Yes. My point was that it is not the bolts that are in single sheer, but the welded on parts (bosses as you call them). My point being that it is not a black and white comparison, if the Whiteline had actual bolts in single sheer it would be more concerning than the welded in pivot points.
cortex watts link
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Yes. My point was that it is not the bolts that are in single sheer, but the welded on parts (bosses as you call them). My point being that it is not a black and white comparison, if the Whiteline had actual bolts in single sheer it would be more concerning than the welded in pivot points.
SoundGuyDave
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Why? Take a step back and think about the forces applied, and how they are routed. A weld may or may not be stronger than the shear capacity of a bolt. Either way, there is torsional (prying) force being applied to the "thing" that holds the linkage arm to the bracket. Whether that "thing" is a welded on threaded boss that takes the load or a bolt, there is still prying load being applied. If the load is continually increased until something fails (weakest link), you could have the linkage arm bend, the weld fail and the boss pop off, the weld hold and the metal surrounding the boss tear out (HAZ), you could also have the football the boss is welded to bend, or any of a myriad of other things, including secondary effects, like having the football bend, which then applies force to the bolt threaded into the boss which then strips the threads, or puts enough torque on the bushing at the prop bolt to deform it, or..... You get the picture. I agree, the linkage arm bolt itself isn't being shear loaded, but the thing it's threaded into is. Absent a supporting bracket, that makes it a single-shear connection.
Why do you keep making the point that the boss is in single sheer? I never said it wasn't and has nothing to do with my point.
The diameter of the boss, and the surface area of the weld is going to provide a stronger connection than any reasonable sized bolt would. The outer pivots are 20mm in diameter and the center pivot is 21mm in diameter. Which is a pretty significant increase over the 14mm bolts that are usually said to be in single sheer.
Additionally, it is much less likely that the boss will bend or break than the connection points to the bracket. I would much rather this point be welded (properly) than threaded
I would never argue that single sheer is not an issue. Double sheer is clearly superior. This was not about double vs single sheer in the first place and was about where the forces are actually exerted, which would be more concerning to me if it was on the 14mm bolt than the 20mm boss.
The diameter of the boss, and the surface area of the weld is going to provide a stronger connection than any reasonable sized bolt would. The outer pivots are 20mm in diameter and the center pivot is 21mm in diameter. Which is a pretty significant increase over the 14mm bolts that are usually said to be in single sheer.
Additionally, it is much less likely that the boss will bend or break than the connection points to the bracket. I would much rather this point be welded (properly) than threaded
I would never argue that single sheer is not an issue. Double sheer is clearly superior. This was not about double vs single sheer in the first place and was about where the forces are actually exerted, which would be more concerning to me if it was on the 14mm bolt than the 20mm boss.
SoundGuyDave
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In your post, #33, the overall tone seemed to imply to me that because the BOLTS weren't in shear-loading, then everything was goodness, baby kittens, rainbows and unicorn farts. The fact is that is far from the truth. Perhaps I was operating under a mis-assumption, that you had convinced yourself that since the bolts weren't loaded, nothing could possibly be wrong with the design from a pure strength standpoint.
That's all, the sole reason that I was hammering away at looking at the way the component was loaded, rather than how the threaded fastener itelf was loaded. I honestly don't know which would have a superior yeild strength, a double-sheer bracket with a 14mm bolt, or a welded-on 20mm threaded boss, but I CAN tell you that given a choice, I would personally opt for double-shear for ANY load-bearing component given a choice.
That's all, the sole reason that I was hammering away at looking at the way the component was loaded, rather than how the threaded fastener itelf was loaded. I honestly don't know which would have a superior yeild strength, a double-sheer bracket with a 14mm bolt, or a welded-on 20mm threaded boss, but I CAN tell you that given a choice, I would personally opt for double-shear for ANY load-bearing component given a choice.
I would take the double sheered component any day as well, which is part of the reason I recommended the Cortex/Griggs design over the Whiteline on the first page. I was trying to clarify a minor point that it was not the actual bolts. I think we just got our wires crossed here. I definitely could have been more clear. My bad.
jayh007
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A nice feature of the Griggs and cortex is the adjustable roll center. By lowering the roll center to a certain point you could get on the gas a little early coming out of a turn. May be a nice tuning tool.
