Automotive Race car suspension Class

[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.

 

[Ranger Mike]

you have the top link mounted for 53% left side mass. I never was satisfied until it was right but racers are weird like that. the shock is to keep wheel hop away when braking. A 600# compression and 65# rebound is typical for the 3rd link damper. Before you change rt ft camber check your toe - out as the readings are typical for wrong toe out condition.
here are the AVERAGES of the tires
lf ft 145
rt ft 143
lr 151
rr 159
cross weight lft rear to rt ft 147 this Avg should not exceed ft avg or rt side avg.
idea i 6 to 10 degrees less than ft and right side averages
note rt rear average temp is 16 deg hotter than rt ft avg
you are oversteer or loose
avg rr should be 10 to 15 deg cooler than rt ft.
get the rt ft temp fixed and shoot for rt ft tire being hottest temp avg
try to get 5 to 7 degree spread from inside middle and outside

lft ft should be next hottest with 3 to 5 degree spread
the rears should be real close to each other and look for 10 to 15 degree cooler on rt rear to rt ft
i got no doubt you will get a checker soon

 

[SuperTruck]

you have the top link mounted for 53% left side mass. I never was satisfied until it was right but racers are weird like that. the shock is to keep wheel hop away when braking. A 600# compression and 65# rebound is typical for the 3rd link damper. Before you change rt ft camber check your toe - out as the readings are typical for wrong toe out condition.
here are the AVERAGES of the tires
lf ft 145
rt ft 143
lr 151
rr 159
cross weight lft rear to rt ft 147 this Avg should not exceed ft avg or rt side avg.
idea i 6 to 10 degrees less than ft and right side averages
note rt rear average temp is 16 deg hotter than rt ft avg
you are oversteer or loose
avg rr should be 10 to 15 deg cooler than rt ft.
get the rt ft temp fixed and shoot for rt ft tire being hottest temp avg
try to get 5 to 7 degree spread from inside middle and outside

lft ft should be next hottest with 3 to 5 degree spread
the rears should be real close to each other and look for 10 to 15 degree cooler on rt rear to rt ft
i got no doubt you will get a checker soon

Mike, I went ahead and moved my top link bracket further to the left so now the pull bar is at 35.75 and I have it exactly 90° to the chassis. I thought about the toe out you mentioned and I know my bump steer was .33 at 3" so I decided to check my Ackerman and I had 3° more in the left so with it being a flat sweeping corner I'm going to take it out and see if that lowers the inside temp on the RF. I have checked camber gain as well and it's only 1° at 3"of travel. The Hoosier tire has always seem to cut better with a hotter spread than you mentioned but I'm ready to try it and see. I worked real hard to get all 4 tires with a full contact patch and the car slowed drastically so without testing it more I went back to my old set up. Thanks for taking time with me this week and If you happen to think of anything else please let me know. I will be racing it this weekend and will give you a report on how the changes affected it. Thanks again.

 

[MachineMasters]

Mike,

What are your thoughts on the suspension pictures here? Dirt late model...

http://s4.postimg.org/binoikcg9/IMG95866211.jpg

http://s4.postimg.org/6y1i3msqx/IMG_321711.png

 

[Ranger Mike]

can not enlarge them..so can't comment on um?

 

[MachineMasters]

can not enlarge them..so can't comment on um?

used a different file hosting site.

try these links instead: http://f28i.imgup.net/IMG_321711efb6.png

http://k02i.imgup.net/IMG9586621e713.jpg

 

[Ranger Mike]

Nice 4 link from what I can see

 

[Outfront2]

First time poster, long time reader... Lol.
Thanks Mike for this forum, it is very helpful.
What are your thoughts on this new style top link or 3rd link, or lift/pull arm... I work on template late models of cra, southern super series straight rail aphsalt cars

 

[drobbie]

In the Northeast this is referred to as a Torque arm. They have been used on primarily on asphalt modifieds. I have seen them mounted to both the left and right sides of the rear ends and used successfully. You show a solid link at the front, many guys around here use a rubber biscuit and control the amount of bite" by how much play is in the biscuit.
I know when I look at it, I see a three link suspension with different mounting point. I would be curious to hear what others opinions and experiences are with this setup is as well.

 

[Ranger Mike]

Thanks Drobbie
Welcome Out front, nice to hear from you.
Your inquiry tells me you have the car handling going in and turning in the middle ok. Now its time to hook it up on exit. Or I would say it is a safe assumption.
If the competition is handling going in and coming out as good as you are, Congratulations. You are now in the drag race phase and the first one to come off the corner with the best hook up wins. The new concept has definite merit.

