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.

 

[Ognib]

Hello Ranger Mike. I found this forum a couple of weeks back & was excited to discover this thread.

I'm an old goat now, 70 yrs, and have been working on & "building" my own cars since the age of 14.
My favorite rides have always been the corner cars, which up to now have been limited to tuning stock suspension pieces, as much as possible, with bars, springs, adjustable shocks, tires, etc.

Decided to push it to the next level & am in the design stage of a formula SAE style open wheel car like the college kids build.
I've been welding & working with steel all of my life, so feel confident in my abilities with the cage, engine placement etc.

I've been studying Smiths book, "tune to win", & noticed that in many of his suspension illistrations they are shown with IC outside of the tires.
Your suggestion that this point should be about an inch inside the lower ball joint has left me somewhat confused over the differences in approach to the situation.
Was hoping you would expound on this a bit further & help a noobie wrap his head around the design & layout of a basic, workable first time scratch built suspension.

Many thanks.

 

[Ranger Mike]

Thanks for the kind words and welcome ..nice having a long term wrench chime in!

Steve Smith is excellent in his explanation of Instant Center (IC) width on page 19 of his great book, Paved Track Stock Car Technology.

His advice on IC width states his recommendations presented for Roll Center Height and IC width take into account all considerations on body roll and right tire contact on corner entry and mid turn.

His book is focused specifically on Left turn round track racing.Carroll Smiths excellent book is for the left and right turn chassis design and build and is correct as well.

IC widths controls how the RC acts in body roll. Wider IC means less camber gain. Narrow IC width means radical migration both on location and height. This effects right front tire load and we want to add down force on the rt ft tire to make it grip.

You do not want to bias the right front on a road course as this can make things slightly interesting for the driver.

On road course you want wide IC to minimize RC movement and camber gain.It depends on which pig you want to roast!

 

[Ognib]

Thanks for the clarification. I went back & re-read some stuff & there were a couple of things I had not retained.

Going to do a 2 dimensional model out of poster paper & play with it a bit to help me visualize how this all works.
With the small size of the formula sae cars, I can build it 1:1 for good perspective.

 

[Signguy]

RM,
I've been lurking on these pages for at least 5 years, learning and applying some common sense and mathematics that I learn wherever possible. Thanks for taking the time to share.

We as a group have been asphalt racing for 30 years, with some good success and several periods of no racing at all due to more important life issues. Currently, my group has been part time racing for the last several years with a super late model chassis under several rules packages on 1/2 mile and 1/4 mile tracks (14-18 degree banking). We had little success in tuning the car to have speed or just better tuneability. The engine made good horsepower but has iron-heads with a heavy block. It was Ford package with a Dart block, N35X heads, dry-sump and was nearly 35lbs heavier than a comparable steel-head Chevy. More than that against aluminum-headed engines. At the lower weight rules, we couldn't get more than 49.5% rear and at higher weight requirements we couldn't develop the comparative speed we thought we needed. I raised/moved the RC and tinkered with many other adjustments with no real relative speed improvements. We have subsequently developed a lighter weight engine package, having blamed some of our ills on the engine mass. Our first visit to the track with the new engine was very encouraging.

My question relates to cornering performance as it relates to engine mass. I happened upon thread about Formula Ford racing where the discussion centered on the aluminum vs. steel head cornering performance. It was stated there that on a road course the lap times would be measurably different just from the mass difference of the heads (assuming equal HP). Using some math and Performance Trends software I can see some statistical backup for my conclusion, but not necessarily the entire performance gap. What is your experience with trying to compete with heavier engine package, all other things being equal? I understand geometry and rear-steer gimmicks can't fix mass problems, but I'm just trying to make sure I'm not missing something before re-configuring a nice engine over handling concerns.

Thanks again!
---Signguy.

 

[Ranger Mike]

og, you can get a good idea with the cardborad cut outs but...circle track analyzer is $175 and a must. period. you would not want to try an engine rebuild without a good torque wrench would you?
the software is a must.

