Automotive Race car suspension Class

[mikey531]

Ranger Mike I have a question. We are trying to duplicate our setup when we put tires on at the track. I try to get the same size etc but never seem to get it right. If we have the car parked in exactly the same spot with the old tires and measure the play in the front sway bar, when we put new tires on the sway bar is either looser or tighter. If we adjust the car so the sway bar is the way it was on old tires will we still close to our setup? Thanks Mike

 

[Ranger Mike]

i assume you are using a stagger tape measure to get same size on the tires. Old tire s and new tires should measure the same. Make sure you jounce the suspension ( jump up and down on each corner before you measure. When we scale the race car we unhook front and rear ARB (sway bar). I run all ARB neutral setting with no preloads.

 

[mikey531]

Yes I am using a stagger tape but we put on at least 2 tires each race and even getting the same chalk mark, unmounted tape size and mounted tape size it is still a guess as to what it will come in at. We set our bar neutral at the shop. I was just looking for an easy way to adjust the car if we get a tires that are bigger than what we scaled with even though even we have the same stagger. We had a right sifde tire at 84 3/4 and left at 81 3/4 which was ideal but we scaled with tires that were 84 and 81 that is where I am having a problem. Thanks

 

[Ranger Mike]

Worry about stagger before worrying about a 3/8" height change from the tire. read page 29 post #572 on why i built the heat cycle machine, get nitrogen and use in t he race tires. get a vacuum pump from an old refrigerator and suck out the moisture containing air and replace with Nitrogen.

 

[mikey531]

We do use nitrogen but at some races we have to use their tires and we draw for picking tires well with our luck we seem to always pick last when there is not much to choose from. I was hoping my thought of getting the sway bar back where we had it would work but I guess not. Thanks

 

[mikey531]

Another idea that kinda worked but not really on our asphalt modified. We tried to reduce the rear weight by moving as much as we could to the center leaving us with a rear percent of 51.2 I want to put about 25 pounds of lead behind the fuel cell and see if I can get the rear up to 52% I think this will help with power off the turns. However the car owner says it will act like a pendulum and cause more problems. I did it on a metric chassis and it worked awesome. but can't convince the owner to let me try it. Anyone had success or failure? Thanks

 

[Ranger Mike]

A lot of penalties in NASCAR lately about rear suspensio n components not properly mating to mounting surfaces. These cars use pickup truck trailing arms and “passenger” car differentials. The rear ends are cambered to better contact the track surface when using stagger tires. A shim is placed between the differential and trailing arm to align the drive shaft pinion angle. Car rolls thru the pre race tech inspection and all is well. If you fabricate the shim with a large knurl so that it will grind down over a few laps, the rear end will twist and change angle. You will introduce rear steer into the car.

The rear end moves to the left during the race, wears off the knurl job and the rear end is skewed to the left.
The object is to obtain as much aero side force as you can get. When the right rear quarter panel and spoiler get more air than the other race car, you get more down force and grip. This years NASCAR restrictions call for low down force package.So now you know why some race winners do a 50 mph sprint then throw the car into a violent RIGHT turn for his 360 burn out It is to slam the rear end back into place for post race tech inspection. You will only find this when you take the car apart and check for this “non contact” violation.

Rear steer helps on short tracks but on the long tracks its about Aero downforce.

 

[mikey531]

New question, We have been playing with stagger and last night we had 4 inches of stagger. The car was very fast for the first 20 laps then when tight. We were lucky to hang onto third. We knew the tires would grow to more stagger that we have ever run so we lowered the track bar 1/4 inch to compensate for the increased stagger. Did we go too far on the track bar and maybe should have gone 1/8 inch? The car has never been as fast as it was last night. What are we missing? Thanks

 

[Ranger Mike]

4 inch is huge amount. you may be racing a three legged stool and the right rear burns off too quick.

