WTH Spider Rear Racing Suspension!

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atruscott
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Re: WTH Spider Rear Racing Suspension!

Post by atruscott » Sat Aug 31, 2019 7:30 am

If you’re not releasing it commercially - why not disclose? I’d be fascinated - as I’m sure others would be. Now, it will inevitably obtain critique... if you’re ready for that however, why not?

A
1960 Autobianchi Bianchina Transformabile
1970 238 Camper OHV
1974 124 Wagon TC
1974 124 Special TC
1975 124 Sport Coupe
1976 124 Sport Spider (The Racer)
1981 Spider 2000 (The Resurrected)
1985 Pininfarina Azzurra
2017 124 Spider Abarth Elaborazione
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ST3Racer
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Re: WTH Spider Rear Racing Suspension!

Post by ST3Racer » Sun Sep 01, 2019 12:32 am

Andy,
It seems in setting up the new Vintage chassis, that the rear is dog-tracking a bit, so I will be dropping the wishbone bar to adjust for thrust and side to side alignment. This will allow me to make good pictures to show what this set-up does, and how it does it. I am not sure exactly when I will do this, but it will be soon. Hang in there. I will do a full write-up.
Bill McMahan
Parker, Colorado
'69 124 Spider 2L ex EP racer, ex Volumex NASA ST3 Racecar - retired
'69 rebodied with '79 backdated chassis as '72 DP 1.8L Vintage Racer
'74 124 Abarth Stradale Replica
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ST3Racer
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Re: WTH Spider Rear Racing Suspension!

Post by ST3Racer » Thu Sep 12, 2019 1:40 am

Finally, I have made time to change out the rear springs, and adjust the axle locating “wishbone arm” for a dog-tracking adjustment. So, here is the key details for this Tri-link racing suspension, as promised. The first picture shows the connection of the top middle link, and the connection for the wishbone arm.
IMG_1683.jpg
attachment points
IMG_1683.jpg (2.19 MiB) Viewed 1047 times
This shows the fabrication for the connection of the wishbone arm heim joint and bracket to the axle housing. The channel brackets have shims inserted and welded to locate the nuts for the attaching bolts.
IMG_1890.jpg
axle fabrication
IMG_1890.jpg (69.38 KiB) Viewed 1047 times
This allows for the the bolts to be tightened without the need for a wrench on the nuts, and for the nuts to be replaced as needed.
The wishbone arm attachments to the body, are modified stock trailing arm brackets that also locate the ends of the wishbone arms. All attachment points on the suspension are heim joints, mostly from Aurora, or Speedway.
IMG_1685.jpg
body mount
IMG_1685.jpg (2.88 MiB) Viewed 1047 times
IMG_1938.jpg
double body attachment bracket
IMG_1938.jpg (77.23 KiB) Viewed 1047 times
The truly key piece is the assembly to attach and locate the axle-end heim joint to the axle. This heim joint is a 3/4” X 3/4” heavy duty heim that is rated at 40,000 lbs shear. It is threaded into a tapped Schedule 160 pipe that slip fits into the wishbone fabrication. Schedule 160 pipe is mostly pipe wall, and very little ID. It is used for high pressure and high temperature corrosive process piping. This allows for the heim to be threaded in without the need for a thread-o-let fitting in this high shear point. IDs and ODs were matched for this slip fit from available piping. A dab of bearing grease keeps the slip fit lubricated and free. The bolt for the heim threads into a thread-o-let on the bracket, and does not thread into the axle drain.
IMG_1859.jpg
heim bracket
IMG_1859.jpg (159.43 KiB) Viewed 1047 times
IMG_1861.jpg
slip fit
IMG_1861.jpg (151.91 KiB) Viewed 1047 times
IMG_1862.jpg
slip
IMG_1862.jpg (152.35 KiB) Viewed 1047 times
IMG_1864.jpg
bracket/heim end-on
IMG_1864.jpg (97.94 KiB) Viewed 1047 times
The result is a bind-free mechanism that is tight in it’s location, but loose in it’s movement, in multiple planes of movement. Please reply with your questions or comments.
Bill McMahan
Parker, Colorado
'69 124 Spider 2L ex EP racer, ex Volumex NASA ST3 Racecar - retired
'69 rebodied with '79 backdated chassis as '72 DP 1.8L Vintage Racer
'74 124 Abarth Stradale Replica
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engineerted
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Re: WTH Spider Rear Racing Suspension!

Post by engineerted » Thu Sep 12, 2019 9:42 am

Ok, Bill you little trickster!! this is a 4 link, not the three link i was thinking about. Nice!!
1978 124 steet car
1974 124 EProd race car
Farmington Hills, MI
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SimcaBertone66
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Re: WTH Spider Rear Racing Suspension!

Post by SimcaBertone66 » Thu Sep 12, 2019 4:09 pm

Well done … like that "slidy" bit …. would love to see you make a set of plans to scale so it could be duplicated... once again nice work … waiting for you to begin track testing.
Joe DeGasperis
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ST3Racer
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Re: WTH Spider Rear Racing Suspension!

Post by ST3Racer » Mon Sep 16, 2019 12:03 am

Ted,
It is truly a tri-link. The wishbone does nothing more than provide a linear non binding side to side location alternative to the stock Panhard bar. The slip feature eliminates it as a fourth link. You should think about doing something like this on your EP racer.

