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croston71
09-24-2011, 06:49 AM
;)
If you aspired to be a dirt late model chassis builder how would you go about the task?

1. Get a con senses of the generally accepted center of gravity & start with the left or right frame rail. No, start at the front & work your way to the tail. Possibly begin on the tail & run frame rails forward to the front.
2. Start on the outside & proceed inward assuring the center of gravity never gravitates while giving lateral reinforcement.
3.Position the center of gravity in the co-median & plot all intrigueal adjoining components!
4. Ask god !

hpmaster
09-24-2011, 07:36 AM
Do what I think most people do. Copy what you understand and know how to make work then modify and improve what you don't like or understand about that design.

croston71
09-24-2011, 07:54 AM
My thought is when a chassis builder/driver starts believeing he or she is going to make/force a defective design work/win he or she has already lost cause-train of thought!

MasterSbilt_Racer
09-24-2011, 08:40 AM
When you start from scratch designing any racing vehicle, you design the suspension first. Once you know where those pickup points will go in space, you design a chassis to support those points and to hold all the necessary components that it takes to move the chassis. I would design something that looks nothing like a current DLM.

croston71
09-24-2011, 09:05 AM
Again?! I think a point from which all other il-lust-rations can be attached in a logical & numerical sequence for form & function!:confused:

Ronin
09-26-2011, 09:58 AM
This is how I approached the design of our racecar:

Step 1 - study the rules to ensure you understand them.
Step 2 - study the rules again to identify any loophole that you can exploit to your advantage :p
Step 3 - design the front suspension keeping in mind the intended wheel offset as this will affect the suspension characteristics.
Step 4 - design the rear suspension allowing alot of scope for adjustments. Because your design works on paper (or CAD) it does not mean it will work in practice.
Step 5 - Mount the large parts in space to calculate the center of gravity. These include engine, transmission, fuel cell, radiator and driver. Also mount the shocks in space as you need to know where the mounts on the chassis should be.
Step 6 - design the chassis frame around everything else.

Cheers
Arno

hpmaster
09-26-2011, 10:21 AM
My thought is when a chassis builder/driver starts believeing he or she is going to make/force a defective design work/win he or she has already lost cause-train of thought!

First you may be very wrong to think a design is "defective" to start with. The constrants, large componets, construction materials and rule restrictions have already been addressed in virtualy all modern chassis designs. Trying to reinvent the wheel shows how little a designer may understand these factors. Check out the Cadillac CTS or the Ford GT 40 design stories.

EAMShater
10-04-2011, 12:51 PM
i cant wait til someone comes out with another canitlever car like the old custom chassis that frank mcclendon built back in i think the late 80's early 90's. now those were crazy. or something like the daytone prototypes with the shocks mounted over the rearend facing outward and the motor in the back with dual independent rear suspension. we cant stay 4 link forever. something has to be better.

zeroracing
10-04-2011, 10:15 PM
The four link we currently use creates a large amount of forward traction, all the other road racing types typically don't need to so have not been made too in the past. I am not sure how you could tune an inboard type suspension for the level of traction we need, in addition you would see a return to old old school flat cars, those cars get minimal body roll, to get large suspension travel the linkage would become too large and hard to fit within everything, given each pieces motion paths.

EAMShater
10-05-2011, 02:14 PM
I saw an old custom chassis car a few years ago in a shop owned by greg brown of phenix city and it was ran at EAMS back when they still ran supers on a reg saturday night and he and bobby thomas would go at it every saturday night. idk what king of suspension it was but it had rods that ran up and down behind the axle tubes and on the top connected to a shock somehow that ran horizontally in the car facing frontwards on both sides. it had a pull bar type deal in it over the rear end that was about 5 feet long in it that connected almost by the front of the deck on the frame and from all the stories i've heard that car was unbeatable at EAMS in the mud he and bobby thomas would turn lets just say 15.20's as an example and bobby would be close in the old jigalo cars but when it dried off that car never lost a bit of speed and would still turn the same relative times while all the other cars would fall off tremendously. i would just love to see that car run. frank was a heck of a designer and one of the smartest men in dirt racing. not many have heard of him but he and c.j. rayburn worked together alot from what i've heard and you can ask any chassis builder and tell them your from phenix city or columbus georgia and they'll ask if you know him or how he's doin. he now has nothing to do with racing(thanks to the Thomas family at EAMS i believe) but he does still do machine work at a head shop here in columbus. I am only 21 and have been racing full size late models for about 4 years and have sure heard alot of stories about him. Terrance Nowell is a good friend of mine and we go to each other's shops alot helping one another and he drove for him for sometime and he said his front ends to this day are better than any that you would ever drive and thats what made his cars. the rears were kinda crazy with all the cantilever stuff and all cause the man hated 4 bars and torque arms even tho from what everyone around here says he built the first of each and said theyre junk and still believes that to this day but the man could design a front end they said.

MasterSbilt_Racer
10-05-2011, 03:34 PM
The four link we currently use creates a large amount of forward traction, all the other road racing types typically don't need to so have not been made too in the past. I am not sure how you could tune an inboard type suspension for the level of traction we need, in addition you would see a return to old old school flat cars, those cars get minimal body roll, to get large suspension travel the linkage would become too large and hard to fit within everything, given each pieces motion paths.

I don't think a lot of forward traction is really needed. You don't need ANY if you don't slow down. A 4 wheel independent suspension car would smoke what we have today and it wouldn't be able to use a lift bar or pull bar.

