Race car suspension Class

[Ranger Mike]

I would go with 1600# spring as more spring is for unlimited hp engines and super wide tacky slicks.

I always ran an axle damper ( shock absorber) at 1 to 2 ° up hill angle over the spring loaded torque link. Now we have double acting torque link. I like simplicity of the cheap spring loaded torque link simply for maintenance and cost. Static pinion angle should be 5 to 6 ° .Wide is always good and watch out for too much back space as it may impact on left side weight limits.

Personally…master the basics first.Wheel spacers are not going to win races…knowing if you have roll under steer will. Knowing where the front and rear roll centers are static and in dive and roll will. Knowing how much shock travel you have on all four corners will. Knowing how much stagger growth you have will. Knowing tire temps will.

From the communication so far I got no doubt you better pack a card board box in the tow vehicle!

 

[Thayne14]

I am extremely meticulous with everything. I blue print the car after every race weekend so I know where I am at before I change anything. So if there is any information about the car you want to know I will have it in my notes.

You have an amazing grasp on all concepts it seems, so if there is anything you need to know to make a suggestion to me feel free to ask. I have this weekend off and can test on multiple nights so always willing to try something new!

 

[Thayne14]

Okay, I just measured the car and have a 67" wheel centre to centre. Through that formula it works out to 37 3/4 inches from rr centreline. That is 4 1/4" left of centre. Mine is mounted exactly 36 3/4 right now.

Does this sound right? Haha.

 

[Ranger Mike]

Thane you are spot on. That additional one inch will Tighten up the car on exit. Its equalizes the loading of the rear tires. Optimum application of forces which is what we want.

The 7 degree angle will tighten the car as well. See attached pic. Its all about the Instant Center. The torque wants to twist the rear end under the race car. The steeper degree of the angle of the 3rd link is increased the more force to the instant center. This plants the tires more,
( relative to the initial 4 degrees you have) and adds " down force " to the tires , thus additional traction.
When a spring loaded 3rd link is used, you have about 1/2 inch movement as the rear end pulls and compresses the spring. Besides cushioning the hook up to the tires it stretches the wheel base by about 1/4" adding to rear under steer ( over steer).

Pic from Steve Smiths Paved Track Stock Car Technology.Get a copy.
one word of caution- if you put more than 10 degrees in the 3rd link your rear end will be too loose during braking so watch it.
You still need to determine rear steer ( under steer or over steer) as this is the final factor. Good job!

 

[Thayne14]

Awesome. Thank you!

What do I need to do to figure the under steer and oversteer? Is there a formula as well?

 

[Ranger Mike]

No formula Thane , just a little precision work with the old tape measure.

Roll Over steer- the right side wheel base gets longer in bump and roll relative to the left side wheel base
Roll under steer – the right side wheel base gets shorter in bump and roll relative to the left side wheel base
see post # 81 on page 5 for photo
air up all tires and get car race ready
measure left and right wheelbase
measure the 4 ride heights to the floor
measure each wheels hub center point to floor
these are your bench marks
jack up the race car enough so the rear end can swing free
measure the left rear ride height
find out the difference from benchmark to raised position
Example ( you measure left rear ride height at 4 inch in 1st step now it is 24.5 inch so
you have 20.5 inch incremental displacement. )
Adjust the other 3 ride heights so they are exactly the bench mark reading plus increment.
On front tires jack these up so you get the original hub center point to floor reading plus incremental.
Block the front tires at those readings
go to the rear end and jack these up so you get the original hub center point to floor reading plus incremental
readings on both rear wheel hub center points.
Now you have a “ level” car elevated above the floor at simulated ride height.
Measure both side wheel base and you should have exactly the same readings as benchmarks
take off the rear wheels and
take out the rear springs
I use 2 Carpenters L squares ( 2 ft. x 3 ft.) but tape measure will work too.
The drill is we are going to drop the left rear hub one inch and on right side hub we bump the center up one inch. Measure both side wheel bases. I use a floor jack with a large 1/2 drive socket under the rear end center section and bottle jack under the right rear trail arm. You get the idea.
Repeat this at 2 inch droop left side and 2 inch bump right side and measure wheel bases
go to 3 inch droop and bump repeat wheelbase measuring on both sides.

