Automotive Race car suspension Class

[Ranger Mike]

When you sweep out the garage with that shop broom you get the best job done when the broom handle is at 45 ° angle to the floor. If you were to hold the handle at 90° and push it you would not get much done. If you were to lower the handle to 12° to the floor and push it the broom would scoot over the rubbish and you would not get a clean sweep.

Looking at the attached pics on Page 27 Post # 479. ( I am not good at white out, boys) . The stock set up with roll center at car centerline and at 3 inch height has a pretty good set up for left and right hand turns. The tire contact reaction force is at 15° to the RC. The cars CG is at 90° to the RC. When you enter the turn, the tires grip, create the reaction force, the body rotates , the ARB or sway bar counter this and and weight compresses the front springs. This is pretty good and the best you are going to get when you must turn right AND left.

If we offset the RC to the right side by 3 inches of car centerline and at 3 inch height as with a stock car late model set up the tire contact reaction force is now at 22° to the RC. The cars CG is almost straight line to reaction force vector ( 20° offset ). Now when the CG wants to rotate about the RC and since we only want car about turning left we have the maximum weight loading the right front tire ( if we have the shock spring package correct). If we have the Roll Center offset too far to the right we get closer tot the magic 45° angle and start to lift the left front tire like the old sprint cars did.

If we offset the RC to the left side by 3 inches of car centerline and at 3 inch height we have trouble. The tire contact reaction force is now at 12° to the RC. The CG is 133° to the tire contact reaction force vector and bass ackwards. Not much rotation force wil be resisted by the tire reaction force with this set up. When you enter the turn, the tires grip, but the reaction force is very weak. We have not created the reaction force necessary to resist Centrifugal force. The body rotates and weight compresses the right front spring but not enough to provide the necessary down force. Since we have no front grip we push going in (under steer condition at turn entry). The right front tire will be pushed sideways. Since we did not compress the springs enough, and the sway bar did all the work since we only had severe body roll and very little spring compression , under acceleration there is not be enough weight transfer from left front to right rear to hook up the car. Loose coming out ( over steer on turn exit).

a note to Radracer- when you make major chassis changes like re-mounting control arms and relocating Roll Centers it is vary hard to compare old set up notes to current set up because you have changes the chassis geometry in a huge way.

 

[radracr]

Update:

1050 RF, 1000 LF, 250 RR, 200 LR = Text book. The car was terrible - loose all the way through. The RF is sticking better but not great. Tire temps improved.

Changed to 1050RF, 1000LF, 200RR, 175LR. We also changed the front ride height so that it was 7" across. It was 6. MUCH BETTER. The RF is digging hard. The car was also more stable through the turn. The effect here was improving the front RC. And it did.

Shock indicators = 1.0"RF, 1.4"LF, 2.0"RR, 2.4"LR

The car is getting better. Based upon the shock indicators we have some work to do on the front. With the motion ratios of .6 and .67, the RF and LF are traveling 1.67" and 1.94" respectively. Simply not enough.

Rear motion ratios .66RR and .70LR, the tires are traveling 3.0" and 3.33" respectively. Close.

If I'm going by travel, then the LR needs a stiffer spring (200#?)and the RF needs a softer spring (950#?) and maybe a 900# on the LF?. I would also suspect that we would need to start with a much higher front ride height (7.5"?) so that the RC stays where we want.One note: the right side tires have very little rubber left. We put the bald tire on the RF to get the stagger we needed across the rear. The car simply pushed up the track but remarkably appeared to want to turn better. When we put the bald tire on the back - reducing rear stagger - the tire was wicked loose and didn't turn as well. The car was also faster when it was tight.

We did not check droop. Based upon video that I saw the droop is near what we want.

Lot's learned.

 

[Ranger Mike]

Lots learned...this is the whole point of this forum. Rad- now you know what the car is doing ( not doing) and more importantly, you know why! And you are getting real close to the winning set up. The old bald tire was getting more down load and the car was trying to pivot on it in the turn but still not enough download because the springs are not soft enough to dump the required load. I agree the fronts may be a tad stiff..I would not mess with the rear springs as softening the front is same as stiffening the rears. Your rear shock travels are very close. You are two weekend away from the checker and there is not much more i can do front the bench. Keep good notes and change one thing at a time though in this case the front springs may both get swapped out since it looks like they are stiff.

