Differences between '83 and '85 RX-7

[jake7140]

As long as they are on the same spec line, and you are not creating a combination assembly that couldn't be purchased ....
[/b]

????? You couldn't go to a Mazda dealer and order an '82 with 20mm lower mounts, nor could you have gone to a dealer and ordered an '85 with 20mm higher mounts.

[Tak]

I believe that running a tri-link and pan-hard bar makes the rear suspension change a moot point. With the recent weight reduction for 1st gen Rx-7's in ITA, I would think the LIGHTEST chassis will be the best chassis. I've built 3 gen 1 cars (79, 82, and 84). The 79 was the lightest. The 84 is the heaviest.

I do have one very speculative question though...Why aren't the rear upper links traction bars??? Traction bars are free...

Tak
#29 ITA
SFR SCCA

[ddewhurst]

***do have one very speculative question though...Why aren't the rear upper links traction bars??? Traction bars are free...***

Tak, to my understanding of the ITA rules the upper & the lower are traction bars. Per ruel 17.1.4.D.5.c. traction bars may be added or substituted. On my 1st gen I have a Tri-link (sponge upper traction bar bushings) with lower traction bars made with a internal threaded tube with S.B. rod ends.

If either the upper links or the lower links are not traction bars try disconnecting one set & see how much traction the car has. One set of links on the axle horizontal center line would locate the axle.

As a side note how can someone call the upper links traction bars & not call the lower links traction bars. 0h, I get it, they have nothing to sell for the lower traction bars.

[Tak]

David- I read the rules the same way (and have exactly the same suspension setup at the back of my car...). The whole 'traction bars are free' seems like an invitation to change mounting points...the substitution of longer upper traction bars with different chassis mounts has the opportunity of correcting the 4 link geometry...
It just doesn't feel right though! Nuances in the definition of "Substitute"...

[lateapex911]

????? You couldn't go to a Mazda dealer and order an '82 with 20mm lower mounts, nor could you have gone to a dealer and ordered an '85 with 20mm higher mounts.
[/b]

No, but you couln't go to the dealer in 81 and get an 85 carb either. Or vice versa. Nor can RX3 dealers sell you a 74 with a 77 transmission. But as they are all on the same spec line, as long as you aren't creating an assembly that never existed, (like swapping gear ratios) I don't see why you can't do this..
IF the chassis are the same, EXCEPT for the bracket difference.

If someone can point to the flaw in my logic, please do.

[ddewhurst]

***If someone can point to the flaw in my logic, please do.***

Jake, are you doing selective reading ? Please read my post Mar 5 2006, 12:48 AM page 1..............

[lateapex911]

So, you think the VIN number makes the difference. Because the year is coded in the vin.

So...........IF we wanted to do this, (A theoretical discussion here), the assembly would be different because the VIN disagreed with the proper setup for the VINs year. Now, if the VIN was swapped as well,...what then?

To take the silly discussion further, ..if that logic holds, you can't put a different gear set in another years case if there's a different p/n, even if the p/n is only a date change, right?

In both cases the actual performace advantage is nil, as they are all on the same spec line.

[Jim Susko]

"I do have one very speculative question though...Why aren't the rear upper links traction bars??? Traction bars are free..." -Tak
#29 ITA
SFR SCCA

Tak, I've never interpreted the rules as calling the upper links traction bars. They are original suspension links that cannot be altered except to change bushing material. The soft upper bushings supplied with the Tri-Link comply with the rules to retain the original links, however they allow the suspension to articulate around the revised geometry of the Tri-Link. Otherwise the axle would be "locked in place" and bending of the body would be required to allow any roll movement. That is in fact what happens when solid bushings are substituted for the Watts link and trailing links of a stock suspension.

Likewise, only the bushing material may be altered in the lower links. You cannot cut the ends off and substitue heim joints.

Traction bars are not "free." One may be added per the rules, and it must fit an exacting definition. Don't see anywhere where a stock traction bar may be removed, so no matter what you call the trailing links, they must stay.

Just my take on the rules.

Jim Susko

[ddewhurst]

***Traction bars are not "free." One may be added per the rules, and it must fit an exacting definition. Don't see anywhere where a stock traction bar may be removed, so no matter what you call the trailing links, they must stay.***

My take on the rule would be that as long as traction bars "may be addded or substituted" (not free when subsituted) a threaded tube with rod ends with the whole assembly being the same length as the OEM traction bar using the same diameter assembly bolts may be subsituted for the lower traction bars. Just as someone many of us know added the Tri-link for the functional upper traction bar.

