6UL wheels still cracking...
09-12-2019, 08:49 AM
#44
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Location: Quebec city, Canada
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Guys, failures happens on track cars, not much you can hope from the supplier... I can understand why they don't reply to this type of forum threads. Maybe they are working on something with there own cast supplier, maybe not.
If the failures would happen on road cars and causing injuries and what not, it would be a different scenario.
At least people are aware and can make their own decisions when it comes to buying a new set of wheels.
If the failures would happen on road cars and causing injuries and what not, it would be a different scenario.
At least people are aware and can make their own decisions when it comes to buying a new set of wheels.
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09-15-2019, 12:29 AM
#45
On miata.net on the 6UL ND wheel thread, page 10, someone does math analysis of the 6UL and points out a design flaw. I'm not a math whiz and don't understand the math but he uses the term "infinitesimal stress factor" to show the wheel is poorly engineered. If he's right that's a game changer from a legal and ethical standpoint.
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09-15-2019, 01:10 AM
#46
On miata.net on the 6UL ND wheel thread, page 10, someone does math analysis of the 6UL and points out a design flaw. I'm not a math whiz and don't understand the math but he uses the term "infinitesimal stress factor" to show the wheel is poorly engineered. If he's right that's a game changer from a legal and ethical standpoint.
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09-15-2019, 02:38 AM
#47
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09-15-2019, 04:18 AM
#48
On miata.net on the 6UL ND wheel thread, page 10, someone does math analysis of the 6UL and points out a design flaw. I'm not a math whiz and don't understand the math but he uses the term "infinitesimal stress factor" to show the wheel is poorly engineered. If he's right that's a game changer from a legal and ethical standpoint.
A lot of assumptions would have to be made regarding loading before any calculations could begin. Choosing what loads to design for would be quite a difficult task. Go too far towards safety and you end up with a wheel nobody wants. Customers want cheap and light weight and good looks.
If his wheels are failing more than they should, then most likely one or more of his assumptions was off and worst case loading is higher than expected thus shortening the life of the wheel. I think it sucks if this happened but it's a pretty complex problem to solve, and if people want cheap and light you can't have super high safety factors on your product.
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09-15-2019, 09:18 AM
#49
Retired Mech Design Engr
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"Fatigue Life" and Aluminum do not go together, unless there has been some recent breakthrough.
Posts 30583 and 30584 shows where 949 has addressed the subject.
Here is a copy of the email:
Posts 30583 and 30584 shows where 949 has addressed the subject.
Here is a copy of the email:
We have always recommended frequent inspections of the entire car if it is used for off highway high performance use or competition. Components that last a lifetime on street driven car can reach their design limits and fail in competition. Items like hubs, control arms, sub frames, miscellaneous brackets, engine mounts, and wheels can all reach their design limit sooner than expected. Impacts, excess heat, higher cornering, braking or acceleration loads from heavily modified cars-can overwhelm OEM or light weight aftermarket components. The aircraft industry performs constant and rigorous inspections on the most highly stressed and critical components. Professional race teams know of this need for regular inspections and therefore many components become consumables in this environment. But it can be a surprise to the weekend warrior new to high performance track day or HPDE events.
Since we launched our company in 2006, we have occasionally had customers directly contact us to report of their 949 Racing 6UL wheels cracking after extended use on a racetrack or in competition. Almost without exception, the wheels are many years old. In some case, they were purchased used with an unknown history. Reviewing samples, we find the wheels in question were designed, engineered and manufactured properly and to current industry standards. Digging further we find examples of similar LHP wheels from other brands cracking or breaking under similar usage conditions on track or in competition. This has led us to review the widely accepted test standards the wheel industry uses, JWL.
