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Billet Suspension ARM design problems.

Suspension Tuning & Optimization

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HiI'm using Alfa Romeo 159, it's relatively heavy car. Front Wheel Drive and Front has double wishbone suspension.As you can see, it is cold formed forged aluminum, and it is very tough. But bushings and rod end is pain in the ass. Every time there is a problem, we need to buy whole assembly. And it costs too much. Rod End has life time of 15.000km :( Also I want to to track days with this car. I don't trust the ball joints of factory.I have a CNC, and I can make it from billet aluminum with replaceable bushings and with motor sports ball joints. But I don't know if it will have good life . I saw some aftermarket billet arms. If they can make it. I can make it too. Can you give me hints. Or direct me, suggest me a material. Or I can go welding tubes ?

Mean while escaping from Covid19 I did some progress in Suspension geometry and design.

3D Scan of Upper Arm

3D Scan of Lower Arm

3D Scan of Knuckle

3D Scan of Wheel Arch

Dirty Work of Solidworks Assembly

I've finished the Upper Arm CAD model. And I'm very pleased with that. I'll use FK ball joints in front and at chassis I'll use Original Design + PowerFlex Bushings.

The Problem that I have is the lower arm ball joint area. I want to use bigger diameter eye for Ball joint. "30mm Stock" vs FKS14 "Ball diameter is 33.32mm"

The Problem is the thickness of the material left outside of the arm aluminum.

That is a terrible service life,is the vehicle running higher offset wheels and/or much firmer suspension that may be loading the joints excessively?

Not sure if they're a different manufacturer, or just different packaged distributor, but TRW seem to have a product line that may be a superior product - https://www.gazzellaracing.com/cart.php?target=category&category_id=5756

CAR is suspension geometry vise completely stock. Stock Tire diameters. Stock Wheels 17" No Offset difference... etc you name it. BUT it has twice as power & almost twice the torque. But even with stock power those joints don't have long life. MAX 2 years on stock car.

1) I've been using the car since 2013. I've bought almost all the brands to check quality. But no good. And Car is Tuned only for 4 years.

Worst brand has 6 months of Life.

Best One is "Lemforder" only has one year life time - 30.000km

2) Generally first Upper Joint brakes. After that if you don't change it. It will kill the lower arm as soon as possible.

Also Even though I don't make any billet part or anything else. I want to use PowerFlex bushings. I think the suspension is so soft for the joints. I mean it moves too much on other axis. And It brakes the joints. So Maybe after using harder bushings. It Arm will articulate on only one axis. And maybe It would help the life of the Joint. I know it would be hard on car but I feel like I'm helpless.

I want to add more pictures...

If you are unable to increase the OD of the material supporting the spherical on the outer joint on the LCA, your best bet is to either downsize the bearing OD or convert to a rod end design to remove the need for surrounding material. If designed correctly, you'll add in some adjustability to the trackwidth/KPI/etc, with a little sacrifice to unsprung weight. This is how I had to address a similar problem when I designed an angle kit for the Nissan Z34 chassis which is very similar in design. As for material, a good 6061-T6 is sufficient in most cases, but run an analysis. I had to go to 2024 or 7075 in some products depending if I needed better fatigue (2024) or ultimate (7075) strength. Those are the three alloys I recommend for 99% of billet suspension designs.

I went 7075 for my arms I machined for the front of my kit car.

Consider getting them coated rather than anodised.

Remember to radius any stress raisers.

DON'T machine them on a rubbish little Chinese mill...it takes WEEKS!

Attached Files

Hello again. I'm sorry I was absent for a time. I had to work my ass off in my daily job. And I'm swapping the gearbox on the car from M32 to F40. Lots of problem came within swap. Now I'm waiting parts from Europe to finalize the swap. Anyway another subject.

Here is some news. I've checked the some dimensions on the car. And I found that I have 2 more millimeters between disc and the arm. So It means now I have more material to cover the ball joint. It's a good new.

Also I've bought Aluminum Knuckles from a younger car. Before the Alfa Romeo 159 out of production, Engineers put the car on diet and lost 80kg total. And knuckles are on of the part that we can bolt-on swap to our Steel Knuckles.

Steel -

Alu -

Weight of Alu -

Weight of Steel -

Together -

Together -

As you can see. Alu seems to have more material than steel. Bulky design, but less weight.

I wish I could find what material they are using in "forged aluminum arms" I've talked lots of guys in the market. They say our 7075 or 6061 has no strength.

Forged Alu is the key. They say if you go billet, you have to add material to compensate the strength. I've asked some data. I know they tested those materials for life expectancy, but I could not find any good data.

Some said go to China market and bought untouched forget material. And put it on CNC. That would be better. And I think its not. I saw lots of Billet arms on the WEB. And they are using them even on Off-road. I don't know how many years can you use your Billet Arm. But I'm curious.

I have two new CNCs and German cutters. I don't I'll have any problems on that side. I wish only I could trust the materials. Even I have the Factory designs of the arms. But I could not find the Design Calculation Forces to check and redesign the billet arm.

This may be a silly question - won't be my first or last - but as the bearing carrier appears to bolt to the upright, can't you add (a) spacer(s) between them to gain more clearance between the disc and the knuckle? Even a couple of mm could help.

I would be cautious about running the knuckle too close to the disc, because there is going to be some flexing of the upright when the car is loaded during cornering - keep an eye on them for witness marks indicating contact.

"They say our 7075 or 6061 has no strength."

Buy from a decent reputable supplier.

I always buy from our big supplier. I work with them for about 15 years. Materials always comes with certification. I build machinery with them. Otherwise I'm in trouble with my customers for 22 years of work :D People who say they are weak, means 7075 is weaker than forged aluminum.

Would like to see the hard numbers/tests on that statement. Certainly if you were forging the whole upright in one piece that may be true (grain structure etc)...if you are taking a lump of forged ali and then milling most of it out...that would be a very different situation.

The heat, or other, treatment has a big affect on the serviceability of aluminium alloys - what were they citing it for?

Why not space the brake disc away from the hub?

you can move the disc until the caliper contacts the wheel, this may or may not be enough. but its far easier than a custom forged upright.

That would have the same issue my suggestion, in hindsight, would have - the caliper will also need to be offset. It isn't just a case of having the disc run within the caliper body, it requires close centring it so piston travel allows the pads to be fitted and also maximise piston support within the bores to reduce wear and sticking as the pads may wear with a taper, as it's very likely it has all the same diameter.

Relatively easy if there's a factory adaptor, less easy if it's a direct bolt-on to the upright as it means material will need to be removed, safely, from the caliper lugs and/or the upright. There may also be regulations against ANY modifications to calipers, as it's definitely a safety issue.

well its a radially mounted caliper so there is an adapter so it shouldn't be that hard...

oooooo I think there is a misunderstanding :D I don't want to make an upright. All I want is a good low Suspension arm. Upper Arm is very easy to make. There is lots of space. But Lower Arm is the key in the project now.

Well spotted, Josh, I missed that.

Enre, we weren't thinking of a new one, just the use of a spacer to move the disc and/or hub assembly a little for clearance.