MADCAPRACING22
10-05-2011, 08:17 PM
Thank you EAMShater dude! I have been screaming for years that I would like to bring back a Custom Chassis! Ricky Williams has one still that his son ran in crate. It was a 4 bar. Mr. Richard Turner had one sitting behind his shop that had some Rocket 4 link brackets welded on it. Dean Garland drove it and wrecked it. I tried to talk him out of it but my buddy Cowboy told me I was living a pipe dream trying to bring that rust bucket back. I wish I would have scooped it up because he sent it to the scrap yard. Them Custom Chassis were the thing back in the day! I thought Greg Brown was a Rayburn man in those days. He ran good at Seven Flags too! That Cantilever is very interesting and I think still has potential.

EAMShater
10-05-2011, 09:35 PM
Good luck getting frank to build one lol. From what I hear he don't even wanna look at a dirt track car. But as far as the Rayburn and greg browns I ain't sure. Too young to know. I just love hearing all the stories and I know what I seen in that shop was a custom chassis built by frank mcclendon with an all aluminum runion racing motor in it. But frank and c.j. were pretty close back in the day from the stories told. I would love to chop the front end off my bwrc and weld his onto it and see what happens

croston71
10-05-2011, 09:47 PM
I helped a guy who ran a cantilever(Rayburn Chassis)it was very interesting. I believe wieght may be a factor by today's standards. I remember the car being very difficult to push. I believe we may have been too soft on the spring setup = rolling resistance=poor gas mileage. I read that Indy cars use a cantilever setup in the front end turned sideways so weight may be able to be trimmed with composite materials.
4 bar is hard to beat but as I see it a guy who releases the throttle at corner entry allows the rearend to square itself when the lr is most desperately needed to drive the rearend to the right. I see the cars a a balance beam the control is put in the driver's hands by a properly adjusted front end. I guys I see at the track seem interested in the rear end only. Am I the only person who visualizes the the mechanical aspects in this manner?

MasterSbilt_Racer
10-06-2011, 08:40 AM
An Indy car uses a system with bellcranks that get the shock/spring combo up in the chassis and parallel with the ground. The advantage is that much of this mass becomes sprung weight versus unsprung weight. A cantilever is much the same concept. I have always been intrigued about building a dirt car with similar design ideas. You could easily build a car where the roll stiffness and spring rate at each wheel were totally independent adjustments.

dualdj1
10-06-2011, 03:42 PM
An Indy car uses a system with bellcranks that get the shock/spring combo up in the chassis and parallel with the ground. The advantage is that much of this mass becomes sprung weight versus unsprung weight. A cantilever is much the same concept. I have always been intrigued about building a dirt car with similar design ideas. You could easily build a car where the roll stiffness and spring rate at each wheel were totally independent adjustments.

Sounds like you need to get busy :cool:

It's an interesting through process though, cause there's only so many ways you can attach a solid axle to a car and generate thrust to move the car. It's all about positioning and thrust angles.

racin6mod
10-06-2011, 05:55 PM
I've designed and built my own modified. the first thing to do is get the rule book for the class and that will set your wheel base and alot of other points like motor set back chassis ht,wt even the width and from that you can start with the rest.I've take two years and used my old car as a test bed for some of the idea's. even won with what some might call off the wall ideas.

cassellracing24
10-06-2011, 08:27 PM
#4....I would ask God what Bloomquist is doing....:D

Ronin
10-10-2011, 06:27 AM
Sorry to focus on one aspect of this discussion, but here in South Africa our premier dirt oval class primarily uses independant rear suspension. The suspensions mostly come from road going Mercedes cars (mid-80's) as the components are very strong. Our racing is full contact, so cars must be strong. I know these suspensions are not the most effective as they are transfered straight from the road cars, but they are cheap to biuld and maintain.

There is a slow change towards 4-link rear suspensions. Our car will not be the first, but the few already running a 4-link setup is so much quicker than the independant cars. A 4-link car running an almost standard 327 is much quicker than an independant car running a 600hp+ 383. Keep in mind that we use 206/65/16 road car tyres, so traction is more important than power.

Remember that in an independant setup you cannot easily control the steering of the rear wheels. Also, considering the body roll you will most likely loose wheel contact area with the ground and experience large camber changes. Keep in mind that the j-bar adds side bite whilst the torque/lift arm also aids traction. It will be difficult to recreate these forces with independant suspensions. I am not saying that there is nothing better than a 4-link, but it will take some clever thinking to build a suspension system that is more adaptable than it.

Arno

gdaagent
10-18-2011, 12:54 PM
The problem with Frank is that he would never build the same car twice. Some may like that, but he likes to experiment too much. He could have been nationally known if he would have become a chassis manufacturer. It took him too long to build just one. I saw one at Mack Waugh's shop in LaGrange a few years ago. Old cantilever suspension.

He was very smart but never consistent. Experiment at someone else's expense.

gdaagent
10-18-2011, 12:56 PM
I don't think a lot of forward traction is really needed. You don't need ANY if you don't slow down. A 4 wheel independent suspension car would smoke what we have today and it wouldn't be able to use a lift bar or pull bar.

I don't see independent rear suspension working on a high banked oval.

Ghopper
10-19-2011, 05:41 PM
Independent rear suspension is the way to go if the rules allowed.

It would allow more fine tunning of toe/camber of the tires. The South American gentleman mentioned a verison of IRS that I am guessing is lacking the anti-squat we run now in the traditional 4-bars cars and therefore dynamic wedge on corner entry and exit.

Important qualities to look at are tire vertical load/toe/camber, overall vehicle dynamic wedge and torque vectoring (fixed in our case with tire stagger).


