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| Truck Reviews (15215 Posts)
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Deep breath, count to 10...
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On 6/8/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
Merk, I love and your trucks. I want to see you continue to support the industry by making these things It is of great value, and in ways that dollar signs can't measure. It helps, in part, to demonstrate how good things can be, and good WE can be. When I first use your trucks, it was on a race-day. I was instantly comfortable with them and was a better competitor because of them.
It may not be my place to be afraid for you, or to give you father advise (I could be older), BUT...
...you better pray that no one gets hurt badly and has a lawyer who can read. The time for all of us so called "expert wtnesses" is NOW, where we have an oppoertunity to solve a problem. The bandaid "legal" fix is to distribute some instructions indicating that the kingpins need to be replaced at every 10,000 pumps or 12 month period, whichever comes first. If that sounds totally stupid it's because it is stupid. You gotta solve the problem. One percent is a small number, until you compare it with a tenth of one percent. Stated that way (and any decent lawyer would), it is "ten times more likey to break than other trucks that cost one tenth the price..." "There are people who have had their kingpins break not once but twice, even though he changed them routinely..." Trying to prove that someone DIDN'T swap them out is impossible to prove.
So there sits little Jessica, once a vibrant young woman, in the prime of her life, gurgling and pooping herself between spastic episodes, in a wheelchair in the middle of the Florida courtroom, or all the jury to see. Meanwhile, Adam has been diposed and must printout the entire Trucks Forum banter for the jurors. An angry mob marches outside with signs saying "How Could You Mark?" and "McGreed must not be Freed". The amount of the settlement skyrockets when the jury finds out that little Jessica had become pregnant during a Black Leathers Racer / Radikal sponsored party in Paris. You, you, you wreckless rich architect you...
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OK
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On 6/8/2005
MARK MCCREE
wrote in from
United States
(65.40.nnn.nnn)
Boy that felt good.
Chuck, You are right. The areospace and flight industry does have life spans on parts and replacement schedules. Challenger did fall to the ground despite the schedules. Go figure.
I must say that I do agree that the typical truck design, where the king pin is essentially a cantilever, leaves much to be desired. I have raced 27 years wondering how to get around this fact. So far to no avail that makes better sense.
Chuck has a good idea-- make the sucker bigger around. Make a 7/16" king pin maybe. Or even 1/2". I don't think this is the answer to a question that is not a universal issue.
I think the events of failure less than 1% does not justify the added weight and non-compatability with other bushing manufacturers etc. etc. etc..
Again I appologize to the readers of this forum regarding my response to Eric.
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X
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On 6/8/2005
MARK MCCREE
wrote in from
United States
(65.40.nnn.nnn)
You know, he pushes and pushes. Serious injury? Your rantings cause serious injury to our brains.
I've calmed down-- I think.
No.. I havn't
Geeze, Kiss my rosy red a#&^%$@ss.
When YOU start producing winning trucks let me know-OH I will know--We ALL will know. You just keep TINKERING with 60's designed trucks and justifying your useless existance in this industry.
You are THE junk man of trucks as far as am concerned.
THE JUNK MAN. Do you hear me??? JUNK
I said JUNK
Stick with building vehicles. You have no clue how to build a real truck. In fact- Ok I will calm down now.
You are an engineer like I am a gynacologist.
Sorry guys, This SOB knows how to press my button. I have more respect for a wanabe garbage collecter than this blowheart.
Sorry.
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Fatigue, Stress Concentration, and Root Cause
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On 6/8/2005
Chuck
wrote in from
United States
(192.249.nnn.nnn)
Some random thoughts on the matter:
Bola's post on fatigue was only half on the money. There are two types of fatigue, two different failure mechanisms and two different life limits. Fatigue can be broken down into low cycle fatigue (LCF) and high cycle fatigue (HCF). LCF is caused by higher magnitude stresses, under a lower number of cycles. Stresses are typically near or slightly above the material's static yield strength, cycles can range from single-digits on up to about 10**5 cycles (beyond that HCF will predominate). HCF is a failure at much higher number of cycles, much lower stresses (typically some fraction of the material's static yield strength). This is the endurance limit Bola alludes to...typically a part that can survive 10**8 cycles is considered to have infinite life. Without even seeing the broken kingpin in question, I would be willing to bet money it failed in a combination of LCF followed by shear overstress. The fact that the kingpin's failure surface was described as having half an angular face means the other half was flat. The flat part would probably be able to be shown to be an LCF failure region (hint: look for faint curved lines in the flat portion of the failure surface, radiating from a point on the outside edge of the part much like ripples in a pond); then as the crack propagated into the kingpin it was weakened to the point where it failed through in simple shear overstress (45 degree angular break being the classic sign of shear failure). I am betting the failure is LCF because there simply isn't a driver present in a skateboard truck that can generate high enough stresses for enough cycles for it to be HCF...unless you are skating for thousands of hours on some reall, really, really rough roads.
