Race car suspension Class

[Garage Engineer]

Hi Ranger Mike,
Pavement racing on a high bite surface, and no banking

If given the choice between increasing left side bias by a large amount ( or ) Widening out the overall wheel base [left to right] which option would you take?

 

[Ranger Mike]

Garage eng- welcome. Please see post 255 page 13, post 264 page 14 post 322 page 17 and post 505 page 26
for the left side % see post 783 page 40
recap - ( not the hobby stock tire) add 4 inch track width will pick up slight amount of cornering ability. You up the Gs from 1.30 Gs to 1.33Gs
Depending on your tires , hard spec tires limit you to 55 to 56% left side weight. Super late model slicks can do 58% before the side bite goes away.

As always i remind all racers to look at camber build, bump steer, ackermann, rear roll steer and know what the chassis is doing and when its doing it.
Know where your front and rear Roll Center is and where it goes on the track (dynamically). Know the COG and what it does.

 

[Garage Engineer]

Thank you for the feedback, I read through all the suggested post and it was very insightful.

I do have one more question for you Ranger Mike: Looking at a Supermodified with solid axles front and rear

" Whats the difference between adding rear steer to a race car (vs) Front Axel Lead?"

It seems to me that regardless if you push the RR back (or) Push the RF forward you are achieving the same results - Right? So what am I missing?

Thank you again for helping us all learn a little more about our cars.

 

[Ranger Mike]

Big difference.

Some Racers lead the RF while others trail the RR. Usually the amount is between 3/8" and 1/2".

Let’s look at the front end and leave the trail arm lead to later.

The advantage to leading the RF is that it will create more of a "caster stagger effect" without having to run as much actual caster stagger.

Typically on a manual steer car you run 1° left side caster and 3° right side (power steering ups this to 1° left side caster and 4° right side.

Putting lead in means you won't have to run as much caster in the RF, and that means you won't have as much LR weight jacking when wheel is counter-steered.

See post 319 page 16

For caster. You see the caster split or stagger is not to steer into the corner easier, it's to assist you when you exit the turn with your counter steer.

I am a big fan of square cars. Everything parallel and square. I like this set up as it is a lot easier to replicate after a crash. Adding lead in means fabrication and extra work.Look at rear roll steer on post 81 page 5, post 116 page 8, post 858 page 43 and post 1200 page 60. Real roll steer is great for dirt cars and can help on paved track cars.Trailing the RR means more static rear steer and means more dynamic roll steer. Now for certain very restricted car classes, let us suppose you were to move the LF geometry back 2 inches. To avoid the wheel base check you would have to make sure you could crank in 2 inch to the left rear trail arm before tech inspection. Let us suppose the rules said no engine set back as measured at the spark plug. Let us assume some sneaky crew chief made access to the right side spark plug a very easy measurement to the top ball joint. The left side required some gymnastics to get a good measurement due to alternator, power steering and oil cooler placement.

Some low life cheating sob could set the whole engine back 2 inch and the car would have more rear weight bias and had a 2 inch shorter left side wheel base. Car would turn left like a bandit and had 52% rear weight bias when everyone else had 49 to 50%. But this would be considered “cheating” in some corners of the {all things are equal} universe.

 

[Ranger Mike]

handy Index for this class see page 1

 

[Wheelman71]

New member to the forum. I stumble across this forum looking for set-up advice. I've read through this thread a few times and relearned a lot of great info. I raced Street Stocks and Limited Late Models on both dirt and asphalt for 10 years, had some some wins; but had to stopped 10 years ago. Life got on the way. I was told by my wife that we are racing next year so I'm trying to get prepared. Cut my 108" car apart yesterday, shorting it up to 103". Much to do.

I wanted to Thank Ranger Mike and others for keeping this thread going. I'll have some questions in the near future. Thanks again.

 

[Ranger Mike]

welcome...lot of help from other racers here..some may even be valuable...just kidding!