 

[radracr]

Ranger Mike - thanks for continuing to follow me along. I truly appreciate the feedback and insight. You have forced me and my team to continue to hunt for information. AND, measure…measure…measure...

Now, I know you say that I can't compare this year to last year BUT…I've studied the videos from this past weekend… guess what? That RF…in the second race where it had a 'good' tire looks A LOT like when we broke the track record! The rim is pushing out of the tire! My point is that, while the set ups are vastly different the net output is remarkably similar! I'll be putting 900s across the front. But before I do that I'll be verifying the shock travel and converting to wheel travel. Goal = 3.0" at all four corners.

Who knows I may opt to put a pair of 175s in the rear. They give us three practice sessions so a rear spring change is pretty easy.

Also, as if all the changes weren't enough we switched out the 'heavy compression' shocks and put the 12/4 shocks back in. The jury isn't out quite yet on this.

I'd be curious to see some posts by you on shocks…err, dampers…

Cheers!

 

[rick7343]

"I'd be curious to see some posts by you on shocks…err, dampers…

Cheers! "

And tire pressures!

 

[Ranger Mike]

been real busy this month.. since 2 hours from INDY...i will get on the shock ' damper ' reply when i return..mean time please post your two biggest questions on this subject so i can cover all the bases..

 

[Ranger Mike]

I contacted Jim Stimola about dampers / shocks. He does our formula car shocks.
Please post your questions about shocks ( dampers) and I will ask Jim as he has decades of experience in this field.
the only stupid question is the one you DONT ask.


James Stimola
SRP Engineering
www.srpengineering.com

 

[radracr]

I know shocks by numbers: 4, 6, 8, 9, etc. but I'm sure these correlate into velocites? And, which is a better way to undestand a shock - number or velocity?

Next, how to establish a shock baseline for each corner? Do both front shocks need to be equal? Both rears equal? Or is assymetry better?

Next, I was reading where shocks are selected based upon a driving style? True? And how to determine? I tend to be the type that drives in DEEP, applies brake pressure and wheel and then let's off and rolls into the throttle fairly quickly.) I have since learned that not so much brake, dragging the brake and picking up the throttle is better.)

Do compression and rebound correlate? In other words, you have to match a specific rebound and compression because of the freqency of motion?

As I understand it, a shock with very low compression, say '4', allows the weight to hit the spring faster. But is this ideal? Or do you want the weight to be gradual as in a 6, 7, 8, etc?

Lastly, do a shock and spring need to be matched for a particular corner?

 

[Ranger Mike]

i have a conference call tomorrow with Jim Stimola about the shock questions so will post after the call..last chance to ask about shocks dampers...

 

[rick7343]

Views on the latest suspension trends for popular classes would be a great topic.

Around here it seems the winning builders are going softer springs but stiffer shocks in our non bump stop classes.

 

[British Menac]

I too have heard of the current trend in BBSS set ups being popular and having success too. (Big Bar Soft Springs that is)
I do have a question about dampers. ...
Are more damper manufacturers rating and testing their dampers WITH springs installed?
Regards
BM

 

[the dr.]

After a computer crash I lost the link to this site, and I just now reinstalled old hard drive in new computer and presto it popped up,! I have wanted to thank each of you who helped me on here a couple years ago, we won 2 back to back track championships, with the car that is mentioned above, I would post a photo but not really sure if I can or how to, we finished the last season with 11 top 5's 2wins an only 1 DNF it was a great season and the stuff I learned here really helped .. they told me you can't hang the "J-bar" on the right side in a dirt car...lol well I proved them wrong... thanks to each of you...
the dr.

 

[Ranger Mike]

Shocks are called shock absorbers in the good old USA only. They are dampers to t he rest of the world. Since this is a technical forum we got to stick with the right name. I will use the word shock simply due to the fact that I don’t type well and dampers is a pain to spell out. Springs take the kinetic weight transferred and dampers control t he rate of transfer by dampening the kinetic energy through internal valving that converts this energy to heat. This rate of resistance can vary a whole bunch due to the many configurations of internal valving in the shock. A chassis without these dampers and only having coil springs would oscillate badly. This is dangerous as you have no control of a car that has gone pogo on you.