Now you know if you have rear roll steer. You may not have any rear steer. Now is when you can crank on the trail arm rod end and see how much 4 turns crank into the rear steer. Keep notes, write it down.

tip- I use two tape measures and two big magnets to affix them to each front hub. Mark each tire with a line pointing straight down so the tire / wheel does not move during this process. You do not have to have these “ centered” the hook can be at the front of the hub cover as long as both tape measures are placed exactly alike and are not moved from this first bench mark reading. I have also used small zip ties thru the center hub cover bolts. As long as you have consistency through the process.
Also make sure that both tape measures read the exact same at 15 feet. One time I had 1/8 inch difference between the two over 15 feet because one was cheap tape measure the other was a quality name brand.

 

[Thayne14]

Ranger, just did the above and I have 1/2 lead in RS wheelbase already with the rear steer at 1" it shortened 1/16 and at 2" it shortened up an 1/8th. At 3" it shortened 3/16" so everry inch was a 1/16th.

I'm not sure that I am getting enough. Every 2 turns on the trailing arm was an 1/8th or so.

What do u suggest for rear steer?

Thanks as always!

 

[Ranger Mike]

I did a lot of thinking about your last post. You could run the set up but it is not the winning set up. For ultimate handling i recommend changing the rear end squareness.

I am not a big fan on rear roll steer.
Large Static roll steer is NOT what you want. I like a race car that is straight and square and running 1/2 inch lead is like running 1/2 inch toe out and is a waste of tires and scrubs off speed.
Your car is loose off the turn so I would take out the 1/2 inch lead. You know you will pick up at least 3/16” DYNAMIC roll under steer with trail arm angle setting you now have. Adding a spring loaded 3rd link will help as you will add another 1/4” to 3/8” inch depending on spring selection.

As last resort you can even go with spring trailing arm that compresses under acceleration. The book says, on asphalt, to keep wheel base change to under 1/2” during cornering. If you have to exceed this then change rear springs. NASCAR limits wheel base change to 1/4” by the way.

We have not discussed the rear panhard bar and this is a huge tuning factor as well.

I was looking over my chassis notes on rear roll steer and a typical GM metric chassis will have 3/8” rear roll under steer with stock trail arm set up.Joes racing in Washington has some great chassis set up articles..good reading
http://www.joesracing.com/kb/category.php?catID=2

 

[drobbie]

Must be some heavy racing going on here as there doesn't seem to be much activity.
Any way I thought I would start it back up.
I have been looking around the pits at many of the tracks I visit and I am seeing many cars using a heavier LF spring versus RF spring. What is the advantage of this type of set up? They say it keeps the car free for the race but I can't see how this helps based on the fact weight is transferred to the RF first. In my mind is would shift too much weight to the RF from both the LR and the LF. Am I thinking about this correctly?

 

[Ranger Mike]

I see no advantage to this set up. Just to review, no weight is transfered. We have to deal with force of momentum which makes the springs feel like more weight is acting on them. You are correct in that a stiffer LF spring will make a constant loose condition causing " over steer". Some drivers like " dirt tracking" the car as opposed to running into a push condition. A lot of monkey see, monkey do going on there i imagine.

 

[01racer]

Any thoughts on adding Ackerman to a open wheel modifed with steering box and what is the best way of doing it. Going to Fab a center link to help bump steer.?

 

[Ranger Mike]

welcome Racer01
yes i believe in ackermann and this comes from the spindle arm mount location. get turn plate to find out how much you have at the start. you can rig up plastic protrators to measure things if the cost of turn plates is prohibitive. smear some grease on large sheet metal plates so they turn easier when tires are rolled on them. You can and scribe a line on the plates to mark zero. it is a pain but i have done it.

