Automotive Race car suspension Class

[Dirtracer8]

Good stuff right there.
4 link info.
Come on may 12th let's go racing!

But for real , good info ranger.

 

[GREG STOEHR]

first time poster ,long time reader,im not and engineer ,but thirty plus years wrenching and building race cars,we race winged midgets on pavement,im building a new car fro my daughter,tired of running cookie cutter stuff,will be a wishbone rear susp with panhard bars,74 inch wheel base ,65 inches wide front and rear,56% left side ,I know you need more info,will supply as it comes,but my question is this,im going to run rear wishbones with torque tube,live axle,6 inch offset,most tracks 3rd mile or less slight bank,cars are 1100 lbs,400 hp,what is your advise on anti squat,(how much upward angle for rear wishbones,wheel travel runs about 3" at shocks,mounted on birdcages,also would jacobs ladders front and rear be a better choice(weve tried on last chassis,but she says she can't feel the car as well as with a panhard bar)sorry I am not supplyong as much info as you need,,,lmk how to help you,help me,,,thanks guys

 

[Ranger Mike]

greg, thanks for the kind words

im in airport heading to europe. do not have access to my notes..from memory, i do not like anti squat. i like parallel linkages. when you add in weird angles during suspension travel this adds odd ARC and it complicates trying to tune in a set up.you have torque tube to control rear end hook up. jacobs ladder is good but the rapid instant center change compared to the panhard bar set up. as i have said many times, anyone can learn this it just takes time and buying a few books...get the suspension software program best for you car and use it. i would run the cookie cutter set up as it works and the head aches trying to figure out if the problem is the car or the drives techniques is a hand full let alone re-inventing the wheel. so avoid jabobs ladder, stick with tried and true set up and fine tune the tork tube.
my opinion

 

[GREG STOEHR]

thanks ranger mike,that was fast! so the torque tube provides the anti squat through the motor plate? or with a torque tube setup the rear geometry(I will use parralle bars for this question)the rear geometry would only influence rear steer(wich would only create bind at the torque ball ,not good)in all my experience no binding would be more advantagious than the limited amount of rear steer that i could build into this setup,sorry if I am confusing,and thank you for listening this is an amazing resource!

 

[Ranger Mike]

you can set up tork tube so it is pretty neutral non binding.

see Passmore Racing Dirt Late Model Torque Arm Video post 1200 on page 60

 

[Dirtracer8]

Ranger I don't think sprints can run a "lift arm"
I could be wrong..
I'm actually not real sure what sprints run in the pull bar or lift arm aspect. I know they use the "torque tubes" and torsion arms as a spring on rear. But what keeps the rear end from rotating on the birdcages?
Can anyone chime in?

 

[mikey531]

I have been using this forum as my setup bible for almost 4 years now. We have been removing weight from our pavement modified, and so far have taken out 74 pounds from the car. We just moved the 22 gallon fuel cell ahead about 2 1/2 inches. We are hoping it will help balance the car or did we waste our time? I also can't find how much axle end play in a Winters quick change axle. I have slightly rounded the bolt head but no idea how where to set the bolts for proper end play

Thanks!

 

[Work Hard Play Hard]

I just signed up and this is my first post. Why I joined was closed but I found this topic and I haven't read all 61 pages but there are obviously some sharp participants here. As I scanned the 61 pages instead of racing I'm reminded of street rodding and lost friends that believed suspension issues(among many issues) are solved with someone's catalog. That new Mustang 2 front suspension geometry doesn't match the stock geometry regardless of convenient fabricating or what the supplier says. Replacing a straight 6 with someone's big block will have some effects also on frame and suspension considerations.

Ranger Mike, I don't know anything about "Suspension Analyzer," but I have a question about your statement, "The first critical thing to do. . .." A chicken or the egg question and your opinion, design a suspension to match a tire application range or choose a tire application range to match a suspension design? Drivers have preferences and sponsors have expectations.

 

[Ranger Mike]

i am in Germany now..left merry old England yesterday..welcome work hard...

mikey,

that 2.5 inch can help a lot. try to find your polar moment and mount accordingly

dirt...of course you can run lift arm on bird cage..you are not limited in this respect

 

[Work Hard Play Hard]

Ranger Mike,

I Don't know if this is appropriate here but what's up in Germany? Are you there to race? Work? Other pleasures?

Fortunately I have zero issues concerning tires except for the family cars and pickup. My question was a chicken or egg question for your opinion because of your experience. My inner geek enjoys seeing, hearing or reading about the different processes people use in doing their job or avocation in racing and how the process developed..

 

[RaceMan12]

Ranger Mike,
Thank you so much for all the info on here ! I've been reading it over the last few years and coming back often for refreshing.

