Kore control arms?

[jrobinson2]

the frame would twist into a pretzel before a solid iron control arm would give way.



-Ryan

I've thought this through and decided that if I hit something hard enough to bend something its a lot easier to replace a control arm than repair the frame mounts or the axle mounts I've seen the axle mounts collapsed with the stock arms



Jared

 

[rbattelle]

I've thought this through and decided that if I hit something hard enough to bend something its a lot easier to replace a control arm than repair the frame mounts or the axle mounts I've seen the axle mounts collapsed with the stock arms



Jared

Good point. I thought about that, but would probably use iron anyway. I don't drive off road at more than about 5 MPH anyway, and have no interest in the Baja-like conditions where Kore is run.



-Ryan

 

[GTani]

The billet control arms are made from 7075-T6 aluminum. This material is very unstable when machining. It moves. It should be "rough machined"(with in certain cross sectional parameters)and then stress relieved. Then it can be finish machined. Also the threaded portion of the control arms should have steel inserts(not sure if they do). There is quite a bit of set-up time involved even with good tooling and fixturing. . What I am trying to say that they didn't save much if any production cost by going to aluminum.

 

[JOblenes]

I should probably have listened to the angel on my right shoulder instead of the devil on my left, but oh well, here goes… I have said this on another thread but I think it bears repeating, I believe this is the age old problem of “when all you have is a hammer, evey problem looks like a nail” or said another way “when all you have is a CNC machine, everything looks like easily machined aluminum”. In my mind when something is “engineered” then the most suitable material is chosen to give you the best performance for the lowest cost and, clearly, CNC machined aluminum control arms do not fit this description. Just because something is machined from aluminum, and looks really cool, does not mean that it is well engineered. In my opinion, just my opinion mind you, said control arms are just so much bling. Personally I would also stay away from using aluminum in such an application from a fatigue perspective. Unlike good old steel which can be designed for an infinite fatigue life, aluminum has no asymptotic stress level where they will survive cyclical loading indefinitely, see curve below (or this link http://ussautomotive.com/auto/steelvsal/basicfacts.htm). At best you can make sure the aluminum will survive enough cycles to have “practically” an infinite life, i. e how many bumps will you really hit in 10 years of driving. The caveat here is that the product does truly need to be engineered and not just machined to look cool, there is a big difference, and I don’t buy the “I survived Baha, where’s my T-shirt” bit, driving Alberta back roads for 5 years will put many more cycles on a suspension then one 500 or 1000 mile race. Look at what goes in to aircraft design (mostly aluminum) and the level of inspection for , you guessed it, fatigue cracks. I will be interested to see the longer term integrity of aluminum control arms. I will be happy to have my worries put to rest.

 

[rbattelle]

Jonathan - great post!



There's certainly a tradeoff here. Aluminum is light, which makes it desireable for "unsprung" components. But it's not anywhere near as strong as steel (or iron), nor does it handle fatigue as well. In a work truck, never intended for high-speed off-roading, I'd much prefer iron (or steel). In my world, that implies the "cheap" Kore arms are the better buy.



There are certainly precedents for aluminum control arms (F-150 comes to mind), so it is a candidate material. Ever seen the control arms in an F-150? They're HUGE! Ford advertises it like "hey, look at how much bigger these are than the little steel arms on Chevy and Dodge". Of course, they don't bother pointing out that their arms are gigantic because they're made of a much weaker metal! But I digress...



-Ryan

 

[kparker]

7075 is not good for welding, but it actually machines quite well. It is also very strong. As for the threads, as long as the thread engagement is calculated properly, threading directly into aluminum should not ever be a problem. It is not an interface that will be re-torqued a couple of thousand times. JOblenes, that is 5052 they are graphing. They are talking about skinning body panels in the article you referenced. Fatigue cracks are a legitimate concern in aircraft wings and panels where thin sheet metal(aluminum) flexes continuously. Those overbuilt control arms KORE has are a completely different beast. The analogy just doesn't fit. I will agree with you that DOM could give the best all-round, cost effective control arm for the money.



As for production costs? I bet there are pro's and con's, of every possible type of control arm.



RBattelle, heavy, nodular iron control arms don't really make much sense. Not to be used offroad more than 5 miles an hour. Why even make any? You would be better off cutting the middle out of your stockers and doing some creative fabrication to gain tire clearance. I wouldn't recommend it, but it would work for your application.

 

[GTani]

Kparker is correct ,5052 condition o is great for forming and bending for low strength requirements. The o designation means "annealed".

 

[JOblenes]

... JOblenes, that is 5052 they are graphing. They are talking about skinning body panels in the article you referenced. Fatigue cracks are a legitimate concern in aircraft wings and panels where thin sheet metal(aluminum) flexes continuously. Those overbuilt control arms KORE has are a completely different beast... .

