Offset front lower spherical bearing?
09-15-2017, 09:40 AM
#11
not a spherical but origin and a few other places have made offset UCA bushings to artificially shorten the upper arm. You don't get the benefit of a wider track but its another option to skin the proverbial cat.
I think I'm ok with cracking the knuckle as a failure point, it's relatively inexpensive piece to purchase and easy to access and repair. If we shift the failure point else where, I would guess it's only going to get more expensive (control arms, subframe, frame) and more technically challenging to fix.
I think I'm ok with cracking the knuckle as a failure point, it's relatively inexpensive piece to purchase and easy to access and repair. If we shift the failure point else where, I would guess it's only going to get more expensive (control arms, subframe, frame) and more technically challenging to fix.
Well....if you crack a knuckle while on a track...the knuckle itself is going to be the least of your worries.
Its like saying you're not worried about your lug nuts coming loose and flying off because lugs and studs are cheap.
09-15-2017, 10:25 AM
#12
The offset is small, but the forces are very large, since you're getting all sway bar and spring/damper forces translating through the LBJ. The lower knuckle is very thin, because it's only designed to deal the moment created by cornering forces pulling through the ball joint. When you then add to that the moment created from offset spring/damper and swaybar forces, you're probably doubling the bending stress (give or take).
I don't doubt that there is an additional bending moment.
And maybe the forces are doubled, quadrupled, tripled, or billioned. But...is that enough to matter? Doubled from what? And what is the knuckle designed to carry?
your friends are the only ones I've heard of to be cracking knuckles.
Offset lower joints are a very popular mod. I haven't heard of anyone's knuckles coming apart.
Did your friends have badly made offset plates that weren't level? Over torqued bolts?
Over torqued bolts are a good guess to failure origin. Ball joint cases aren't cracking...the threaded knuckle is.
09-15-2017, 10:34 AM
#13
The knuckle has 3 points of contact: balljoint, tie rod and the UCA. I haven't experienced a failed knuckle, bent knuckles yes and those were from some massive offs, but I'm guessing it doesn't crack at all 3 connections simultaneously.
My point is that if the knuckle is the low hanging fruit for failure and shift the failure point upwards - where does it go up from there?
- lower control arm - that connects to the subframe and frame
- upper control arm - that connects to the frame
09-15-2017, 10:46 AM
#14
That's not equitable - if you degrade a product lower than OEM strength that's just plain stupid.
The knuckle has 3 points of contact: balljoint, tie rod and the UCA. I haven't experienced a failed knuckle, bent knuckles yes and those were from some massive offs, but I'm guessing it doesn't crack at all 3 connections simultaneously.
My point is that if the knuckle is the low hanging fruit for failure and shift the failure point upwards - where does it go up from there?
- lower control arm - that connects to the subframe and frame
- upper control arm - that connects to the frame
The knuckle has 3 points of contact: balljoint, tie rod and the UCA. I haven't experienced a failed knuckle, bent knuckles yes and those were from some massive offs, but I'm guessing it doesn't crack at all 3 connections simultaneously.
My point is that if the knuckle is the low hanging fruit for failure and shift the failure point upwards - where does it go up from there?
- lower control arm - that connects to the subframe and frame
- upper control arm - that connects to the frame
Wat?
I was responding to this:
not a spherical but origin and a few other places have made offset UCA bushings to artificially shorten the upper arm. You don't get the benefit of a wider track but its another option to skin the proverbial cat.
I think I'm ok with cracking the knuckle as a failure point, it's relatively inexpensive piece to purchase and easy to access and repair. If we shift the failure point else where, I would guess it's only going to get more expensive (control arms, subframe, frame) and more technically challenging to fix.
I think I'm ok with cracking the knuckle as a failure point, it's relatively inexpensive piece to purchase and easy to access and repair. If we shift the failure point else where, I would guess it's only going to get more expensive (control arms, subframe, frame) and more technically challenging to fix.
Are you saying that different methods (like upper joints and bushings) make other more expensive parts more liable to break?
09-15-2017, 10:56 AM
#15
^Nevermind.
I think I know what you're saying.
You're saying that the knuckle is the weak point in a stock system anyway.
Yes.
Lets call the knuckle a mechanical "fuse".
But...OP is saying that the offset joint takes this "fuse" and weakens it further.
You're assuming the failures came from crashing. In which case...fine...the knuckle broke. You already crashed or went off. So who cares?
In the above case, the crash is the cause of the failure.
But OP isn't specifying that the knuckles are cracking as a result of going off or crashing.
The problem is the potential of cracking a knuckle by creating a bending moment....while you are still ON track. With stresses from cornering/braking/driving. That would make the failure the cause....and the following crash the result.
Big difference.
Unless OP means his friends are cracking knuckles AFTER they've already crashed or gone off.