Ghopper

abe_05
10-19-2011, 07:15 PM
4-bar does have problems that we all adjust around. If you were to design a new chassis, you must start at designing a new rear suspension. What good does rear springs do in most 4-bar setups? On throttle springs are useless. Car is standing up on 4-bars which is loaded by the forward force of the rear end and springs are completely unloaded unless you are on a tight track were car stays rolled over on right rear but left rear is never loaded by spring on throttle. Rear springs for the most part controls corner entry and chassis roll. So changing design were springs play a more important part would be my first idea of attack. What if you could load springs on acceleration? By theory this would be best scenario. This would control car and make it more stable. Cantalever design might be a good idea with current 4-bar.

dualdj1
10-20-2011, 03:54 PM
I tend to agree with GHopper. Independent would be a world of difference, as you could make your geometry change on both rear wheels separately based on travel. IE, as car rolls over, wheel base either lengthens, shortens, or stays same, for desired effect.

Matt49
10-20-2011, 03:59 PM
Independent rear suspension is the way to go if the rules allowed.

It would allow more fine tunning of toe/camber of the tires. The South American gentleman mentioned a verison of IRS that I am guessing is lacking the anti-squat we run now in the traditional 4-bars cars and therefore dynamic wedge on corner entry and exit.

Important qualities to look at are tire vertical load/toe/camber, overall vehicle dynamic wedge and torque vectoring (fixed in our case with tire stagger).


Ghopper

This brings me to a point that I have often pondered. With as much as we can get the cars to turn these days with rear-steer, should we not be tuning stagger toward optimum camber? I look at rear tire wear and often ponder this.

supercomet32
10-21-2011, 06:56 AM
How many of you missed the comments of the indepedent not having the forward bite that the 4 bar has in real world test on cars in australia?....what part of that computes to some how two seperate side working seperately somehow work together to create more speed?....speed is the common denominator and one side deciding to do one thing while the other does something else just splits the possible horsepower distrubution effectively down the middle there has to be a trade off and in my opinion it would require more motor... you would be spending money on both ends....face it the 4 bar works and isnt a crutch. it works plain and simple...bell cranks work but once again adding more moving parts to the equation..JMHO

MasterSbilt_Racer
10-21-2011, 08:09 AM
How many of you missed the comments of the indepedent not having the forward bite that the 4 bar has in real world test on cars in australia?....what part of that computes to some how two seperate side working seperately somehow work together to create more speed?....speed is the common denominator and one side deciding to do one thing while the other does something else just splits the possible horsepower distrubution effectively down the middle there has to be a trade off and in my opinion it would require more motor... you would be spending money on both ends....face it the 4 bar works and isnt a crutch. it works plain and simple...bell cranks work but once again adding more moving parts to the equation..JMHO

The independent can be tuned to give you everything the 4 link does and more. I guess a big block mod wouldn't be faster with an independent front suspension?

There hasn't been any work put into it, so sure if you just bolted a wishbone suspension under a late model it would be slower. How many road course cars have wagon-axle rear suspensions? Do they not have to accelerate rapidly out of slow corners?

dualdj1
10-21-2011, 10:26 AM
the major difference between independent and solid axle is the lift effect you can get from the twisting of the axle itself (vs the standard way independent is setup). But since independent isn't used on dirt, no one has been able to play around with different ways to mount the center section to get the same lift effect as a solid axle. The center doesn't have to be mounted solid right where the center of our current solid axles are (as it is on say the mustang cobras or vettes, etc); it could be mounted on pivots with a lift arm to have the same effect as our current axles do. There are so many things you can do with independent, that while requiring a lot of learning, tuning and some creative engineering, would decimate solid axles.

racin6mod
10-22-2011, 03:12 PM
back in 82 my father owned a 4 cyl. stock car with an independent rear susp. I think it was out of a toyota car but my piont is it was fast as he$$ many night the driver had a half lap lead when the thing broke an axle or the hub flange. the design was for street us so it could not hold up to the side loads of a dirt track.but I think this could be done right if you over design the weak areas around the outer ends of the axles and drive hubs plus it took a lot of rear percent.

supercomet32
10-24-2011, 06:24 AM
how many of you missed that it had been tried tested and concluded that a independent suspension on an oval track dirt car DID NOT provide more forward bite that a 4 bar rear suspension. It has been done and does nto work and also those road cars that have an independent suspension have a power to weight ratio much higher than a dlm and is part of the equation.....like i said in my opinion if it were to work you'd need a drastic increase in horsepower to gues in the neighborhood of 1200 HP or higher if you keep the weights in the current configuration. their is effective HP loss to the ground in an independent setup. your turning to systems that increase the scrub off of your numbers makign it ineffective with the current motors in these cars. 850hp wont cut it. and even if you get all of that worked out the tires simple will not hook up on dirt/clay

MasterSbilt_Racer
10-24-2011, 07:32 AM
how many of you missed that it had been tried tested and concluded that a independent suspension on an oval track dirt car DID NOT provide more forward bite that a 4 bar rear suspension. It has been done and does nto work and also those road cars that have an independent suspension have a power to weight ratio much higher than a dlm and is part of the equation.....like i said in my opinion if it were to work you'd need a drastic increase in horsepower to gues in the neighborhood of 1200 HP or higher if you keep the weights in the current configuration. their is effective HP loss to the ground in an independent setup. your turning to systems that increase the scrub off of your numbers makign it ineffective with the current motors in these cars. 850hp wont cut it. and even if you get all of that worked out the tires simple will not hook up on dirt/clay

Where is this extensive test? An independent suspension will cause the drivetrain to have a 300 hp parasitic power loss? :confused:

sj valley dave
10-24-2011, 03:03 PM
I have to agree with MB Racer on the 300 HP parasitic loss! Either someone is just tossing info around out there and has no idea or is just yanking peoples chains...IMO...LOL

dualdj1
10-25-2011, 12:00 PM
how many of you missed that it had been tried tested and concluded that a independent suspension on an oval track dirt car DID NOT provide more forward bite that a 4 bar rear suspension. It has been done and does nto work and also those road cars that have an independent suspension have a power to weight ratio much higher than a dlm and is part of the equation.....like i said in my opinion if it were to work you'd need a drastic increase in horsepower to gues in the neighborhood of 1200 HP or higher if you keep the weights in the current configuration. their is effective HP loss to the ground in an independent setup. your turning to systems that increase the scrub off of your numbers makign it ineffective with the current motors in these cars. 850hp wont cut it. and even if you get all of that worked out the tires simple will not hook up on dirt/clay