 

[Ranger Mike]

Real good hook up on paved track by street stock. Do not like brake lines tie strapped.Stock control arm bushings ‘ worn out” in the right places.





When you are at the track hot lapping, try this to fine tune the car set up. Hot lap at mid speed and note the steering wheels degree of turn at mid track. The mid track is usually marked o the wall. If not, pick a point and use this mid turn location on the wall for reference. You should have the 12 o’clock position marked already for easy of centering. So note the 12 o’clock of the steering wheel when you are at the mid turn wall location. Use a piece of tape to mark it.

Next thing to do is hot lap the car at you best speed and again note the same mid turn location and the new mid turn steering wheel 12 o’clock position. Mark it and make sure you note which was at slow speed.

If the steering wheel hot lap mark is more than the slow speed mark, the car is tight. If the hot lap speed is less that the slow speed tape, the car is loose. Adjust accordingly.
Excellent video on using rear steer to tune. I recommend a total of 1/4 inch wheel base change when first tuning with rear roll over steer. Make sure you have no chassis bind and the rear end remains centered when in dynamic roll.
This is on dirt but nice how the wheel base on the left side shrinks up under power and returns to stock setting off throttle..extreme but a little on paved track will aid turning car mid corner
another view of rear roll over steer on dirt

 

[Ranger Mike]

600,000 views..wow..thanks Racers!

 

[drobbie]

With the off-season upon us and time to make our cars better, I have a question. I have and will again measure my front to plot out the roll center in hopes of improving our performance. But before I embark on that task I have a question concerning determining the correct center line.
When laying out for the roll center should I use half distance between the frame rails or the midpoint between the tread width. When reading through the posts here I have seen both mentioned but not in a clear manner to understand the correct method. The reason I ask is we have a asphalt modified and not only is the chassis is offset several inches the wheels differ in offset by 2+ inches.
We also have different length lower control arms to compensate for the chassis and wheel offset. I am trying to get the most accurate determination of the roll center and make the car better for 2019.
Thanks in advance

 

[Ranger Mike]

I always used the center line determined from the lower inside A-arm mounts and painted a center line on the bottom of the frame and top at several locations. This was done with the wheels and A-arms off the car when I was going thru the rebuild process annually. I liked to see just how much offset the car really had. Real easy to do if the air cleaner center bolt is sticking up like a flag on Iwo Jima up and the center line is 4 inch to the right of it!

I always put a piece of roll bar foam over the top side marking. Just paranoid crew chief thinking I guess.

Another advantage is the center line travels with you and can be used to rebuild the car at the track if you wad it up. Down side was that a sharp competitor could see this too if he got close enough while the car was in the pits. The Track width method is ok as well but remember to set aside a complete set of tires and wheels marked SET UP so you will have the same set up each time.

 

[drobbie]

Thanks Ranger Mike, To me it was the most logical place but in seeing other references I was wondering if I was ding it wrong. As always great info here to keep referring back to.

 

[Ranger Mike]

Handling diagnosis at the track
Sorting out a just rebuilt or just purchased used race car can be a challenge. It is assumed you can tell if the car is pushing going in, or at mid turn or on exit otherwise you would not be reading this.

One way to determine what is going on is to hot lap the “ new” car. You should have the 12 o’clock position marked already on the steering wheel for easy of centering. If you don’t……shame on you!

Hot lap at mid speed and note the steering wheels degree of turn at mid track. The mid track point is usually marked on the corner wall. If not, pick a point and use this mid turn location on the wall for reference.

Note the 12 o’clock of the steering wheel when you are at the mid turn wall location. Use a piece of tape to mark it.

Next thing to do is hot lap the car at you best speed and again note the same mid turn location and the new mid turn steering wheel 12 o’clock position. Mark it and make sure you note which was at slow speed.

If the steering wheel hot lap mark is more than the slow speed mark, the car is tight. You are having to turn the tires more at higher speed and almost always will cause a snap loose condition once you are at turn exit.If the hot lap speed mark is less that the slow speed tape, the car is loose. Now some will argue that you can race a loose car but this is dangerous. I maintain you can race a tight car but it will be slow.