I would like to see the tire temps. From what you said, you probably have identified the situation. When you change stagger you move the roll center up or down. Too bad you cannot fabricate a hydraulic cylinder to raise the rear panhard bar ¼” from the cockpit. But that may be cheating…
I would like to see the tire temps. From what you said, you probably have identified the situation. When you change stagger you move the roll center up or down. Too bad you cannot fabricate a hydraulic cylinder to raise the rear panhard bar ¼” from the cockpit. But that may be cheating…

 

[mikey531]

4 inch is huge amount. you may be racing a three legged stool and the right rear burns off too quick.

I would like to see the tire temps. From what you said, you probably have identified the situation. When you change stagger you move the roll center up or down. Too bad you cannot fabricate a hydraulic cylinder to raise the rear panhard bar ¼” from the cockpit. But that may be cheating…
I would like to see the tire temps. From what you said, you probably have identified the situation. When you change stagger you move the roll center up or down. Too bad you cannot fabricate a hydraulic cylinder to raise the rear panhard bar ¼” from the cockpit. But that may be cheating…

I will post the tire temps later today. I had thought about an adjustable panhard bar like NASCAR has.

Thanks

 

[mikey531]

These are the temps that we got after the race. We did them on the front stretch as we had go there for 3rd place finish..
LF outside to inside 123, 121, 98
LR 140, 143.146
RF 146. 134. 119
RR 167,157.148

We also discovered today that the right rear lower control arm had moved up about an inch increasing the angle I don't have the setup sheet with me but I think we set it at 4 degrees.

 

[Ranger Mike]

You need more NEG camber ON RT FT. the rtf t outside temp is over 20% cooler than the inside temp

Same on left side add pos camberFirst we find average of tire temps

LF 114

Rtf t 133

LR 143

RR 157
Front avg temp – 123

Right side avg - 145

Lft rear to rt ft avg – 138We need the diag avg to be 6 to 10 degree cooler than either the ft avg or rt side avg

In this case you have 5 degree hotter diag avg vs the ft avg which means you have too much cross weight and will push

(when you have more than 10 degree cooler dia temp you will be loose due to lft rear tire not doing the work)
We want rt rr tire avg 10 to 15 degree cooler than rtf t avg , you got it 24 degrees hotterYou said the lower arm angle was 4 degrees down per troyer…please clarify?

We usually set the lower trailing arms at 5 degree uphill angle. The housing being the bottom of the hill the chassis being the uphill mount point.I do not know on your chassis the effect of the rt rear lower arm angle but you should measure it to see what the wheelbase is doing but suspect you added in more roll over steer?

 

[FISCH]

hello anyone I am trying to find a part that will adapt my steering pressure hose early style to my new 12-1 f3 sport steering box , i have tryed many items and they all leak, anyone i ask just look at me funny and offer od ball reasons and solutions, I don't think I am the only one to replace a16 to 1 ratio box for a g body race car ?

 

[FISCH]

I found insert to adapt inverted flare to o ring box .

 

[Vintageracer13]

Well the racing season is over so now it is time to make some changes for next year. The radius rods I have on the front of my car are 35 inches long so I am shortening them up to prevent them from bending easily. My question concerns the mount to the frame. I wonder if it will help to angle the rods up to rear. I wonder if it will make the car more stable on corner entry. Thoughts?

 

[Ranger Mike]

it is great that you have refined the car to the point of being able to look at the longevity stuff. Have the rods got bent by flexing only or are they just designed too skinny? On a race car longer is usually better due to less chassis change. ie longer trailing arms mean less rear end arc while cornering. My only advice is to measure the front chamber build and wheelbase with current setup and mock up the shorter set up and see who it effects what you now have. Then you can evaluate the change empirically.

 

[Vintageracer13]

I would like to say I'm doing this to improve things but a hitting Sandusky Speedway's front stretch wall is really what started this! My question really concerns the angle of the radius rods. The car was good on entry this year but I read that having the rods higher towards the rear would help on entry

 

[Ranger Mike]

The thinking on this is the rods are higher in back at static but level out once right front is in Dive. But what happens to camber build and wheel base length?