Mark, I'd love to take a look at the kingpin sometime if Chris B sends it in to you and Sparky...
As far as the root cause of the problem...I would also be willing to bet the crack originated either due to a material flaw or a stress concentration. If the kingpin is threaded in so a thread root is right at the highest stress point, that would represent the worst stress concentration possible and might explain the random nature of Radikal kingpin failures...luck of the draw, orientation of the kingpin. If it is a material flaw, either inspection methods pre-assembly are not stringent enough, or the part's design is marginal enough that a flaw too small to be detected by normal methods is sufficient to start a crack which will eventually propagate to failure. Has anyone broken a kingpin yet with the recessed baseplate threads? The answer to that question could a big piece of the puzzle.
Also regarding root cause...*if* LCF is the root cause, the corrective action is to change one of the driving factors. This can be lowering the bulk stress (fatter kingpin?), better material properties (material/processing change), reduced stress concentrations (redesign, no threads in highest stressed areas, etc.), or limiting the parts' lives to something less than the LCF life (periodic replacement of the kingpin). So, replacing the parts at or before a safe life limit is one method of addressing root cause, it is done all the time in avaiation/aerospace. However, a more concrete life limit than "once a year" might be desirable, at least to those who put in a whole lot more hours practicing than most.
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kingpin schmingpin
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On 6/8/2005
sc
wrote in from
United States
(64.60.nnn.nnn)
as some old duffer somewhere must have said:
t'aint no right answers to the wrong questions
but while yer barking up that particular tree,
don't forget to evaluate the cantilever post for bending
and use a material with the proper ductility after hardening
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broken kingpins
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On 6/8/2005
buddy rawls
wrote in from
United States
(128.158.nnn.nnn)
on reverse kingpin style trucks. remember Gullwings, they developed their support bracket for a reason. 70's technology may prove to be worthwhile. I know I broke many kingpins in my phoenix and split axles. our local supplier always had a few laying around. at the time, the support bracket was an eyesore and made adjustments sort of hard. Now, riding gullwings, you cant afford to break the kingpins, so the support brackets (and correct installation) is a requirment. maybe the other reverse kingpin trucks could benefit from a similar add-on device.
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The King of P(a)in
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On 6/8/2005
Geezer-X (-X-)
wrote in from
United States
(151.200.nnn.nnn)
Chris, Michael...thanks.
If anyone want to send me a Radikal, I'll sort out a simple solution to use a kingpin with a non-threaded interface, or design a kingpin with a shoulder.
See pic of titanium shouldered kingpin for old school Lazer truck
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Kingpins
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On 6/8/2005
AP
wrote in from
United States
(207.114.nnn.nnn)
I've pretty much broke every kingpin out there, doing flip and big gaps and such, but never have I broke a kingpin in slalom, I take that back, I broke one. It was on a RADIKAL, but it was I proto type that Mark had given Jackie Lee. Must have had 100+ hours on it. It broke becuase I had loosen it the wrong away. I exposozed the threads. I Pumped up hill and I snapped the damn thing. No biggie, I knew It was my fault. I have never snapped one again. But at the park, I snapped a Indy Kingpin, what seemed to be a simple ollie transfer. Does that mean I stop rideing Indy. Ha, never. Stuff breaks, no fn biggie. Went back the same day on the same truck. Go fig?
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Two Ideas
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On 6/8/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
Here's the idea about having the pivot cup cap (removed in the drawing) and another idea about how you could put in a kingpin without having to take the trucks off of the board.
Of course you'd want to make sure that pivot cap could withstand all of the forces on it. It would have to be quick and easy to remove and replace with a skate key.
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it could be threaded...