I'd like to know if you could tell me what you think about running a shorter wheel base on the left side ( left front back ) on an oval track car ? We race a car like drobbie ( and actually his boy has driven my car) on many different tracks throughout New England. Also if possible could I get your thoughts on setting caster from the lower struts or our slotted upper control arms, we have done both but over the years I've had many people tell me it's best to have the lowers square to your cross member and shim or slide the uppers , for years we didn't have those slotted uppers so we just shimmed the control arms like we do on passenger cars.
Sorry if I missed this somewhere .
Thanks!

 

[Ranger Mike]

Thank you for the kind words Raceman

I personally like things square , straight and level on a race car. Things like lower A-arms being level but not necessarily equal. So I have always dialed in caster at the top. As far as a non-square wheel base car, the whole point of making the suspension work is to have both front tires working the same. That’s is why I am a fanatic on proper Roll Centers and the right front tire down load. Offset wheel base means you are running a non-square rear end or the front spindle has be relocated and the steering linkage and Ackerman, bump steer and the like has to be re-worked. For me , too much head ache. And you know the chances of a wreck with front end damage is big. Over the years and beers, I tried a lot of wacky ideas to get the car to win, pick up a half second. For ME, Sticking to the basics is best. Get the car to turn in, roll thru and properly exit.
But hey, racers are a creative lot...good luck..
My opinion..

 

[Ranger Mike]

Your question about wheel base offset triggered a brain cell on a problem we cured back in hobby stock days.One area you can get a huge advantage and will never be called on by the track tech boys is Axel Stagger. We have to run a locked differential in these classes to get maximum acceleration off the corner.

Wheel hop or on throttle “PUSH” occurs when you nail the gas and the car wants to head to the outside wall. You cut the wheel to the left to compensate.

If we could reduce or eliminate this In street stock and lower horsepower classes this can be significant.

For years we added stagger to assist this condition but run head on into stagger growth.

Even with nitrogen you still will grow stagger and race cars hate variables.

One way to compensate for this is the make sure the 3rd link is properly mounted at correct % weight bias. This will help a bunch but is not curing the problem.How do we get the maximum power to the ground off the turn with a locked rear end?

Let us look at the mechanics of this. We have maybe 575 H.P. to apply to the track (dirt or paved). This power has to go thru the 9” Ford read end and to the tires.

The axel shafts that come with that Ford 9”‘ rear are way big for the HP you are limited to. Over engineered you might say. Yes the dang things are bullet proof but the name of the game in these classes is to out fox the competition and not get “ caught”.Typical 9” Ford rear end means you have a left axel length of 28.5” and right axel length of 32.5”. Both axels are the same outside diameter. This means the under acceleration, both axels will not respond ( twist ) the same because the shorter one will hook up before the longer one. You have a 4 inch axel stagger and the car will throttle push on corner exit. On re-starts the left rear will break traction first.One thing we can do is make the right rear axle diameter thicker than the left rear. This will equalize the twist and reverse this throttle push or loosen up the car vs. a throttle push off the turn.One trick is to run a solid axel on the right side and gun drilled axel on the left. This will affect the on throttle response. Not recommended unless you re big on H.P. like over 600 hp.Do not forget that you can twist an axel in two if you race out of the pits and nail the gas with one wheel on the pavement and one on gravel. SNAP.

So do some web work and consult the race car axel manufacturers and look at this for future planning on the rebuild.

You risk this even more once you cut down the outside diameter of the axle form “ stock” dimensions. But hey, it is an advantage.

 

[RaceMan12]

Ranger Mike,

I'm not at my shop but I believe we have about 2 inch difference in axels length , we only have a about 300 hp and the car weighs 1900lbs . I'm thinking that that would still apply to some point. One of the very accomplished chassis guy's I work with a lot likes to get as much weight up on the left front to keep weight on it so he's told us to move it in and back on his chassis's , I've always thought that might keep more weight on it through the turns. We've done very well with my boy's car and really haven't moved the left front as much as we have in my bigger car.
One other question or opinion I'd like to get is on the roll center in the little car I've got it to 2.2 right and 2.2 up with the spindles and upper mount we have, I can get it over more but then it migrates a lot to the right on drop, I believe it would be better not moving so much and leaving it were it is for now ? The roll center pic is close but not exact one the finale one is on my shop computer .
Thanks !

 

[Ranger Mike]

raceman
how much track width are you limited to? You have the exact tool you need to finalize the front roll center and migration. I plugged in your numbers and got closer tot eh 3 inch offset and kept migration under 4.5" by playing with the track width and left lower ball joint height. I increased it. You can do this by milling off the bottom of the spindle. Maybe " 0.050" and you can lower the top left ball joint height by milling off the top of the spindle. You are on the right track.