Are you that dense that you think one test proves that it doesn't work?? All it might prove is that someone taking a road setup and putting it on the dirt doesnt work. The reason road race cars run such high power to weight ratios is because they have much more traction, it has nothing to do with losses in the suspension setup. There is no way possible that an independent suspension causes more than 15-20hp difference over a live axle, and I doubt it's even that much. You obviously don't know much about independent suspension.

EAMShater
10-25-2011, 12:50 PM
well I guess since an independent suspension causes a loss of 300 hp I need to take the motor out of my new can am side by side and put in a 350? Cause if what you say is true then the speedometer is way wrond when it says I'm running 70. It shouldnt even move if the suspension causes all that drag.. right? Just askin..

supercomet32
10-25-2011, 06:30 PM
the estimated HP number was just a draw from a hat what i was saying was that yes extensive testing of a Dlm chassis with an independent suspension setup had been done in australia and concluded that as it stands now there isn't enough forward bite in an independent setup like there is from a 4 bar setup. one the reasons being the hp loss not necessarily 300h[ but it was enough to drop considerable time on the stopwatch. my guess on hp was simply picking a larger number than the typical 900 950 or whatever because that much wouldn't do enough.at least to the power to weight ratio to equal the road race cars numbers that was brought up.

while the independent rear would let the tires have a smoother ride around it simply does not equate to faster times on the stop watch.

disagree all you want but their isn't anything on a independent suspension the tis going to launch a car forward nor allow you to corner like a 4 bar. the independent rear doesn't change the wheelbase totally changing your desired line around the track. also as you turn you going to have to lift more. the 4 bar lets you use your momentum to turn the car and get back on the throttle sooner which increases your corner speeds and as a by product dropping your lap times

TALON75
10-26-2011, 12:11 AM
I think it could work, we run a BMW 320i in our mini stock class(it was a former track champion car which won 10 of 13 races), 1.9 engine which i believe is the smallest CC engine in the class, the car gets through the corners better than any but the key is to not get it too sideways . With independant rear being able to toe and camber the rears independantly is a big help . Too me if the LM you tested struggled with forward bite then you were overpowering it and it could be better with less HP and being real smooth . what kind of torque absorber was used in this test? was the diff solid mounted? these are some of the first issues I would consider, solid mount your 4 bar car and see how well the forward bite works for it . Who did this testing?

supercomet32
10-26-2011, 06:28 AM
your comparing apples to oranges. no ministock has a 4 link in the rear. as for the differential from the article i read it seems the differential was solid mounted similar to the diff in a military hmmwv. the car had a 800hp motor from what i remember and running it side by side with another 4bar with the same motor it lost forward bite it also could not enter the corner as hard like you said it had to either slide it or slow down and stay as straight as possible thus giving it a serious disadvantage in the corner adn then it couldnt get up off the corner due to the drive lose.

other than the rear differences the cars were identical.

in their street stock type cars the independent rear is the norm and simply converting one of those cars to a 4bar drastically changed the lap times. .75+ sec faster or so on a the stop watch.

the 4bar allows you to stear through the corner faster using your momentum and the rest of the suspension gives much more forward drive. you just have to learn what to do with it to make it work.

TALON75
10-26-2011, 12:59 PM
I would love to see this article, where was it published, do you have a link?

MasterSbilt_Racer
10-26-2011, 01:46 PM
your comparing apples to oranges. no ministock has a 4 link in the rear. as for the differential from the article i read it seems the differential was solid mounted similar to the diff in a military hmmwv. the car had a 800hp motor from what i remember and running it side by side with another 4bar with the same motor it lost forward bite it also could not enter the corner as hard like you said it had to either slide it or slow down and stay as straight as possible thus giving it a serious disadvantage in the corner adn then it couldnt get up off the corner due to the drive lose.

other than the rear differences the cars were identical.

in their street stock type cars the independent rear is the norm and simply converting one of those cars to a 4bar drastically changed the lap times. .75+ sec faster or so on a the stop watch.

the 4bar allows you to stear through the corner faster using your momentum and the rest of the suspension gives much more forward drive. you just have to learn what to do with it to make it work.

A street independent rear is designed to turn equally well left or right. A street independent rear has zero anti-squat geometry. Anti-squat is where the forward bite comes from.

racin6mod
10-26-2011, 05:40 PM
the power loss thing is bs flat out! I would bet it really has less power loose over all. I have a vetter rearend in the shop now and the torgue required to turn the unit is with in a couple inch pounds of a 9inch 3rd member.the forward bite is were I think the problems would start showing up.if I remember correctly we had a 62 percent rear in a 4 cylinder car that was easy to get but with a lm it's a problem.

supercomet32
10-27-2011, 06:53 AM
you test is a static test when the independent rear is travelling through its motion range it uses different amounts of torque to spin.

for all the engineers here that think itll work please go waste your money doing a test that has already been confirmed.

im done talking either you get it or you dont. you probably also think a nitro'd ricer can beat 400+ hp on the street too right.

there are numerous reasons why the independent works in some cases and doesnt in others...on a dirt oval it does not work better than a 4 bar

MasterSbilt_Racer
10-27-2011, 07:57 AM
you test is a static test when the independent rear is travelling through its motion range it uses different amounts of torque to spin.

for all the engineers here that think itll work please go waste your money doing a test that has already been confirmed.

im done talking either you get it or you dont. you probably also think a nitro'd ricer can beat 400+ hp on the street too right.

there are numerous reasons why the independent works in some cases and doesnt in others...on a dirt oval it does not work better than a 4 bar

The 4 link was once confirmed to be slower than the monoleaf. The swingarm was once considered superior to both on slick surfaces. I would say the swing arm/pullbar is probably superior to the 4 link for "going forward", but what difference does that make at a place like Eldora Speedway?