Lets review the old 3 link and what's happening.
The 3 Link set up has evolved from the old truck rear end set up with long training arms and two upper links. The 4 link evolved as well and took off in the dirt track world with the bird cage and many tuning variations. This long Traction Arm is a variation for the 3 Link set up. The geometry of the 3 link linkages are such that Acceleration caused by the engine translates into rotational force via the differential. We have Tires contacting the track in one direction, axle wrap in the opposite direction.
Various linkages ( 3 or 4 link) react to the forces by lifting and pushing. It just so happens that if we draw a line from these links to the front of the car we construct an Instant Center (IC)where they meet. From this IC we have a Torque Arm ( lever) and this all results in the application of force during acceleration. This force will compress the springs and cause Anti-squat.
Anti-squat causes the rear end housing to apply more force to the chassis and down loads the tire for more traction. We get 100% anti squat and we do a wheelie! Not good in round track racing!

The longer the Instant Center the less the IC will move around during rear chassis roll, wheel and suspension links moving up and down and will provide the driver with a more stable feeling under acceleration. I think we ran a pull bar from the traditional mount on the Quick Change all the way to the transmission chassis hoop one time.

The whole point of this is try to maximize the control of the rear ends rotational torque for optimum tuning. The big draw back to anti-squat is that it will have an equal and opposite reaction under Braking. You could suffer wheel hop and a light rear end under braking conditions.

Bottom line is – Any time you can have an Instant Center closer to the front of the race car, it will have less movement during chassis roll. You will have a longer lever to counter rear end axlel wrap. This will make for a more stable car under acceleration and braking.

One note for the readers who are trying to understand the forces we are dealing with. Think Drag Racing.
Anyone who was around in the 1960s ( I was) will remember the Detroit Iron Muscle cars were the rage and just about every Camaro and Mustang had traction bars sticking out in from of the rear tires. No one bothered to tune them but the looked mean as help and did manage to hook up half way good. Of course the Chrysler boys engineered the proper set up and had a pinion snubber working with Hemi leaf springs but that is another matter.
There are three points to ponder here. Traction Bars use rear end rotation to slap the traction bar to the chassis and hook up the tires under acceleration. The Suspension links still formed an IC. Traction bars were mounted only at one end. Again, Anti-squat causes the rear end housing to apply more force to the chassis and down load the tires for more traction. We get 100% anti squat and we do a wheelie! Not good in round track racing!

 

[drobbie]

So from what I hear you saying about anti-squat, is 50% the best number to achieve a balance of wheel hop under deceleration and traction under acceleration? Or am I better off assuming it is car specific and just another tool to be used for tuning.

The other part I would like to understand is the left or right mounting. Up here they use a left side pan hard rod with a right side Torque arm and vice versa. From what I have read here you want the third link to be in line with Left Side weight distribution. Seems to me this configuration might make it hard for cars with large LS weight.

 

[Ranger Mike]

One can not make blanket assumptions with race cars simply because the cars are not symmetrical.
There is too much variation on the left side weight , rear % weight, cross weight.

Ref- torque arm mounting – as I posted a few posts back- try to push that chainsaw with that broom handle at a location other than center of mass.
As you stated correctly, for best results the 3rd link or torque arm should be mounted at same % as left side weight. I know the practical side of things mean you mount it as best as you can but try to hit a happy balance . You have to decide if the % of races you have won is because of out accelerating the other guy or out braking?
That will ultimately determine the locations.

There is some fuzzy thinking on the mounting location for the top link. When looking to the front from the rear end of the car, the engine torque twists counter clockwise. The thinking was that this loaded the left side more than the right side. Since the left was loaded more the car would shoot toward the right side because of this twisting motion. So this ideas was to mount the third link more toward the passenger side or right side to counter this. Maybe in drag racing but not on a round track.
Looking at this in detail as torque is applied from the driveshaft to the rear axle, multiple forces begin to leverage the car. Engine torque multiplied by the transmission gear ratio and axle ratio generate a few thousand ft. lbs. of twisting motion. The first thing the pinion gear tries to do is climb the ring gear. This forces the nose of the rear axle upward. As the car begins to accelerate, the torque wants to lift the front of the carupward, causing more down force on the the rear tires. As viewed from the rear of the car, engine torque twists the body clockwise, lifting the left front and compressing the right rear spring. As the pinion continues to apply this massive torque through the ring gear, the rear axle housing is also being leveraged in a counterclockwise direction lifting the right side of the axle and planting the left. As the car accelerates, it appears to be planting the right rear tire but is really unloading the tire, thus reducing traction. Torque over steer.