Joe,
The fabrication is a bit difficult, but not in any way impossible. If the fabrication can be figured out by someone who wants to duplicate this set-up, no further instructions should be needed. This is a true racer ‘figure it out’ thing. I will be testing the new racer very soon, and will report on this site when I do.

If anyone is interested, I can provide more information as needed for that party or parties to build this. Just not on this forum - by PM or by phone collaboration.

All I can say is that it is dramatic in how well it works under racing conditions, over any 4-link with panhard bar, even fully heim jointed. I believe it would be a waste of time, materials, and effort for a street car. It would necessitate installing a roll cage to acommodate the third top link, and also eliminate the rear seat. It is not practical for a street car. I have no problems with the stock 4-link and Panhard bar when I track my street Spider. For compliance, I used new, stock, replacement elements when I build the Stradale replica. I saved the delrin and poly bushings for the front suspension on that build. It handles quite well. I believe I covered that set-up in another thread - BS front springs front and rear, stock height on the rear, and 1-1/4 coil cut on the fronts. Koni Yellows set to middle stiffness. 25mm front bar, and no rear bar (not needed if the spring rates are right...). Delrin front bushings, polyurethane swaybar bushings, fresh stock rear trailing arms and panhard bar.
Bill McMahan
Parker, Colorado
'69 124 Spider 2L ex EP racer, ex Volumex NASA ST3 Racecar - retired
'69 rebodied with '79 backdated chassis as '72 DP 1.8L Vintage Racer
'74 124 Abarth Stradale Replica
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vandor
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Re: WTH Spider Rear Racing Suspension!

Post by vandor » Mon Sep 16, 2019 10:17 pm

Wow, that is pretty neat! Could you have the top link as the triangular one so it would provide both side-to-side location and be the upper torque-arm (trailing arm) at the same time? Or is it too much to ask one piece to do both?
Csaba
Parts: http://www.autoricambi.us
Cars: http://italiancarclub.com/csaba/Fiat.html
'71 124 Spider, much modified
'72 124 Coupe, new project, ex-Pete, ex-Eli, ex-Jack car (all Mira members)
'73 124 Wagon, no floors
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engineerted
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Re: WTH Spider Rear Racing Suspension!

Post by engineerted » Tue Sep 17, 2019 9:27 am

Csaba,
Yes, you could in add this to the top of the diff, minus the telescoping part. This would move the roll center to the top off the diff affecting the handling of the car, (you would also need to break out the sawsall and start cutting up that rear shelf area to make it fit). I think this is done on a lot of off road race trucks.

Bill, adding the triangle locator to my car would be fairly easy as i already have the other three link setup. One advantage i have in my current setup is that i can adjust the rear roll center heights. I have a race at the end of Sept., so i will try lowing it all the way down and see how she handles. It should end up about 1/2" higher then what you have.

The effects of rear roll center is very dependent on the cars Center of Gravity, spring rates, Chassis stiffness, shocks, etc. Below is some general statements about roll center and it effects.



Effects of Front Roll Center Adjustment

Front roll center has most effect on on-throttle steering during mid-corner and corner exit.



LOWER front roll center



* More on-throttle steering

* Car is less responsive

* Better on smooth, high grip tracks with long fast corners



HIGHER front roll center

* Less on-throttle steering

* Car is more responsive

* Use in high grip conditions to avoid traction rolling

* Use on tracks with quick direction changes (chicanes)



Effects of Rear Roll Center Adjustment

Rear roll center affects on- and off-throttle situations in all cornering stages (entry, mid, exit)



LOWER rear roll center

* More on-throttle grip

* Less grip under braking

* Use to avoid traction rolling at corner entry (increases rear grip)

* Use under low traction conditions

* Increases traction, reduces rear tire wear



HIGHER rear roll center

* Less on-throttle steering

* Car is more responsive

* Use in high grip conditions to avoid traction rolling

* Use on tracks with quick direction changes (chicanes)
1978 124 steet car
1974 124 EProd race car
Farmington Hills, MI
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ST3Racer
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Re: WTH Spider Rear Racing Suspension!

Post by ST3Racer » Tue Sep 17, 2019 7:09 pm

Ted,
By all means, give the wishbone locator a try. The goofy geometry of a panhard bar is worth getting rid of if you can. The NASCAR boys are constantly adjusting it during any given race to adjust the handling characteristics.

Csaba,
If I could have combined the top third link with the wishbone locator I might have done it that way. The sliding action would have to be eliminated. The intrusion into the rear seat area of the top third link is shown in the following picture. A good portion of the rear seat pan (more than the cutout than is there now) would have to be cut out, and the forward attachment points of the wishbone would also have to be calculated and fabricated into the lower crossbar in the main roll bar fabrication assembly. Really crazy fabrication. I (and my Brother Mark who fabricated it) never thought about it that way....
IMG_1674.jpg
top third link
IMG_1674.jpg (3.01 MiB) Viewed 906 times
Bill McMahan
Parker, Colorado
'69 124 Spider 2L ex EP racer, ex Volumex NASA ST3 Racecar - retired
'69 rebodied with '79 backdated chassis as '72 DP 1.8L Vintage Racer
'74 124 Abarth Stradale Replica
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