I have seen a fair number of S-N curves for various types of aluminum (I only used that one because the graphic was readily available on the web) and have not found one yet that has infinite fatigue endurance life, in fact I believe based on my current level of knowledge, and reading the reference book in front of me, that they don't exist, though I have been wrong before. You are saying that the Kore arms are overbuilt, based on what? Based on a single application of a straight axial load they may be, but for fatigue loading they will see in service I am not so sure. The loads that they can see from impacts with pot holes can be pretty horrendous. Please understand that I am not saying they are not properly and safely designed, because I am not saying that. I am only saying that less than optimal choices of material and manufacturing techniques also makes me wonder about the "engineering" side.



I have winches on my truck. I was looking for d-loops strong enough for doubling my 12,000 lb front winch. It turns out the ones on the back of the Hummer are strong enough. I phoned GM for a price, almost $Can 400. 00 for a set. I thought too much, go aftermarket. Found nice stainless ones offered by "reputable" aftermarket parts manufacturer for half of what GM wanted. I enquired about load ratings, this went from vendor, to distributor, to manufacturer, to product R&D department and then they decided not address my question. The reason, they had never really done the engineering, other than looks cool (bling) they could not say one way or another what they were good for. And this is from a reputable aftermarket parts dealer, go figure.



Jonathan

 

[rbattelle]

RBattelle, heavy, nodular iron control arms don't really make much sense. Not to be used offroad more than 5 miles an hour. Why even make any?

Most of the things I build make no sense. :-laf I just have an obsession with building everything 10 times stronger and heavier than is necessary. Some might call it wasteful. I call it "accounting for future requirements creep".



Jonathan - for shackles check out Crosby. They make some of the finest clevis' in the world. I have a set of 4 9. 5-ton working-load clevis' that I plan to use as recovery points whenever I get around to getting new bumpers.



-Ryan

 

[GTani]

JOblenes,why do you think aluminum is an inferior material?After all pistons are Aluminum. Piston speed must be tremendous even in our low r. p. m. Cummins. Plus 35lbs of boost,heat and needing to come to a stop(not exactly) and reverse directions. They need to cycle more than a set of control arms. Maybe I'm off base. Just curious.

The stock control arms are plenty strong for the most part. But they don't look like they can take much side-load. I think that is where KORE tried to increase strength.

Do 99. 99% of us need them?I'm sure, no. Again I might be of base. Just my thoughts.

 

[NVR FNSH]

The caveat here is that the product does truly need to be engineered and not just machined to look cool, there is a big difference, and I don’t buy the “I survived Baha, where’s my T-shirt” bit, driving Alberta back roads for 5 years will put many more cycles on a suspension then one 500 or 1000 mile race.

Never been to Baja or spent any time in a desert racing vehicle have you? I worked for a small design firm that did the design work on a Class 4 - full size 4wd - SCORE race truck that was also backed by GM Corporate. Actual vehicle testing was ultimate approval used for new designs on that truck. Trying to estimate/simulate the number of cycles on an offroad race vehicle is almost impossible.



Brian

 

[NVR FNSH]

Jonathan - great post!



There's certainly a tradeoff here. Aluminum is light, which makes it desireable for "unsprung" components. But it's not anywhere near as strong as steel (or iron), nor does it handle fatigue as well. In a work truck, never intended for high-speed off-roading, I'd much prefer iron (or steel). In my world, that implies the "cheap" Kore arms are the better buy.



There are certainly precedents for aluminum control arms (F-150 comes to mind), so it is a candidate material. Ever seen the control arms in an F-150? They're HUGE! Ford advertises it like "hey, look at how much bigger these are than the little steel arms on Chevy and Dodge". Of course, they don't bother pointing out that their arms are gigantic because they're made of a much weaker metal! But I digress...



-Ryan

There is a lot to be said for the geometry - ie section modulus - of the part compensating for the material strength.



Brian

 

[JOblenes]

JOblenes,why do you think aluminum is an inferior material?After all pistons are Aluminum. Piston speed must be tremendous even in our low r. p. m. Cummins. Plus 35lbs of boost,heat and needing to come to a stop(not exactly) and reverse directions. They need to cycle more than a set of control arms. Maybe I'm off base. Just curious.

The stock control arms are plenty strong for the most part. But they don't look like they can take much side-load. I think that is where KORE tried to increase strength.

Do 99. 99% of us need them?I'm sure, no. Again I might be of base. Just my thoughts.