Gray Ghost GT
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I think I'll stay with my Fays2 watts link based on the other designs in the market, but I do like the Griggs unit too. They talk about double shear vs. single shear too.
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jayh007
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It looks like the Fays also has a adjustable roll center. Am I correct?I think I'll stay with my Fays2 watts link based on the other designs in the market, but I do like the Griggs unit too. They talk about double shear vs. single shear too.
Roadracer350
Senior Member
So does Whiteline. Granted its only 2 position you need to remember its geared to the street. Griggs and cortex does have more adjustment but it is geared to race cars. Now with that being said this is corner carvers so we are all geared to the racing side but I will say it again look at the Vorshlag guys. Terry has not only proven the Whiteline suspension will take a beating week in and week out he has won with their watts. It all in how you set it up and seat time. My car is dropped almost 3" and it tracks like its on rails! I get NO wiggle out of the rearend even when going around corners with bumps at the apex at full throttle. Plus no noise and with the coil settings backed off she rides like a caddy on the turnpike!
Gray Ghost GT
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Yes, it has multiple settings you can use to support your overall suspension setup. My car is a daily driver and I've had no problem with unusual noise from this watts link. Very rugged and performs very well.
JesseW.
Member
i bought a Fays2 a few months back and like it a lot. from a price, ease of install, quality and performance standpoint i think it is top notch. it just doesn't have the Bling factor the cortex or whiteline units have. but it does have way more adjustability.
from a performance standpoint, a little adjusting on the roll center in the rear seems to have a big difference on how the car sticks at autocross. the top hole has about the same roll center as a phb, and feels about the same without the difference in left and right turns. the lower i have moved it, the better grip i have gotten out of the back end until it started pushing the front pretty badly. so at that point i moved it back up until i hit my comfort sweetspot.
before this i was running a rod end PHB. the car had a much bigger change in feel going from the stock panhard bar and lowering springs, to the rod end phb and stiff springs/weight jackers than it did going from that to the watts link.
where the watts link shines over that setup is the roll center adjustment, but that comes at many times the price.
from a performance standpoint, a little adjusting on the roll center in the rear seems to have a big difference on how the car sticks at autocross. the top hole has about the same roll center as a phb, and feels about the same without the difference in left and right turns. the lower i have moved it, the better grip i have gotten out of the back end until it started pushing the front pretty badly. so at that point i moved it back up until i hit my comfort sweetspot.
before this i was running a rod end PHB. the car had a much bigger change in feel going from the stock panhard bar and lowering springs, to the rod end phb and stiff springs/weight jackers than it did going from that to the watts link.
where the watts link shines over that setup is the roll center adjustment, but that comes at many times the price.
Norm Peterson
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Not an ME, but there seems to be some confusion between shear stress (in any given component) and the use of the word 'shear' to describe a joint in the fewest words.
Shear, meaning the amount of force trying to cut a plane through the cross section of a part ÷ the cross sectional area of that part through that plane isn't really the concern.
What is, is the bending moments that also result, and those are what will result in a fatigue failure if the part is going to fail at all.
Understand that single shear is structurally a cantilever beam analysis, which will result in the maximum possible bending at the fixed end of the bolt/stud/tube/stand . . . and the largest bending stress and the greatest rate of accumulating fatigue damage. Structurally this isn't the best solution, but it can be used in safety provided that sufficient margin is built in to the design.
Double shear splits the applied force - and not always in a 50-50 distribution like you might first think even if the pin is loaded right in the middle of its span between what constitutes its bracket (I'll get back to that later). But the maximum bending moment at the threaded end of a bolt or the boss that it is threaded into is considerably less than it would be if a second shear plane (out there just inside the bridge on a Watts link propeller pivot point) isn't present. Worst case, if one side of a double shear connection failed, you'd still have whatever resistance the remaining side could muster (and probably a little advance warning that something was seriously amiss back there).