 

[RaceMan12]

Ranger Mike,

Rule Book:
"Chassis Offset: The center of the chassis is measured between the front frame rails. All cars must have OEM type upper and lower ball-joints. Chrysler screw in, GM and Ford bolt in types are allowed. No spherical rod ends are permitted to replace ball joints. A maximum offset of 10 inches is allowed at the left side chassis rail. The inside of the left rear tire may not be any further to the right than the inside of the outermost left side chassis rail. The driver’s body must remain within the frame rails and the roll cage area. Door bars may not extend more than 6 inches outward beyond the outer frame rail. Maximum allowable track width is 76 inches, measured to the outer sidewalls of the tires."

I did fool around with the left side chassis height and got it to the 2.2 right / 2.2 up and very little migration.
I think I'll have to go with what you are suggesting to get it better. It's funny the Performance Trends software won't give me the camber gain on my laptop but works fine on the desktop at my shop,I may have to uninstall it then reinstall it's nice to have it at home to fool around with at night . Thanks again for the suggestions !
Heading off to to a much warmer place for 12 days tomorrow night so I'll let you know how we make out when I get back .

 

[Ranger Mike]

are you currently running 63 inch track width? can you increase this one both sides? can you add 2 inch to each side? remove 2 inch? what offsets are you running on the tires? what is rigth side tire width? offset? left side?

 

[RaceMan12]

We do have track width at 76 , it comes out on software as 63 but because of the center of chassis to center of contact patch ( Hoping that is right?) I guess that measurment could be off a little and when I get back I'll double check it. , the offsets are 2 inch rights and 4inch lefts and we are at 60% left side weight which is limit.. wheels are 11inch with 10 inch wide tire ( or contact patch of tire) we do have 1/4 inch spacers we use to get maximum track if it needs to be adjusted but right now it's close .

 

[Ranger Mike]

go enjoy the tropics.. i will play around a little on software..i would rather have the RC work properly and nix little left side weight.

 

[Work Hard Play Hard]

RacerMan12, If you have the time before going what are your caster angles? Lead? Also, what exactly are you referring to with "swing arm?" How long are the tracks your running on? Might as well ask about the banks too. It would also be helpful if your son, as the driver, can give an indication about how far he is turning the steering wheel in the turns. 12 to 15 degrees? 20? If the car alignment is being setup for 30 to 40 degrees, performance may be getting traded away for nothing in return.

 

[von klit speedshop]

great stuff Ranger Mike

Are you still in Germany? We could use a good guy to set up our race car!

 

[Ranger Mike]

Well Thank you very much...it is nice to be appreciated..long gone from Frankfurt area. but
I'll be back!

 

[John LNZ]

Hi Ranger Mike
I have a query please. What are the effects of the front roll centre migrating either right or left during roll? I know it will change the loading of the front tires but would like to understand it further. Thanks John

 

[Ranger Mike]

Hello JohnL

We took an old refrigerator to the city dump one time. (after removing the electric motor and vacuum pump. We used to suck the tires of all air before replacing with nitrogen.)We dropped the tail gate of the old pickup truck and pushed the huge heavy refrigerator to the end of the bed. We picked it up and tilted it upright when the tail gate gave way and guess the outcome?

(the edge of the tail gate being the Roll Center in t his example)The whole mass of the car is rotating about the front roll center and rear roll center in body roll. If the RC is moving, it makes things difficult. We have down force on the right front tire either overloading or diminishing. It is a big unknown variable. The down force is out of control and now we can not adjust things to make the car turn because of this variable. The perfect scenario is to have the RC stable and not migrating. In real life if you can keep it within an inch (25 mm) you should be ok. I always map out the RC migration in roll to see where it tends to linger. I then adjust the initial setting to get best result for paved or dirt track as required.

 

[Tyredone]

Hi there, was hoping you can help me? I talked to you maybe a year ago, about an old 70's 6-cylinder race car. I want to put a v8 in it, change steering box to rack, fit 9" in rear with 3 link suspension. Your suggestion was to buy a couple of Steve Smith's books, which I did, and they have been very helpful thank you. But I'm still unsure on a couple of things. A little more info on car: it would be like a 4-door 70's Camaro, it's made in Australia, right-hand drive. I am building it for asphalt flat track racing, with left and right hand corners. The car is an empty shell. I have cut out the rear floor and existing frame rails, and fabricated new rear frame rails, etc. I am mounting a 9" diff with 3 link suspension; the housing is pinion centred. My first question is: Is there an ideal bar length for the wheel base - which is 110"? And the other question: The offset of the top link on the diff - you had recommended to work it out on wheel weight percentage and track width - however, as I am unable to corner-weight it @ this stage, I'm not sure how to work the calculation. My track width is 55", and I am hoping to have the rear fairly evenly balanced. If you could help that would be much appreciated. (Please let me know if you need more info to go on.) Kind regards, Pierre

