Automotive Race car suspension Class

[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.

 

[Ranger Mike]

corvette spindle and the wilwood spindle was about $220.00...not bad...
in my opinion..quit re-inventing the wheel and buy these...if you are scratch building you got enuff other details to worry about. ref- A-arm length...any time you can keep the camber build down to 1 degree per inch or less..is a good way to go..in this case less is better..

 

[autodoctor911]

I guess one important factor for choosing spindles that wasn't even discussed yet is steering arm placement. It will determine where the rack and pinion has to go.

 

[bigbolt52]

I am trying to correct a Mod-Lite dirt car, 1300 lb-14,000 rpm-1/4 to 3/8 mile dirt tracks. Looking for some ballpark numbers on where the roll center should be located, any help greatly appreciated.

 

[bigbolt52]

Here is some numbers.

 

[Ranger Mike]

Welcome Bigbolt
That is one light narrow car! Geometry looks pretty good. Roll center height is a little high in my opinion. Where is the rear RC?
what is % ft to rear and lft side weight?


I have never worked on a car like yours so all i can do is speculate what works on metric E-mods and the like on dirt.
In an ideal world 3.5 to 4 inch high front RC would be good and having it located 4 inch offset to the right side would provide more down force to load the rt ft tire.

Glad you got a good software program to analyze the camber build. You are well on the way to a checker.

 

[bigbolt52]

Thanks Ranger Mike it is basically a dirt Legend car, 74" wheelbase, a lot less restrictive rules class too. 57.8% rear 52.4 left and 52.8 cross, and a 1/2 wider wheel base on the right. Still confused on roll center moved to the left or right, the car seems to set and fall back down and tends to make my son feel like he needs to drive the turn harder to keep it set up.

 

[bigbolt52]

Back roll center.

 

[bigbolt52]

I think there is too much difference front to back on the roll center, and I am leveling out the lower control arms which is dropping it even more, and I want to raise the inner upper arm points too which should drop the RC even more to around 3".

 

[Ranger Mike]

Big bolt i will get back to you shortly on this.

I have been talking with Peter Walker at

http://www.walker-partnership.com/
on his unique suspension CC&AR. The question was posed to him...How is the front Roll Center calculated. He gave me permission to reply. Here it is.
"As the upper wishbones of the CC&AR system are free to float laterally, its roll centre is purely determined by the lower wishbones. It’s very easily missed but you will find it marked in the diagrams on the CC&AR page of our website."

Anyone who is interested in this system should post questions as Peter has agreed to share some info about this unique system but I have to channel it to him.
I must spend some time with the software to figure this out. My friend Conrad is thinking of going to this on his special built car project.

I have to prepare the formula car for race next week and am getting very busy so post will come later i am afraid.

 

[bigbolt52]

Thanks Ranger Mike, I wish our rules didn't say " No cant-a-lever or cant-a-lever type device will be permitted in or on any area of the race car". So I guess everyone that use a traditional shifter is illegal, lol. I better go order a cable shifter,lol and swich to a cable throttle, looking forward to your reply.

 

[Ranger Mike]

Ok, Big Bolt sent me private message and authorized me to share set up info so all you racers can follow along.

Bigbolt, please post the following info.
Left front spring, tire pressure you run, caster, camber and ride height. same on RT Ft.
on the rear I need ride height, spring rate and tire pressure, stagger unless you run open Toyota rear end.
I need toe out on the front. Whats is the wheel base on the left side and right side. Are your rule open on tires or do you run spec tires?Are you running camber cut tires?
are you using 3 link or 4 link rear set up?
Have you squared the rear end lately?

 

[bigbolt52]

Springs-LF 180, RF 180 (trying 200 this week0, LR 160 (trying 180 this week) RR 140 (trying 160 this week)

Air 6# Left 8# right

Caster L 4, R 6

Camber L -3.6, R 2.25

Ride Height Front 5" Rear 5.5"

Stagger in the rear is around 1.5" ( recently switched from 3"-big improvement)

Wheel base Left 73.5 Right 74 ( recently went to this from squared up, seemed to help but not sure if it was just a crutch, was having trouble keeping car down and this did help it from drifting up the track.

Toe out 3/16"

Tires Spec 40 duro American Racers, Hoosiers are too stiff. And the are grooved but not camber cut.