A little reduction can go a long ways. I'm mostly retired now, but within the industry I spent most of the past 35 years in, the commonly used relation between stress and fatigue life was "inverse 5th power". Basically, that says if you double the alternating stress (think left to right turn loading), the fatigue life drops to less than 5% (3.13% to be mathematically precise). Stated another way, halving the stress if you could attain truly equal shear sharing would net you 32 times the fatigue life of the single shear arrangement.
Other industries may use a less conservative approach than we did in powerplant situations (including nuclear), but I don't think you'll find fatigue life estimates taken as anything less than an inverse cube function of stress (that'd be 12.5% life for a doubled stress, or 8 times the life if stress is halved). And in truth, this relation is not fixed. From known fatigue data, the exponent varies considerably, and IIRC generally in the 3rd to 5th power range.
In some other post I mentioned only a little earlier this morning that the load (shear force) distribution in the pictured Watts link would not be 50-50 like you might think. That is because the load path directly into the diff housing will deflect only as much as the bolt or central pin will deform in shear. The path through the bridge, on the other hand, will add at least the bending and shear deflections of the stands to pin shear deflection on the bridge side of the propeller. Since load divides in proportion to the stiffness of the load paths involved, the bridge path won't actually carry 50%.
There isn't really enough information to say how it divides without making a lot of assumptions, but let's just say that only 10% of the lateral load goes through the bridge. That puts 90% still going directly to the diff housing. Rather than waste time arguing whether inverse 5th or inverse 3rd is appropriate, let's just use inverse 4th power. That 90% stress then corresponds to about 52% greater fatigue life. At an 80/20 load split, fatigue life goes up nearly 4 times (3.85-ish).
Norm
Shear, meaning the amount of force trying to cut a plane through the cross section of a part ÷ the cross sectional area of that part through that plane isn't really the concern.
What is, is the bending moments that also result, and those are what will result in a fatigue failure if the part is going to fail at all.
Understand that single shear is structurally a cantilever beam analysis, which will result in the maximum possible bending at the fixed end of the bolt/stud/tube/stand . . . and the largest bending stress and the greatest rate of accumulating fatigue damage. Structurally this isn't the best solution, but it can be used in safety provided that sufficient margin is built in to the design.
Double shear splits the applied force - and not always in a 50-50 distribution like you might first think even if the pin is loaded right in the middle of its span between what constitutes its bracket (I'll get back to that later). But the maximum bending moment at the threaded end of a bolt or the boss that it is threaded into is considerably less than it would be if a second shear plane (out there just inside the bridge on a Watts link propeller pivot point) isn't present. Worst case, if one side of a double shear connection failed, you'd still have whatever resistance the remaining side could muster (and probably a little advance warning that something was seriously amiss back there).
A little reduction can go a long ways. I'm mostly retired now, but within the industry I spent most of the past 35 years in, the commonly used relation between stress and fatigue life was "inverse 5th power". Basically, that says if you double the alternating stress (think left to right turn loading), the fatigue life drops to less than 5% (3.13% to be mathematically precise). Stated another way, halving the stress if you could attain truly equal shear sharing would net you 32 times the fatigue life of the single shear arrangement.
Other industries may use a less conservative approach than we did in powerplant situations (including nuclear), but I don't think you'll find fatigue life estimates taken as anything less than an inverse cube function of stress (that'd be 12.5% life for a doubled stress, or 8 times the life if stress is halved). And in truth, this relation is not fixed. From known fatigue data, the exponent varies considerably, and IIRC generally in the 3rd to 5th power range.
In some other post I mentioned only a little earlier this morning that the load (shear force) distribution in the pictured Watts link would not be 50-50 like you might think. That is because the load path directly into the diff housing will deflect only as much as the bolt or central pin will deform in shear. The path through the bridge, on the other hand, will add at least the bending and shear deflections of the stands to pin shear deflection on the bridge side of the propeller. Since load divides in proportion to the stiffness of the load paths involved, the bridge path won't actually carry 50%.
There isn't really enough information to say how it divides without making a lot of assumptions, but let's just say that only 10% of the lateral load goes through the bridge. That puts 90% still going directly to the diff housing. Rather than waste time arguing whether inverse 5th or inverse 3rd is appropriate, let's just use inverse 4th power. That 90% stress then corresponds to about 52% greater fatigue life. At an 80/20 load split, fatigue life goes up nearly 4 times (3.85-ish).