You can still see this dramatic body twist at the drag strip. You have very sticky drag slicks ( not hard spec tires that you have to use) you have 50-50 left to rt side weight % and up to 100% anti squat. All the linkages are set up to do one thing, provide maximum down force to the rear tires under acceleration. The body is really twisted under axel wrap. Because this car was originally designed to be a family grocery getter, the suspension was made to give the softest ride with best the best handling and comfort. The 4 link rear suspension gave good traction in rain and snow. When it grew into a romping stomping muscle car with a 396 cubic inch engine, spring rates were upped and heavy duty shocks were added as were bigger tires. The design was still based on the comfortable balanced 4 link package. No wonder the darn thing wants to climb to one side and fish tail out of the gate!
The classic 3 link suspension negates a lot of this simply by the fact that you have only one top link. Where it is mounted and the angle it is mounted relative to the rear end is critical. If the link is not mounted at the center of weight of mass of the car the tire loading will not be equal when accelerating. It is that simple. On a locked rear end you need to load both rear tires equally.

Power torque over steer is negated by cross weight or wedge. When you put that greasy 1/2 socket on the floor jack and jack up the rear end, the right rear tire moves about 3 inch off the floor before the left rear does. Wedge or cross weight.
You use this static set up to counter the force of inertia created when entering a turn. It is a must for you to properly apply power equally on the rear tires on turn exit.

When you bomb into turn one, think of three vectors or force arrows. 1. from the rear to the front. 2. from the left to the right. 3. from the left rear tire to the right front tire. These three vectors are the momentum forces at work. The entire spring / ARB/ shock package and the tires are for countering these forces. You have good phase one and phase two handling and now want to exit.

You ROLL on the gas and power torque over steer putting down force on the left rear tire. This is some what canceled out because the whole chassis was trying to lift the left rear tire due to that diagonal force vector #3. You are still in the middle of the turn and the right side springs are still compressed some what. If your top link is mounted correctly and at the proper angle you will be putting some down force on the rear tires ( commonly know as weight transfer) by lifting the chassis through the linkages. If you have the right cross weight you should have equal traction as tire temperatures will tell you.

 

[CGruhlke]

Ranger Mike,

I signed up so that I could participate in this thread. This thread contains an amazing amount of information and there's a good chance this question has been asked and answered but it's so long I hope you'll forgive me if I'm duplicating your efforts.

I'm a Certified Mech Eng Tech up in Canada. I'm in the process of building a 2 seat tube chassis track day car which is based roughly on Mazda MX-3 chassis dimensions, but uses C5/6 Corvette running gear. I've used the stock C5 pivot points and BJ locations to identify the RC and IC's and I've manipulated the track width slightly and using Suspension Analyzer I've decided that the small decrease in width hasn't had a dramatic affect on the roll characteristics of the suspension. My question is in regards to the roll axis.

My wheelbase will be in the neighborhood of 18" shorter than a stock C5 Vette. If the front and rear RC heights don't change, the shorter wheelbase will cause a somewhat significant change in the roll axis angle. How will this affect the handling of the vehicle? I anticipate it will have the most impact on dive but will it affect roll?

thanks for any insight you may have.
Charlie

 

[Ranger Mike]

Welcome Charlie and thanks fro the kind words.
Please see post # 264 on page 14 of this post. Has benefits of long vs. short wheel base. Given a mandatory weight and no stated wheel base, go with the shortest practical.
Biggest advantage to a shorter wheel base is weight. If you can chop out the extra frame length and shorten the wheel base, you can then place the required weight ballast to where it will be at polar moment and do the best for you. The additional advantage of shorter wheel base is the ( I hate to use this ) weight transfer occurs faster. As you have read in previous posts THERE IS NO WEIGHT TRANSFER! The ability of the shorter wheel base car to react to the inertia ( momentum ) caused by cornering takes less time than a longer wheel base car. The untold advantage of a shorter wheel base car is it can fit in holes better in traffic.
In a purely technical point, this momentum is directly proportional to the weight of the race car , the height of the Center of Gravity and the rate of acceleration in Gs. It is inversely proportional to the wheelbase.
Why are you selecting a wheelbase like 87”?
any idea % ft to rear weight?

Ifin I remember correct the CR corvette has about 2.4 inch front roll center and 4” rear rc on 105” wheel base
real good package developed over years of solid engineering
the mazda miata has about 91 inch wheel base and 2.4 inch frt rc and 4.7 inch rear roll center
so if you are going the short 87” wheel base using the C5 geometry you should have a nice handing package
If i remember right, the shelby corbra had a rear roll center lower than t he front on a 90 inch wheel base. i think the front rc dove to one side on wheel turn in and the darn thing pushed. i think it did not turn in well. i drove a replica of one of these that had a small block chevy v8...but that was years ago. i remember it was tail end loose but with that much power...it had to be.