 

[Ranger Mike]

signgy welcome...we ran class a few sized up from formula ford. There a big brew ha ha about running an aluminum head. Lower swing mass, lower CG bigger hp (not). Like i predicted, the HP was down when forced to run the same compression ratio as the iron head. All the pros went back to the iron and we kept our. My main thing is the head gasket issue on the al head. We won many many division championships wit ha formula car that was constantly 20 pounds over weight.
do not take this the wrong way but..have you changed drivers? has another racer hot lapped the car to see if maybe it is technique?

 

[Signguy]

Well, the driver is very experienced. We also had 2 other drivers practice the car with the same conclusion. I measured, calculated, squared, plotted everything and never got a glimmer of hope that we have been headed in a positive direction. This winter we cut the car up and put it back together with a new rear clip and an aluminum-headed engine. Now we are in the speed neighborhood with some tuneability, but we are wondering about the direction for the second engine. For the classes we run it's almost as economical to buy a crate/sealed engine than it is to build up a set of full race aluminum heads comparable to N351's.

My conclusions ranged from "can't run against 2700lb cars at 2750 and only 49.5% rear weight", or "N351 heads/dart block are heavier than a stock engine", to must be something stressed or bound on the chassis.

I vaguely remember a Gary Balough story that had him running a brand new concept car (Dillon maybe?) that had a composite tub as a stressed member. Supposedly they couldn't get the car to perform until they cut it loose from one of it's mounting points. I know that we want to control motion with our suspension components, however, and that's why I'm doing the post-mortem.

I read from your answer something that reinforced a tip I got from a spec-Miata racer. 10 or 15 extra HP in factory spec class that features 150hp max... is hard to beat in the corners.

A related question, in my PT software, I set up my points off a marked chassis centerline. When we talk about the RC location, and your conclusion that ~3" right is a good starting point, are you referencing a geometric center of tread, or 3" from the lateral CG location? Right now I'm 3" Left of geometric, 2" right of CG. I'm setting up test configuration moving it further to the right. This assumes I am fairly accurate on my CG approximation. My apologies if you went over that earlier, I couldn't find it.

signgy welcome...we ran class a few sized up from formula ford. There a big brew ha ha about running an aluminum head. Lower swing mass, lower CG bigger hp (not). Like i predicted, the HP was down when forced to run the same compression ratio as the iron head. All the pros went back to the iron and we kept our. My main thing is the head gasket issue on the al head. We won many many division championships wit ha formula car that was constantly 20 pounds over weight.
do not take this the wrong way but..have you changed drivers? has another racer hot lapped the car to see if maybe it is technique?

 

[Ognib]

No, I would not do an engine without a good torque wrench...you have convinced me of the need. However, when reading their web site, I see circle track mentioned but nothing about road course or autocross type cars. am I missing something? My build needs to turn equally well in both directions.

 

[velocity_boy]

references _ Paved Track Stock Car Technology by Steve Smith
Tune to Win by Carroll Smith
Software - Suspension Analyzer by Performance Trends
In order to understand the complexity of a Formula Cars suspension, a basic knowledge of the stock car suspension should first be mastered. When designing a (front) suspension , geometry layout is critical. spindle choice and dimensions, kingpin and steering inclination, wheel offset, frame height, car track width, camber change curve, static roll center height and location and roll axis location are major factors.
The first critical thing to do is to establish the roll center height and lateral location. The roll center is established by fixed points and angles of the A-arms. These pivot points and angles also establish the camber gain and bump steer.

I have used Suspension Analyzer for years on Super late Model stock cars as well as formula cars and it is as critical as a tire pyrometer and stop watch, in my opinion..Saves tons of time figuring the roll center and will show the roll center movement as the suspension moves through its travel.

You say you worked with F1 cars?

Then you're aware no doubt that their suspension is even more complex than you mentioned?

