How would you design a late model ?

[dualdj1]

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

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]

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]

#4....I would ask God what Bloomquist is doing....

[Ronin]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

once again

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