How would you design a late model ?

[supercomet32]

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]

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?

[dualdj1]

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]

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]

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]

All wheel drive car!!!!!! That's the real ticket in Dirt Racing's future!!!!!!

[Ghopper]

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]

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]

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]

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]

Camber change is bad when it does not optinize wheel contact area.

[dualdj1]

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]

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]

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]

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]

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]

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]

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]

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]

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?