3 link as per rules with a 24" right bar and 19" left bar,

Panhard bar to the center, left side to the frame ( pondering switching to a J bar to move roll center over to the right)

 

[Ranger Mike]

all springs are on soft side.
car is about an inch too high on ride height.
springs -
try 185 LF ft., 200 RF., 165 LR , 145 RR
You are real close on LF and LR so do not change these
One legend racer here runs LF 185, RF 200, LR 165, RR 145
another runs LF 200, RF 225, LR 165, RR 145 so I am pretty confident on the above recommendations..

use pyrometer to get best tire pressure
no reason to go to J-bar yet. Is side bite a problem? Can not address side bite coming of the turn until we manage to enter the turn properly..

lower the rear roll center to help side bite, add down angle to increase it.
I would square up the rear end as you have introduced rear roll over steer.
go to at least 1/4 inch toe out. up to 3/4 inch toe out on 1/5 dirt track
on front roll center I am firm believer in offset roll center to plant the right front tire.
If possible try to get at least 3 inch offset to the right, 4 is better and you need this on dirt.

 

[bigbolt52]

Offset the front roll center towards the RF tire? And am I thinking correctly that the heavier sprung corner will get the most traction? Another piece of info, the front running cars, well most of them, run the LR coil over in front, and the RR behind the axle, that is how we are, not sure on the dirt Legends.

 

[bigbolt52]

It is also getting over on the right rear very hard, body clear down to the tire. Rear tire temps have been close together and the RF less than half the rears, and the LF is stone cold cause we usually are carrying it off the turn, I have to do some surgery up there to get it to lay down because it limits out on the Mono ball joints.

 

[bigbolt52]

Here is a video of our last race, our car got toe knocked out to 3/4" on the first lap. http://youtu.be/8kNNFME3F8k

 

[Ranger Mike]

offset the frt roll center toward the right side tire...yes..drop the roll center as well..i held off on this until you can tell me if the ride height can be lowered by an inch. we have the right side springs too soft. the car is pan caking the right side springs. This makes for a loose car going in. the tire temps are indicators and the right front should be the hottest tire on the car. detroit muscle cars had the left shock mounted in front of the axle and the right shock in back of the axle tube to stave off axle wrap under acceleration.

note in the video the driver is sawing the steering wheel in the turns. the rear end wants to come around..looooose...Bigbolt if you can not change the Roll Center in time...change the springs out and get tire temperatures right so you have similar temps across the tire face on the right front..and the other three. concentrate on this and worry about front to rear temps after you have close temps on inside, middle and outside of each tire. make good notes..

 

[bigbolt52]

I can do everything but get temp in the LF, geometry just won't let it hang low enough. and I can't lower the car or stuff will hit the ground.

 

[bigbolt52]

Roll center on the front is no problem and I can drop the panhard bar 1" in the rear.

 

[Ranger Mike]

Once you get stiffer rt ft spring it will throw some weight onto the left front tire

 

[bigbolt52]

I hope its enough to get some temp. I'll update after this weekend, I have the roll center down to 4" in the front and to the right 2", with a ride height of 4.75", I'm dropping the back down to 5" ride height and dropping the roll center over 1" in the rear also, with the spring changes recommended, thanks for your help.

 

[Ranger Mike]

Me too.. Got huge race next weekend
Oil cooler has leak
Transaxle layshaft pinion bearing is toast
Broke thrust washer
And replacement bearing has no flange face
Got to get on the lathe and tool up a spacer
And it's 88 degrees in the garage
Ya got to love racing

 

[autodoctor911]

If you ever need to go lower with the rear RC than possible with the Panhard or Watts can achieve there is also the Mumford Link:
The RC is the imaginary point where the two long links would intersect.

 

[bigbolt52]

Well it worked awesome on Friday night in hotlaps then got rained out, Saturday night car was junk, horrible. Took a huge swing on something I wanted to try for a long time and moved to both coilovers in front of the axle, wow! My son started coming through the pack like gang busters and then on a restart the leaders started playing brake check games, a car got turned sideways right in front of my son (15 yrs old) and bang, no more car. We are done with this class, unpredictable cars, and terrible drivers we have had enough, going into the late model class.
On a positive note the front end was awesome thanks to your help but now its a mangled mess, but my son is ok, I do appreciate the help.