Check out LG Motorsports drop spindle to lower the car 1 inch and use same stock geometry

https://www.lgmotorsports.com/corvette-c5-parts-1997-2004/c5-chassis/lg-corvette-drop-spindles.html

 

[Ronorlin]

Greetings!
it took me about three weeks on and off to read this thread. Awesome information. I am hoping to ask a few questions of you all. Especially Ranger Mike. First time poster.
I run a asphalt sportsman/streetstock type car. Camaro clipped metric rear, ford 9". Impala spindles, howe adjustable parts in front.
Ive read all the books by SS and Bolles I could get. I have his roll center software and would like to know your thoughts on using a 1" taller BJ on the right to aide my geometry. You have been so adamant about where the roll center should be located I just have to ask. I really don't want the difficulty of different spindles right and left. Crash repairs are excruciatingly slow as it is.
After losing track of things during the season, and repairs, I just blue printed my front end and the roll center was 4" up and 10" left! I can't even explain how i let that happen. I am mandated to run a 1.5" bar. I've seen you mention Salem a couple times. Thats a tough place to go and race against guys that have been doing for a ton of years. Mixed results there, crashed bad once, 14th next time.
Thanks in advance, I look forward to the info. I am leaving for the week tomorrow so getting back on here may be a few days. Thank you.
Ronorlin

 

[Ranger Mike]

welcome Ron, good to know I have fellow Salem racer here. Salem is a fast 1/2 mile high bank track and you need lower roll center to race there. You need good camber curve as well.

see post # 284 on page 15 and post #809 on page 41,

A stock Camaro has a centered roll center about 0.5 inch above the ground. Swapping in Impala spindles was a trend to assist the camber build curve slightly and all things being the same a taller spindle makes the top A-arm angle more down hill and thus raises the roll center. Let's say your camshaft centerline is 18.5” above ground. This is a good approximation of the Center of Gravity. In stock form you have a Moment (lever) 18 inches long between the stock roll center (.5” above ground) to the COG. When you raise the roll center to 3.375” you reduce the Moment to 15.125” long. Less body roll and better camber curve. There are other advantages covered in this thread previous posts I won't go into like jacking effect, tire loading etc..
You said you have front RC 4 inch height and 10 inch to the left. I doubt you have enough down force to plant the right front tire to turn the car to be competitive.
If you want to WIN, you need to do the following:
1. Buy Street Stock Chassis Technology by Steve Smith. see www.stevesmithautosports.com
This book details how he took a Stock Camaro and made it competitive. The track rules he had to go with did not permit him altering the suspension enough to place the roll center where it should be but it was a lot closer than wheat you now have.
2. You will need to swap out spindles and ball joints to move that Roll Center 3 inch to the right of center and 3.375 height. It needs to stay on that side during roll and dive.
3. You will need to modify the cross link so your bump steer is correct. This is critical.
4. You have the best tool available. the software. Use it to bench mark your current set up and run it thru 4 inch of bump right side and 4 inch rebound on left side.
5. This will take much work and some $$$ initially but once you got it you can be competitive with those hard spec tires you have to run and can start winning.
FYI
Big metric spindles everyone talks about are Chevy Impala/Caprice 1977- 1996 spindle is identical to
Camaro/Firebird 1970-1981 spindles but much lighter, is 8.75” tall, 2.5” pin height.

Next up is the popular 7 1/4 tall spindle used in
1967-1969 F body Camaro / Nova
1964 –1972 A body Chevelle, Maibu ,GTO, LeMans 442 Cutlass, GS, Skylark
1968-1974 X body Nova, Apollo, Omega, Ventura – all with spindle height is 7.25”

1982 –2004 Chevy S 10 2wd pick up truck 7.5 “ spindle height
1980-90 GM full size car (Impala/Caprice) spindle has overall height of 8.6875”
"Short Arm" Metric Spindle. Based on a 1979-Up GM Metric midsize spindle- This spindle is 7 1/2" tall and the spindle snout is 1 3/4" up from the bottom of the spindle.

1974-1980 Ford Pinto and 1974-1978 Mustang II spindle is 7 5/8” tall and 2.4” pin height.

With your software you can plug in suspension numbers and figure how to get the roll center to proper offset 3 inch to the right.
If you are limited to stock A-arms, and you are permitted to replace ball joints, you can grind the Ball joint hole oblong to offset the ball joint by up to 3/8” to the inside on lower left side or outside on lower right side. and weld in Screw in ball joints like Chryslers. These will stick the spindle up about 3/4 “ higher from bottom A-Arm and move the upper A-Arm 3/4” higher for even more angle. Afco, U-B Machine , Speedway Motors, Coleman racing, have these. Check our Colman racing. Adjustable upper ball joints.

http://www.colemanracing.com/Integral-Ball-Joints-for-Lower-Control-Arms-P6201.aspx
http://www.colemanracing.com/Ball-Joint-Mono-Ball-Upper-GM-18-Degree-P3688.aspx

Don’t forget. You can move the A-arm inner mounts as well so there should be enough wiggle room to get the roll center close to the proper height and offset.