Automotive Race car suspension Class

[prankster16a]

So ...Mike. Here's one for ya. I've got 4 pavement sprint cars that I tune. Two of which I built. 2 of the 4 are a long 4 bar ( to the motor plate which is 42" to rear axle CL ) both of these cars use almost the exact same setups and are both very quick. The third has a z link rear like a BEAST chassis. set up is also the same as the long 4 bar cars with the exception of rear spring rate due to the coil over being mounted to the lower arm and not directly to the birdcage. The rear arms are 14.5" CL-CL and the coil over is mounted 4.5" back. I come up with a motion ratio of 1.9 ( I round it up to 2 - 1 for ease of conversion ) This car is VERY quick and at times has been almost a second quicker then the rest of the field. Now...the last car. I built this one with a short 4 link ( 27.5" CL - CL ) this car has allways wanted to push coming off....actually more like lifts the front wheels under excelleration. I've gone up in rear split ( 50# more on the RR...I usually only run 25# split ) moved the top wing forward and put a bunch of rebound in the front shocks. This has made the car waaaaaaaaaaaay better, but allways near the end of the main, the car goes tight again.
Any thoughts ?

Thanks....Kenny

 

[Ranger Mike]

Kenny
i been in chicago at trade show..btw..best show in years...
i have not heard back from my software guy yet on software..
ref car pushing at end of the race...

push or under steer means the car has too much rear weight and the front tires can not turn the car so it snow plows toward the wall, not good..
we know in order for the right front to work properly it needs enough weight transferred to it to stick...( take a front tire off the car and place it on the garage floor and stand it up like its on the car. now place eahc hand at the max diameter and slide it across the floor..pretty easy..right..now get the fat kid next door to come over and sit on the tire and try this again...putting fat boys extra 100 pounds on it makes the sliding more difficult..right--DOWN FORCE)

think about this...the fuel has been used and you have a lot less weight on the rear of the car...normally

this coupled with the fronts heating up, change in stagger, the wedge changes..all contribute to late race push..one thing you can do is switch to nitrogen in the tires..will cut out thermal growth and this will control wedge change to some degree..

 

[prankster16a]

Mike.....I do use Nitrogen in the tires. All tires grow exactly 2lbs

 

[prankster16a]

One more thing Mike. All 4 cars run the front panhard bar uphill to the chassis 1/2". This is good for about 2 - 3 tenths on all 4 cars I tune.When I run the front bar level, the cars are all loose on initial turn in. Is this telling me that I am a little light on my front springs ? I run a 400 on the LF and a 425 on the RF. Should I level the front bar and put more spring in the front ? Keep the front springs the same, level the front panhard bar and lower the rear bar ?

Thanks...kenny

 

[Ranger Mike]

Kenny.. just got home and dug up my old dirt track notes..

If my memory serves me correctly, and your talking about your roll center along your panard/j-bar axis, raising the roll center will minimize the roll. But, this will only work solely for roll center if your raise both ends of the panard/j-bar. If you only raising the chassis end, you're now introducing a percentage of bite in wheel loading depending on your rearend geometry. As for the left or right, that is dictated by the length of your bar in relation to the center of your chassis and weight distribution. The more you bring it closer to the center, the more you'll allow the chassis to roll.

Lowering the roll center will help the car roll over more which helps generate more side bite. The roll center is the axis of rotation for the car when the body rotates left to right. The lower you place the roll center, the longer the "torque arm" you are generating. Longer torque arm's give the chassis/body more leverage which produces more roll which makes the right side tires grip the track harder. The principal is the same as a torque wrench. The roll center on a torque wrench would be where the socket attaches. The torque arm would be the location you place your hand on the wrench. The point you position your hand around the wrench is where the force gets applied. The further you move your hand away from the socket(roll center) the longer the torque arm you produce. This helps multiply the force you are generating with your hand generating more leverage.
So back to the racecar...The weight of the chassis/body is the force that causes the car to roll. The chassis/body is the same thing as your hand turning a socket wrench.

Increasing the distance between the roll center (socket attachment point) and the center of mass of the chassis/body (where you stick your hand on the wrench handle) you create more roll (leverage) due to a large torque arm or lever arm.