Basically you have a piston attached to the chassis and a tube attached to the A-Arm / control arm/ Axel/unsprung weight.
As the piston moves it forces hydraulic shock oil thru a series of small holes and valves. Oil as we know is non compressible. The oil fills a chamber that has a bladder filled with nitrogen gas. If all we had in the chamber was air, we would have aeration and the shock oil would be useless as its viscosity would change. As the oil fills and compresses the bladder the gas is compressed. On tube dampers this pressure is fixed by the manufacturer. The degree of pressure can be adjusted via amount of nitrogen you put into the damper ( Penske type shocks only). Todays automotive shocks are all gas shocks. Shock oil can go bad after a period of time due to heat. The only real way to monitor these is by using as shock dyno. The stiffness of a shock is controlled by the valving and the degree of compression and rebound can vary greatly.
Valving can be linear, digressive or progressive. Linear means the dampening builds us the same as the piston speed. Progressive means the dampening builds faster than the piston speed and digressive allows the dampening to build quicker than the piston velocity. We want digressive in a racing shock. We want quick build up at low piston speed (0 to 10 inch per second) and not too high a dampening at higher speeds ( 12 to 25 inch per second). This is accomplished by adding a blow off valve to the construction of the internal valving.

Do not get hung up on velocities , spring harmonics or that jazz..yet. From here on out we will be discussing the common dual tube shock absorber used on very restricted class stock cars doing battle on Saturday nights all over the country. One thing became apparent talking with Jim Stimbola. You can have two identical race cars but the DRIVER will dictate the shock set up. Its all about driver style. You can get close on base line set ups but on round track racing every corner of the car will have different shock set ups. Fine tuning means calibrating the RATE of weight transfer to the drivers corner entry and exit technique. We will attempt to cover the main points here and leave the fine tuning to you.

Looking in the race parts catalog you see a typical race shock with about 15 different dampening numbers. 155/155, 260/100, 260/370 etc...
These are dampening compression and rebound numbers rated in pounds. In some cases manufacturers place a valve code on the shock. These codes run from 2 for a very soft shock to 8 for very stiff dampening. A single digit like 5 designates a 50/50 ratio. Valve code with 2 digits mean a split valve shock. Example- 57 would be a 5 on compression and 7 on rebound.

Base line for a 2800 to 3200 pound door slammer running 3/8 mile paved oval- LF- 76, RF –76, LR –95, RR – 95.I personally like the Penske gas shocks because they are of great quality, parts are readily available and they can be re-built. At the track you can change the compression, rebound and shock pressure ( 125 psi to 250 psi) to dial in the car to the track that day. They are not cheap but they are for the serious racer. I can not afford a shock dyno so I have Jim re-build them annually. This is a must for the serious racer as each car set up is custom when you get to this level and Jims Dad did this at Indy for years until he passed away a few years ago. Jim carries more set ups in his head than then you can shake a stick at! There are other shock rebuild guys so check google and find one close by.

The BBSS set up has been discussed in previous posts here and I know of no manufacturer dyno testing shocks with springs at this time. i am sure it has been tried but both harmonics can be scrutinized easier when separated.

 

[radracr]

Ranger Mike,

It took me a few days to pick my jaw up off the ground...9C on a rear shock?! WOW...it seems to me the fronts would be trying to transfer weight to the rear (6R) but the 9C rears would be resisting?

The 7C on the fronts and 5R is 'close' to what I'm currently running.

Referring to your door slammer baseline, is that in stock location? Or outboard mounted?

WOW...also, I've always read the shocks the pther way around = 12/4 = 12 R and 4C. In your speak they woud be 4/12. Obviously, you can grab a shock and figure out which-is-what.

Wow...

 

[Ranger Mike]

Rad – the base line above was for stock car with coil overs and tube A-arms not restricted stock car class. More on this restricted stock class later. I put in appearance at the old track..wow!

pogo stick..a childs toy which was a huge spring mounted between two foot peg and a set of hand grips that a kid could bounce merrily along. was like driving like a 57 Buick with 200,000 mile shocks down I-75 in Michigan after a brutal winter...boing boing boing..
pogo – severe oscillation of springs

exactly..don’t forget we want the right front planted. We do not want the right front spring doing the pogo to the left rear. So the weight comes off the left rear to the right front and we want it to stay there ( hence the 6 on rebound up front acts some what like a “ tie down shock”) and not pogo back because the LR shock is too soft ( so it is pretty stiff at 9 compression to resist the weight return until you are thru the turn entry). Then the spring returns the weight that then compresses the rear shocks back to neutral. When we get on the gas at turn exit we jerk the nose up and dump weight on the rear to hook up the rear tires.