Thoughts??????????

[Jim Susko]

David Dewherst wrote "My take on the rule would be that as long as traction bars "may be addded or substituted" (not free when subsituted) a threaded tube with rod ends with the whole assembly being the same length as the OEM traction bar using the same diameter assembly bolts may be subsituted for the lower traction bars. Just as someone many of us know added the Tri-link for the functional upper traction bar."

Interesting take, but I didn't have to stretch any definitions to add the Tri-Link as a traction bar. The subtlety here comes with putting very soft bushings in the top links. They still qualify as legal stock links as well. So do the bottom links with all metal bushings pressed in the stock ends.

The difference in our arguments comes down to whether the stock links can be considered to be redefined as traction bars. I think it is a stretch. A traction bar is generally considered to be a supplimentary link solely to prevent axle windup, not a primary locator like the trailing links are. If you take out a traction bar, the suspension should still be fully defined by the remaining links.

The new GCR says it is "A link to an axle housing or hub carrier which resists torque reaction from the wheel by acting in compression or tension." I note the older reference to mandatory heim joints is no longer a part of the definition, which changes things a bit, and that there is a certain appeal to applying this to the trailing arms. Still, whether you could turn around the GCR definition to qualify all of the links as traction bars is doubtful.

Using this logic, then I oould substitute all the stock bushings with foam rubber and create a whole new "traction bar" trailing arm suspension of whatever geometry I wanted using full- as opposed to semi-trailing heim-jointed arms, since the number being "added" is unrestricted. Would you show up in the tech shed with this and tell them that the stock links are all trailing arms so anything similar to them can added? I don't think this would work more than once anyway. This would allow sweeping changes to almost every suspension out there.

Putting it simple, I think by common technical suspension definitions the stock arms are trailing links only.

Jim

[steve s]

i see it jim's way .the 4 links are locating link not traction bars,that's why you have to keep the upper link intact and substitute the foam bushings.the tri link is put in as a traction bar.that's why it's legal.

[jake7140]

I think the rear bumper is a traction bar (I think there's at least one piece of steel formed in a bar shape under the plastic). It adds weight to the back end, providing more downforce/traction at the rear wheels. Wonder what I could do with that?????.....

Maybe I'll just pick up 1/10th per lap by learning to drive better; I'm sure there's room for improvement THERE.

[ddewhurst]

If the OEM links are not traction bars please remove either the upper set or the lower set (without the Tri-link) & infrom me how much traction your rear axle generates. If the only purpose of the four bars is for longitudinal location of the rear axle one set of links at the horizontal center line of the rear axle would locate the rear axle very nicely.

[Jim Susko]

David Dewherst writes:

"If the OEM links are not traction bars please remove either the upper set or the lower set (without the Tri-link) & infrom me how much traction your rear axle generates. If the only purpose of the four bars is for longitudinal location of the rear axle one set of links at the horizontal center line of the rear axle would locate the rear axle very nicely. "

There is a universal language of suspension engineers from which the definitions typically come. A traction bar is different from a trailing link, even though they look the same in many ways and resist similar forces. Usually a traction bar is added after there are a sufficient number of trailing or semi-trailing arms plus lateral control arms to fully define the motion path of the suspension, which the four Mazda trailing link and one Watts link do. The purpose of that bar is to enhance the torsional stiffness of the rear end only in order to control wheel hop, so it should be located purely fore and aft to fit the definition. There are other types of traction bars which don't actually fit the limited GCR definition.

However, if as you argue a link is a traction bar just because traction gets worse when you remove it then literally every suspension link known could be defined as a traction bar. Any argument that is this inclusive is prima facia suspect and generally not accepted by rules makers.

If anyone remains unconvinced, let me know how you do in Tech if they ever check you for your "trick" parts.

Jim Susko

[ddewhurst]

***However, if as you argue a link is a traction bar just because traction gets worse when you remove it***

If you remove either the upper set or the lower set as you well know the axle will rotate untill the Watts links will be in a radial bind acting like the traction bar.

***However, if as you argue a link is a traction bar just because traction gets worse when you remove it then literally every suspension link known could be defined as a traction bar.***

Naw, I wouldn't consider a wound up Watts link a traction bar. Do suspension engineers call a wound up Watts link traction bar?