We categorize all 6UL wheels as "LHP" wheels (Lightweight High Performance). As with any brand or model LHP wheels used on track or in competition, we recommend careful, regular inspections of the entire wheel surface for cracking, bends, any signs of fatigue or impact damage that could reduce the wheel's ability to support the vehicle load. A cracked wheel that remains in service could fail catastrophically with the hub portion completely separating from the outer barrel. It is very unlikely that any wheel will catastrophically fail during hard cornering without cracking from fatigue or impacts first.
So perform this inspection on any LHP wheels you use, regardless of the brand. Going further, go through the whole modified car at regular intervals. Tell your friends and help spread the knowledge.
Statistically, your LHP wheels will probably never crack, regardless of brand. This is not a promise of course, merely a prediction based on available data. Just because it is not very likely however, doesn't mean you should avoid inspecting your high performance car regularly. You always wear your seat belt even though an accident is very unlikely.
As with virtually all LHP wheel manufacturers, we provide a one year warranty against defects, materials and workmanship. Please contact us if you have any further questions. Click the link below for more information on our warranty. Click the link below to learn more about wheel industry test standards.
-The 949 Racing team
Since we launched our company in 2006, we have occasionally had customers directly contact us to report of their 949 Racing 6UL wheels cracking after extended use on a racetrack or in competition. Almost without exception, the wheels are many years old. In some case, they were purchased used with an unknown history. Reviewing samples, we find the wheels in question were designed, engineered and manufactured properly and to current industry standards. Digging further we find examples of similar LHP wheels from other brands cracking or breaking under similar usage conditions on track or in competition. This has led us to review the widely accepted test standards the wheel industry uses, JWL.
We categorize all 6UL wheels as "LHP" wheels (Lightweight High Performance). As with any brand or model LHP wheels used on track or in competition, we recommend careful, regular inspections of the entire wheel surface for cracking, bends, any signs of fatigue or impact damage that could reduce the wheel's ability to support the vehicle load. A cracked wheel that remains in service could fail catastrophically with the hub portion completely separating from the outer barrel. It is very unlikely that any wheel will catastrophically fail during hard cornering without cracking from fatigue or impacts first.
So perform this inspection on any LHP wheels you use, regardless of the brand. Going further, go through the whole modified car at regular intervals. Tell your friends and help spread the knowledge.
Statistically, your LHP wheels will probably never crack, regardless of brand. This is not a promise of course, merely a prediction based on available data. Just because it is not very likely however, doesn't mean you should avoid inspecting your high performance car regularly. You always wear your seat belt even though an accident is very unlikely.
As with virtually all LHP wheel manufacturers, we provide a one year warranty against defects, materials and workmanship. Please contact us if you have any further questions. Click the link below for more information on our warranty. Click the link below to learn more about wheel industry test standards.
-The 949 Racing team
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09-15-2019, 09:52 AM
#50
The guy posted some equations. He did not do any analysis that points out a design flaw and he did not show the wheel is poorly engineered. They guy posted a few equations for calculating fatigue life.
A lot of assumptions would have to be made regarding loading before any calculations could begin. Choosing what loads to design for would be quite a difficult task. Go too far towards safety and you end up with a wheel nobody wants. Customers want cheap and light weight and good looks.
If his wheels are failing more than they should, then most likely one or more of his assumptions was off and worst case loading is higher than expected thus shortening the life of the wheel. I think it sucks if this happened but it's a pretty complex problem to solve, and if people want cheap and light you can't have super high safety factors on your product.
A lot of assumptions would have to be made regarding loading before any calculations could begin. Choosing what loads to design for would be quite a difficult task. Go too far towards safety and you end up with a wheel nobody wants. Customers want cheap and light weight and good looks.
If his wheels are failing more than they should, then most likely one or more of his assumptions was off and worst case loading is higher than expected thus shortening the life of the wheel. I think it sucks if this happened but it's a pretty complex problem to solve, and if people want cheap and light you can't have super high safety factors on your product.