This one off test proves nothing. Were the control arms mounted perpendicular the the frame rails? Parallel to them? Somewhere in between? Were all of these iterations attempted? Various amounts of anti-squat angle? Two wheels tied together cannot grip as well as two that are free to do their own thing. A dirt car needs more than forward bite. We are not drag racing. Food for thought.

You are correct that there is some power loss when the differential is driving a wheel that is at a 20 degree angle to the center of the differential. The amount of loss is going to depend on the u joint. A latemodel cannot use all the power it has, so that doesn't concern me too much.

Besides, when have the Aussies not been 10 years behind in dirt racing technology? :cool:

dualdj1
10-27-2011, 03:50 PM
im done talking either you get it or you dont.

All you have done is talk. I have not seen one shred of evidence or proof of what you say. You've provided no references, no credible numbers, and brought no credibility to yourself in this debate.

As MBRacer points out, there are so many different variables you can change, that even if you could provide us with the evidence of this test, one test still proves nothing. "Independent Suspension" is a broad generalization, the same as "Solid Axle" suspension (ie 4-bar, swing arm, leaf spring, tortion bar). How you apply it can be very different.

Ghopper
10-27-2011, 08:11 PM
Independent rear suspension....If it becomes legal, it will be faster in ~2years or less.

No one will waste time on testing it till it is legal. Other benefits are component lower replacement cost and safety. I dont want to write an essay on this...but involves decoupling and containment.

The solid axle only lives on because it is all we are allowed to run. Any previous dirt IRS test was done without our most recent knowledge. For example: did you know that F1 cars completely unload their left front tire when turning left under thottle? mmm - just like a dirt car (i say unload, not hang it in the air)


Ghopper

Ronin
10-28-2011, 06:23 AM
Unfortunately I was not able to access this site for a while and could not comment as posts were updated. I will post some comments below but cannot reference each relevant post....

If you were able to make an independent suspension differential rotate about itself (as a live axle does) it will not produce the same reaction torque on the wheels as a live axle does. An independent suspension differential will have to be mounted on the chassis, so the reaction torque will be absorbed by the chassis, not the wheels as in a live axle. This reaction torque aids traction and is controlled using a torque arm or pull-rod. Joining an independent suspension differential to the wheels will make it a live axle.

One advantage of an independent suspension is that you will be able to independently adjust traction and steering. On a 4-link there is a degree of change to either variable as you change the other variable.

Keep in mind that the j-bar ads a considerable amount of side bite to a dirt oval racecar. Replicating the effect of a j-bar on an independent suspension could create undesirable motion ratios of the outside/inside wheel (depending which side you mount the bar on the chassis).

Independent suspensions always have a degree of camber change as the chassis roles. Remeber that asphalt racecars do not roll as much as dirt race cars, so camber changes can be controlled much easier. The freedom of movement between the chassis and a live axle in a 4-link allows the rear wheels to always be in perfect contact with the ground as there is not camber changes.

It is always good to reduce unsprung mass. However, considering the suspension travel on 4-link suspensions it will be very difficult (dare I say impossible?) to use rocker arms to actuate the shocks. If you draw a rocker arm arrangement you will notice that the angle change makes it very difficult to maintain constant ratios. A system like this will require very large rockers which might become impractical.

ALF401
10-28-2011, 06:35 AM
All wheel drive car!!!!!! That's the real ticket in Dirt Racing's future!!!!!!

Ghopper
10-28-2011, 08:43 AM
Ronin - For IRS, rocker arms are not necessary and I would prefer not to use them.

I was looking for different camber and toe from my live axle, which had me drafting up a knuckle/tierod addition. Conclusion was that IRS would just be easier. Then I could mount the transmission to the differential housing, also allowing the driveshaft to be better shielded and less likely to evacuate the vehicle. Replacing some linkages in an accident is easier and cheaper than axle tubes and birdcages.

The current j-bar is all about dynamic wedge from lateral force (more angle increases wedge). The 4-bars are controlling dynamic wedge from longitudinal force and rear steer from resulting body roll (lateral acceleration dependent). We can make this work in an IRS. Most likely it will be more radical than the current asphalt setups. Much of this is determined by our tire and variety of track conditions.

We have optimized the live axle over the last half century to find what kind of wedge we need at corner entry and exit. I pretty sure we can figure out how to make the IRS work.

Sounds like fun.....should we start lobbying the sanctioning bodies now? I mean NASCAR is going to fuel injection, so anthing is possible!



Ghopper

Ronin
10-28-2011, 10:13 AM
Ghopper - the rocker comment was in reply to another post proposing to reduce unsprung weight in the 4-link setup by activating shocks through rocker arms like a single seater racer.

I understand the dynamics of a dirt racer and your comments regarding component costs. With 4-link the dynamic wedge is easy to control as the wheels are solidly connected.

If you seriously intend promoting IRS for late models, be careful not to limit the number of suspension links too strict - the dynamics you can achieve is determined by how many links you can add.

Please do not think I am against IRS, my dirt experience shows live axles are more efficient., I am all for new designs and innovation - good luck.