A quick check of the racers parts catalog for restricted class metric cars offers three types of shocks ...50/50, the tie down and the easy up. And various combinations of these.

A “tie-down” shock is a popular shock option for many circle track racers but is a crutch used instead of swapping out the spring.

A “tie-down” shock has more rebound and less compression.

This type of shock can help keep your race car more free through the corner and help increase forward bite

by slowing the weight transferring on corner exit to the right rear tire.

Too much rebound can limit the amount of weight transferring and negatively impact forward bite
, so some experimentation is required to find what fits best for your race car.

A typical “tie down “shock on the right front of many street stock type classes is a 4-10 shock.

An “easy-up” shock has less rebound than compression.


I went to the local “ bull ring" on Saturday night and talked with a lot of old racers...here are some tip for metric restricted heavy stock car racers. If you have to run stock type shocks use Bilstein street stock shocks for your chassis or if you can run regular racing shocks try bilstein: LF 220/120 , RF 200/180, LR 230/78 , RR 208/72 . this is a popular set up on 3000# cars.

A 5-3 on the LR and and a 3-6 on the RF was told to be by a track champ and is a good starting point when venturing into split valves for a 3000# street stock.

One racer told me he runs a metric chassis in the street stock class. He changed to a 7/2 on the LR a couple weeks ago and it changed the car completely. It drives off the corner and down the straight much better.

the following are recommendations from a guy racing in the class .BTW, it’s a 3/10 paved track at 18 degree. Car is 3200# he runs P
Pro shocks – LF 7700, RF, 7700, LR 9500, RR 9500
My old driver has Afco shocks LF 1077, RF 1077, LR 1095, RR 1095
Fast time pole sitter told me he runs Monroe shocks LF 77, RF 77, LR 86, RR 86


Note the trend to have the RF shocked to be on high end of stiff on rebound as a “tie down “ the car and the rear shocks run high compression numbers to keep the load from kicking back. But like rectums everyone has one and advise is free...and I am out of beer..

 

[autodoctor911]

I may have missed this somewhere, but did you ever cover rear IC that is offset in plan view. Presumably to the right on asphalt oval track car. I was wondering what effects on mid corner and corner exit handling it would have to offset the upper link of a 3 link to the right side to the point that it compensates for the lifting effect on the right rear due to driveshaft torque on the pinion shaft.

Would it be counterproductive, since there is already weight being transferred to the right from turning left?

If so, would it be beneficial to offset it to the left?

I am presuming it would be similar to adding wedge in if it is offset to the left.

If it was already covered, just say so, and I will search for it.

 

[Ranger Mike]

welcome doctor..
Good questions all-
Look up post #253 on page 15 and post # 301 on page 17.
The 3rd link should be located at the % left side weight for the door slammer on paved short track. In the example on page 15 we have 60” rear track width with 58% left side weight so the 3rd link will be located up to 5 inch offset to the left of the vehicle Center line. Look at attached photo and note the rear RC is already offset relative to the vehicle center line. The dotted line between the rear roll center and the offset front roll center CRC ( calculated roll center position for proper right front down forced) is still at an angular position. So we already have big angular things going on and need not complicate the set up with more variables.
We are already trying to race an ill handling three legged milk stool around a washer board track with a bunch of want to be AJ Foyt's on Saturday night. Good guys but what a hand full!

So we try to make the Rear Instant Center location as long as possible and as parallel to the vehicle center line as possible to keep everything simple. Then we can tune the rear 3rd link to hook up the tires properly on corner exit. You have lower links and the 3rd link angles to play with. Don’t complicate life by adding offsets.
my opinion..

 

[autodoctor911]

OK thanks. I am working on a 2nd gen Celica mini stock. It currently has stock rear 4 link. I was thinking about just eliminating one of the upper links for now. I will check how close the left one is to the lateral center of mass/left side weight bias once I get the engine in and determine how much ballast I will be using.

