Part critique please

[King Tut]

Originally Posted by OrbitalEllipses

Good choice but pricey. I didn't need the fancy adjustment and weight savings of aluminum so I went with SPC steel arms. Not fancy and probably not as strong either, but I'm not competing...just want equal and not overly high negative camber.

I bought the Cusco ones to eliminate the rear negative camber, and I wish I had waited longer and done more research. As long as the Whitelines are easily adjustable without removing the arm from the subframe, then I will go with them. These Stance arms look like they will suffer with the same issue as the Cusco arms in that the adjusters are near impossible to get a wrench on to tighten once attached to the subframe.

[EarlQHan]

Originally Posted by OrbitalEllipses

Good choice but pricey. I didn't need the fancy adjustment and weight savings of aluminum so I went with SPC steel arms. Not fancy and probably not as strong either, but I'm not competing...just want equal and not overly high negative camber.

steel is a stronger metal than aluminum. the benefit of aluminum is that you can make the cross section a lot larger for the same weight as steel, making back the strength and making it stiffer.

[OrbitalEllipses]

Originally Posted by EarlQHan

steel is a stronger metal than aluminum.

Of course but it's all in the design of the part. The SPC arms are unboxed and honestly not all that strong looking to my untrained, un-engineer mind. They were significantly less expensive while giving me the options I wanted without the frills I didn't need.

[Sccabrz192]

Originally Posted by Pete156

Seriously? Is that why Jeeps use them in every aftermarket control arm?

Originally Posted by fatoni

or any decent endlink for a sports car

I used to work for an aftermarket suspension company that made them... the warranty due to that component is atrocious. The dirt particles get in the joint and wear away the PTFE liners.

Just because it's common doesn't make it good or correct.

and for racing applications, wear-out isn't a big concern because they are meticulously maintained... so replacing a heim joint isn't difficult.

For a street car... it's just bad practice.

[DNAPoPo]

What is the recommended after market Daily Driving Control arm? I would prefer one that gets my camber back to not wearing out my rear tires as fast....

[ZDan]

Originally Posted by EarlQHan

I know the engineer who designed this piece very well. The biggest concerns he had when designing the piece were making sure the geometry and camber curve remained unaltered with the ride height difference.

Structural integrity should be the #1 concern! All else secondary.

Then making sure it was able to handle the loads was the next concern.

totally inappropriate priorities! Still, better than some aftermarket parts where *zero* consideration is given to strength!
IMO, in designing aftermarket parts, the OEM strength should be the minimum strength baseline.

It was originally designed to withstand 4G's of loading as the SF, but the piece was deemed too heavy.

Again, structural integrity should be the #1 priority! Making it lightweight while maintaining structural integrity is the art of structural design. Again, just on a cursory glance the geometry of the part isn't going to be efficient given how it is loaded.

This design is meant to withstand in excess of 2.5G's of loading.

Are we talking 2.5x *static* load? I hope not. That's *woefully* inadequate.

Just like with any other design, this has its compromises, but it a good option for those who run out of bump travel at their current ride height.

I'm a huge fan of sticking with OEM structural components, as most of the aftermarket stuff hasn't been developed properly to ensure structural integrity.

I have modified control arms and other structural components on my cars, but with a keen eye towards maintaining or improving structural strength and strength- and stiffness-to-weight.

Throwing out critical primary structure that was developed by a small army of competent engineers and subjected to countless hours of structural/reliability/durability testing, and replacing it with something where when strength goals weren't met by the initial poor design, the requirement bar was lowered? Bad idea if you ask me...

[Dimman]

Originally Posted by ZDan

Structural integrity should be the #1 concern! All else secondary.

totally inappropriate priorities! Still, better than some aftermarket parts where *zero* consideration is given to strength!
IMO, in designing aftermarket parts, the OEM strength should be the minimum strength baseline.

Again, structural integrity should be the #1 priority! Making it lightweight while maintaining structural integrity is the art of structural design. Again, just on a cursory glance the geometry of the part isn't going to be efficient given how it is loaded.

Are we talking 2.5x *static* load? I hope not. That's *woefully* inadequate.


I'm a huge fan of sticking with OEM structural components, as most of the aftermarket stuff hasn't been developed properly to ensure structural integrity.

I have modified control arms and other structural components on my cars, but with a keen eye towards maintaining or improving structural strength and strength- and stiffness-to-weight.

Throwing out critical primary structure that was developed by a small army of competent engineers and subjected to countless hours of structural/reliability/durability testing, and replacing it with something where when strength goals weren't met by the initial poor design, the requirement bar was lowered? Bad idea if you ask me...

ZDan, I'm curious about why manufacturers went to this 'inside a box' design, after using the lower 'fork' mounting (like a Mk4 Supra rear LCA, 48730 in the diagram.)?

[EarlQHan]

Dimman - It allows the control arm to be "hollow" and save a little weight by putting the LCA in double shear. I assume that MKIV LCA is solid aluminum or boxed steel. On the BRZ/FR-S, the lip only on the upper side, but I speculate there are two reasons: 1. it's cheaper and easier to manufacture. 2. It strengthens it in compression where the part is weaker and sees more force. In tension the force is equal to the weight of the corner only.