The roll center is located between the two heims on your panhard bar. If you are using a J-bar it is in the center of the two heims as if the bar was straight. The more weight you put on the right side of the roll center the more it will allow the chassis to roll. This is why you use a j-bar or a shorty bar on a dirt car and a long bar on an asphault car. You want roll on dirt and not on asphault.

Raising the chassis mount on a long bar tightens up the car. It's from the increased angle on the bar.

i think you have stagger growing on right front..late race push comes from right front diameter growing due to heat..this is like running a stiffer right front spring, this means the front end is not accepting the same amount of weight transfer from left rear to right front going into the turn and at end of race you are keeping more weight on the rear springs ( rear springs are acting like softer springs) and the car starts to push. your " wedge" is changing.

as far as swapping out the front springs...and changing the attack angle of the bars...i would first start with trying to get a set up running same size springs and tune to that set up.
all cars are different but the trends are there and you found them..you obviously got the hot set up on the present angles and there is some weight jacking going on.

The handling balance for a Sprint Car needs to be a dynamic balance just as in a stock car. All four tires need to be in contact with the racing surface and have the most load ending up on them as possible. If we have a truly balanced setup, the LF tire will carry a decent load and the car will turn better.

For a winged Sprint Car, it would make sense that our spring rates, side to side, would be the same. Spring split on a solid axle suspension has a dramatic affect on roll tendencies. Since the cars roll first to the right on entry and then left at mid-turn due to the aero forces on the wing, we need to have the same roll stiffness in both directions. If a stiffer RR spring (over the LR spring) promotes roll stiffness in a roll to the right, then the reverse would be true for a roll to the left.
Our handling can be much different from corner entry to mid-turn if we run different rate springs on each side for winged Sprint Cars. The Panhard bar height, or Watt's link moment center height, must also be tuned to the spring stiffness as well as the spring base. The idea is to develop a setup for your Sprint Car that has the same roll characteristics for the front and rear of the chassis so that the handling balance is equal all of the way through the turns. Again, this has been tried and proven to work.

The setups for the winged Sprint Cars vs. wingless Sprint Cars is necessarily much different due to the high amount of downforce produced by the wings. The spring stiffness must be more for the winged cars, especially on asphalt. The speeds are much greater when Sprint Cars are racing on asphalt with wings attached.

More loading means more traction and the lateral g forces go up considerably with the increased speed through the turns. This necessitates a higher overall spring stiffness and in some cases, a spring split with the right side springs being more rate than the left sides.
Here too, we see a definite need for chassis setup balance. We really want all four tires to carry maximum load. At the LF, we need for that tire to carry load to help the car to turn. Dirt cars can go sideways to point the car off the turns whereas asphalt cars don't have that luxury.

Kenny all these set ups are band aids to deal with weight transfer that THIS SET UP has...any time you change a par setting you change degree of weight transferred and rate of transfer. hopefully my software guy will tell me Monday about the capability of using it on sprint car set ups..what we really have to do is find the front and rear roll centers and figure how to lower them in a practical manner and get as nuetral a set up as possible..then by tweaking the P-bars we can adjust to the changing track conditions..

these are from my track notes and may be rabbling but i am not a dirt tracker..and only helped a winged sprint car team one season..hope it helps

 

[prankster16a]

Mike.....I value all your input. I run 25 split across the front ( 25 more RF ) because I have found the car to " squirt " loose on initial corner entry with anything less. I have also found that almost every car has had better corner entry with the front panhard bar running uphill to the chassis 1/2 ". I have been running 25 - 50 rear spring split ( more spring on the RR ) for two reasons. I have tried it straight up as well as more LR spring. Both of which made the car push horribly coming off the later of the two being the worst. Also with less then 25 pound rear split the car wants to hike the LF coming off...my goal has been to keep the LF on the track, as I feel this has to help the car turn.
I guess what I would like to know is this...If I lower the panhard bar...either front or rear...do I have to go up in spring rate to control chassis roll ?
Ive also been thinking...I run a very low crank height in my cars...7". I am wondering if I might be able to help bite by running the motor a bit higher...lets say a 9" crank height. much like a dirt car.
Thanks...Kenny

 

[Ranger Mike]

Kenny t he following messgae came from my software guy..


