe out or is there a more percise route to take to get a consistant toe out measurement. Our current way of measuring toe out is horrible, I am embarrased to say how we do it. Anyways, I just don't like the idea of measuring off the tire as I am sure there are to many imperfections/writing on the tire to make for a bad toe out measurement. is it best to use a toe bar and a tire scrib to scribe a line on the tire tread and use the toe bar to measure from that?

Thanks all,

Chris,

 

[Ranger Mike]

Welcome Chris..we have these at the local tracks...nice clean racing...see post 293 on stinging the car..measuring toe is best deon with scribing a line on the tire but this takes two people t o scribe the line and hold " dumb end " of the tape measure...we use a toe gage..i will see if i can get photo of this on line..onme person can check the car and adjust...really close results..the Legends or Dwarf cars are real fun but rules say you can not do a lot to them..which does keep cost down...

 

[chriswh86]

interesting. here are a couple items I found at longacre

tire scribe
toe gauge that will measure to 1/32"

seems like a good setup.

Yah the dwarf cars are pretty cheap to run. We are just a local club so we designed our own rules there's a lot of grey areas etc but they also state if its not in the rules you can't do it so I am not to sure. But you can still design the setup however you want pretty much, which is quite nice.

I will look over the string line post. Thanks!

Chris,

 

[Ranger Mike]

Anti Squat and Anti Dive

Anti-dive and anti-squat ( I didn't explain calculations on post 314 so here it is)

Please read post 314 on page 20-

I had a question from Conrad on setting up his front suspension. Both Anti Dive and Anti-squat refer to the front diving under braking and the rear squatting under acceleration. They came about because passenger cars would require very stiff springs to counter act braking and acceleration forces and the difference in design is due to the different design goals between front and rear suspension, assuming symmetrical design between the left and right of the vehicle.

Percentage is the method of determining the anti-dive or anti-squat and this depends on whether the suspension linkages react to the torque of braking and accelerating. For example, with inboard brakes and half-shaft driven rear wheels, the suspension linkages do not, but with outboard brakes and a swing-axle driveline, they do.

To determine the percentage of front suspension braking anti-dive ( outboard brakes like GM metric chassis uses)

1. Determine the tangent of the angle between a line drawn, in side view, through the front tire patch and the front suspension instant center, and the horizontal.

2 Determine the percentage of braking effort at the front wheels.

3. Multiply the tangent by the front wheel braking effort percentage.

4. Divide by the ratio of the center of gravity height to the wheelbase.

A value of 50% would mean that half of the weight transfer to the front wheels, during braking, is being transmitted through the front suspension linkage and half is being transmitted through the front suspension springs. Passenger cars are as high as 30%, stock car racers run 5 to 7% if they even bother to figure it.

For inboard brakes, the same procedure is followed but using the wheel center instead of contact patch center.

Forward acceleration anti-squat is calculated in a similar manner and with the same relationship between percentage and weight transfer. BUT..you can have Anti-squat values of 100% and more (common in drag racing). all of the weight transfer is being carried through the suspension linkage but remember, this does not mean that the suspension is incapable of carrying additional loads (aerodynamic, cornering, etc.) while braking or during acceleration. 50% or less are more common in cars which have to undergo severe braking. Higher values of anti-squat commonly cause wheel hop during braking.

 

[chriswh86]

Off topic

we run a 235 60 13 tire in our dwarf car class, I've seen some people running 13x7 rims but most on 13x8 rims that stretch the tires out pretty good.

I am wondering if there would be much benefit to going to a 13x9 if that would pull the side walls a little straighter and maybe take away some tire roll...

Chris,

 

[Ranger Mike]

is wider tire better

like everything in racing , its all about compromise..we went thru this mind drill in FC ( Formula Continental) a few years back. In a class that races open wheel and limited horsepower the traction benefits of wider boots on all four corners may not be worth is. The key factor is engine output ( torque and HP). Open wheel cars get killed with big aero drag and tires account for at least 40% of total drag.
If.. and this is a big if the tire and wheel combination is the same as your current combination, and yoor wheels are under the car not hanging out in the air stream..Id run them. But if they are heavier than the current set up (come on...it takes more metal to make them... more metal = more weight). There's also more rolling mass. More rolling mass = slower rotation = slower speed. Figure about 2% more grip per inch tire width you add,,,but,,,parasitic drag is a BEAR...esp in open wheel limited hp racing.

see post below on General Physics forum,

How does traction compare to the width of a tire?