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On 6/8/2005
duane
wrote in from
United States
(68.15.nnn.nnn)
if you increase the size of the thread to 7/16" or 1/2", then make the rest of the kingpin the same as it is now, with a nice fillet radius down to the plain shank. Not ideal but it would work without re-doing the entire design, and current product could be re-fit, and hanger travel would not be compromised. Not sure if there is enoug meat on the baseplate to accept a 7/16" insert, probably is.
root areas of unf threads are only about 75% of the plain shank diamater so 7/16" root area is about the same as 3/8" plain shank, and of course 1/2" is a lot more.
another possibility would be to make the plain shank area thinner, so that the kingpin deflection is distrubuted, reversibly, along the length, rather than concentrated at the thinnest section where the first thread starts
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No, Yes, No
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On 6/8/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
Mark, No.
-X-, Yes.
ChrisB, No.
Mark, No, no, no, no, no. You're gonna get creamed if you ask skaters to behave like responsible adults. It ain't gonna happen. And you can't very well defend this issue after attacking PVDs and Seismics for the need to tweak and/or use too many wrenches. We crave simplicity and you really loved us, you would ask us to be tweakers. Give us a truck that doesn't have these issues and you won't have to worry about what we do or don't do. Your truck is amazing and it's 95% there (safe AND effective). A simple solution to a complex problem will make you golden.
-X-, Spot on.
ChrisB, The Gullwing kingpins that were always breaking shared the common characteristic of being threaded.
In Thread We Dread!
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kingpins
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On 6/8/2005
MIchael Dong
wrote in from
United States
(67.161.nnn.nnn)
Concerning X's post below:
1. below is the way to go.
Also, "Engineer to Win" by Carrol Smith says it all.
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pivot cups
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On 6/8/2005
glenn
wrote in from
United States
(68.0.nnn.nnn)
how do u take the pivot cups out
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Kingpins
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On 6/8/2005 Chris B
wrote in from
United States
(204.78.nnn.nnn)
Man, i'm surprised this is getting so much ink.....
I'm thinking though that it's the angle of the pin itself that causes the break, just as much as it is the threading. That being said, it's the angle that also makes it a great truck, so we have to accept the good with the bad.
Look a the Gullwing split axle...those kingpins bent under the same conditions that we 're talking about here, yet were a complety different design and composition.
That being said, couldnt SL2002 hanger supports be modified to support a Radikal?
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Failure cycle
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On 6/8/2005
-X-
wrote in from
United States
(151.200.nnn.nnn)
"These are high maintainance trucks. bearings should be oiled etc. As in any high tech product, there are maintainance items. The king pin is one of them. I don't know anyone that objects to changing breaks,clutches,or even starters on a car. High precision cars-high maintainance costs. High precision trucks-------???
good luck guys."
This seems like a pretty cavalier attitude for someone whose product has failed resulting in a serious injury.
Replacement in this case is being suggested rather than addressing the root problem.
In my years of racing cars, karts, bikes, bicycles, skateboards, r/c cars, etc., I've had very few mechanical DNFs as a result of good preparation. I do some work for a motorcycle endurance racing team who have literally written the book on endurance race bike preparation.
A big part of this, and one which is covered in great detail in a book every one of you should own, read, and refer to, "Engineer to Win, the essential guide to racing car materials technology or how to build winners that don't break" is determining the failure cycle for parts and replacing then in a timely fashion.
That said, there are parts that have a finite life span due to the stresses accrued by cumulative loading, such as components in the reciprocating assembly of an engine. Valve springs, valves, connecting rods, rod bolts...all of these will last for hundreds of thousands of miles in street use, but typically a season or less of road racing. When you grenade an engine and oil everyone else’s track, if you hadn't missed a shift and over-revved, how many hours were on the motor?
There are parts which are consumables, like tires, brake pads, clutches, chains and sprockets. These are more easily monitored, and subsequently maintained on regular basis. Different tracks cause different patterns of wear.
There are parts that due to design are proven to have a finite life, or despite having not experience failure, are easily enough replaced that keeping failure at bay is an easy exercise.
As an engineer/mechanical designer/fabricator/machinist who has built many successful race vehicles, my take on retaining ANY type of rod in a fixture (read "kingpin" and "base plate") is that you should NEVER use an unsupported threaded interface.
Threads are to be loaded in tension only. ONLY. A Radikal axle is a perfect example of threads used properly. So is any bolt. The threads are there to pull the assembly tight. The hexagonal boss on a Radikal axle bottoms against the end of the hanger, and the threads are loaded in tension holding it there.
A threaded rod is not and has never been designed to support any load other than tension. Screwing a male threaded rod into a female threaded hole until the threads bottom and loading the other end of the rod (lever) with deflection, shear, and impact is going to result in a failure at the stress raiser (notch, or thread).
