Register to reply

Race car suspension Class

by Ranger Mike
Tags: class, race, suspension
Share this thread:
the dr.
#73
Dec25-10, 05:09 PM
P: 16
Quote Quote by mender View Post
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... 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.
#74
Feb10-11, 10:16 PM
P: 16
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
#75
Feb11-11, 12:35 AM
P: 563
Check the angle on it as well.
Ranger Mike
#76
Feb11-11, 03:40 AM
Sci Advisor
PF Gold
P: 1,478
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
#77
Feb11-11, 11:11 AM
P: 563
Maybe you could describe the mounting location and bar length as well. What adjustments can you make?
the dr.
#78
Feb19-11, 03:07 PM
P: 16
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
#79
Feb20-11, 01:51 AM
Sci Advisor
PF Gold
P: 1,478
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.
#80
Mar20-11, 05:43 PM
P: 16
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
#81
Mar21-11, 04:28 AM
Sci Advisor
PF Gold
P: 1,478
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
Attached Thumbnails
rear steer.jpg  
the dr.
#82
Mar27-11, 01:35 PM
P: 16
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
#83
Mar28-11, 03:17 AM
Sci Advisor
PF Gold
P: 1,478
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.
#84
Apr2-11, 10:33 AM
P: 16
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
#85
Apr2-11, 12:20 PM
Sci Advisor
PF Gold
P: 1,478
still snowing up here in yankee land

get that checker , Doc!
the dr.
#86
Apr10-11, 08:59 PM
P: 16
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 dont 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
#87
Apr11-11, 02:45 AM
Sci Advisor
PF Gold
P: 1,478
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
#88
Apr22-11, 01:49 AM
P: 4
i have a question about a car im 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. alot 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
#89
Apr22-11, 02:30 AM
Sci Advisor
PF Gold
P: 1,478
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
#90
Apr22-11, 10:34 AM
P: 563
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?


Register to reply

Related Discussions
Car Suspension Explanation General Engineering 6
How does a Physics class differ from an Engineering class? Academic Guidance 38
In class final for a graduate EM class? Academic Guidance 3
Car Suspension Engineering Systems & Design 3
Spring suspension on car Introductory Physics Homework 4