Did you know it is also computerized? And involved telemetry? Where it can be tweaked during the race remotely by the drivers crew? According to what comments he may make about the cars handling during the race? And that, like tires and aerodynamics, as well as braking system, the suspension and other chasis components can be altered before each race, depending upon the track and weather conditions. Also due to the particular strategy the race team will employ during the race.

Did you know that the downforce of an F1 car is such that it can pull manhole covers up and send them flying? Or that the cars at full speed could actually drive upside down?

Yeah...you could say I'm into racing a bit! LOL. F1 and motorcycle, mostly.

NASCAR bores me stiff.

 

[Ranger Mike]

Og, suspension analyzer should have all the capabilities but is true 3 deep so you must measure mount location height , offset and front to rear position. This is a must for road course cars.

Sign - on road course i always use the vehicle center line as everything must be symmetrical. On round track racing, i use the vehicle center line since the engine will be off set a least one inch if not more and the wheels will be whacky non symmetrical off sets. Dirt track racers swap out wheels with a lot of offset changes as the track changes. Same with paved track.

I use a center line calculated from bottom ball joint centers. I paint a center line at he bottom frame, top frame rail and anywhere else i can access.Signguy - if you find the RC is to the left of center as you indicated..you may have located one problem.
Has the car ever hit the wall?
Have you ever checked the rear end ( assume 9" Ford) to see if it was bent?
This is one very often over looked area that will really screw you up. You have to remove the entire rear end from the frame, leave the wheels on both sides. You need to scribe center lines on both tires.
Measure the center to center distance.
Flip the rear end 180 degrees and measure.
do the same at 90 degrees so you have checked the rear end at each 90 degree position.
Many times you tape measure the rear end thinking it is ok but it does not show up until you actually remove it and check it.

 

[Signguy]

Signguy - if you find the RC is to the left of center as you indicated..you may have located one problem.
Has the car ever hit the wall?​

The QC has been checked regularly. It has aluminum tubes, cambered snouts and a bridge so checking it is a routine maintenance item. We'll run again soon so I'll update you on performance. Next testing item will be running a smaller KPI/SAI spindle on the RF. Seems that it's commonplace now, but I've never tested it "back to back".

 

[Ognib]

The formula SAE cars as built by the college competitors are smaller...usually 75 inch or so wheelbase with 50ish inch track width.
This is the general format I've chosen to use as reference...a smaller build is less expensive than a larger car...I'm retired, you know, & on a bit of a tighter budget than in my younger days.
But I've got to build something...I'd go nuts without it.
I'm doing some preliminary drawings on the project & the question has come to mind as to the actual length of the control arm links.
Is their a ratio for determining this relative to wheelbase & track width. I've looked for this but so far haven't found anything.

 

[Ranger Mike]

Og...are you asking about front or rear? are you using 3 link rear suspension?
Are there any governing rules on this area?
in general, the best geometry you can have is equal length and parallel links. The next best is unequal length parallel links and least desirable but most common is the unequal and non parallel set up. How much room you got to hang mounts and provide proper travel and clearance for coil overs will dictate what you end up with. This is why the chassis software is critical.
Dwarf cars and Legend cars have 73" wheel base and about the same 50ish track width. They use 3 link and run paved and dirt. i would research those for some start info as well. Good info on anti squat and instant centers.

 

[Ognib]

I'm in chapter 4 of "Tune to win", suspension geometry. It seems that the double wishbone 4 link is where it's at. Both front & rear. With a wider base.
I'm still sorting through what he has to say about the different combinations & configurations.
What he does say that has stuck with me is, "I believe it's a lot more important to get the roll center locations & movements happy with each other & with the mass centroid axis than it is to get the camber curves perfect - which we can't to anyway."

There are no governing rules to deal with. This is entirely for my own enjoyment & learning.
The only person I'm interested in competing with is myself.

At this point, the chassis & suspension are a blank sheet of paper so I can design as much or as little space for mounts as needed.
I'm not planning on wings or body work on the car...just a bare bones tube frame/cage with steering, suspension, brakes & power train.

 

[Ranger Mike]

PegasusAutoRacing.com
save a ton of time and searching if you are custom fabbing everything.