 

[01racer]

I measured the difference the wheels turn with 10' string and turning the wheel a 1/4 turn this car being 0.5 i have Measured other name brand cars around 2-3"

 

[6t5mustang]

Hey Ranger Mike,

I'm in the very early stages of design of converting my 65 mustang from a unibody to a full frame car "pro-touring" car. I want the car to be capable of street and track use. Using some of the guidelines you've talked about in this thread, I have gone through several iterations of the front suspension design. Can I either post or email you some of my schematics to see if you think I'm on the right track?

This thread has some awesome information! Thanks for sharing!

Joey

 

[Ranger Mike]

i thank you for the kind words. Post on here as this is a teaching experience. By the way, I sure do not have all the answers. There are a lot more smart people on here than I as i am reminded quote often when i Step in it! welcome racer and post away!

 

[6t5mustang]

OK, I'll give it a shot. My original goal with this car was to do a vintage racer. After I got to looking in depth, both rear frame rails are completely rusted through. So my mind got to churning if those are shot, what other structural issues am I going to run into on this car. So I started researching and found where some folks were converting their cars from a unibody design to a full frame. Unfortunately, I have not been able to find a lot of info on specific measurements and dimensions of chassis created by other folks. So being an engineer, I decided I would try it myself. I took hundreds of measurements, and with the help of this thread in particular have come up with the following design (so far).

I think I have the front roll center squared away. I did not label my CG on any of the drawings, its about 10" above RC (assuming cam CL = CG). I'm still 50/50 on the rear. Part of me wants to do IRS like my Cobra, and the other part wants to do a 3 link for simplicity. My goal right now is to make sure I'm on the right track so I can get the front frame horn dimensions locked down. From there I'm going to start work on designing both an IRS and 3 link rear setup. I apologize for not have everything dimensioned out! I will work on that before the next post.

Thanks for any feedback.

Joey

 

[badfat71]

Hi I have a question I have a dirt pro stock Camaro clip 3000 pounds 3 link and I was wondering if it would turn better with a wider front end putting on ford lowers it has factory Camaro lowers with a 60 inch rear end I come from asphalt racing where wider is better and I wondered if it applied to dirt also I do have a performance trands computer program for roll center and I know I have to compensate for the front roll center

 

[Ranger Mike]

6t5, having owned a 67 corvette and now flogging this rear engine formula car with independent rear suspension..go with the 3 link. Get the front end right. Go with good solid rear 3 link set up..my opinion

 

[Ranger Mike]

badfat, welcome...good to have you in with other racers here!

read these on this thread
post # 255 on page 13
# 264 on page 14
#322 on page 17
# 505 on page 26
go as wide as rules permit
but don't do anything until you benchmark the car and know your current set up

 

[6t5mustang]

6t5, having owned a 67 corvette and now flogging this rear engine formula car with independent rear suspension..go with the 3 link. Get the front end right. Go with good solid rear 3 link set up..my opinion

Ranger Mike - did you see anything from the attachments that I need to revise or am I on the right track? Let me know if I need to provide more info.

 

[Ranger Mike]

without some numbers i can't tell. I can tell you that you should not be afraid to start welding once you think you are close. Things can be changed later..nothing is permanent. I would say you need to know as a minimum the caster, camber, camber build, roll and dive over 3 inches, ackermann, bump steer if you can. what is king pin inclination? any idea of your scrub radius..the basics.

 

[6t5mustang]

without some numbers i can't tell. I can tell you that you should not be afraid to start welding once you think you are close. Things can be changed later..nothing is permanent. I would say you need to know as a minimum the caster, camber, camber build, roll and dive over 3 inches, ackermann, bump steer if you can. what is king pin inclination? any idea of your scrub radius..the basics.