So what should you fix first? Cars that are loose on entry should be fixed immediately before even thinking of any other action. Make a single big change to cure the loose in situation. Higher front spring rate or softer rear spring rate.

Swap out the ARB to stiffer one. You can preload the ARB (sway bar) but I hate this arbitrary choice. I try to use the panhard bar adjustment for fine tuning. The same with using less stagger.Cars that are pushing going in need the same large change like going softer on the front spring or stiffer on the rear spring. Use a softer ARB. Cars that are pushing at mid turn will usually be loose off because the car moves up in the groove and is off the best race line and

runs out of room. The car gets loose because of the late exit and driver over reacts to the pit wall growing bigger in the windshield..yikes!I personally view cross weight (wedge) stagger and panhard bar adjust as fine tuning options and recommend these not be used as at the track fixes when you should be changing out the springs. Change out the front spring/springs to cure turn entry problems and use rear spring changes to cure traction off problems.

One tool you must have is a tire pyrometer. See post # 468 on page 24 on reading tire temperatures.
You must keep good records on the tire temps and tune accordingly.
The above scenario assumes you have the springs and wheel weight close to a good set up. For the rookie just getting into the game it can be confusing. Is the car pushing because the front spring is too stiff or too soft?

Each wheel must have a shock travel indicator on it. You can fabricate these easy. But you must be able to tell how much each right side wheel is compressing and each left side wheel is drooping in a turn. So ifin the car is pushing going in and the right front spring only compresses an inch ..the spring is too stiff. If it is compressing 4 inch you got too soft a front spring. Savvy?

 

[Joshua Ryan]

Hello, name is jc. I have a question and I’m hoping Someone can possibly answer. There are these new trailing arms for a 3rd link setup. And they are the center pull style that mount to the back side of the rear end housing. A few guys run them and basically say that the forward bite is great. So my question is why is the center pull so much better then the traditional trailing arm mounted with the shock on the bottom, any info will be highly appreciated.

 

[Ranger Mike]

do you have a manufacturer name or website i can look at? I assume you are NOT talking about the top link. you are talking about the traditional truck type trail arms that are made up of threaded tube and two rod ends. And the new style has a spring that compresses built into the trail arm

 

[Joshua Ryan]

No I’m not talking about the top link. But yes to the truck arm style. And I know about the spring loaded ones but this goes over the rear end and mounts to the back side. Mainly made by port city. Here is the link to the website. https://www.portcityracecars.com/Center-Pull-Rear-Suspension/ also a picture https://goo.gl/images/g5VFNy

 

[Ranger Mike]

Josh ,
Good catch on evolving technology. There are a few definite advantages for this J-Bar rear mount linkage on the asphalt rear suspension. I think 1962 Citroen 2cv pioneered this rear suspension with the rear mount concept to the point of actually mass producing it successfully. Note attached diagram for the Paved Track Stock Car Technology by Steve Smith. Every racer should have a copy of this.

1. It is easier to pull a chain then push it. This means pulling forces are easier to manage then trying to control the same forces pushing the same load. Looking at the typical 3 link suspension we have a single top link being puller as the car accelerates. The two trailing arms are pushing up on the cars suspension. The trailing arms must be beefier much the very nature of the forces they are dealing with. The mount location of the top link is critical as it must be mounted at the proper location proportional to the percent left side weight for maximum traction.
2. The J-Bar mounting handle force vectors twice as effective as you have two links transmitting the pulling force instead of just one top link. These two links offer a lot more adjustment and chassis tuning.
3. Braking may suffer but in round track racing, braking seldom wins races, acceleration and traction does. Road course racing usually means you have one maybe two places on a 12 turn track to PASS but many opportunity’s to out brake the other driver. I doubt braking will suffer with this J-Bar suspension.
4. It is indeed quite curious that the aluminum J-bar style mount has metal housing surrounding the J-bar. Speculation and rumors will abound I suspect. Could there be a compression spring device hidden? Could the wheel base actually be changed under acceleration because of this? The verbiage in the catalog says “This Style Allows You to Run The Trailing Arm Behind The Axle Tube For Less Roll Steer” and some cynical crew chief may take that to mean you don’t need STATIC roll steer with this device. But you can take out all the rear steer in the traditional 3 link set up. Hhmmmmmm?