I don't think it is a matter of you being off base, more that my message was not understood as well as I hoped. Above you are asking why I think aluminum is an inferior material. Actually I don't believe it is inherently inferior. What I am saying is that aluminum has some unique properties that make designing with it a little more critical than designing stuff with carbon steel. With carbon steel basically if you can make it survive for 1,000,000 cycles it will be good for life (of course not exactly because of wear, corrosion, etc. but from a fatigue perspective hopefuly you get the point). What I am questioning above is the reason for choosing the material. Now if the reason is "unsprung weight was the first and only consideration" fine, maybe I would buy into it... some, but in a critical review of the design, through my own eyes, I don't believe that was the motivation. Instead I believe the material was selected because of a pre-existing desire to use a certain manufacturing technique that the manufacturer is familiar with. This approach of fixating on one particular process makes me suspicious of the soundness of the rest of the "design process".



(Note to everyone: please understand in all that I have written above and in previous posts not to take these values as without exeption, not every carbon steel has an infinite fatigue life at 1,000,000 cycles, etc. but in general it is a good rule of thumb. When designing real parts the designer must obtain the mechanical properties for the actual materials they are using. )

 

[JOblenes]

Never been to Baja or spent any time in a desert racing vehicle have you? I worked for a small design firm that did the design work on a Class 4 - full size 4wd - SCORE race truck that was also backed by GM Corporate. Actual vehicle testing was ultimate approval used for new designs on that truck. Trying to estimate/simulate the number of cycles on an offroad race vehicle is almost impossible.



Brian

Nope, never been to Baha. I am not doubting that Baja puts the hurting on vehicle components and I am a huge believer in actual phycsical testing when it comes to assessing the suitability of a particular design from a fatigue perspective (it is a requirement in my mind). Its just that I don't believe a 500 or 1000 mile race is sufficient. I have had the pleasure of visiting several heavy equipment manufacturers and have witnessed the testing programs that some of them use to qualify their products and it is amazing to see. Imagine taking a forklift and automating it to lift a pallet to full extenstion, set it on a rack, lift it off again and set in on the ground and repeat. The forklift is instrumented with strain gages to capture the material response during each of the lift cycles so they know where they are on the S-N curve. If the lift is rated for 1 ton - they will put typically 4 - 5 tons on the pallet and they will run the thing until it has exceeded the fatigue endurance limit or it fails prematurely. With steel this is easy (easier than aluminum) to do because if they can surpass 1,000,000 cycles they are good to go (though they typically do more). With aluminum you could still break at 2,000,000 or 3,000,000 or so on. Doesn't mean you can't make an aluminum forklift just a whole lot more thought (and testing) needs to go into it. As you can imagine the lift cycle for a forklift is not rapid, assume that they are doing fast lifts and the cycle takes 15 seconds to complete, that is 173 days of running the thing 24/7 to prove it will last and with steel they would be absolutely justified in their claims of an infinite fatigue design at the rated (1 ton not the tested 4 ton) design capacity. I have seen them get to say 300,000 cycles and fail, back to the drawing board.



Now back to the reason I don't believe Baha is sufficient, you just don't get that many cycles in, I am sure Baha is bumpy, and some of those bumps are huge, but I put a lot of miles (hundreds of thousands) on my truck on some very bumpy roads. As an engineer I prefer to see things tested in a rigorous fashion. I personally view Baha type testing as more of a marketing type testing. Sure my car might have survived Pikes Peak, but my VW still blew a head gasket just driving around Calgary, go figure.



After re-reading this post: I guess I am just one of those folks who is always sizing things up from a technical perspective and always asking my self "why did they do it that way?" and "Is there a better way to do that?" That and in my day job I do a fair amount of mechanical testing (when I am not surfing TDR :-laf ) and have develloped a "show me" attitude when it comes to claims of product performance. Maybe I need to move to Missouri.

 

[JOblenes]

And as you have probably guessed, despite the fact I don't like their furniture, I sit there mesmerized every time I shop at IKEA. Maybe we should see if they will slap a dodge suspension on their chair!!



Jonathan

 

[evldsl]

I don't think it is a matter of you being off base, more that my message was not understood as well as I hoped. Above you are asking why I think aluminum is an inferior material. Actually I don't believe it is inherently inferior. What I am saying is that aluminum has some unique properties that make designing with it a little more critical than designing stuff with carbon steel. With carbon steel basically if you can make it survive for 1,000,000 cycles it will be good for life (of course not exactly because of wear, corrosion, etc. but from a fatigue perspective hopefuly you get the point). What I am questioning above is the reason for choosing the material. Now if the reason is "unsprung weight was the first and only consideration" fine, maybe I would buy into it... some, but in a critical review of the design, through my own eyes, I don't believe that was the motivation. Instead I believe the material was selected because of a pre-existing desire to use a certain manufacturing technique that the manufacturer is familiar with. This approach of fixating on one particular process makes me suspicious of the soundness of the rest of the "design process".