Caster = 7*
Camber = -0.5*
Camber Gain (+3" vertical) = -4.5* (gained)
Camber Gain (-3" vertical) = +2.2* (lost)
KPI spindle = 11*
KPI installed = 11.5*
Scrub radius = 1.7"

The spindles I'm basing this design on are Mustang II with 2" drop. I've seen some others out there but don't have dimensions in order to apply to the model. I will look into the Ackerman and bump steer. I will also post some diagrams of the information outlined earlier.

 

[6t5mustang]

Here is what I was able to come up with. I don't think that the scrub radius is large enough. I'm going to check around tonight to see if I can find some wheels with different O/S. If I can find what I'm looking for, all of this will change. BTW, did I calculate the Ackerman correctly?

 

[Ranger Mike]

7 degrees is a lot of caster...KPI is big too in my opinion but if it works on mustang... copy it...i like at least 2 degree ackermann but understand I am old school before a lot of computer modeling came in..can you adjust it to crank in another degree?

 

[6t5mustang]

7 degrees is a lot of caster...KPI is big too in my opinion but if it works on mustang... copy it...i like at least 2 degree ackermann but understand I am old school before a lot of computer modeling came in..can you adjust it to crank in another degree?

What would you recommend using for final KPI to do the initial design? A lot of the Cobra guys use 7* caster, I was using that for a starting point. What would you recommend?

 

[01racer]

Ranger Mike with a "stock" front suspension on an open wheel modified using stock spindles metric or pinto, how would You go about adding ackerman?

 

[Ranger Mike]

6t5, if you are running power steering you may be ok at 7 degrees caster. Manual set up ...it sure will build up your arms.

01racer, are you on asphalt or dirt? how much ackermann do you have now?
please look at the link
http://www.longacreracing.com/Userfiles/Articles/Text/Ackermann-the-other-alignment-phenomenon.pdf

 

[SuperTruck]

I have a Asphalt Super that has a 3 link rear suspension with coil overs. I run a flat 1/2 mile track and no matter what I do to it I can't get aggressive on exit. We are very fast and winning races but when I pick up throttle I have to roll it to a mat or it will blow the rear tires off. Entry is good and rotates in center with no wheel in it so it's definitely not a tight loose condition. Lr Trailing arm is up 1" 4/6 shock and a 175 spring. Rr is up 1 degree and 4 shock and a 275 spring. Top link is a spring loaded pull bar with 7 degrees down. Any ideas or suggestions on what else I can do?

 

[Ranger Mike]

welcome Supertruck
Loose off is usually stagger ,how much stagger are you running?
tire temps? is right rear reading good at all three points? inside middle outside temps?
what is the car weight, left side weight, rear weight , cross weight?
where is the 3rd link mounted? See post # 253 page 13 and post # 707 on page 36.
what is spring in the top link pull rod? do you have shock with top link?
Are the trail arms solid or do you use Rt Rear pull rod?
do you run front ARB (swaybar)? how big is it # wise?
any idea where the rear roll center is?
Is rear end square to the center line ? Are you running roll steer?

 

[SuperTruck]

welcome Supertruck
Loose off is usually stagger ,how much stagger are you running?
tire temps? is right rear reading good at all three points? inside middle outside temps?
what is the car weight, left side weight, rear weight , cross weight?
where is the 3rd link mounted? See post # 253 page 13 and post # 707 on page 36.
what is spring in the top link pull rod? do you have shock with top link?
Are the trail arms solid or do you use Rt Rear pull rod?
do you run front ARB (swaybar)? how big is it # wise?
any idea where the rear roll center is?
Is rear end square to the center line ? Are you running roll steer?

 

[MachineMasters]

Mike,

What are your thoughts on the typical dirt modified/dirt late model 4-link suspension? Specifically, the left rear suspension?

Everyone is using a suspension droop limiter (chain or underslung bar). This seems silly to me. Could we use the left rear droop limiter to add load back to the tire? With a type of cantilever that turns the pulling motion on the limiter chain into a pushing motion on the rear coilover?