 

[Vintageracer13]

I just wanted to report in. I had my first race May 13. I had cooling system woes so I didn't finish well but the improvement in the way the car handled was incredible. It felt very stable and didn't want to step out or push. Thank to Ranger Mike and the rest of you that have helped me understand the concepts discussed here. Next race is June 11 and I'm hoping for a good finish!

 

[Ranger Mike]

thats some good news..i am a tad busy this weekend as it is THE race weekend in the USA..

 

[Vintageracer13]

thats some good news..i am a tad busy this weekend as it is THE race weekend in the USA..

I am crewing a Little 500 car Saturday so I am super excited!

 

[Ranger Mike]

Whatever you are racing, the set up in the garage is critical. You have to do everything you can think of to eliminate variables and arrive at the consistent set up.

One major thing is to use that measuring tape for set up only. Paint a red stripe on it and store it in your section of the tool box reserved for crew chief. You know, to drawer with the pyrometer, caster amber gage, Rolaids.

Tape measures can vary up to ¼” over 3 feet…junk. Terrible. You can buy a certified tape measure form the manufacturer for about $100. I bought a 8 foot steel scale from a machine shop going out of business a while back. Had it certified by a gage repair shop along with a set of feeler gages. Bottom line is whatever you use, use one tape only and set it aside.Temperature will cause you problems too. Try to maintain it within a few degrees.

The linear coefficient of thermal expansion for steel is 10.8x 10^--6/degree Kelvin at 20 degrees Celsius (room temp). (Degrees Kelvin are identical to degrees Celsius except the reference level is absolute zero, or −273.15° Celsius, which is immaterial to this calculation. So the thermal expansion coefficient for steel is: 0.00000645in/in/deg °F

A 100' steel tape would be 1200 inches, and it would expand/contract 0.00774 inches per °F.If we have a temperature swing of 40 degree F (cold winter garage of 50 degrees F to hot summer day of 90 degrees F temperature change), a 100 foot steel tape will expand 100X12X40X(5/9)X10.8X10^-6, or 0.288 inches.A 50 °F temperature change would cause a change of 0.387 inch. This may not seem like bunch but it adds up to 1/32” at ten feet just by temperature.Rambling on, I cannot over stress the absolute requirement of a flat surface for car set up. If your garage floor has a drain in it, your floor is NOT flat. It slopes toward the drain. So you can not use it for set up. Find a flat surface to set up and scale the car.

Set aside a complete set of tires and wheels. Paint them red. Mark each wheel with your race air pressure and mark which corner it goes to. Use them to set up car every time. Make sure to air them up. This gives the proper stagger /wedge you want. Use a stagger tape measure as described above. Hoosier makes a good one.

Mark the frame in back of each front wheel and in front of each rear wheel. I use a paint pencil from NAPA. These are your bench marks for ride height. Cut 4 pieces of 2 x 2 tubing to it under these marks. Paint a mark on each set up riser and store them with the red tires. I have two sets, one is for set up one is for the pits. Really saves time if you get wadded up in the heat race and have to quickly re-establish the set up.

I bought a set of tractor weights from a farm implement dealer to replicate the drivers weight. Was a lot easier than using 40 pound bags of salt. Was way cleaner than using bags of grain! BTW, the joke was the tractor weigths had higher IQ than my drive.

Don’t forget to top off fuel tank when scaling. Unhook all the ARB (sway bars).
Don't forget cardboard box for Trophy.

 

[drobbie]

Great Post Ranger Mike, I can't tell you how many times I see teams make small mistakes on t consistency, especially with stagger tapes. Those things stretch easily, or even worse I see one guy with one tape measure on each tire and their yelling across at each other the numbers.

I like the tractor weight reference to IQ, for us it was the use of cinder and deck blocks because we could simulate the driver's position together (also having a 140 lbs driver means we didn't need many) See pic and yes there was a joke about who was better the driver or the concrete blocks.

Thanks for your continued words of wisdom.