Here is the accident https://www.youtube.com/watch?v=7Yb4uHdPM9E&list=UUsdXuwezocDERdqB0LdvvuQ

 

[Ranger Mike]

anytime you can walk away it is good..glad he is not hurt...that is the important thing..
thanks for the kind words...and good racing in the late model class

 

[mikey531]

We are racing a 2550 LB asphalt modified. What are the advantages and disadvantages of having the left rear spring in front of the rear end and the right rear spring behind the rear end? We also have a decel/acel push/pull bar on the center of the rear end. Approximately 600 lbs of torque from the engine.

 

[mikey531]

welcome...nice to meet a fellow racer..short answer is spring mount location can help a little bit on spring wrap under acceleration..torque link is to dial in hook up under acceleration as well..long answer is both questions are addresses in above post Race car suspension Class
by Ranger Mike

rm

Thanks I have read the posts and the big problem we have seems to be traction off the turns. The third link is supposed to increase bite off but they have tried it with staggered springs. Here is the info.
http://www.rightfootperformance.net/...4121065422.pdf
We have the accel set at 14 degrees down and the decel at 5 degrees up I think. I will have to double check the angles.

Thanks for the info above!

 

[mikey531]

The track is low banked 1/4 mile, we have been trying to get more bite off the corner by changing the angle on the accel bar. I think we are going to move the left rear spring behind the axle and try that. Unless anyone has another idea?

 

[Ranger Mike]

Usually a Loose Off condition is caused by too little Stagger. Another cause is too soft a right rear spring.
Typically 3rd links are used to tune the chassis. You have to have it handling properly before monkeying with the fine tune settings.
my main concern is the mounting location of the 3rd link. It should be mounted at the center of weight of the car. i.e. if car has 60 inch track width and 53% left side weight then
60 x .53= 31.8 inch and 3rd link should be mounted 31.8 inch to the left of the RIGHT TIRE CENTERLINE. Is it?

Next question is what springs are you running and how much stagger?
Is the 1/4 mile track tight radius or wide sweeping radius. Is track a paperclip or more of an oval?
any idea of shock absorber rates you are running?
what is % rear weight, left side and cross weight?
The good news is that it sounds like you have mastered the corner entry and now have Phase Three problems coming off. You are getting close.

Detroit muscle cars used to have the rear shocks mounted in back of the differential on the Rt Rear and in front of the diff. on the Lt rear to fend off axle wrap under acceleration.
In my opinion all coil overs and sliders should be mounted in back of the differential. This gives you the longest spring base (maximum distance between spring mounting points over the wheelbase to deal with sprung weight). Screwing around with one in back and one in front is asking for trouble. When you mount the left side spring in front of the diff. you have shortened up the left side distance by 5 or 6 inches. That adds up to 5% diff.

Mikey and bigbolt..not directed to you..just in general...
Rant to follow – Why in the heck do racers mess around with tricks and gimmicks to make a car handle when the car is not even close to the basic setup! Happens every time I'm in the pits...current trends, fads about super low tire pressures , trick locker rear ends..concealed sway bad loaders, tire soaking tricks..arrrrrr!

Square up the car. On a “ flat “ garage floor level up the race car frame. At your four bench marks make sure it is same distance from the floor. Take out the frt spring and disconnect the ARB (sway bar). ALL A-Arm /control arm frame mount points had better be parallel to the floor. if not..fix them. (may not be possible if you run metric frame but make sure the left and right side are mirror image of each other. The ARB should be parallel to the floor. Move to the rear end. Make sure it has not been bent. check it for rear steer. Square it up. Make sure the mount points are the same and make sure it moves parallel thru bump and rebound. Put 5 degree down in the 3rd link and put it back together.
rear end. Get the left side, rear and cross weight right. get the caster camber, toe and bump steer correct. get the spring rates in the ball park. Stagger should be close to what everyone else is running. ( if you want to win make sure the roll center is where it should be on the front and rear). Take it to tune and test and use a pyrometer. don’t forget the cardboard box!

 

[mikey531]

RM with the spring in front of the rear axle the distance between the front mounting point and the rear mounting point shortened the spring base about 16 to 18 inches. You said 5 to 6 inches would be 5%. 5% of what?

Thanks
mike