ZDan - Engineering's all about compromises though, whether it's weight, strength, stiffness, cost, etc. but I think that's where structural engineers and motorsport engineers differ. In most forms of engineering a safety factor of 3+ is normal, in civil a SF of 10 is common. In motorsports, that means you're carrying way too much unnecessary weight. It's not unheard of to have a SF of 1.5 or lower, but they have low volume, high quality manufacturing, that are meticulously maintained, and replaced on a schedule.

[philstar]

I thought STANCE has a great reputation on here. I've seen several people chime in with these on their FRS/BRZ and all I've seen are positive reviews. From what I see, their Super Sport coilover is an entry-level priced coilover with great customer support and their brand is used in many forms of motorsport successfully.

I know I personally cant wait to get their coilovers with Swift springs, these rear lower control arms, and their subframe collars for my FR-S which I am building primarily for drift.

My 2 cents, Im sure many of you guys know way more about this engineering stuff than me like EarlQHan, I just drive and know what feels good to me.

[ZDan]

Originally Posted by Dimman

ZDan, I'm curious about why manufacturers went to this 'inside a box' design, after using the lower 'fork' mounting (like a Mk4 Supra rear LCA, 48730 in the diagram.)?

I'm sure there are a number of reasons. It could be to do with design heritage. How has Subaru been making rear LCA's for the Impreza? No doubt cost is a huge driver, as well as weight. Many considerations.

One thing is pretty sure: the structural requirements are the same, and there are multiple ways to meet the structural requirements while keeping weight and cost minimized. Cast or forged I-beam is one way, stamped hat-section (with lightening holes in FR-S/BRZ case) is another.

In any case, the difference is not for no reason, but then again it may not be for any major reason, either. The arm has to withstand tension/compression and vertical bending forces. Multiple *good* cheap easy ways to do that while keeping weight minimized.

[ZDan]

Originally Posted by EarlQHan

ZDan - Engineering's all about compromises though, whether it's weight, strength, stiffness, cost, etc. but I think that's where structural engineers and motorsport engineers differ.

You talk as if they are different disciplines. As in aerospace engineering, in motorsports, you MUST have structural engineers who know the score and how to design to meet the actual structural *requirements* for the specified usage (including expected off-course excursions and contact). Which are, of course, different for a road car vs. a dedicated race car.
In race teams, there is no "motorsports" engineer who overrides the structural engineer because the environmental requirements make the parts heavier. All the engineers (aero, structures, systemes, etc.) are working to the same goals.

In most forms of engineering a safety factor of 3+ is normal, in civil a SF of 10 is common.

"Safety factor" by itself is meaningless. How were the loads developed? If these guys are designing to static weight, or even max cornering loads, with a factor of 2.5 applied, that's not likely to be sufficient to ensure structural integrity over the usage these parts are likely to see.

In motorsports, that means you're carrying way too much unnecessary weight.

Again, it depends on what loads are being designed to. If it's a 2.5 or 3.0 factor applied to 1g static loads, that's not likely to last a 20 minute sprint.

But if the supplier isn't giving an inspection interval and inspection method, the part had *better* be as durable and reliable as the factory part.

It's not unheard of to have a SF of 1.5 or lower,

We designed to a 1.4 design ultimate factor of safety on the space shuttle external tank, (and 1.5 is typical for aerospace), but then we knew a LOT about the loads environment, and that factor is applied to the MAXIMUM expected loads. How much do these guys *really* know about the loads on this part? What loads exactly were they initially applying a 4.0 factor to, and then backing it down to 2.5 semi-arbitrarily? I'd like to know...

but they have low volume, high quality manufacturing, that are meticulously maintained, and replaced on a schedule.

IF their part doesnt' have the lifetime of the factory part, it is incumbent on them to inform the customer what the part lifetime is and give detailed inspection requirements of critical areas to ensure they don't have failures in the field. Anything less is bullshit.

If they were *smart* about it, they could replicate the OEM part strength and durability while giving adjustability and reducing weight. THAT would be worth an enthusiast's money.

[Ro_Ja]

Sooo... are there any rear lateral links currently on the market worth buying or are they all pretty much bling bling junk? Anything in the pipeline I should wait for instead?

[Calum]

Originally Posted by Ro_Ja

Sooo... are there any rear lateral links currently on the market worth buying or are they all pretty much bling bling junk? Anything in the pipeline I should wait for instead?

GTSpec and SPC both have decent looking offerings. The SPC does away with heim joints and uses a unique camber adjustment method. The GTSpec look better then most other offerings because of the position of the heim joint threads in that they are as far out as possible, reducing the force on that area. Both are stamped steel which gives me a warm fuzzy.

[EarlQHan]

ZDan - Motorsports doesn't have structural engineers per se. It's tasked to the individual design engineers to carry out the process from cradle to grave. I agree with your logic wholeheartedly though.

Without breaking confidentiality, I can say the arm was developed to withstand the following loads:

10G instantaneous bump
1G braking + 2G cornering + 1G bump combined
2.5G cornering

Weight transfer effects were considered.

Are there more efficient designs? Yes. Are there more effective materials? Yes. But there were other aspects they had to consider.

Stance is a value brand that offers good quality at a good price. If I had to compare suspension brands to stores, with Megan Racing being the dollar store and Ohlins being Whole Foods, Stance is like Target. You get everything want and need without breaking the bank.