A kingpin which is properly designed should not fail, and should not require regular replacement. If you contrast the load strength of the typical skateboard truck with the typical (hell, maximum) load encountered in use, you'll see that there is an ENORMOUS safety factor applied.
The stuff that should be replaced is stuff that has been pared down to the degree that the safety factor has been decreased in the name of light weight.
The interface between the kingpin and base plate needs one of 2 things:
1. If the kingpin must be threaded in to base plate, it requires an incorporated flange so that the threads can remain in tension. The locknut on pre-fixed kingpin trucks served this purpose.
2. A non-threaded interface between the kingpin and base plate. Bore the base plate, press the kingpin in, cross pin it. Adjust the shape of the hanger and base plate so you can fish the hanger's spherical bearing onto the kingpin and still get the tip of the pivot into its bearing.
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great talk
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On 6/8/2005
MARK MCCREE
wrote in from
United States
(65.40.nnn.nnn)
These comments have been great. I would like to say that one option was to insert the king pin through the bottom of the base plate. This option would have required the user to totally remove the truck from the board. This was not an option.
The RADIKAL design/opperation begs for more user "fiddleing". I love watching CBARK with his trucks. It's tinkering at it's best. With all the racing and practicing he does, he has never broken a pin.
These are high maintainance trucks. bearings should be oiled etc. As in any high tech product, there are maintainance items. The king pin is one of them. I don't know anyone that objects to changing breaks,clutches,or even starters on a car. High precision cars-high maintainance costs. High precision trucks-------???
good luck guys.
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Let's try this again
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On 6/8/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
Presently, anytime that you have a spherical bearing or a very small hole in the cushion seat area of a hanger, the kingpin has to be pulled (or pushed) out of the way in order to assemble the truck. That's because the way it is now, the pivot point is positioned into the pivot cup first, and then there isn't enough clearance to swing the hanger over the top of a fixed kingpin.
What I am suggesting is "Radikally" different. Imagine that the Radikal baseplate has a fixed (or removeable) kingpin inserted through the bottom of the baseplate, and that the only threads are at the end for the locknut. Now imagine that at the top of the pivot cup is a removeable "cap" that holds the pivot point or pivot ball in place. Whenever you wanted to change (or shim) the bottom cushion, you'd simply remove the "pivot cap" and the kingpin nut, and then the top cushion and hanger would slide out with ease. It would be great if the pivot cap used a 3/8" or a 1/2" or a 9/16" locking device so that all you'd need is an ordinary skate-key to make any changes. There'd be one less wrench to worry about.
This could potentially solve the "dreaded threaded kingpin" problem, and kingpins could still be replaced whenever the truck was off the board.
The current "solution" to the assembly problem (threading the baseplates and kingpins), just may turn out to be the snapping kingpin problem.
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some Radikal assembly required
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On 6/7/2005 PSR
wrote in from
United States
(69.161.nnn.nnn)
Well, Chris, luckily hanger/kingpin fit, that's one issue, as you'd never get to the lower bushing once the hanger was in place... But, there's also the slight bit of adjusting available to the bushing tension, though the real means of steering-tension adjustment is by changing bushings, so, yup, the kingpin needs to be removed so that the Hanger fits back in place.
The Tail sometimes Wags the Dog.
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Just lucky I guess
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On 6/7/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
Fortunately I've been raised in a grade-8/threads away from the kingpin world. Downhillers and streetlugers make so many hanger swaps that I almost never use a Randal with its "original" kingpin orientation. Also, drop-through decks like our speedboards allow us to pull the kingpin out of the top of the deck for easy packing. Trackers, Indys and Invaders all have the threads away from the baseplates and haven't given me any problems. I tend to use longer grade-8 kingpins because I like a tall cushion on the top as well as the bottom. This allows the hanger a wide range of motion and no metal-to-metal contact.
I pump the hell out all my trucks and I haven't had any problems. I guess that I've just been lucky so far.
I love my Radikals and haven't had any problems so far, but I wish that the kingpin wasn't thread into the baseplate. How about having a more standard fixed kinpin in place and allowing the pivot cup assembly to release the hanger for cushion swaps? I'm assuming that the kingpin was designed to thread into the baseplate because it's the only practical way to assemble the truck with a hanger that's tethered to the pivot?
