Race car suspension Class

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 lets 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 ya gotta run...
but this is just my opinion
ps ifin ya want to email your measurements, i can plug um into the program and send um back to you

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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.

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... thats 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/201...s-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/201...k-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

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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 cant 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 with out 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!