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09-15-2019, 03:04 PM
#52
https://www.amesweb.info/Materials/M...ty-Metals.aspx
That chart shows various aluminum alloys as having roughly 1/3 the elasticity as compared to steel. Aluminum is therefore more brittle than steel.
https://www.amesweb.info/Materials/M...ty-Metals.aspx
Seems aluminum does have a fatigue life but has no fatigue limit.
That chart shows various aluminum alloys as having roughly 1/3 the elasticity as compared to steel. Aluminum is therefore more brittle than steel.
https://www.amesweb.info/Materials/M...ty-Metals.aspx
Seems aluminum does have a fatigue life but has no fatigue limit.
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09-15-2019, 07:39 PM
#53
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Join Date: Apr 2010
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Tire Rack article on checking your wheels for track use.
https://m.tirerack.com/tires/tiretec...jsp?techid=110
https://m.tirerack.com/tires/tiretec...jsp?techid=110
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09-16-2019, 12:19 AM
#55
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It's not a 1-to-1 relationship. Steel is 2.5x denser than aluminum, but it's not 2.5x stronger. You could design a steel wheel that is exactly as strong as an aluminum wheel, and it would be thinner, but because of the density of the material, it would still be heavier.
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09-16-2019, 12:33 AM
#56
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It's not a 1-to-1 relationship. Steel is 2.5x denser than aluminum, but it's not 2.5x stronger. You could design a steel wheel that is exactly as strong as an aluminum wheel, and it would be thinner, but because of the density of the material, it would still be heavier.
the same as how many people are shocked to find out that titanium is heavier than aluminium. (roughly 60% denser from a brief google)
But since it's about double the strength, you can use much less of it for the same strength as alu
From memory Magnesium (or at least, an alloy containing it) is another fairly strong, yet lightweight, material used for wheels.
But I remember it being fairly brittle, and cracking more readily than alu (plus the whole reaction to water thing once it ignites)
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09-16-2019, 12:38 AM
#57
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Magnesium is used because it's stiffer AFAIK. Back in the day all of my karting wheels were magnesium for that reason. The new hotness for wheels is carbon fiber, not because it's dramatically lighter, but because it can be made much stiffer. Wheels move A LOT under normal use. At the spokes, up to 2mm of flex under normal operation. At the inner bell of the wheel, a lot more than that. That flex degrades tire performance.
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09-16-2019, 08:58 AM
#58
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I have no dog in this fight, but there is a lot of trash engineering speculation going on in this thread.
We keep talking about “aluminum”, but there are lots of different aluminum alloys, and we have no idea which alloy these wheels are. I would speculate that they are 6061, but there are even different variations of 6061. The mechanical properties of the different alloys vary dramatically.
Aluminum doesn’t have less “elasticity” than steel. It has a lower elastic modulus, which means that a similar size/shape object will be less stiff if it is made from aluminum.
The failures being discussed are fatigue failures, not static failures. This makes things like elastic modulus almost irrelevant.
There are two steps to fatigue failure, crack formation and crack propagation. Aluminum is more notch sensitive than steel, meaning that a small scratch or defect can generate a fatigue fracture more easily. Unless there’s a sharp step or corner designed into the wheel where the cracks are starting, there is probably not a design defect per se. The recommendation to inspect wheels frequently is good advice.
The most important characteristic with regard to fatigue is how cracks propagate through the crystal lattice of the metal. As Sav pointed out, all aluminum alloys are inferior to steel in this regard, because cracks propagate more easily. Steel has a way of partially “healing” these cracks, where aluminum does not. Therefore steel has a finite fatigue limit, where aluminum does not.
https://en.m.wikipedia.org/wiki/Fatigue_limit
None of this is unique to 6UL’s, every manufacturer has to wrestle with these inherent properties and design accordingly. The “fix all” for these problems is to make the heaviest smoothest wheels possible, which none of us would probably buy.