Mar17-12, 07:03 AM
Mender had some good insight

 

[Liju GKM]

sir, we are participating in mini baja. can you tell the steps of designing suspemsion in the correct order?

 

[Ranger Mike]

how high is the sky?

 

[chriswh86]

Interesting question I am having a hard time figuring out.

As I've seen, most circle track cars run some sort of offset on the rim backspacing to create more left side weight?

I recently got a newer used dwarf car which has set multiple track records, multiple points championships etc and it runs 13x8 aero rims @ all 4 corners with 1" backspacing.

I am having a hard time figuring out what the benefits of running this type of offset is at all 4 corners. there's a few other cars in the club running 1-2" backspacing at all 4 corners and they are fast as well.

Is it a way to better load the contact patches on acceleration? I just can't seem to get an answer i understand as to how this works.

Chris,

 

[mustngthundr]

Greetings! Just my general opinion on the wheel offset post above, iv seen a lot of circle track cars run both ways, equal offset side to side and different offsets to move the left side wheels further under the car. Iv talked to a few racers that feel it improves the left side weight with a higher offset wheel on the left. Maybe in static state on your scales it does, but in the dynamic state while your in mid corner it actually may be hurting you. Track width is one of the components that effect weight transfer. The other components are cornering force(Gs), weight, and center of gravity height. One of these components must change to effect weight transfer. In other words, there will be less weight transfer left to right if the track width is wider. Watch for wheel scrub when making your track width wider with wheel offset alone, however. Too much wheel scrub can be detrimental to handling as well, but in my opinion, that's why it's set up that way and that's at least part of the reason that the other fast cars are doing it too.

Mustngthundr

 

[Ranger Mike]

Wheel Back space

when you lay the wheel on the garage floor with valve stem up and measure distance from floor to the center section you measue the back space. The lower the number the further the tire is located from the car centerline. Too much offset really applies a big lever to the wheel bearings and on heavy cars you are asking for trouble. Some hot dogs in legend cars and dwarf cars run huge offsets ( real low numbers ) thinking the wide is right scenario works. I did some posts on the wide vs narrow thing on post 255 @ page 16, post 322@22 post 264@17. As limited as you are in this class, about ther only thing you can do is mess with wheel offset and chassis adjustments.
One way is to go W I D E... I helped a guy one season on a legend car and we opted to go left side ...low amount of back space on right side and high number on the left side..you are shifting the vehicle weight slightly to the left.
So the question is..go WIDE or max left side weight...??

Wider track offers less load transfer through the middle of the turns and therefore more retained left-side weight. If the wider track reduces the load transfer by more than the difference in left-side percentage, then it would be best to go with the wider track.

If the difference in left-side percent is more than the load transfer difference, then obviously you would go with the higher left-side percent.

If all were equal, I’d go with the wider track. With the low center of gravity of your Modified, there’s less load transfer than would be seen by a Late Model or stocker. But, why not try for both?This is where tune and test comes into play..these cars are so light that no way will you damage wheel bearings over one season running a 1 inch back space...I have no data on amount of left side wieght increase you can get since the racer who had the legend car did not own scales...if I had to guess...if you are already at 58% left side weight..if you can add 4 inch track width ..go for it..

 

[chriswh86]

Most guys in the dwarf class tend to run right at our max tire width, as measured from the outside of the left front to the outside of the right front, same on the rear...max 62"

Im currently running 1" backspacing at all 4 corners, so If i was to try a 4" on the left, id have a very short track width as I am close to 62" as is.

I like the 1" backspacing all around because it has obviously worked wounders in our class, I just had no clue how it worked.

But from what I have gathered from the last 2 posts, having 1" backspacing on the left side tires is probably saving a large transfer of weight from left to right at the center of the corner thus helping mid corner and exit?

Correct me if I am wrong. Cheers to all

 

[Fahlin Racing]

I see this thread has grown quite a bit, been pretty busy myself. I have to get some snacks and sit back and read again.