Mike,

Our Circle Track Analyzer DOES allow for straight axles on the front. However, it does not do all the detailed 3D analysis of the Susp Anzr. Click on Link below:

http://performancetrends.com/Circle_Track_Analyzer.htmIt won't do all the jazzy stuff the door slam software does but is well worth the dollars to see RC change when you change mounting points..
i swear by it for my late model and formula car!



Thanks.

Kevin Gertgen
Performance Trends
feedback@performancetrends.com
248-473-9230 fax 248-442-7750

 

[the dr.]

I was directed here but a friend, who reads here but never post, and I have spent the last 3 nights reading the info here and find all of it to be very informative, I have been in racing for over 30 years, as a driver mechanic and crew chief, this year I have been talked out of retirement, to work on a car racing in the heart of the south, on dirt tracks, this willl be my first venture in the 3link's, I have worked with the 4 links and torsion bars and leaf spring cars in the past, anyone got any pointers or links where I can cram on the 3 link? it is a full body 2800 lb car, tube chassis firewall back, stock clip on front, I feel I have a pretty good understanding of chassis' just have never worked with a 3 link before, been reading all I can find on the variations of the 3rd link, solid bar VS buscuit bar, and spring bar... looking for any input what so ever...thanks

the dr.

 

[Ranger Mike]

Welcome, Dr. It is always great to meet a fellow racer. As you state, you will be running a stock arm front end ( metric) and 3 link rear. This is ok but most dirt guys run 4 link to hook up better. A three link can run ok and I recommend the two following books from Steve Smith Auotsports
I.M.C.A Modified Racing Technology by Steve Smith
PAved Track Stock Car Technology bu Steve Smith..it goes into a lot more physics
the IMCA book deals with metric frame economy modifieds using stock front suspension and both 3 and 4 link rear..AND IT IS HEAVY ON THE TRACK TUNING INFO.
Personally i would get several poster board sheets, tape them togeather , put it under the car and and note all front end mounting points. This will give you a base line record of exact suspension points and you can calculate the roll center height and location from this..and use it when you have to rebuild the front end..and we both know that happens more than we would like.
I attached print out from Performance Trend software
one is circle track analyzer and one is the more advanced suspension analyzer
I swear by this program as it let's you fiddle with mounting points and A-arm lengths to get a better roll center height and location
Dr. it depends on how much you want to win...most guys do monkey see monkey do at the track and never understand how the suspension works..they just bandaid a replicated suspension that everyone runs ( except for the track hot dog) and fiddle with stagger , wedge and maybe sway bar tuning...I believe in relocating the stock roll center and modifying the suspension into a best case situation under the handicap regulations you got to run...
but this is just my opinion
ps ifin you want to email your measurements, i can plug um into the program and send um back to you

 

[the dr.]

Thanks Ranger Mike, I understand exactly what your saying, about monkey see monkey do, I will share a story with you you will get a kick out of...
a couple years ago while running the local track we had won 7 out of 11 races and run second or 3rd in the rest of them, when one of our local drivers felt the need to help us into the wall, well we were able to repair all of the damage except for the right side header, which we were told by dyna-tech it would be 10 to 14 days before itwould arrive, so we dug around in the shop and found an old header to use for one race, only problem was it was an over the frame style not the under the frame style we had been running, no problem I mounted it and fabricated a shield and ran it out the side of the car ( where the passenger door should be) instead of under the car, well, it sure made the car sound different, since the header was pointing the exhaust right at the wall down the straights, causing a reverb effect, everyone thought I had broke out my "big " motor, and me being the sort of person I am, did nothing to dispell the rumor,well we won, so we take the car home, new header arrives and we put it on patch the hole in the door, and on the following saturday we go back to the trqack... 5 cars suddenly had headers running out the door! so yeah monkey see monkey do...
now back to the topic, a 4 link is out of the question since rules will not allow it thus the reason for us running the 3 link, I will be looking at the books you listed and checking out the sheets you provided, the car will be here the week of christmas, and I will be spending some time touching each and every bolt of it and getting to know it very well, and soon as I do I will be sending you the information.
I am glad I have found this site since with my reputation around here no one wants to share too much info...lol looking forward to reading more post and getting to know each of you, should any of you ever find yourselves in the NW Ga area please holler at me , we can do some bench racing and maybe vbenture over to the track... we got some good racing round here... my blog is listed in my profile and there is a link to my photo album there, please check it out and take a gander at my photo's I am proud of some of the shots I was able to get this year...

thanks again
the dr.