 

[Ranger Mike]

Watts linkage
this is a good source of the pros of the WATTS linkage. I recommend this system for sedans turning left and right. the panhard bar is excellent for dedicated left turn only racing ..although this Watts linkage has many advantages over the P-bar and J-bar, if you can afford to buy it. I sure would use it just for the quicker set time and better control of rear roll center migration.
http://www.griggsracing.com/pdfFiles/Watts%20Links%20011414.pdf

 

[BEI77]

Hello Ranger Mike! You’re doing a great job on here. My question is about rear end set up. We run a 2800 lbs straight rail Pro Late Model on asphalt. A couple of years ago our rear end got slightly bent in a wreck. There’s a guy close that was the chassis specialist for Bobby Hamilton Sr when he won the truck series championship. He has shop now where he builds chassis’s and straightens rear ends.
We took ours to him and he suggested we let him put some toe in and camber in the rear end. He said under acceleration the toe would straighten out due to the force on the rear end. And upon deceleration the toe in would stabilize the car through the turn till you get back on the throttle. The toe was only a couple of degrees and it seemed to help. What are your thoughts on this.

 

[Ranger Mike]

welcome BEI
This is considered Advanced Race Car suspension class topic! good job!
read Post # 1326 page 67.also Herb Adams book “Chassis Engineering” has a great read on adding negative camber on page 81.

Wrote excellent advice. On left turn tracks negative camber on right rear tire and positive camber on left rear tire is desired. You will have rear end flex on the Ford 9 inch axel because the front face of the housing is weak, just by accelerating and braking. Adding a 1/16 inch toe in will help stabilize this condition. Toe out under acceleration will make the car oversteer or go loose. Make sure you do not have toe out when checking static rear toe in.

 

[BEI77]

welcome BEI
This is considered Advanced Race Car suspension class topic! good job!
read Post # 1326 page 67.also Herb Adams book “Chassis Engineering” has a great read on adding negative camber on page 81.

Wrote excellent advice. On left turn tracks negative camber on right rear tire and positive camber on left rear tire is desired. You will have rear end flex on the Ford 9 inch axel because the front face of the housing is weak, just by accelerating and braking. Adding a 1/16 inch toe in will help stabilize this condition. Toe out under acceleration will make the car oversteer or go loose. Make sure you do not have toe out when checking static rear toe in.

 

[BEI77]

I have a winters quick change, would it have the same flex you’re talking about? How would you suggest we square the rear end?

 

[Ranger Mike]

All aftermarket quick changes i saw were extra beefy just to prevent this flex. Most all can be equipped with camber snouts on each side. I am not sure about toe in being available on these camber snouts but i would call the factory to see ifin i were you. Personally, i would stay away from the toe in thing since a square rear end means one less variable to figure out.
once you get into dynamic variables like rear end flex, dynamic toe change, caster cross weight swing, roll steer and the like, you got a lot of variables to think thru once a handling problem occurs.
my opinion..

 

[BEI77]

All aftermarket quick changes i saw were extra beefy just to prevent this flex. Most all can be equipped with camber snouts on each side. I am not sure about toe in being available on these camber snouts but i would call the factory to see ifin i were you. Personally, i would stay away from the toe in thing since a square rear end means one less variable to figure out.
once you get into dynamic variables like rear end flex, dynamic toe change, caster cross weight swing, roll steer and the like, you got a lot of variables to think thru once a handling problem occurs.
my opinion..

Thank you for all the information and help you give.