 

[Ranger Mike]

chris..yes i think you nailed it..the go W I D E crowd is dominating. I have not doen the math on the max left side weight thing but i suspect the % will not " out weigh" ( sorry, bad pun) the wide is right argument since what ever the left side weight is..will transfer regardless vs the wide is right theory of minimum transfer...
plus . correct me if i am wrong..you have prety hard Spec tires to begin with..not good for max Gs anyway

 

[Ranger Mike]

The following is index listing Post and page
Anti Squat 314@20
Bump Steer 13 @ 1
Caster 319@20
Eccentric 298@16
Four Link 132@9
Four Link Instant Center 301@19
Panhard Bar 246@16
Rear suspension motion rate 308@20
Rear Steer 116@8
Roll Center, front 251@16
Roll Center 229@15
Scrub Radius 325 @ 21
Shocks Penske shocks 217@14
Shocks Rubber Shock stops 220 @ 14
Spindle Angle 325 and 332 @ 21
Spring Rate Calculating spring rate 19@2
Spring Rate vs Wheel Rate 17@2
Stagger 36@3
Stringing the car ( measurements) 293@19
Third link Top Link 81@6
Third Link Mount 253@16
Third Link Spring Rate 261@17
Track Width 255@16, 322@21, 264@17
Upper Arm Angle 312@20

 

[chriswh86]

Ahh ok, Ranger - would you know of maybe a cardboard experiment i could do to understand the differents between high and low offsets and weight transfer. I realize I got the right idea of what the low offsets are doing and how they are dominating. But in my head i can't understand how it works :)

And we use american racer uhh Nedwarfs or something like that. The ratings on the tire are HORRIBLE...As for class rules...we can do ANYTHING we want basically. We have no left % max or anything like that. I am currently at left 52%, The car is extremely light weight, I am at 1220 race ready, 1200 is the minimum we need to be after a race...Sorry i don't have the best info yet, but there is at least 40pnds of lead by the left front tire...I always here. get to the max left weight %. Now with an open rule book on that and such a light car. I am guessing a lot of left weight won't be benefical? Id also like to get my weight back down to say 1210, enough weight left over for tire wear and gas at the end of the main. But i think the left weight is benefical in getting the front and back % close to each other, and sticking the left front

 

[Ranger Mike]

look at illustration on post 255 @ page 16...note the cornering Gs increase with 4 inch wider track..
thats a lot of weight but...if you need it to be legal...what size battery are you using?
are you running three link rear set up?
if it is wide open...i would be in hog heaven with all kinds of ...innovatative stuff...

 

[chriswh86]

Got to remember our track width, 62" max is a rule
Wheel base is 73" +/- 1/2" that's another rule


I am running a pretty small battery, a little red top, measures about 4" long, 5" in height and about 2-3" thick. Also I've see a SMALL battery on a bike that i don't think even weighs a pound. Mine is a few pnds.

its a 3 link rear setup. Long panhard, Long trailing arms, and a long 3rd link that is mounted on the rear end just above the RR trailing arm...

I need to find ways to loose more weight though :)

 

[chriswh86]

Something id love to see ranger, which may be a lot of work, is to list some good books folks can get.

ex.

Front Asphalt suspension designs by. blahblah

"Ranger Mike" -> i find this book good because it explains... and so on.

So maybe like a book title and what you feel its good for ect.

How do you feel about this? I used to have the circle track suspension book but its gone to some other racer probably

 

[chriswh86]

Hey all,

Something I've been thinking of lately. I've recently decided to move my car from the shop its normally at, to where i live. I've got a 7x16' enclosed trailer that will now be my tow trailer to the track as well as a bit of a shop when I am at home. A place to store my tools and so on.

Now i have a carport where I live but the cement is cracked in a few spots and its definantly not level.

I am woundering what options i have (im not made of money) for a rig/place etc to setup my car. I live 250km+ to each race track, so quick use of there flat pad won't work, nor do I have an area near where i live for it, so I am looking for what i can do at home in the carport for car setup.

I had thought of scale pad levelers which i could do and it sounds like it would work out with a scale system, but now I am a bit lost at how i could get proper frame height measurements, that's most of my concern.

Also, I am looking for ideas on how I can create a flat pad system or something for where I can put the car (no scales) and check the car settings/frame heights etc etc

I have a dwarf car, 1220pnds 73" wheel base, 62" track width, 113" long (bumper to bumper)

Thanks all, I can't wait to here what ideas are out there

Chris,

 

[Ranger Mike]

I think a scale platform ( 4 roll off ramps..maybe connected??) is what you need. Easy to make with plywood or OSB. You can make roll off ramps and use these to check set up chassis height. I have a set and i spray paint each roll off ramp and the scale pad location after i made a shim plate of proper thickness to " level" that pad at that location relative to the other three. The platform is cheap, easy to make, light weight and easy to transport ...some times ..wood isa good..