 

[Ranger Mike]

good to hear from you again..
since you are turning left and right ,set the car up neutral with 50-50% left to right and maybe 52% rear weight bias.
The longer the trail arms you have the less dynamic change you will have on the rear end.
Locate the top link at center of the track width. Make sure you check bump steer and Ackermann up front. Center the RC. Get good camber curve.
Wheel scales are your best bet when building the car from ground up as you are doing. Engineer the thing to be easy to work on too.
Make sure no rear roll steer in the rear end.

Get on any SCCA forums for your class car and see what the hot dogs are doing on road course set ups.

build it wide and light then add in the ballast to make weight for class you are running.

 

[drobbie]

To follow up with John LNZ's question. When you speak of migration within one inch, I assume you are speaking about 1 inch left or right and not up or down.
From my studies RC movement in a straightline up and down is the optimum. Am I correct?

 

[Ranger Mike]

The 1 inch rule of thumb is strictly a ball park rule I made up. I do not have the time to tweak the race car to be perfect nor the dollars to buy/fabricate the goodies needed to make it perfect.

RC movement to the left or right will add downforce or take away down force on the right front tire. One inch migration will not hurt us and depending upon which way it goes may even help.The formula car we run has 2 inch RC height centerline and dropped to .9”, ran great.Assume a 2800 pound late model, 112” wheelbase, 66” track width, Center of Gravity (CG) = center of gravity and is 13” height.

If we have the Roll Center located in the centerline of the car, 66” track width, RC is 33” from each tire centerline.This 2800 pound car has 56% left side weight. Subtract the unsprung weight and we get 2100 pounds sprung weight. I am assuming things are pretty symmetrical so we will use 56% of this unsprung weight or 1,175#.If the RC was centered it would be located 33” from each front tire centerline and theoretically, we have ½ of the 1,175# or 587# left side sprung weight pivoting on the roll center and going to the right side slamming on the tire. (If the RC is located to the right by 3” we now have a lever between the RC to the tire centerline 3” longer on the left side and 3” shorter on the right side.

36/66= 55% so in effect we have increased lever by 5%. Now we have 55% of the left side inertia force thru the RC planting the right front tire.

55% is 646# so you get 60 # additional down force.Now add an inch of offset to the right 37/66= 56% and this adds 12 pounds. The point is we need to use body roll to create down force (not applicable on BBSS set ups). If we get too aggressive with the RC offset we start to lift the left front tire.So far this is all speculation. Let’s plug in some real numbers.

Weight Transfer due to body roll

First of all, by now, you know I hate the term “weight transfer” but since I poached the illustration off of http://www.autozine.org I will use it since they did a great job explaining it.In this example Weight is both sprung and unsprung weight.Lateral displacement of the CG is d. In this case, d = CG height in inches x sin of roll angle. Sin of 3° degrees is .052, sine of 5 ° is .088 sine of 10° is .173 and CG height is 13”If this racecar rolls over 3° we have .052 x 13 = 0.676Weight transfer to the outside wheel is (Weight x (RC location + d)) / track width2800# x (33” + 0.676) or 2800 x 33.676 = 94,29394,293 / 66” = 1,429# on outside wheelsCouple of things about this drill, folks. The Roll Center is assumed to be on the ground. Note the fact that we use the Sine of the angle of roll to find the additional length of the lever arm and add it to the RC to tire centerline lever length.Compare this to the Race car with centered roll center and no ° roll.2800 x 33 /66 = 1400 – conclusion, 3° roll gets you 30 pound down force, big deal (actually we should do the math right and figure exact RC location to get the true picture but hang with me here..)When we offset the RC to the right 3 inch and calculate

2800 x 36 / 66 = 1527 poundsAdd in 3° body roll and we get 1,555 poundsAdd 5° roll and we get 1,575#

Just for kicks that super dirt late model with 4 inch offset and 10 ° roll
2800 x (37 + (13 x .173)) = 2800 x (37 + 2.49) = 2800 x 39.49= 1,675#
What this tells us is the Roll Center location is important. One inch movement won’t hurt too much.

 

[drobbie]

Great explanation and example. I can now use this to understand what happens with my car. Thanks for the awesome info.

 

[Ranger Mike]

thank you Drobbie, all you all can figure it out as i got a lot of it from books and web sites. I just cut some corners and brought it to you a little quicker.