Why the offset rear RC? Is it due to space limitations. I will be using a full length rear Panhard rod. Should I try to line up the front and rear RC.

Also, It has stock front struts with puny solid rotors, and I was thinking of upgrading struts. There are different Kingpin angles for various struts. On the Toyota RWD struts the strut angle pretty much follows the kingpin angle. I was thinking I should get the most angle I can to lower the RCs while shortening the IC distances. I would also get the benefit of increased track width, since the control arms will be longer for the same camber measurement. I was going to offset front RC by using a RC adjuster(spacer between steering arm and spindle) on the right side only to lower the outer BJ. I will be measuring it all up and putting it into a modelling program eventually, but with the struts, it's pretty limited what I can do. The RC has to move with the IC unless I can change the strut angle at the spindle somehow(welded on). I think somebody already did on the old struts, since the right side has a lot more negative camber and the tire is closer to the tube.

 

[Ranger Mike]

it celica a front wheel drive or rwd?

 

[autodoctor911]

It is a RWD Celica.

 

[Ranger Mike]

I have been working with one racer who is custom building a street car and had a lot of questions about mounting points for suspension members. He is well on his way to a very nice ride. Just recently Euro Dan has asked to help with wishbone construction on his sports racer. I have both their permission to discuss these project as I suspect there are a lot of you racers out there doing the same. I can only add what I have found out over time. Before the rise of custom race chassis shops pioneered by Ed Howe, Port City Racing and the like, we had to do it our selves. There was no software programs to help calculate Roll center and camber build. It was a lot of cardboard cutting and long hours on a cold garage floor over the winter. Hopefully this post can save you guys the trouble.We covered the basics early on Page 1 and 2 of this post of laying out your race car suspension.
You need a software program that shows front end movement in a dynamic mode. This is as important as your tire pyrometer- you need this!
Now the specific question of how long should my control arm be and where to mount it. What spindle should I use.

Again we have to look at the rule book. Just about every race course is governed by some organizations rule book. As a minimum it will dictate the minimum weight, length and width of the vehicle. It may even specify the Tires you must use. For this discussion we assume the chassis configuration is wide open except for wheel base and track width. We also will assume the race car will be turning left and right so this is a symmetrical build. Next question is – Where is the power plant? Is it front engine rear wheel drive? In this case it is mid engine rear wheel drive. This is good as most drivers are skinnier than engines and this means we have a lot more room up front to play with mounting locations. We find the maximum track width permitted and work backwards. Next we have to look a Page 22 of this post # 389 and # 390. If you can, use the equal length and parallel wishbone set up. The backup plan is to go with the unequal but parallel control arm arrangement. Spend some time and determine which of the two setups you are going to use.Euro Dan asks which to use - Chevy Corvette spindle or Wilwood pro spindle. I think from a cost standpoint and availability the Wilwood has a lot of appeal. The stock Ford Mustang II weighs in at 3500 pounds so the spindles are more than beefy enough for your application. I suggest you plug in the spindle mount points in your suspension software program and look at the inboard wishbone mount points to give you the longest possible lengths. Don’t forget you have a drivers legs mixing into this equation as well.
I have to wait until Euro Dan messages me back before going on.

 

[autodoctor911]

I would think when choosing between Pinto spindles and Corvette spindles, the main consideration will be kingpin angle and scrub radius, as any roll centers and camber gain could be worked out with either one, but kingpin inclination and hub offset, together with wheel offset will determine the scrub radius and when combined with caster and trail, the amount of jacking effect from turning.

I think the Corvette spindles would be better for achieving a more modern steering geometry with high offset wheels and low kingpin angles, as well as having much more durable sealed wheel bearings and the possibility of using ABS.