Thanks,
MM

 

[SuperTruck]

Thanks for responding Ranger Mike, My traction problems are when the throttle is first picked up in center of corner, if I let it roll past center and the car is straight I'm able to mat it quicker. It's not loose on exit of straight away.
I'm running 3/4 stagger on front and around 1 /3/4 on the rear.
Total weight is 2850
Left side is 56.1 right has to be 1200l#
51.2 rear which = 1466#
I run usually around 52% wedge and we check our bite more so and it will be from 230 lbs to 280 lbs depending on track.
My front tread width is 64 1/2 and the rear is 63 3/4 and I string my Right side tires to be even.
My third link was centered and I've moved it to the left Its now set at 34" from the right.
I'm running a 1800# spring in Link with no shock. I moved the front of the Pull bar to the left tonight so it will be straight inline with rear heim?
Solid Trailing arms. Ls is 38' Long and the right is 59" long.
LFShock is a 4/10 200 Spring
Rf Shock is 6 with a 185 Spring on the flat Tracks
LR Shock is a 4/6 175
RR Shock is a 4 with a 300
Normally on the banked tracks I run a 200 on Left and a 225 on Right
1 3/4 Sway Bar 12 1/2" arms and that equals 2262lbs at 1" travel. I run a slapper on Lf instead of a heim.
39" J bar mounted on left axle tube usually around 10" and Frame mount is fully adjustable so its 11 to 13 1/2"
Frame mount on Jbar is is 12" in front of axle tube so it puts good angle in Jbar.
I have no idea what the rear roll center is. I run the rear end square to the chassis.
Thanks for your advice.

 

[Ranger Mike]

Machinemaster
Thank you for the great question- Welcome to the forum.
in my opinion, the 4 link dirt track suspension is the only way to race dirt. It is specifically designed to tune in and hook up on a dirt track. It is tunable as the track changes during the night. The 4 link is made to use the car’s body ROLL to jack in Roll Over steer. When you add a chain to act a droop limiter you just made a really big Go Kart. But...
Todays racing shocks ( dampers) should never be used as a suspension travel limiter. You can use a chain on left and right rear to limit travel just under the maximum extension of the shock so you don’t pull it apart . A hard stop or cable is better as chains do stretch over time. This is the only use of the chain I recommend on a race car and is not to be used to tune tha car. Set it up to save the shocks and don’t use it to adjust.

Think about the sequence of events. You fly into the turn, throw the car sideways and steer with your big toe. Looking at it frame by frame, Forward momentum is still going forward as the tires plant and counter this force. The Body is still traveling straight until the tires stick and the body now rolls thru the roll centers to down load the right side tires. We have jacking effect and the right front, right rear compresses as the left front lifts and left rear goes to droop. Then BANG, the chassis/rear end hits the chain limit and you SNAP load the right rear tire to to the point you loose traction. Now you are loose and back on the gas working the turn to exit. To the driver it feels like the chassis is really working but you just made the car a giant go kart for a brief amount of time. It works but not the fastest way around the track. What is really happening is the 4 Link is making traction as it is designed to do and the car is set up too tight. The Snap Load is a way to make the car turn.

I when thru a mechanical droop limited period in the Formula car days before I found a fellow who rebuilt shocks for Indy cars and taught me a thing or two about racing. Joe is dead now but he was the best. My advise is to forget the chain AS A MEANS OF TUNING and tune in the chassis with the shocks (dampers ). Think about retaining Momentum and back of of thinking Traction thru the turns.
I do not race dirt so I am the least knowledgeable on this matter but I recommend you read these links by dirt track racers and try their suggestions.

http://www.racewise.net/answers.html

http://www.stockcarracing.com/techarticles/39098_four_link_tips_advice/

 

