Suspension pickups - race build 1978 X1/9

Ulix said:
I had read that the rear suspension design has a toe-change built in that results in an increase in toe-in as the suspension compresses so that the oversteer tendency is reduced as the car leans into a turn.

So is this incorrect?
GregS showed above that the rear toes OUT as the suspension compresses. 🤔
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I believe this is correct for standard ride height, perhaps Greg's car varied from this because it's lowered. The angle of the toe link (relative to the ground line) is then different with a lowered chassis as the inner point (even though it's mounted to the control arm) will drop down to some degree, whereas the wheel end would stay the same (with the same sized tyre), Greg corrected / compensated for this by lowering the outer attachment point.

SteveC
 
GregS said:
View attachment 69513

May not be legal for road use, but this is essentially a track car.
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A rod end isn't technically illegal for road use, I've used them on loads of rally cars I've built that are also road registered, what the road transport people do get hot on (as should a good scrutineer) is the lack of a second locking device for the fastener holding the rod end to the hub. All steering / suspension points all have two methods of locking threaded fasteners to prevent (catastrophic) loosening of the parts (it's actually an ADR, and I'm pretty sure there is mention of it in the CAMS motorsport manual under general safety requirements) usually one locking method is a taper, the second is some form of self locking nut (or in the old days a castellated nut and split pin)

From the above picture it looks like you've fitted a taper into the hub, and drilled down offset (as much as you could and still make a thread) to fit the cap head bolt... that's the safety issue here, no locking device on the cap head bolt. Lock wire is your friend here and you can buy cap head bolts with the head pre drilled for lockwires.

SteveC
 
Perhaps mill a part to take the place of the spacer and minimize the cantilever. Features could be added to orient the part to interfere with the cast arm to keep its orientation under load.

Blind hole instead of the through hole I quickly threw in there for the fastener for the rod end.

One could make it taller to offer more vertical placement options of the rod end.

Screenshot 2023-01-13 at 10.30.23 AM.png
Screenshot 2023-01-13 at 10.30.12 AM.png
 
fiatfactory said:
The angle of the toe link (relative to the ground line) is then different with a lowered chassis as the inner point (even though it's mounted to the control arm) will drop down to some degree, whereas the wheel end would stay the same (with the same sized tyre)
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However it seems the angle of the control ("A") arm also changes the same amount as the toe link when the car is lowered. Both will have a different angle relative to the ground, but there shouldn't be any difference in angles between those two arms. So with regard to those two arms, it seems the toe setting should not be affected by the lowering of the car per-se? I can see how it would if the toe link and control arm were not fixed to one another at both ends, but they are.

I'm with Greg, we need to see a model of both system designs to find out the actual effect. Science is our friend and we are only speculating until then. :)

I also would love to see what models might show of the chassis mounting points/pivot locations (for the control arm) being parallel (in-line) to one another vs the offset axis on the stock design. I'm not sure why it was designed that way? As the A-arm articulates it puts those two pivots in bind with one another. And it will also create a stress on the arm itself. With these arms being so flexible, are they intended to "move" and change shape as the suspension travels?
 
tightwadracers said:
Hi Mike
In your photo of the lower arm set up, I am very interested if you know the origins of the ball joint used.
cheers
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Great question. I wonder if you could use a reamer tool to convert the hole in the Fiat upright to accept a more universal BJ? I know we did that on early VW's to make custom control arms fit.
 
Steve Thomas said:
I would be replacing that bolt very, very often. 1/2 inch is a big step down from M16 and it is cantilevered as well as single shear
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Actually a 1/2" Unbrako bolt at 190,000 psi tensile strength = 37,000 lbs load (at shank dia), a 16mm ball joint shaft assuming typ 8.8 strength grade (116,000 psi tensile) = 36,000 lbs load.
Edit: comment from Steve C on another site regarding the factory Fiat part, "seldom does the tie rod end fail though, but if you need them I have these in stock." So it seems they are over engineered for the job, I think I will be ok.
 
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GregS said:
Actually a 1/2 Unbrako bolt at 190,000 psi tensile strength = 37,000 lbs load (at shank dia), a 16mm ball joint shaft assuming typ 8.8 strength grade = 36,000 load.
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LOL. Love the mixture of imperial and metric! Assume the Unbrako is genuine = 12.9? Good stuff but there is a substantial load multiplication due to the cantilever. Haven't done any numbers and not going to but it feels like a bolt to be replacing. Basic risk management - if that one does let go, it will be at speed and may result in the need for new underpants.
 