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flipped randal kingpins
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On 6/7/2005
peters
wrote in from
United States
(24.18.nnn.nnn)
David you summed a critical point up well which I'd forgotten to mention--the root of the threads has been the breaking point, every time. Flipped kingpins put the smooth shank of the bolt right where the breaks will always occur otherwise. Around the same time I started flipping grade 8's, I switched from RII's and Gullwings over to Carvers (now the Carver CX) for flatland, and haven't gone back to 'traditionals' since, so I haven't been testing the theory to the failure point--and would rather not, honestly. But it does seem radically stronger.
Unless there is some big drawback to this, I wonder if manufacturers and deck builders might sell their RII trucks with the kingpins in flipped orientation from the start?
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Radikal and Khiro bushings
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On 6/7/2005 PSR
wrote in from
United States
(69.161.nnn.nnn)
Isaiah, Radikals are much bigger around, and are all 'barrel' shaped. They're the closest thing to Tracker Stimulators that's still available. They're also made with Kryptonics Urethane, so they've got respectable rebound, even in the harder durometers. These are shaped to fit Radikal trucks, and may not fit on your trucks. Two of mine have been shaved in height to fit my Turner TTC trucks.
Both of these companies color-code the bushings for easy selection of the hardness you want.
Khiro has The Softest bushing that's readily available (white ones) at some 65A Shore durometer, and it's bouncy, too. The Blues have good resilience, and the Reds (92A?) are still respectably bouncy, though maybe only as resilient as Doh-Doh's. Once you get up into the harder Khiros, the bounce is lacking. Still, the fact that there's 4 shapes, and that Khiro has actually published the sizes, means that getting a truck set-up 'dialed in' is a fairly simple, straightforward process. They sell kits that get you the bushings you're most likely to use, too. That beats doing what I used to do, which was buy Doh-Dohs, use the Barrel shaped bushings on a board, and glue the conical tops on under my toilet seat...
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Kingpins
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On 6/7/2005
David
wrote in from
United States
(66.14.nnn.nnn)
I think stress concentration is the main problem with most of these broken kingpins. Kingpins should be pressed into/thru the baseplate for maximum strength and life. Kingpin threads should be kept as far away from the baseplate as possible!!
If the kingpin threads into the baseplate like a stud, or you run the locknut in the baseplate like a stock RII or Grindking, stress is "concentrated" on or near the root of the last thread/threads. This gives you a system that is considerably weaker than running the same kingpins in the "correct" orientation.
Flipping a stock Randal RII kingpin around greatly increases the assembly's strength and life. Using Grade 8's in the "correct" orientation results in kingpins that can last a lifetime....like Chaput's.
The changes that Radikal has made are steps in the right direction to make their system better. Dropping the last thread 3mm into the base should help, but I don't think it will stop all of the failures. A stronger fix would be using a kingpin without threads at the baseplate interface. The kingpin could be held in place by a setscrew or two so it could still be easily removed from the hanger side.
I've seen many kingpins break at the threads due to this type of stress concentration...I've never seen a grade 8 kingpin break in the middle of the unthreaded shank.
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There IS one more thing here...
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On 6/7/2005 Steve in AZ
wrote in from
United States
(192.175.nnn.nnn)
...and that's how well (if at all) is the kingpin insulated from DIRECT shock or contact. A Kingpin in a standard truck has virtually NO metal-to-metal contact between the kingpin and the hanger...provided that the range of motion is limited by the travel of the cushion or bushing, and NOT when the inner ring of the hanger makes contact with the kingpin.
It's for this reason that ALL of my Randals, racing & DH trucks ALL have been tested to make sure that no matter how much the truck turns, the hanger will never make contact with the kingpin. I'm also using custom filed top bushings ("Toppers" if you will) that recess some of the top bushing in the space between the hanger and the kingpin. This not only insulates the kingpin, but it also makes for a much more accurate turning truck...not like having a spherical bearing in there, but more like that than not.
I agree that all kingpins take forces...but make sure that force is balanced across the kingpin instead of just one point, and you're pins will last alot longer.
-=S=-
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Khiro vs Radikal
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On 6/7/2005 isaiah
wrote in from
United States
(24.21.nnn.nnn)
I dont want do ask which of these bushings are "better" but is there much of a difference between the two in terms of radikal may be meant for slalom tight turns and khiro is better for park boards or downhill?
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Just when I thought it was safe to skate...
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On 6/7/2005 EBasil
wrote in from
United States
(63.206.nnn.nnn)
Man! Off to Lowe's Home Improvement Store again, for another round of Grade-8 kingpin upgrades... and I was just starting to get comfortable with leaving them alone on the new boards.
At least the Grade-8's are "gold". Bling-bling.
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