Norm
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barbaro
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I know the Fays 2 works and all, but doesn't it look like something they hang in the zoo for monkeys to swing from? It is not visually simpatico. Can a Cortex survive a crash better than a panhard bar? I don't care because if I think about what will happen when I crash . . .as night follows day; I will crash.
Cortex is not heavy (19.9) lbs and probably lighter than the Fays II. The differential cover is a beefy cast unit with a nice finish. It's race. Mine is the street version and it has never made a peep.
SoundGuyDave
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jayh007
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What welding was required to install the cortex? Did you install yourself?
Your kinda right if you didn't know better you would think it was one of those new exercise machines they sell on a late night info commercials.
Gray Ghost GT
Road Racing Fanatic!
Interesting to see comments on a Corner Carver Racing Tech forum that places emphasis on the appearance of a part vs. its actual functionality and superior design; especially given that the fact that you don't see the part unless the car is on a lift... face palm indeed. I knew I was doing something wrong... my parts and car may perform better, but I guess they won't win a beauty contest.
JesseW.
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+ juan
Department Of Boost
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And on that note, I'm outta here. This thread has obviously been maxed out.
PLee
Member
ok, I'll try not to add too much fuel to this "which is better" fire, but I can add some factual information about one of these watts links. Because of my employment, I have some pretty unique hands-on experience w/ the Boss-S & -R race cars. I can tell you that very recently, the Cortex unit was tested & approved for use by one of the Ford Racing engineers, on a Boss-R that we sponsor (Alec Udell). His car also happens to be one of the fastest cars in the World Challenge series.
Long story- the Ford Racing guys keep pretty tight control over what parts are used on those race cars; they don't really want anything on the track that they haven't had a chance to test and approve (think- if a bunch of Mustang race cars use unvalidated parts and crash, it won't look good for Ford's Mustang racing program). Udell's team wanted to use the Cortex unit, and Ford agreed so long as they could validate it. We installed one in one of the mules and tested it at a semi-local track. FRPP and Cortex are working together to make some very minor bracket changes (where it welds to the body), but other than that, it has been approved for their use.
I can tell you with complete certainty that every part that goes into either the Cobra Jets or Boss race cars (and ultimately into the FRPP catalog) is tested to the n^th degree. The new rear parachute bumper on the '14 CJ has at least 5-8 design revisions and probably 30+ passes on it (with load cell testing), to know exactly what happens when the chute is deployed. So... I'm fairly comfortable with anything they've tested.
Does that mean all of the others suck? No. Just means the Cortex unit is one they have tested and approved. And Filip is an outstanding guy if you ever get to meet him and share a drink or two.
Long story- the Ford Racing guys keep pretty tight control over what parts are used on those race cars; they don't really want anything on the track that they haven't had a chance to test and approve (think- if a bunch of Mustang race cars use unvalidated parts and crash, it won't look good for Ford's Mustang racing program). Udell's team wanted to use the Cortex unit, and Ford agreed so long as they could validate it. We installed one in one of the mules and tested it at a semi-local track. FRPP and Cortex are working together to make some very minor bracket changes (where it welds to the body), but other than that, it has been approved for their use.
I can tell you with complete certainty that every part that goes into either the Cobra Jets or Boss race cars (and ultimately into the FRPP catalog) is tested to the n^th degree. The new rear parachute bumper on the '14 CJ has at least 5-8 design revisions and probably 30+ passes on it (with load cell testing), to know exactly what happens when the chute is deployed. So... I'm fairly comfortable with anything they've tested.
Does that mean all of the others suck? No. Just means the Cortex unit is one they have tested and approved. And Filip is an outstanding guy if you ever get to meet him and share a drink or two.
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Gray Ghost GT
Road Racing Fanatic!
^^^ Excellent post. Very informative and good to know.
I think it would be good if Cortex provided an addendum on their website or instruction sheet that outlined the suggested modifications made by Ford Racing when they installed their parts.
I think it would be good if Cortex provided an addendum on their website or instruction sheet that outlined the suggested modifications made by Ford Racing when they installed their parts.
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