I was wondering what you think of the DAX camber compensating suspension linkage. It seems to act somewhat like a hybrid between a parralel equal length and a live axle as far as roll camber and track change.

see animation here: http://www.walker-partnership.com/

 

[Ranger Mike]

AutoDoc that is one good link! i will eb doing some serious investigation on that...would love to show up at the local track with that under the hood...the tech inspectors already hate me...would make their day...thank you, Doc911

Wilwood Pro Spindle Kingpin Inclination Angle is 7.2 degrees. Wilwood has nice pdf of this spindle.
The Corvette C5 spindle has 7.1 degrees.
From limited surfing of the web I got the following -

The C5 Corvette front track is 61.9" and the standard wheel offset is +58mm. That makes the front end mounting width 64.18" wide. The early C4 is 61" wide, and the late C4 is 62" wide.
The C5/C6 stuff uses a taller spindle to put the king pin Inclination more straight up and down to allow be able to allow better scrub radius with wider tires.
The lower arms are longer and and better dimensions to allow for better camber gain in the upper arm.
The C5/C6 stuff uses a taller spindle to put the king pin Inc more straight up and down to allow be able to allow better scrub radius with wider tires.
To reduce the scrub radius with wide tires, you generally need to move the inclination angle away from vertical. This is just simple geometry - the wider the tire, the further outboard of the ball joints it is. But running negative offset wheels such as C4, 5 and 6 Corvettes do means there is little to no scrub radius already. Working to eliminate the scrub radius can be good, but you do tend to loose some "feel" in the front end which may not be the best for all drivers. Again, it is all about compromise.

BEWARE !
from a post on a corvette forum I surf up on -
“I just did an internet search and found a source that says the SAI for the C5/6 vettes is 9.55 degrees, while for the C4 it is 8.744 degrees per a spec book I have.”


Same forum – different poster- which I will believe!


”Well Sir, When it comes to internet searches don't trust every thing you find. There is some C5 geometry floating around on the internet that is just not true.

So what I have here is a Solidworks File that I got from SEMA's tech share program that gets all the parts you request from the desired manufacturer. They send you complete assemblies to help with the design work of new products for new cars. We use the complete suspension system and parts to help with the design work of the cars we are building. So what I have here is the exact C6 vette spindle. I drew a line through the the upper ball joint and through the center of the tapered ball joint hole on the lower end of the spindle to show the angle discussed. As you will see it is not 9.55 it is 7.10.”

http://i616.photobucket.com/albums/tt248/ironworksspeed/SAIforC6spindle.jpg

 

[Ranger Mike]

from the link in above post

 

[autodoctor911]

Yeah, the DAX linkage cars seem to do extremely well in street type kit cars used for racing in the UK, against conventional suspension.
The Track and roll camber are both really good. What the animation does not show is single wheel bump, which is where this design has it's compromise. Just like a live axle, when only one wheel is pushed up, as when you go up on a curb in road racing, or have some track irregularities, both the wheel in bump and the opposite wheel get some camber change. It's kind of like looking at it in roll, then tilt the picture so one wheel is higher, and the chassis is level. I guess you can't ever get perfect camber at all times with any suspension.

 

[autodoctor911]

Might the variance in specs be due to static camber changes causing SAI to be different from the Kingpin angle, which would be the same as SAI only at 0 camber?

As to scrub radius affecting feel: I have found larger scrub radius having increased kickback and negative impact on feel. Increased caster and the resultant trail on the other hand gives a very nice feel, to where the steering gets lighter as grip is diminishing.

If you look at the scrub radius and it's orientation to lateral forces, the amount of feedback due to lateral forces will be minimal and varies a lot with steering angle, and feedback from longitudinal loads(ie braking and bumps) will be much greater, Trail is the longitudinal distance from the contact center to the steering axis, and is oriented much better to have an effect on "feel" for cornering forces.

I believe this is the reason almost all front wheel drive vehicles and most modern rear wheel drive vehicles have near zero or negative scrub radius. If the scrub radius is negative, the feedback from longitudinal loads like braking, bumps, and in the case of FWD, drive forces are self correcting. when the brake force is higher on the left side with a positive scrub radius, it will pull the steering to the left, which is the same way the forces are already pulling the car. With a negative scrub radius, the higher braking force on the left side will pull the steering to the right, helping keep the car going straight. The same principal works for bumps and drive forces. If you've ever driven a FWD car that has much wider wheels than stock, offset in the negative direction(to the outside) increasing scrub radius in the positive direction on a FWD car, you can notice torque steer is almost unmanageable.

The only problem I see with negative scrub radius is that with a positive kingpin inclination, there is negative jacking forces. This is why it would be ideal to have very high(positive) offset(rim to the inside, hub center to the outside) so you can actually get a negative scrub radius and a negative kingpin inclination. It takes very wide inner rim shells and very narrow outer rim shells, and a narrow spindle setup with as little as possible offset from the ball joints to the hub surface to achieve this though.