Small differences in wheel design can make big differences in stresses. For instance, a 15x9 wheel is going to apply a lot more stress to the spokes than a 15x8 wheel because the inside edge of the barrel is a cantilever, and the stress on the spokes goes up exponentially with the length of the cantilever.
Manufacturing methods play a critical role in fatigue properties. Good wheels are forged or cold formed because it work hardens them, which basically means that the crystal lattice gets all tangled up and the material gets stiffer. If the work hardening is not evenly distributed then the stresses won’t be properly distributed either, which could lead to point stresses and crack initiation. I am in no way implying that there is an obvious issue with 6UL’s, but I would guess that there are substantial differences in how different wheels are made, and that differences here could be important to fatigue life. OEM auto manufacturers have teams of PhD’s that do things like forging and mold flow analysis.
We keep talking about “aluminum”, but there are lots of different aluminum alloys, and we have no idea which alloy these wheels are. I would speculate that they are 6061, but there are even different variations of 6061. The mechanical properties of the different alloys vary dramatically.
Aluminum doesn’t have less “elasticity” than steel. It has a lower elastic modulus, which means that a similar size/shape object will be less stiff if it is made from aluminum.
The failures being discussed are fatigue failures, not static failures. This makes things like elastic modulus almost irrelevant.
There are two steps to fatigue failure, crack formation and crack propagation. Aluminum is more notch sensitive than steel, meaning that a small scratch or defect can generate a fatigue fracture more easily. Unless there’s a sharp step or corner designed into the wheel where the cracks are starting, there is probably not a design defect per se. The recommendation to inspect wheels frequently is good advice.
The most important characteristic with regard to fatigue is how cracks propagate through the crystal lattice of the metal. As Sav pointed out, all aluminum alloys are inferior to steel in this regard, because cracks propagate more easily. Steel has a way of partially “healing” these cracks, where aluminum does not. Therefore steel has a finite fatigue limit, where aluminum does not.
https://en.m.wikipedia.org/wiki/Fatigue_limit
None of this is unique to 6UL’s, every manufacturer has to wrestle with these inherent properties and design accordingly. The “fix all” for these problems is to make the heaviest smoothest wheels possible, which none of us would probably buy.
Small differences in wheel design can make big differences in stresses. For instance, a 15x9 wheel is going to apply a lot more stress to the spokes than a 15x8 wheel because the inside edge of the barrel is a cantilever, and the stress on the spokes goes up exponentially with the length of the cantilever.
Manufacturing methods play a critical role in fatigue properties. Good wheels are forged or cold formed because it work hardens them, which basically means that the crystal lattice gets all tangled up and the material gets stiffer. If the work hardening is not evenly distributed then the stresses won’t be properly distributed either, which could lead to point stresses and crack initiation. I am in no way implying that there is an obvious issue with 6UL’s, but I would guess that there are substantial differences in how different wheels are made, and that differences here could be important to fatigue life. OEM auto manufacturers have teams of PhD’s that do things like forging and mold flow analysis.
Last edited by Schroedinger; 09-16-2019 at 09:12 AM.
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09-16-2019, 09:00 AM
#59
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Pretty much.
the same as how many people are shocked to find out that titanium is heavier than aluminium. (roughly 60% denser from a brief google)
But since it's about double the strength, you can use much less of it for the same strength as alu
From memory Magnesium (or at least, an alloy containing it) is another fairly strong, yet lightweight, material used for wheels.
But I remember it being fairly brittle, and cracking more readily than alu (plus the whole reaction to water thing once it ignites)
the same as how many people are shocked to find out that titanium is heavier than aluminium. (roughly 60% denser from a brief google)
But since it's about double the strength, you can use much less of it for the same strength as alu
From memory Magnesium (or at least, an alloy containing it) is another fairly strong, yet lightweight, material used for wheels.
But I remember it being fairly brittle, and cracking more readily than alu (plus the whole reaction to water thing once it ignites)
Berrylium is the true baller metal.
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