Ghopper
10-28-2011, 06:50 PM
Ronin - ok

I will add a negative point so I don't appear too one sided- IRS may initially have a negative impact on participation in the sport. The is a fairly large rule change that could alienate teams and increase costs if it were to be too successful out of the box. Like when skip arp mounted his LR spring in the back of the birdcage....a relatively low cost change that you had to have to be competitive. IRS would require a different car to be done cleanly.

Ghopper

MasterSbilt_Racer
10-28-2011, 07:03 PM
Unfortunately I was not able to access this site for a while and could not comment as posts were updated. I will post some comments below but cannot reference each relevant post....

If you were able to make an independent suspension differential rotate about itself (as a live axle does) it will not produce the same reaction torque on the wheels as a live axle does. An independent suspension differential will have to be mounted on the chassis, so the reaction torque will be absorbed by the chassis, not the wheels as in a live axle. This reaction torque aids traction and is controlled using a torque arm or pull-rod. Joining an independent suspension differential to the wheels will make it a live axle.

One advantage of an independent suspension is that you will be able to independently adjust traction and steering. On a 4-link there is a degree of change to either variable as you change the other variable.

Keep in mind that the j-bar ads a considerable amount of side bite to a dirt oval racecar. Replicating the effect of a j-bar on an independent suspension could create undesirable motion ratios of the outside/inside wheel (depending which side you mount the bar on the chassis).

Independent suspensions always have a degree of camber change as the chassis roles. Remeber that asphalt racecars do not roll as much as dirt race cars, so camber changes can be controlled much easier. The freedom of movement between the chassis and a live axle in a 4-link allows the rear wheels to always be in perfect contact with the ground as there is not camber changes.

It is always good to reduce unsprung mass. However, considering the suspension travel on 4-link suspensions it will be very difficult (dare I say impossible?) to use rocker arms to actuate the shocks. If you draw a rocker arm arrangement you will notice that the angle change makes it very difficult to maintain constant ratios. A system like this will require very large rockers which might become impractical.

I do not believe that you have to have a lot of shock travel just because you are on dirt. The 4 link uses a lot of travel to get the dynamic wedge changes it needs to work.

I do like the idea of a rocker arm type suspension, at least for the front. I have had an idea for at least 10 years now for one.

Since when is camber change a bad thing?

Ronin
10-28-2011, 11:51 PM
Camber change is bad when it does not optinize wheel contact area.

dualdj1
10-31-2011, 10:27 AM
Good comments. I still don't see why some think that you cannot use a torque arm or pull bar setup with independent suspension. What says you can't allow your center section to pivot as it does now? Just because most have it mounted solid, doesn't mean you can't install pivot mounts to let it roll. Remember you don't *have* to have your suspension links hooked to the center section. Most companies just do so because it makes a nice package and achieves the angles they need.

I also definitely agree on not limiting the number of suspension links.

Ghopper
10-31-2011, 12:47 PM
Currently the number of links are not limited, I dont think this would change.

Allowing the diff to rotate when mounted to the chassis would not gain anything for performance.


Ghopper

dualdj1
10-31-2011, 03:04 PM
Allowing the diff to rotate when mounted to the chassis would not gain anything for performance.

it's not just the rotation, it's where you're applying the force to stop the rotation. Same as pull bar and torque arm apply force to the chassis differently, a solid mounted center section would apply force differently than one with pivots and a torque arm. And at the same time you better absorb some of the initial torque of the wheels grabbing on throttle, and help to cushion that in the same way a live axle does. I see a lot of performance gain there over solid mounted.

MasterSbilt_Racer
10-31-2011, 03:13 PM
it's not just the rotation, it's where you're applying the force to stop the rotation. Same as pull bar and torque arm apply force to the chassis differently, a solid mounted center section would apply force differently than one with pivots and a torque arm. And at the same time you better absorb some of the initial torque of the wheels grabbing on throttle, and help to cushion that in the same way a live axle does. I see a lot of performance gain there over solid mounted.

How does the force get from the center section to the wheels?

grt74
10-31-2011, 08:23 PM
by no means,im not saying it cant be done but this has been done and tested on trophy trucks,the problem was weight mostly,and let me say it is a very different feeling to drive and get used to,just my experence

Ghopper
10-31-2011, 10:34 PM
it's not just the rotation, it's where you're applying the force to stop the rotation. Same as pull bar and torque arm apply force to the chassis differently, a solid mounted center section would apply force differently than one with pivots and a torque arm. And at the same time you better absorb some of the initial torque of the wheels grabbing on throttle, and help to cushion that in the same way a live axle does. I see a lot of performance gain there over solid mounted.


That torque arm does not allow that much rotation. ~4" of travel at 3' out is like 10 degrees of rotation on something that is turning ~6000 deg/sec in the middle of the corner. That is like a small vibration in the driveline. The carcass of the tire is also not very stiff.

With today's four-bar angles (that are on any car going fast, so don't say it is a crutch) the anti-squat added by the torque arm is not as significant as it was in the early 90's. Today's torque is a pinion angle control device. More angle at corner entry and less angle under throttle.

Timing - It is not a good argument that the torque arm "hits" the tire before the four-bars. The torque arm is moment (force x length) reaction to longitudinal force at the tire contact patch. That is the same longitudinal force is goes through the four-bars that are at a fairly steep angle.

(wow. i just spell checked and nothing was wrong....or spell check is broke.)

Ghopper

dualdj1
11-01-2011, 02:31 PM
No, I agree that it's not much rotation. And I very well could be off in how much effect I think it'd have, but it's more about being able to apply lift further forward on the chassis, as opposed to absorbing rotational torque on the rear of the chassis. Maybe it wouldn't make that much difference, but it seems like trying to lift the front end from the middle would work better than from the rear.