 

[Ranger Mike]

Dr. that was a hoot...speed secrets no doubt..I have been on here for about a year and there are some absolutely top notch people on here..xxchrisxx, Danger, brewnog, turbo1, mender, russ watters..they have insight and knowledge gained over many years and have helped me with many wackey ideas i have had in my racing effort...it is a pleasure to know them and all they ask is honesty and an open mind..i sure learned some humbleness on this site..
ps if i left anyone out, i apologize..

 

[mender]

Good story and pretty typical, dr! I've had the followers tagging along a few times as well!

We run a 3 link system on asphalt road courses with similar car specs but if you have any specific questions I'll give 'em a shot.

And thanks for the pitch, Mike! Great to be here as well!

 

[the dr.]

Good story and pretty typical, dr! I've had the followers tagging along a few times as well!

We run a 3 link system on asphalt road courses with similar car specs but if you have any specific questions I'll give 'em a shot.

And thanks for the pitch, Mike! Great to be here as well!

Thanks Mender, I have only seen the car once since we got it, working 7 days a week stinks,I hope to get to spend some time with this car tween now and season start, now, we just got 6 inches of snow... I have lots of expierence with other types of rear suspensions just never run a 3 link, beat em a few times with a leaf car but... that's another story, just so you can see how I scare people at the track check out my latest blog, it has a pic of me on the top..
http://topofthebox.wordpress.com/2010/12/25/year-end-thoughts-from-the-dr/

the dr.

 

[the dr.]

I have had a chance to go over the car pretty good now and everything looks good so far, I am qwondering about panhard bar mounted on right side instead of the left... this will take some thinking... lol details later, we are looking at first practice some time in march...

the dr.

 

[mender]

Check the angle on it as well.

 

[Ranger Mike]

left side mount is the norm only because its easier to pull a chain than push it...left turns mean the panhard bar is being pulled when you turn...but...the nascar boys run the same thing on road courses so the p bar is being pulled and pushed...go for it..

ps that will really screw up the minds of the competition with this new wrinkle!

 

[mender]

Maybe you could describe the mounting location and bar length as well. What adjustments can you make?

 

[the dr.]

http://topofthebox.wordpress.com/2011/02/19/work-in-progress/
I have posted a few pic's of the track we will be running at this year, on my blog, I am still working on getting the car ready got body going on this coming week. and we have a pracitice on March 26 first race April 2 so if your in the North Georgia area feel free to stop by and say hi!

the dr.

 

[Ranger Mike]

good way to turn winter into spring...plus Daytona this weekend...looks good...bet you can't wait to get the Green flag!
Rm

 

[the dr.]

well our first practice will be this coming saturday evening, I am looking forward to it greatly! I have been overthe car with a fine tooth comb, and found a few things that make me wonder like the j-bar mounted to the right side but while kicking this around in my head this makes sense since these cars are famous for being tight and this will loosen the car up, I have toyed with air pressure and slight tuning in the past so I have decided to go with the set up that the car used last time it ran at ngs and go from there my driver has very limiteed time in a race car much less a 3 link so this coming saturday is going to be a real learning esperience.
anyone got any pointers I can pass along to my driver? he is a pretty sharp guy who has learned tons in the off season and is a quick learner... I just need to guide him in the right direction...

the dr.

 

[Ranger Mike]

on 3 link rear suspension this is what i got as good set up:
top link or third link/toque link should be mounted 12 to 13 " above center line of axle housing and 1 to 3 inch behind vertical center line of axle housing. it also should be mounted at center of weight mass of the car...i.e. if car has 60 inch rear track and 53 % left side weight
60 x .53= 31.8" so center of mass and top link mount location is 31.8 inch to left of the center of the RIGHT rear tire.
Angel the top link down hill about 20 degrees..and usual adjustment is between 15 to 25 degrees..btw on asphalt we run 3 to 7 degrees...

adding more down hill angle will tighten up the car under power off the corners,,,,but the hook up does not last as long and by using a lesser angel the car will hook up more smoothly but not as quickly.