 

[Latemodel94]

Wow! all I can say is this page forum is incredible. I have been using the tips and tricks here to apply to my new car, currently getting a brand new port city front clip. I run a 3000lb asphalt limited late model with a 108 inch wheelbase, stock or aftermarket fabricated camaro stub with stock lowers and stock type spindles. My question is a lot of teams have been reclipping cars and moving the front clip up. I haven't been able to find this addressed in the forum. would it be worth doing to my car? or since we are putting on a port city camaro stub would it be best just to leave it where it is on the chassis. I know this is being done but I haven't been able to find a what or why this is being done.
thanks
kyle

 

[Ranger Mike]

Welcome Latemodel

Read post 830 and 832 on page 42, post 1264 on page 64 and post 1314 on page 66

You need the steve smith book Street Stock Chassis Technology and a good computer software suspension program.

The short answer on why they move up the weld location from stock is to LOWER the whole car. The stock Camaro roll center is about ½ inch above the pavement. When you raise up the whole clip an inch you lower the roll center so now it is “ underground”. This is only step one. Steve Smith goes thru quite a detailed process of eventually getting the Roll Center to where it needs to be height wise and offset wise. Now Steve did not move the clip but made many ball joint changers and pivot arm re-locations to get there. For your case you will have to rely on t he computer program as you are making the moves. He did all the work to relocate the RC and make sure bump steer was correct and most important…the Camber Curve was as good as you can get. You are on hard spec tires and need this for maximum traction.

He ended up having a 3.375 inch RC height and did not disclose the offset but I would target 2.5 inch height for flat track to 12 degrees banking and 2.125” height for 13-18 degree tracks. Try for 3 inch offset to the right for proper down force on the right front tire.
Lower Roll centers mean less camber build. But means longer arm between RC and COG.

Do not forget the relationship between RC and Center of Gravity (COG).

Most door slammers run 18 inch CG Height and super late model cars with dry sump oil pans and aluminum heads get as low as 16” CG Height.
There is a method you can use to measure exact CG on your car with wheel scales and a floor jack. I use camshaft height as it seems to work pretty good.We have 18” COG and 3.375” RC so the fulcrum arm acting thru the RC is 14.6” long. Compared to the stock RC of ½ “ height, The 17.5” arm will cause a lot more action on the springs. No wonder these cars push going in!

Bottom line is to correct the camber curve as best you can with these hard spec tires and this will maintain better contact than the other guy.

 

[Wild Willie]

Ranger Mike and all other members of this very informative thread I would like to say thank you.

I just picked up a mini mod that I'm going to go threw from front to rear , top to bottom.
The car has gone threw 3 to 4 pit crews , so it will be interesting to see what has been done to the car.
It has a 3 link with j-bar located to the driver side.
Rack pin steering
Double A arm
I have cut out a few of the rules specs for review

I can get measurements in feet of the tracks corners and the one straight. Track is in the shape of a D
I also have located an excel spread sheet for your review
http://www.super7thheaven.co.uk/wp-content/uploads/2014/09/SuspensionCalculator.xls
This is my winter project . I'm in the process of stripping the car down.

 

[Ranger Mike]

welcome wwillie
you have a good start to a winning ride

 

[Wild Willie]

Hello RangerMike and members.
Have a question to a remark R.Mike made earlier about running the A-arms in parallel .
I'm a little lost as to setup for a top side run of the track
Running the top grove of the track.
With all this information of angles and offset centres
How does One go about setting up for the high side racing.
The tracks corners are over 15 degrees .
Corners 1 to 2 have a radius turn of close to 260 feet in lenght
Corners 3 to 4 are over 400 feet.
The off set curve length 460 feet
The straight away 440 feet
This a D type configured dirt track.
I get my gearing by looking at top runners lap times .
MPH = (3600 X length of track ) / lap times
Final Ratio = ( Avg. RPM X Tire circumference ) / ( Avg. MPH X 1056 )
I have a copy of Steve Smiths , street stock chassis technology, very good reading.

Another question ,how does off setting the rear coils effect turn in , if RR coil is mounted atop the axle , LR mounted 4 inches out front of the axle and down one inch.