Think of it this way. On an IRS setup, your center section is basically the same as your live axle on birdcages is, just without the tubes. as you apply force it's still going to try and rotate. With solid axle, when you use a solid 3rd link, you don't get as much traction benefit as you do with a pull bar or lift bar, because it cushions the rotational force. when you bolt down the center section in your IRS, you are basically doing the same thing as a solid 3rd link. So why would people be using pull bars/lift arms if a solid 3rd link was better?

dfhotlm33c
11-01-2011, 04:25 PM
A few points:

1. FINALLY, a nice discussion on this board...intelligent conversation and exchange of ideas about a concept and theory..this often leads to solutions not just about the theoretical, but the practical (As in the suspensions used now) as well...

2. I am not an engineer..I decided on pure math as a major, and so I focus strictly on problem solving..so my knowledge of the specifics regarding IRS are shady at best..my knowledge base on 4-bar is decent, but only as I have learned through reading volumes on the subject and analyzing my own situations...but it would seem to me that anyone with the know how could make the IRS work...think about it..regardless of what you say, the 4-bar is still a compromise..an attempt at the fine balance between side and forward bite..even at this junction, we still do not fully utilize all four tires equally on any give track surface and night..the LF is still not being used to its full potential, and we adjust the heck out of our cars trying desperately to plant the LR as we slide through the corner waiting for the perfect transition between side and forward bite..

Think of the advantage between solid front axles and IFS..beyond many of the obvious advantages, it leads us to change the front moment and roll centers..the disadvantage to the solid rear axle is the relatively limited amount of adjustability in the rear roll center..if you watch the big guns at the big events, the guys running in the front have managed to come close to a balanced race car, one where front and rear roll centers work in conjunction with each other and allow the car to truly corner..

IRS would require a different driving style as well..something that would require a talented, pliable driver willing to really work with the engineer/builder to tune the car to work...which leads to my next point..

3. Consider some history...and I'm not old enough to have experienced all of it, but I have seen enough to comment..consider the time when the fast way around the track was with big coil springs, a huge wedge bolt and massive humper tires (the days where late models had 15" wide tires were awesome)..then along came guys like Rayburn and such that decided to manufacture complete cars instead of back-halving Chevelles and Camaros..did they blow everyone's doors off instantly? No! Then came the monoleaf/coil-over cars..not to mention the big wedge cars..those took time to overcome the competition..then came the mid-90's, when the z-link and four bar concepts were "borrowed" from the drag racers who had been using these concepts for strong forward drive off the line since the 60's...and nobody believed they would be fast..and for a time they weren't..but the innovators at mastersbilt, GRT and Bullitt kept pushing and eventually started coming out on top..(all the while engine and tire technology kept changing, as well as weight rules, etc)..then came the 3-wheeling era..and everyone laughed at them..until they got fast..then everyone copied..then the innovators determined how to work a j-bar and four-bar chassis to keep all four tires planted..and now they are faster, and nobody three wheels anymore..and now, even some of the concepts and trends found in books only 5-6 years old are outdated..spring and shock combinations have changed to work towards the perfect setup..even j-bars are being mounted on the right sometimes instead of the left...I hope you get my point...true innovation comes when people aren't afraid to stick with a new idea until it works..and I believe given the opportunity, the IRS cold end up being the fast way around the track..more consistent, more adaptable to changing track conditions..but we won't know til it's legal..

4. Finally, does it really matter? I have looked at lap times from 20 years ago to now at local tracks..and they haven't changed that much.....but I will tell you it was much harder..shoot two years ago I drove a 2500 lb mono-leaf coil over car with a body from 1994, and an engine that was at least 200 hp down from the front runners..and I was keeping up with mid pack just fine..but it was waaay harder to drive than the 4-bar car we have now...

supercomet32
11-01-2011, 06:13 PM
I have to disagree with a lil of what you've said. 3 wheeling around a track is not the fast way to go/ Sure it looks cool but its not faster.

as for the IRS, how do you keep from sliding it in the corner without scrubbing off a lot of speed?

how do you accomplish the rules change, the developmen of your design, and and get chassis manufacturers to change their design without it driving the cost up immensely?

dfhotlm33c
11-01-2011, 07:26 PM
comet..my point may have been missed amidst my lengthy rant...I was actually claiming the opposite...three wheeling WAS the fast way for 4 or five years..then people figured out how to get around fast without it..and the three wheelers started falling to the back...sorry if that wasn't clear...besides, I always thought it looked dumb...

and also, my point was that nobody will know until they change the rules...

and if they do..i guarandarntee the innovators of the sport will jump on it...

dirty white boy
11-01-2011, 10:20 PM
if ya dont think a independent rear suspension will work on mud an dirt,..look at a volks wagon beetle mud buggy,..beem working for years at baja500!!

Ronin
11-02-2011, 02:37 AM
The current 4-link live axle setup imho provides a good balance/compromise between forward bite and side bite. The rotation of the differential aids traction, the 4 links provide forward bite and steering whilst the j-bar provides additional side bite. I agree that some of this is a crutch for an imperfect system, but it does work.

The forward movement of the live axle “under” the chassis prevents the front end from “lifting” off the ground (raising the LF is due to chassis roll) and adds traction to the rear wheels. There is very little load transfer to the rear. How will you achieve this with IRS? IRS rely on weight transfer for traction. Having a lot of squat will transfer weight, but that unloads the front wheels (look at dragsters). Adding anti-squat will reduce weight transfer but will not aid traction.

In dirt oval racing the coefficient of friction between the dirt surface and the tyre is very low. You have to transfer a lot of weight to the outside tyres in order to increase the coefficient of friction between the tyre and the surface – remember that the force required to move an item on a surface is equal to the coefficient of friction between them multiplied by the mass of the item. High roll transfers a lot of weight increasing the coefficient of friction. How will you achieve this with IRS?