I think I know what you're saying.
You're saying that the knuckle is the weak point in a stock system anyway.
Yes.
Lets call the knuckle a mechanical "fuse".
But...OP is saying that the offset joint takes this "fuse" and weakens it further.
You're assuming the failures came from crashing. In which case...fine...the knuckle broke. You already crashed or went off. So who cares?
In the above case, the crash is the cause of the failure.
But OP isn't specifying that the knuckles are cracking as a result of going off or crashing.
The problem is the potential of cracking a knuckle by creating a bending moment....while you are still ON track. With stresses from cornering/braking/driving. That would make the failure the cause....and the following crash the result.
Big difference.
Unless OP means his friends are cracking knuckles AFTER they've already crashed or gone off.
09-15-2017, 11:34 AM
#16
Offset upper control arm bushings. No deflection, more camber, more wheel clearance on the fender, and cheap. Evasive sells the Origin Fabrication ones. I have a lot of friends running them without any issues.
09-15-2017, 11:43 AM
#17
Registered User
Thread Starter
I don't doubt that there is an additional bending moment.
And maybe the forces are doubled, quadrupled, tripled, or billioned. But...is that enough to matter? Doubled from what? And what is the knuckle designed to carry?
your friends are the only ones I've heard of to be cracking knuckles.
Offset lower joints are a very popular mod. I haven't heard of anyone's knuckles coming apart.
Did your friends have badly made offset plates that weren't level? Over torqued bolts?
Over torqued bolts are a good guess to failure origin. Ball joint cases aren't cracking...the threaded knuckle is.
And maybe the forces are doubled, quadrupled, tripled, or billioned. But...is that enough to matter? Doubled from what? And what is the knuckle designed to carry?
your friends are the only ones I've heard of to be cracking knuckles.
Offset lower joints are a very popular mod. I haven't heard of anyone's knuckles coming apart.
Did your friends have badly made offset plates that weren't level? Over torqued bolts?
Over torqued bolts are a good guess to failure origin. Ball joint cases aren't cracking...the threaded knuckle is.
He had one side fail... replaced it, then a few months later, the other side failed. Again, indicative of what you'd expect with similar loading and a fatigue failure.
He's pretty quick, with a lot of miles on R-comps, but it made me pause since I was planning to put on offset LBJ's myself.
The knuckle bending in a big hit is ENTIRELY different than a fatigue related failure. A bend due to a designed point of lower capacity is fine as long as you don't ALSO have cyclical fatigue loading in that section - which we do here. Fatigue failures mean stuff breaks off, a mechanical fuse allows things to bend as it passes yielding in a single loading event.
09-15-2017, 12:45 PM
#19
09-15-2017, 01:11 PM
#20
I saw pictures, and the fatigue failure started above the threaded holes, right where the "lugs" the lower ball joint mounts to starts to taper in. Obviously a fatigue failure in origin, but it's an area that'd be really hard to catch from crack origination, to crack propagation while on track. It's probably the same weekend where a crack would form, then propagate to full failure.
He had one side fail... replaced it, then a few months later, the other side failed. Again, indicative of what you'd expect with similar loading and a fatigue failure.
He's pretty quick, with a lot of miles on R-comps, but it made me pause since I was planning to put on offset LBJ's myself.
The knuckle bending in a big hit is ENTIRELY different than a fatigue related failure. A bend due to a designed point of lower capacity is fine as long as you don't ALSO have cyclical fatigue loading in that section - which we do here. Fatigue failures mean stuff breaks off, a mechanical fuse allows things to bend as it passes yielding in a single loading event.
He had one side fail... replaced it, then a few months later, the other side failed. Again, indicative of what you'd expect with similar loading and a fatigue failure.
He's pretty quick, with a lot of miles on R-comps, but it made me pause since I was planning to put on offset LBJ's myself.
The knuckle bending in a big hit is ENTIRELY different than a fatigue related failure. A bend due to a designed point of lower capacity is fine as long as you don't ALSO have cyclical fatigue loading in that section - which we do here. Fatigue failures mean stuff breaks off, a mechanical fuse allows things to bend as it passes yielding in a single loading event.
Most setups just need an extra degree or so. Stock adjusters get a typical setup to about -2 to -2.5. Most people use offset LBJs to run -3 to -3.5.
At the knuckle...you need like 0.25" or less of offset to gain 1 deg of camber.
Idk...the question is would that be enough to make or break the knuckle. I guess it depends on how much you're loading the knuckle.
Your friend may come close to the fatigue point of the knuckle in STOCK form.
Again...its strange because I haven't heard or seen this issue pop up on the web. I also know plenty of fast S2000 people with tons of miles on their track cars. Never seen this type of failure.
You sure he wasn't torquing these bolts to 5million LB's?