(Note to everyone: please understand in all that I have written above and in previous posts not to take these values as without exeption, not every carbon steel has an infinite fatigue life at 1,000,000 cycles, etc. but in general it is a good rule of thumb. When designing real parts the designer must obtain the mechanical properties for the actual materials they are using. )

"Yea", That is why aircraft are built out of aluminum and there are still some flying from the 30,40's with the original skin and stringers. Now you would think all that airtime and work stress would account for something. Would"nt you? :-laf

 

[JOblenes]

"Yea", That is why aircraft are built out of aluminum and there are still some flying from the 30,40's with the original skin and stringers. Now you would think all that airtime and work stress would account for something. Would"nt you? :-laf

I am not sure I can gage your intentions with this reply. Certainly things can be built from aluminum to last a long time, no doubt about it, I am not presenting any arguments to the contrary, just saying one needs to be more careful with aluminum when considering fatigue. But don't forget that even though there are planes from the 30's and 40's still flying today there are many, many tales of planes from modern times that did fail, just do a Google search with "Boeing fatigue failure". And these guys are some smart fellows with large scale testing facilities.



Am I reading it correctly that you don't believe aluminum has these fatigue characteristics that must be considered carefully when designing?



Jonathan

 

[kparker]

Being skeptical of a design is fine. Smart in fact. Making an assumption that a given product is possibly inferior due to the material isn't. Each material has it's own inherent drawbacks. Manufacturability, price, tensile strength, modulous of elasticity(stiffness), corrosion resistance, impact resistance, weight, fatigue strength... The list go's on. If aluminum were not a viable material, then every dirt bike out there would have rear tires laying behind the rider after every jump. Can you imagine what a swing-arm endures? Some Class 1 cars have aluminum spindles, and A-arms. Bicycle cranks have been made of aluminum, with steel pedal shafts threaded directly into them, in single shear, for a long time now. Not uncommon to see a bent pedal shaft that was sticking out of 3/4" thick aluminum crank. With complex shapes, CNC maching is easier than cool box section fabrication. CNC maching of steel, is slooowww, and hard on tools relative to aluminum.



In any given design, the pro's and con's of each type of material, manufacturability, and price have to come into play. After prototypes have been made, design validation takes many forms. Is racing a 1000 mile race meaningfull? Sure it is. So is sending parts out to testing houses and taking parts to failure. I would imagine both are pretty expensive. Every mile I drive is further validation for the strength and resilience of the KORE shock tower. Is JOblenes concerned that the bearing caps on his shocks, are bling bling red anodized aluminum? Probably not. It's a proven design, even raced in Baja a few times for design validation.



I am not here to pick on JOblenes, blind assumptions are not at all uncommon when it comes to materials in the engineering world. I was once in charge of designing a sonar system for a top secret "platform". Common term for a submarine you are not supposed to know about. The whole thing is skinned with 6Al-4v Titanium, ELI ASTM B265, Grade23. Now 6Al-4v is commonly available, albeit expensive material. The ELI bla bla bla means that it is the good stuff for thin sheet, fracture resistance(submarine hull walls). We were required to use this material on our massive block of titanium that couldn't crack if it were dropped off the Empire State Building. A case where fracture resistance was not an issue, the standard material would suffice. Thin skins of aluminum with rivet holes all throughout them(like a wing), are good candidates for stress fractures. Big chunks of 7075-T6 for control arms really aren't. I trust that the engineering behind them was performed in a professional manner. Until I hear of failures in the field, I will not be concerned by any engineer, designer, fabricator, or other random critic's claims of inferiority. The aluminum control arms fit a need, and they seem to perform their job. Yes they could be made of steel, titanium, maybe even nodular iron... But they are not. We all have options, if you don't like what you see, don't buy it. But don't doubt the engineering behind any product because of any one man's rantings. There is more than one way to skin a cat... .....

 

[rbattelle]

Geez, JOblenes is really taking a beating here. Personally I think he presented a pretty calm, rational argument simply that you must be "careful" when using aluminum in any application - and I agree. I didn't read him ever mention that aluminum is somehow "inferior".



My only issue with the Kore arms is that the design seems wasteful. What I mean by that is, a steel arm could have been made as thin as the "notched" center portion of the Kore arms along its entire length with absolutely no sacrifice in strength. Choosing aluminum, however, requires the larger cross section on each end (for lateral strength?). Under ordinary pure-compressive loading the bulges at the ends don't add much (if any) strength.



I wonder what the relative weight of their aluminum arms and their steel arms is?



-Ryan

 

[GTani]

You need to be careful with any material in any design application.