Here's a couple of pics I previously saved from the web:

Dallara X Rear Susp Design.jpg

I don't know anything about this car. It appears to be a complete drivetrain swap with some sort of custom uprights on this rear susp. And nice suspension arm pivot locations with long arms.



X rear susp - Copy.jpg

On this one notice the toe link's inner mounting point location and type. Basically a solid mount on the A-arm but not near the A-arm's pivot.
 
Dr.Jeff said:
Here's a couple of pics I previously saved from the web:

View attachment 69683
I don't know anything about this car. It appears to be a complete drivetrain swap with some sort of custom uprights on this rear susp. And nice suspension arm pivot locations with long arms.
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Umm , that's a real Dallara. The group 5 regulations it was built under (basically just a silhouette shape) allowed complete suspension freedoms, including altering the wheelbase. The engine isn't a drivetrain swap, as one of the few things required in Group 5 is the use of the original engine block, so it's a 1300 block stroked to 1600, the dry sump system is what you're seeing as markedly visually different. The front end is a full space frame affair.

It's (pretty much) always the case (in race suspension design) that ideally you want the inboard pivots as close to the vehicles centreline as practicable.

But you have to remember that Dante Giacosa and his team didn't design a race car, they designed a road going production car. Building in an "acceptable" degree of bump steer or understeer into a chassis design is something a production automotive engineer needs to take into account, as the driver is not always going to be a razor sharp reflexes race driver, and they need to design in "idiosyncrasies" like these to make the vehicle completely safe in the hands of a not-so-skilled operator.
SteveC
 
Dr.Jeff said:
However it seems the angle of the control ("A") arm also changes the same amount as the toe link when the car is lowered. Both will have a different angle relative to the ground, but there shouldn't be any difference in angles between those two arms. So with regard to those two arms, it seems the toe setting should not be affected by the lowering of the car per-se?
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But there is , and it does, that's how it works.

It's because the arms are at different angles relative to the ground, and they are travelling thru different arcs. The suspension pivot design is actually very clever when you look closely, as it was designed to create (a very small amount of ) toe in (to reduce oversteer) under loading/compression. BUT when you lower the chassis the angle of the arms relative to each other does change by a small amount and then produces a small amount of toe-out on loading/compression.

If they both pivoted from the same inner point, then the relative angle between the two arms wouldn't change as the chassis was lowered, but because they dont pivot in the same plane on the outer end, there will always be some toe change as the suspension travels up/down. The amount of toe change per unit of up/down will probably increase as the chassis is lowered though, as the further away from horizontal any arm becomes , the arc prescribed by it's movement becomes more pronounced in the amount of left/right shift you get at the outer pivot point.

SteveC
 
Comment about placing the pivot point as close to centerline of the car as possible...
Old Ford pickup trucks had a Dual I Beam suspension in the front. It took the notion that you wanted the lower control arms to be as long as possible to the extreme. The "inner" pickup points were located on the opposite side frame rail :oops:! They had real long lower control arms.
That's about all I know about those particular trucks, but I don't remember them being used as an F1 racecar frame.
Now, back to our regularly scheduled post...
 
tightwadracers said:
Hi Mike
In your photo of the lower arm set up, I am very interested if you know the origins of the ball joint used.
cheers
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Sorry I don't remember where it came from. As I said above, I enjoy seeing how others have modified their suspension and collect all the pics I can. Those kind of pics make me think, and most often raise more questions than produce answers.
BTW - I did copy the pics Dr Jeff posted above to add to my collection :) Thanks Dr Jeff!
 
MikeHynes said:
Comment about placing the pivot point as close to centerline of the car as possible...
Old Ford pickup trucks had a Dual I Beam suspension in the front. It took the notion that you wanted the lower control arms to be as long as possible to the extreme. The "inner" pickup points were located on the opposite side frame rail :oops:! They had real long lower control arms.
That's about all I know about those particular trucks, but I don't remember them being used as an F1 racecar frame.
Now, back to our regularly scheduled post...
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Ahhh... the old "Twin I-Beam" suspension. That's going back a ways!
 
fiatfactory said:
It's because the arms are at different angles relative to the ground, and they are travelling thru different arcs.
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If the two arms are connected to one another at both ends they cannot move on different arcs. Simple geometry and physics. But I have those components sitting on a workbench so I'll will look at them again to see if I'm remembering it wrong.
 
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