[Ranger Mike]

supertruck

One thing that sticks out is the top link mounting location. Top link should be mounted at center of weight mass of the car. In your case you have 56.1% left side weight. Your rear track width is 63.75” so 63.75 x 56.1% = 35.76” location from right tire centerline. You had it placed at the center or 31.87” from right tire centerline. No wonder the car was having problems rolling on the throttle.
Think of your old chain saw you laid on the shop floor. The Chain saw is 36 inch long so the center line is 18”. Now take that old green broom handle you use to beat the neighbors dog with and place it at the 18” mark. (see photo). Try pushing the chain saw forward. Now move it to the left and place it closer to the center of Mass and push it. Things move a little more equal..right?
In the case of the top link you are pulling on it and not pushing but you get the idea. This is why we have to use available force , mechanically to our best advantage so now you know why the top link mount is so important.

How much travel is the top link spring compression? Should be 1/2 inch which is ideal?

I would add a top link damper ( shock absorber) mounted 5 degrees up hill. This will assist tuning. Range on mounting up hill is 0 to 7 degrees. Mare angle tightens chassis on corner entry less loosens on entry. Never mount it with down hill angle.

 

[SuperTruck]

supertruckView attachment 86821

One thing that sticks out is the top link mounting location. Top link should be mounted at center of weight mass of the car. In your case you have 56.1% left side weight. Your rear track width is 63.75” so 63.75 x 56.1% = 35.76” location from right tire centerline. You had it placed at the center or 31.87” from right tire centerline. No wonder the car was having problems rolling on the throttle.
Think of your old chain saw you laid on the shop floor. The Chain saw is 36 inch long so the center line is 18”. Now take that old green broom handle you use to beat the neighbors dog with and place it at the 18” mark. (see photo). Try pushing the chain saw forward. Now move it to the left and place it closer to the center of Mass and push it. Things move a little more equal..right?
In the case of the top link you are pulling on it and not pushing but you get the idea. This is why we have to use available force , mechanically to our best advantage so now you know why the top link mount is so important.

How much travel is the top link spring compression? Should be 1/2 inch which is ideal?

I would add a top link damper ( shock absorber) mounted 5 degrees up hill. This will assist tuning. Range on mounting up hill is 0 to 7 degrees. Mare angle tightens chassis on corner entry less loosens on entry. Never mount it with down hill angle.

supertruckView attachment 86821

One thing that sticks out is the top link mounting location. Top link should be mounted at center of weight mass of the car. In your case you have 56.1% left side weight. Your rear track width is 63.75” so 63.75 x 56.1% = 35.76” location from right tire centerline. You had it placed at the center or 31.87” from right tire centerline. No wonder the car was having problems rolling on the throttle.
Think of your old chain saw you laid on the shop floor. The Chain saw is 36 inch long so the center line is 18”. Now take that old green broom handle you use to beat the neighbors dog with and place it at the 18” mark. (see photo). Try pushing the chain saw forward. Now move it to the left and place it closer to the center of Mass and push it. Things move a little more equal..right?
In the case of the top link you are pulling on it and not pushing but you get the idea. This is why we have to use available force , mechanically to our best advantage so now you know why the top link mount is so important.

How much travel is the top link spring compression? Should be 1/2 inch which is ideal?

I would add a top link damper ( shock absorber) mounted 5 degrees up hill. This will assist tuning. Range on mounting up hill is 0 to 7 degrees. Mare angle tightens chassis on corner entry less loosens on entry. Never mount it with down hill angle.

I have it all the way to the left against to bracket on the left side so I can't quite get it to 56%. I moved the front mount to the left the same amount so it won't be pulling in a angle. I assume this is the proper way? Pull bar spring is preloaded a 1/4" and it's traveling close to a 1/2"
If I put a damper shock on should it be like a 90/10 or what would your recommendation be?
I also wanted you to see my tire temps after practice before I moved the link. I normally have a 30° degree split in Rf so I made a minor camber adjustment to bring inside Temps down.