you may want to add a shock damper to the 3rd link mount. this will control rear end looseness and wheel hop under braking..the axle damper should mounted 5 degrees up hill. Never mount it level or down hill. If the rear end loosens persist at corner entry use more axle damper up hill angle adding no more than 2 degrees at a time. max 7 degrees up hill angle on dirt. if axle hop and loosens still is there we have to look at brake caliper mounting..
if rear is too tight at corner entry decrease down hill angle...

lower trailing arms usually mount 3 to 5 inch below axle center line. the most common center to center length for

lower trailing arms is 20 inches.

lower trailing arms normally ,mount 5 degrees uphill. uphill angle gives better forward bite. both links with same angle create slight roll over steer. you can change wheel base to control rear steer by shortening or lengthening one of the

lower trailing arms . Many dirt cars run 20.25 inch right

lower trailing arm 1/4 inch longer than left side , to increase roll over steer.


What shocks are you running on the car?

what is length of the track and what is the angle of the banking in the turns?

hope this helps

 

[the dr.]

Ranger Mike, thanks for the help, we didn't get to try any of it out last night since it came a torrential downpour here but we are going to have a practice Tuesday night and first race this coming Saturday...
question what effect does shortening the 3rd link have? it is 29.75 now and We can't run anykind of dampers at all no busciut bars although I do have a iron in the fire that may find away around that...lol everything else is pretty on track with what you have sugested... I did change the lower bar angel to your suggestions since it seemed more inline with my thoughts... only changed it 3 degrees... but we will see and I want to thank alll of you here for your input...
again its a standing invite to each of you if your in the NW Ga. area on Saturday night holler at me We got a place for you on our trailer! but one little bit of warning... we may put you to work...lol and we pay with hot dogs!

the dr.

 

[Ranger Mike]

Thanks Dr.
In the case of the 3rd link, length does matter..kind of...if you draw a line through the mounting points on the lower links it points to the front of the car, if you draw a line through the 3rd link, it also points to the front of the car..where they cross is the rear instant center (IC). and this point is where they all act as a torque arm. Modified 3link have a shorter 3rd link and a cushioned type of 3rd link to cushion the forces being fed to the rear tires under acceleration. These are spring loaded torque links or rubber biscuit bars. Its about the angle of the 3rd link. If the instant center is moving around a lot under acceleration, you have a very squirrelly car. Th ultimate 3rd link depends on its length. Longer length is ' better' only because the mount point will be lower in the chassis and the reaction to the chassis under acceleration will be more gradual and make the car more drivable than if you have a higher mounting point.

Summary from this and above post- the more the instant center moves around, the more the rear steer changes and goes from rear understeer to rear over steer and you got a hand full of car...during rear chassis movement in the corner. An IC that moves least and is located as low as possible in the chassis will provide best force to the tires as you will get.BTW, we ran a third link that was almost at the rear motor mount point, on out asphalt super late model. Biscuit bars and spring load torque links are Band-Aids to try to cure bad engineering of mount points.
Thanks for the invite and get that Checker in the first race, amigo!
RM

 

[the dr.]

Ranger Mike, we have 26 7/8" lower arms, with a 29" 3rd link, car has bilstien shocks it is long wheel base car... 107" wheel base, tonight we go for our first race last tuesday we went for practice, and driver was just getting used to it and improved DRAMATICALLY! shaving off 2 seconds during the night, had J bolt at rear end work loose and it took us a while to find it so we loaded, and watched... like I told driver "better to park it and check it than to race it and wreck it" . so we are looking forward to tonight.I played with air pressure a little and found that 9lbs worked real good on right rear. NGS is a 3rd mile very high bank red clay track track record for late model is 12.89 and in Mod Hobby we were in the low 15's so I was very happy. looking for major improvements tonight. I want to thank you for all the info you have provided it has really improved my understanding of the 3 link. and with that I feel comfortable in making changes and tuning... we have to weigh 2900lbs and tuesday night we crossed the scales at 2900 exactly.. so I am going to add a little lead today to make sure we will cross the scales at weight... Car has lot's of roll over in the turns but driver says it feels good and car is fast comes off turns really good and picks up fast without all the fishtailing we had issues with on the leaf spring car...we have 2.5 inches of stagger and I have tires to add some if needed latertonight depending on track.. track has new clay and it is worked in really well, I am off to the shop to get car loaded and get ready for tonight... hope everyone has a great weekend... and thanks again for your help...
the dr.