 

[Vintageracer13]

I guess the best way to see is to measure it static and move it to what the shock indicators show and see what change there is

 

[Randy Phillippe]

Hello
Several months ago, I started reading many posts from the race car suspension class trying to get answers on how to make a late model perimeter asphalt race car driveable on the street

I have to blame myself for once again letting my long time friend Larry talk me into another great idea which at the time, sounded pretty cool but had I known the grief combined with literally 100's of hours and several thousands of dollars down the drain, I would have told him to tell someone else
I know there is a lot of knowledge regarding physics being applied in this forum because I have read many posts and have learned a lot, but I am at a point where I can't go any further without asking some questions regarding these suspensions direct

I have the chassis symmetrical from centerline now with matching upper and lower control arms in place with a set of tubular spindles from the car that had different king pin angles that I modified to 10 degrees and 9-1/4" tall that is the norm for road racing asphalt cars

The new arms have a 20 degree inclination due to the tall spindle and the ball joint comes into the top of the spindle close to 90 degrees and what I can't figure out is how that would be done
I've looked at some pictures and you can clearly see the top ball joint area is flat instead of at an angle and looks to be square to the spindle pin

Probably something simple, but I'm toast and can't think straight
Thanks for listening

 

[Ranger Mike]

Actually, your present situation is pretty common to that of a racer after a serious hard fought race season. Car is banged up pretty bad. Frame in question. Do I rebuild it or sell it and get a straight chassis.

you sunk a lot of green into the present cluster fake. Regardless of how you got here, you are here. Spend the money and buy the chassis suspension software that can help you.
The software will save you hours of trial and error fitting different A-arms and measuring.
then you can see where you are and map out a logical path to getting the car in shape.

 

[Ranger Mike]

Am in Caribbean til 11 December with lovely girl friend
Bahaha

 

[Tgun]

Ranger Mike - I apologize if you touched on this already but I was unable to locate it in the thread. I am running a G body metric chassis 85 Monte Carlo asphalt stock car with a stock 4 link rear end. I have had a tremendous forward bite issue and to make a long story short have recently discovered anti-squat and found that my angles on the rear trailing arms were running the opposite direction they recommend due to me lowering the ride height. I have since put adjustment into both the upper and lower trailing arms and can now acquire the correct angles. I understand and can figure the formula relating to anti-squat and thus with the adjustments can move my Instant Center so that the imaginary line that runs from the rear tire contact point through the IC continuing forward and matching the height of the CG at the front axle and in theory giving me 100% anti-squat. (and hopefully bite)

I have found through that I can achieve 100% anti-squat by several different angle combinations. Each combination, although achieving 100% anti-squat, changes the location of my Instant Center both by height and forward/ rearward.

Thus my questions,

Is there a preferred placement of your Instant Center?

Is there a Preferred Trailing arm angle?

Does one trump the other?

Is there a benefit to having a higher or lower Instant Center?

I look forward to hearing your thoughts. Much Thanks!

 

[Ranger Mike]

Street Stock racers
I have been asked many set up questions form new street stock owners. The following are a FEW not all...but a few posts on SS

Page 16 post # 301
Page 27 post # 521
Page 42 # 830 and 832 page 43 # 858
Page 64 # 1264
good starter info so you do not go over ground we have covered

 

[mikey531]

Ranger Mike
What is the correlation between torque and horsepower in a pavement modified. This is my theory, you need torque to get you out of the corners, but too much torque may overcome the traction of your tires no matter what you have for a setup. Horsepower keeps you going down the straights. If you run out of horsepower the car will want to turn because of stagger. If I am thinking correctly I need to balance the horsepower with my torque needs. Now if I have enough horsepower to keep momentum up through the turns I should be able to reduce the torque and the stagger needed to get through the turns? Especially in a 100 lap race? Does any of this make any sense?
Thanks
Mike

 

[Ranger Mike]

Mikey..good analytical thinking. There is a definite relationship between Hp and torque. Stagger is the diameter difference between the inside tire and out side tire on a race car dedicated to turning one direction. You must sue stagger if you race a locked differential. regardless of the amount of power you can put down, you need the stagger to make max use of tire contacting the pavement.