One way I wanted to try and achieve this would be to use a small solid axle spindle, kind of like a sprint car spindle mounted to a short stub axle that is welded to a larger spindle/upright that doesn't turn with the wheels, kind of like the spindles on an early Chevy or Ford independent front suspension. You could put the negatively inclined kingpin spindles inside the brake rotor hat, right next to the wheel mounting surface.

kind of like this:

 

[Ranger Mike]

good points all Autodoc...that is why I asked Euro Dan to post his project for the public..I think your input will help him decide on the spindles...Is is not true the current theme of Mcpherson strut FWD is about zero offset on the tiny wheels they run? I do now the typical KIA the Early Fords with straight axles ran 8 degrees on 49-54 Chevies had 4 degrees KIA, 55-57 Chevies was 3.5 degrees. Tall, skinny tires and zero offset back then. Euro Dan is going with huge wheels. The rims 18x11 with 285/650 and rear 18x13 325-650. One final note- the spindle inclination angle on super late model left hand turn cars runs 5,7,10 and 12 degrees with 10 degrees being the most popular. There is even a new spindle out that offers adjustable KIA. Scrub radius is not too big a problem on light weight cars. Our Formula car has 2.5 inch and the old super late model ( 2500#) had 5 inches.

 

[autodoctor911]

Pretty much all modern cars have some positive offset to the wheels. Usually, it seems, the wider the wheel, the higher the positive offset. The wheel and tire sizes you mentioned are very common on Porsche race cars. The wheels for these cars have about 50mm or 2" of offset, which for the 11" wide wheel would be about 8" of backset, which circle track racers seem to refer to as offset for some reason. To me 0" of offset is a symmetrical wheel with the wheel having the mounting flange right in the middle of the rim, a 8" wide wheel with 4" of offset would have the studs sticking out past the tires and with -4" of offset the mounting surface would be even with the inner rim edge.. Most of the steel racing wheels I've seen on Circle track cars have negative offset, where the center of the wheel is closer to the inside edge of the rim.

I thought the reason for the negative offset wheels on circle track cars was just to increase track width in the cheapest possible way. Increasing the caster is an easy way to compensate for the extra scrub radius and stabilize everything. I wouldn't think anyone would design a front suspension like that unless the rules, or economics required it. I think the direction GT-1/TransAm racing went starting in the 90s shows that there are definitely better ways. The old wide 5 hub conventional large scrub cars didn't even come close to keeping up with the newer "zero scrub" cars with not much else changing at at that time. That happened even before the big horsepower engines started coming in with Yates heads, SB2, etc.

Anyways, I am guessing he doesn't want to use the strut suspension like Porsche did up until the latest 991RSR anyways. Even though they have been very successful with it, it is definitely a big compromise. They can never get enough camber gain to overcome roll, and typically run very high static negative camber, and the way the struts mount to the spindles, everytime you change camber, you change the KPI and scrub radius unless you compensate with wheel spacers. With the extreme negative camber they would run, the negative scrub radius would get to be too much. just think. the lower ball joint is pretty near the center of the rim, and the upper defining pint of the SAI is the strut mount bearing, way inside the trunk. whenever you increase negative camber, you either move the ball joint out more or bring the upper mount in, moving that steering axis further out where it hits the ground.

 

[quazu]

I have been reading and thinking alot, i guess there is no perfect upright.
Specially not from a roadcar. Sure you can buy a racecar upright, it will be expensive. But is it really necessary?

How about build one? I have seen some homemade ones.
http://ajden.se/bentley/Ny/u6.JPG this is an example.

As i understand a long a-arms will work better on a high-downforce car and it´s best to have little camber increase (a kind camber curve)

 

[autodoctor911]

Those look very nice, and very expensive. If you were to pay somebody to make those from what appears to be stainless steel, I would expect to pay upwards of $2000 for the pair, but then that's still less than the Porsche stock uprights from the GT3 RS which is what I need to correct the roll center and camber curve after lowering my Boxster.

Ps: I would definitely try to spec a much larger OD bearing than that if doing custom uprights, even if it was a 1200lb sports racer. G forces and downforce can be hell on bearings.