 

[Ranger Mike]

still snowing up here in yankee land

get that checker , Doc!

 

[the dr.]

well here is an update, we have had 2 races and have had to start in the back on both of them we have an 10th and a 8th, this weekend driver finally learned how to get the car in the corner but i have a question... on the rear shocks we use the rubber rings to show travel. our right side,we are getting 4 or 4 1/2" of travel, on left side its only 2 1/2 " of travel.now I am wondering should I make an adjustment to even it out some and if so what should I change? the car was really good last night and we had an awesome run but I see more in the car and I don't want to chase the car all year I would like to get ahold of it now... our rules say that the 3rd link has to be a solid par no spring loaded or buscuit bars, well we have been racing against a lot of cars that have been running them, this week they announced it was going to be policed strictly this next week so we are already 2 races ahead of some of these guys... it did seem kind of twitchy coming off the corner a couple times but I think that may of been driver error... so I really want to thank you for your help and I hope to be posting a victory lane pic here soon...
the dr.

 

[Ranger Mike]

What stagger you running?

loose on corner exit - look at stagger..is she is loose coming off the turn, reduce the stagger.add cross weight..see set up below. Normally we soften the right rear spring or stiffen the left rear spring but shock travel indicates that we don't need this. if you had run a spring 3rd link we would soften it.What number shocks are you running on the car? i assume you got 7 inch travel on the fronts and 9 inch travels on the rear corners..
What is setting of rear panhard bar?

did you get chance to do tire temperatures?
did you scale the car? set up i use as base line for dirt car is 53 to 55% left side, 55 to 56% rear and 49 to 51 % cross weight

 

[fstock34]

i have a question about a car I am trying to build it is a street stock built out of a 1985 monte carlo and as far as sprung and unsprung weight would it be benefical for me to add weight in the form of heavy gussets to the rear axle housing( on the lower sides of the axle tubes not the topside) to get rear weight percentage and beef the strenth? As well add a few pounds of reinforment to the left rear trailing arm (by melting led into the hollow bottom side on the lower third of the arm toward the rear end housing only leaving the other 2/3rds empty) to add more rear percentage and some left side?? My tracks rule book allows alteration to those items to add strentgth. While i do know that would be adding unsprung weight i also know that the chassis is built very well and with a 56% maximum left side percentage rule a 3000 pound minimum weight rule and a 5 inch ride height rule. a lot of teams in this divison have been forced to set their cars up having weight on the right side of the car to meet those requirements and i think that adding weight right on the rear housing and the trailing arm would help my cars set up quite a bit (this weight would lower than the frame rails by quite a bit as well back as far as it could be before running into polar moment issues). From what i read on this forum earlier this should help add rear grip off the corner being that the track surface is 2 season old with no large bumps to make the tires jump by making the role center higher am i correct or did i read things wrong?? Any thought from the fellow racers on here would be greatly appreciated because this will be my first year in this divison moving up from factory stock to street stock and the set up and things like that are much more complicated for this car than my factory stock was. Hope you all have a happy holiday weekend and i look forward to hearing from you guys.

 

[Ranger Mike]

Welcome..You have been doing your home work well and have a pretty good grasp of getting the handling under control.
Unsprung weight is bad only because you can not control it..as good as.."sprung weight" as far as that can be controlled.
In these " stock"series racers, there is a lot of room to gain competitive advantage, you just got to know where and how...

I am for beefing up the trailing arms. I am not a big fan of doing the melting lead thing as it is a real pain and will not reinforce the chassis member ( welding gussets is the way to go). What do the rules say about adding weight? When do you have to scale the car? Do you have to scale after each race? Or are the top three scaled after the main event? Exactly how much weight are we talking about?
Do you have the battery relocated? What do the rules say about the springs and sway bars?

 

[mender]

The mid 80's metric chassis (Monte Carlo) has a poor camber curve and that either needs to be corrected if allowed within the rules or compensated for with the right suspension combo.

Adding unsprung weight in the amount needed to positively change the weight distribution will complicate your set-up and be more and more of a handicap as the track gets bumpy (it will!). I'd recommend doing only the amount needed for strength and concentrating on tuning the suspension. There are a lot of little things that are legal that when done properly can make more of a difference than a couple % weight change.

Without having the rules it's difficult to advise you; do you have a link?