Ghopper
11-03-2011, 04:50 PM
Guys,

3 wheeling - You are all three wheeling off the corner. A 500-700lb LF spring is not touching the spring perch the moment you look at the gas pedel with any lateral acceleration. Just because your tire is touching the ground does not mean there is much load on it. Only the weight of the spindle/hub/wheel +/- damper loading.

Why 3 wheeling - There are 2 drive tires that you are trying to load as equally as possible. Lateral acceleration transfers weight from Left side to Right side, so to keep LR ~= RR you must unload the LF putting all remaining Left side weight on the LR.

IRS would follow the same principle said above and currently done by a live axle. Only with IRS you can have more control over wheel steering angle and camber angle in a lighter package.




Ghopper

fastford
11-03-2011, 08:16 PM
there is no way you could achieve the same amount of down force to the rear tires with a lift bar or pull bar on a irs no matter how much the center section rotates, on a live axle rear, the lift bar is lifting much of the cars mass and applying it to the rear tires, on irs the force is being contained within the chassis and would have no effect on the tires. the only place to try and achieve this would be at the hubs, which would mean on a 4 bar type set up,. the upper bar would have to angle down

Ghopper
11-03-2011, 11:48 PM
Mr Ford,

We only need enough anti-squat to hit that LR limiter that you use. Then we are near the dynamic wedge used to get out of the corner. Sure there is ~0-1000lb dynamic lbf through the liftarm spring at some places around the track, but dont underestimate how much goes through the four bars.

Maybe in the next few months I can run some tests to get some numbers for the group.

The IRS car would look very similar to a live axle car going around the track, maybe minus as much visual forward movement of the LR....because now you have other ways to steer it.



Ghopper

Matt49
11-04-2011, 11:04 AM
In dirt oval racing the coefficient of friction between the dirt surface and the tyre is very low. You have to transfer a lot of weight to the outside tyres in order to increase the coefficient of friction between the tyre and the surface – remember that the force required to move an item on a surface is equal to the coefficient of friction between them multiplied by the mass of the item. High roll transfers a lot of weight increasing the coefficient of friction. How will you achieve this with IRS?

You cannot increase coefficient of friction by increase weight or mass. You can increase the friction force but the coefficient of friction remains constant. You seem to be contradicting yourself by saying that transfer of weight increases the coefficient of friction immediately after outlining the equation correctly. In that equation, mass and coefficient of friction are independent variables. Increasing one has no effect on the other. You can increase FRICTION FORCE by increasing mass but you cannot increase the coefficient of friction by increasing mass. They are two different things altogether.

Ghopper
11-04-2011, 01:42 PM
Ronin, Matt49,

Maybe we should switch to "load" or "normal force" instead of mass? Normal force being the force perpendicular to the ground plane. Less confusing and would match tire test data.



Ghopper

fastford
11-04-2011, 03:41 PM
Mr Ford,

We only need enough anti-squat to hit that LR limiter that you use. Then we are near the dynamic wedge used to get out of the corner. Sure there is ~0-1000lb dynamic lbf through the liftarm spring at some places around the track, but dont underestimate how much goes through the four bars.

Maybe in the next few months I can run some tests to get some numbers for the group.

The IRS car would look very similar to a live axle car going around the track, maybe minus as much visual forward movement of the LR....because now you have other ways to steer it.



Ghopper
those places around the track would be from the time you pick up the throttle till you let off, and then you gain some advantage braking through the 6 coil which you could not utilize with irs, but please keep us informed of your test mr. hopper , i am interested in your findings.

Matt49
11-04-2011, 03:55 PM
Ronin, Matt49,

Maybe we should switch to "load" or "normal force" instead of mass? Normal force being the force perpendicular to the ground plane. Less confusing and would match tire test data.



Ghopper

Normal force on a flat surface is the mass. Calculating the normal force on a race car tire on a banked track would be difficult because centripetal force would then become part of the equation. And considering a track surface isn't consistent, the coefficient of friction is also a moving target. I'm sure the data acquisition technology is out there for all of this but who has the money to invest in it at this level?

racin6mod
11-06-2011, 08:21 AM
I've been seaching threw IRS and found the Holden system used down under tobe the best with some forward bite adjustment built in. but here's a couple photos of a jag irs chromed up for a street rod but you can see the possibilties.

Ronin
11-06-2011, 11:32 PM
@matt49 - yes you are correct, sorry for my contradiction (was typing faster than I was thinking). Weight transfer would increase the effective vertical force which increases friction force, not coefficient of friction.

Ghopper
11-07-2011, 12:01 PM
[QUOTE=Matt49;1460873]Normal force on a flat surface is the mass. Calculating the normal force on a race car tire on a banked track would be difficult because centripetal force would then become part of the equation. QUOTE]

Normal load on a flat surface is only mass (xgravity) when the vehicle is static. Acceleration vector + aero loads would be necessary.

Ford - I will not be testing anything till the rules change. I have enough trouble getting track time with the current rules :) I am a part-time amateur racer....which means I race every few weekends (I live in Ohio and my shop is in Iowa). I have seen many types of test-rigs and vehicles that gives me complete belief that our community could make an IRS faster than a live axle.


Ghopper

fastford
11-09-2011, 06:14 PM
mr. ghopper me and you are pretty much in the same boat, me and my father and daughter pretty much do every thing, my father has been sick for the last few years so my racing has been limited, but they finaly found and fixed his problem, a tumor on the outside of his small intesten where he was losing blood, thank god it wasnt cancer and hes getting better every day, we buy bare chassis from a small chassis builder and do every thing else our selves including building our engines, but thats what we do, build things, and ive always been interested in irs, but for every positive ive found, there is three negatives, but im not saying its impossible