 

[Wild Willie]

Here's how they have the rear coils setup

 

[Ranger Mike]

look at post # 1382 at top of this page. Take time to look at the force vectors acting on the two spring mounts you have now. I suspect these were fabricated to try to get advantage over the standard stock set up. Or could be case of monkey see monkey do. Is the center of spring to the center of rear end center the same on both springs? You may be dealing with two different motion rates because of the different locations. How much is it worth to you to make them both the same? Or is it worth it?

In my opinion, you can not set the car up to run the top until you have it handling going in, at mid turn and on exit. After you have this then you can adjust to run the high side.

 

[Wild Willie]

a few questions. to help me understand a 3 link
1: the further out front the instance RC , good or bad
2: for less roll instance RC closer to CG , more roll instance RC lower to ground
3: anti squat lower percentage better or higher percentage

Example
Wheel base 103 inches
Geometry
Roll center of 9.93 inches
Instance RC 9.5 inches
Instance RC leverage arm 227 inches
Anti squat 24.7 percent
Roll axes 0.57

In that example am I correct in thinking ,I have a long lever arm with very little body roll ,
I did the calculations with a longer upper link of 48 inches with a 3 inch offset front to back , back Height set at 25 inches front 22 inches
Top 3 link off set 5 inches forward of the rear axle and connects 25 inches off ground.
Lower link offset forward 1.5 inches and 4 inches above ground front of lower link to frame 4.5 inches off ground , 22 inches in lenght

 

[Wild Willie]

Mike I got informed by one of the builders that rear coil setup was, to put the weight back on the LR faster

 

[Ranger Mike]

WWillie

The longer the rear suspension Instant Center lever is, the less geometry error introduced due to the arc swing. Longer means less arc movement and more stable cornering.Anti-squat is the linkage taking up rotational movement thru the linkage and adding traction.

No anti squat means the springs will take any front to rear “ weight transfer” until compressed and we go to the drag racing funny car status of no anti squat and wheelie stand.

Read post # 314 on page 16 and post # 327 on page 17 before proceeding. Anti-squat is expressed in percentage. 50% anti squat means 50% of the rearward Pitch or “ weight transfer” is handled by the 3-link set up you have. 100% means 100% of the pitching or weight transfer is handled by the linkage and the body is actually lifted (wheelie time). Percentage is figured as the distance of Center of Gravity (COG) is compared to the Instant Centers location. Do not that the other point of origin of the IC is the tire contact patch. The COG perpendicular bisector to the pavement is crossed by the IC vector and gives the % anti squat. In the case of Duke Southard diagram from “Short Track Chassis Set-up” we see 20% on the 3 link figure #2.

I always used the camshaft center line as a good approximation of COG and worked for me. Production cars usually have COG between 20 and 22 inch above ground level. Round track cars will have it 18 to 20”. Street stock metric cars that have been worked over and lowered have 16.5” COG and super late model dry sump outlaw cars can be as low as 15” COG.
On our Formula car we ran low % anti squat mainly because the independent rear end was not the solid axle that you have, but has independent springs and swing arms on each side.

The rear pitch would load the individual springs unequally and the tire contact patch could shrink due to camber change. You do not have a lot of options on long links with these cars so 15% is huge.

Add to this the very low COG these cars have, and you are limited to % anti squat.

 

[Wild Willie]

Thank you ranger Mike
I'm finding with 3 link there is many more ajustments to the rear suspension
Moving with in lower forward frame connection points I can a just roll angle , by going side to side , by using washers to + - or zero
Instead of moving arms up or down
I now have the sim calculating an anti squat of 6. 3 % zero roll angle , think that will be a good starting point
Very interest how much a little degree of movement cause changes across the rear suspension in just one area
Looks like I will be building some lock down sliders with some square tubing . Like my j-bar has
I also found by moving my connection points on the rear of housing and frame up helps with ajustments for instance center Z axes
That was hard to get with my last post always giving me high anti squat %
Tuning in this anti squat for entering and exit