Traction Bar: A link to an axle housing or hub carrier which resists torque reaction from the wheel by acting in compression or tension.


Acording to the GCR definition (not suspension engineer speak) I will rest my case. I would beleive that anyone reading this post who understands the rear links of a 1 st gen RX-7 & who understands the definition from the GCR would agree that without either set of rear links the axle will have zero traction untill the axle rotates distorting some other rear axle components out of their normal function range.

I beleive that if a Tech would like me to disconnect one set or links he/she would agree in a hurry that the links are traction bars.

[lateapex911]

So, David, your position is that you have two traction bars on your car?

The upper one sold to you called the Trilink, going from the tunnel to the top of the diff, and two lower ones in the original lower position?

If that's the case, remove one set and see what kind of location control you get.

Basically, it's your argument, but with the words flipped.

I see where you are going with this, but you've left yourself with a car that by your definitions, has only two longitudinal links (the stock uppers) locating the axle, once the traction bars are removed.

[ddewhurst]

Two posts by ddewhurst:

***If the OEM links are not traction bars please remove either the upper set or the lower set (without the Tri-link) & infrom me how much traction your rear axle generates.***


***If you remove either the upper set or the lower set as you well know the axle will rotate untill the Watts links will be in a radial bind acting like the traction bar.***

Post by Jake:

***So, David, your position is that you have two traction bars on your car?***

Jake, when the car was OEM the car had 4 traction/location links/bars. With the Tri-link the car has 3 functional traction/location links/bars. When the car is in the OEM condition the manufacture didn't implement 4 links just to spend extra money. The 4 links were designed into the suspension because the rear axle requires longitudinal location & rotation control.

GCR Glossary definition of traction bar.

***Traction Bar: A link to an axle housing or hub carrier which resists torque reaction from the wheel by acting in compression or tension.***

Jake, please answer the question below using the GCR glossary definition of traction bar. None of your selective speak, use the rule.

If you used whatever words you would use to protest the lower S.B. rod end/threaded tube links within the rearend of my 1st gen RX-7 I beleive that if a Tech would like me to disconnect one set or links he/she would agree in a hurry that the links are traction bars.

[Jim Susko]

Dave,

I see your standing by the GCR definition but for one thing it is not complete. Following your logic almost any link will qualify as a "traction bar." That sends up red flags around the definition and around your logic. and would probably in itself be sufficient for the Competition Board to uphold a protest of your lower arms.

Your argument that if you disconnect something and traction goes down makes it a traction bar doesn't hold water either. It doesn't say that in the GCR. You can't argue that something is a Watts link because if you disconnect it you lose watts.

Even if the name Traction bar is taken as a literal description (which it should not be) your logic is flawed. You are arguing that the definition of water is it makes things wet then anything that wets something is water. That is not good logic. Alcohol wets things, too, but that doesn't make it water.

Semi-trailing arms can also function as lateral locating devices. A Watts link is a lateral locating device. However, following your logic you would look at a semi-trailing arm and feel free to call it a Watts link. It is not.

I hope other readers don't become lured down this flawed logical path. As a Mechanical engineer and practicing Suspension Engineer I know what a traction bar is and have provided readers with an understanding of the nuances that make for a traction bar. 'Nuff said here.

Good race prep is founded on fundamentals like attention to detail, and understanding of suspension geometry and tuning and how to make a car go fast within the rules. Too much attention to twisting definition around to extremes usually isn't productive. You won't go any faster with illegal lower trailing arms, and my stock lower arms with alternate bushing material will pass tech any day.

Jim

[ddewhurst]

Jim, 1st please tell all of we readers what the GCR rule name of the Tri-link upper control arm you sell is. (Darn, you for sales purposes call your part a "Tri-link upper control arm". Which GCR ITCS rule allows a person to change the upper control arm ?)

Anti-roll bar ?

Traction bar ?

Pan hard bar ?

Watts linkage ?

2nd please tell we readers what the total number of different functions your _ _ _ _ _ _ _ _ _ _ _ provides. Please don't get into all your suspension engineer speak. Not required & just muddys the water.

1.

2.

3.

Please add more numbers for additional functions.


*** I see your standing by the GCR definition but for one thing it is not complete.***

Oh, now I get the picture. We shall we use Jim's definition of a traction bar.

[ddewhurst]

Duh, 1st error for 2006.