The amount of torque or HP you put down is controlled by your toe. Unless you can sneak a traction control device into the car build and keep it undetected, your only option is to learn not to mat the gas pedal. You limit the stagger growth by using nitrogen or pop offs on the wheels. You limit growth by not heating the hides by excess wheel spin. A 100 lapper is real tough on a set of rines but i would also maintain you need to look at the brakes just as important as the tires.

 

[shawn wyatt]

hey there everyone, been on this forum for some time now, lots of good information, i love it. now for the question, Ranger Mike or anyone with some good insight. I run a super stock car at a 1/2 mile track, been at same track for a lot of years, car specs below
3100 lbs 55% left and 48.5% rear stock front lowers and tube upper A arms
Have a decent handle on the geometry and such (performance trends software)
without going into huge detail, full tube chassis with modified front camaro clip, we were one of the only rear coil cars in the field and they made us switch to leaf.
have had some good runs but car could hook better out of corner. i am not the driver but owner / chief

lf 550 rf 600 ( large 1 1/4" bar ) soft set up but not to soft
lr 200 rr225 Hoosier tires

temps
lf 145 av rf 198av
lr 166 av rr 190 av ( higher some days) spin off corner, lots of driver induced
the real thing i am asking is short shackles and lots of lowering blocks or very little block and longer shackles, it seems that they are using lots of blocks and making spring deflect of help limit wheel spin then as spring moves back to unloaded the car is straight and able to use all the pedal, or am i completely out to lunch? i currently have in the car less block and longer shackle set up, it seems i need to change those longer shackles are starting to bend a bit even tho they are 1/4 thick. please advise
thanks in advance

 

[Ranger Mike]

Good to hear from you. I have to dig out my old notes as last leaf spring car was old Plymouth Baracudda.

Tire temp averages look like rt ft to lft rear avg. = 182

Ft avg is 171

Rt side avg is 178

The diagonal avg should be 6 to 10 ° cooler than either of these and it is not. Indicates too much cross weight.

RR to Rt ft temp avg should be 10 to 15° cooler. It is borderline.

The lft ft avg should be 10 % cooler than the rt ft avg. NO way. Lft ft not carrying its weight. Way too cool.
Shackle- we want the shortest possible shackels we can use. This prevents lateral distortion between the spring and housing.

You want the rear spring eye to be slightly to the rear of the frame shackle hole. It is acceptable to have it directly under the frame hole but slightly angles is better. You need this to prevent suspension bind.

One thing to measure is to see if you have rear steer. How much and is it rear over steer or under steer?

How you mount the springs relative to the track will make big difference

 

[shawn wyatt]

Thanks for the insight on the shackles, have them with front spring eye up 1 inch from parallel to ground and long shackles in rear, took easy way out by bad advice and time in off season was short from the time they outlawed rear coil in our division. rear eye are splayed outward from lower eye by 1 inch each side, so to act as at trailing arm, i saw slight offset / twist in long shackles on both sides and knew i needed to do something to help, right now it is easier to do the work with the fiberglass body off, thank for the insight, 20 years of racing coil springs and forced to go back to leafs was a kind of kick in the pants. any other thoughts please feel free to tell me, never to old to keep learning

 

[Ranger Mike]

shawn, i do not like the splayed setup as it will produce different arc movements. I recommend parallel mounting. Put some rear roll over steer int he car to help it turn. Get the front roll center offset correct. Shackle twist is not foe the competitive racer. We want clean droop and no bind on left side, smooth compression and longer wheelbase on the right rear.