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| Truck Reviews (15215 Posts)
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speed wobbles
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On 1/9/1999
René
wrote in from
()
I'll say this much, I have been on street bikes (motor) since 1983' and have noticed on some bikes I have had there is a point of instability (120mph) then pass that point it all smooths out, as far as skateboards I think that since you have no torque being generated by the wheels like a motor powered vehicle that the geometry of trucks makes the most difference, (castor, camber) and so on, I do know that the torsions are more responsive and that is what can get you in trouble..Keep skatin guys & gals!! Always keep it fun!!
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rec.speed.wobbles
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On 1/9/1999 Scheckey
wrote in from
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Someone get John Hutson on line and on this board. I had no idea about the phases of stability. Does this really mean that if we can hold on long enough we can gat past the wobbles? This really amazes me and seams to prove the theory Dan put forth on the "oscillations of stuff that goes fast". Could it be that Randal 1s are just "tuned" to wobble at really high speed? And on another front, what happens to spacecraft? Do they go thru sevral "wobble phases"? And if they do, couldent we figure out what "note" they are? Like every "wobble phase" would be the equivalent to an octave? Could we use the info to "tune" a board to wobble at slow speeds instead? like 20 or 25 mph? Id be really interested to see some time put into this, and volenter my body and setups in the name of science (and a good downhill run).
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Speed comments continued. Re. Dan
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On 1/8/1999
Tannis
wrote in from
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That is an intresting comment Dan, I have extensive knowledge of land speed racing and cars, motorcycles, jet powered vehicles, etc. all go through a similar speed versus stability phases or cycle situation. Like you said, stable up to a certain speed, then instability until they reach a higher speed. In some cases there is reverse steering characteristics! That is that they have to turn the wheel opposite normal direction to achieve directional changes. Really strange things seem to happen despite the vehicle when it comes to speed, or so it would seem!
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John Hutson/Speed Wobbles
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On 1/8/1999 tz
wrote in from
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I would love to hear how John Hutson dealt with speed, wobbles and gear considering no one did it as consistently well as him.
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Additional Note on Wobbles
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On 1/8/1999
Dan Gesmer / Seismic Skate Systems, Inc.
wrote in from
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A few years ago racing legend John Hutson told me that in 1979 he assisted in a presentation made by the Stanford Mechanical Engineering Department, in which the stability of skateboards at various speeds was compared with that of aircraft. It's interesting to note that like aircraft, skateboards go through various "zones" of stability and instability as they accelerate up to their highest speeds. For example, according to John, a particular setup might be stable up to 30mph, prone to wobbles at 40mph, but stable again at 50mph. And the "placement" of these zones of stability and instability varies with each setup...
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3trucks
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On 1/8/1999
ken
wrote in from
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Hello,
i sent a mail from japan.
i joined local downhill competition at last year and i entried
begineer class with gravity47.
i reconstructed gravity47. i installed 3trucks on gravity47(
front 2trucks). i made 6wheels gravity board! I thought it'S
very beautiful but i was laughed by everyboby.
at a results, i got a bronze medal(rank 3 of 15persons entry).
it was good result. but everybody said if i entried normal
board, I could win. i don't think so.
i think that 3trucks is faster than 2trucks at downhill.
what do you think my idea? i would like to know your opinion.
thank you,
ken
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3trucks
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On 1/8/1999
ken
wrote in from
()
Hello,
i sent a mail from japan.
i joined local downhill competition at last year and i entried
begineer class with gravity47.
i reconstructed gravity47. i installed 3trucks on gravity47(
front 2trucks). i made 6wheels gravity board! I thought it'S
very beautiful but i was laughed by everyboby.
at a results, i got a bronze medal(rank 3 of 15persons entry).
it was good result. but everybody said if i entried normal
board, I could win. i don't think so.
i think that 3trucks is faster than 2trucks at downhill.
what do you think my idea? i would like to know your opinion.
thank you,
ken
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Re: Tannis' 1/3/99 Post
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On 1/7/1999
Dan Gesmer / Seismic Skate Systems, Inc.
wrote in from
()
Tannis, your comments about Guy Grundy's 55mph speed run on crude 1976 equipment was well-taken! Big cajones is right.
Actually there *is* an international organization for slalom racing, though it's been semi-dormant for a few years: International Skateboard Slalom Association (ISSA), c/o Jani Söderhäll, 14 Allée d¹Arcachon, Verrières le Buisson, 91370 France, e-mail Jan.Soderhall@eu.pnu.com.
As for downhill associations, there have been a number of organizations over the last few years staging both standup and street luge races, though I'm not sure if any of them have yet established themselves as the clear international spokesgroup.
You also asked about the role that the deck's torsional flexural characteristics play in the skateboard's overall vulnerability to speed wobbles. I think there are actually two factors to consider here: torsional flexibility *and* torsional resilience (in other words, the "snap" with which the deck rebounds from a twisted state). Others may have more to say about this, but for pure balls-out speed I would venture to guess you'd want a deck that offers a high degree of torsional stiffness *and* good torsional dampening (in other words, the ability to absorb forces that would tend to twist the deck without throwing the energy back in your face). Any thoughts on this, Randal?
BTW, I'm trying *not* to use this forum for self-promotion, but for the record the Seismic truck was designed to offer a very fine balance between stability and maneuverability on "average" skateboards traveling through a range of "average" velocities. It was also the first (by a factor of years) of the new crop of carving-oriented trucks, introduced to the market in early 1994 right before longboarding came back. Indeed, one of my early ads in TransWorld Skateboarding referred to longboarding (in an effort at reverse psychology) as a "highly unfashionable approach", which it was at the time!
I'll do my best to exercise diplomacy here: The Seismic truck doesn't turn quite as tightly as the "torsion" trucks (specialized for super-tight turns), and it's not quite as stable at extreme speeds as the Randal I (a specialty speed truck, the only one of its kind). But because of its computer-designed progressive-rate spring system and fixed 45-degree steering axis, the Seismic truck offers noticeably superior steering control and energy return. (If you're good at gyrating you will really appreciate this!) It also makes turns that are pretty darned tight with good stability up to "medium-high" speeds.
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eXkates
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On 1/6/1999 Chris
wrote in from
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Just wondering. Has anybody else broken the bushings on their eXkates? I was showing them to a friend in a skatepark parking lot. I was doing that thing where you have them cranked all the way over to the wheel locks and to show how tight a circle they will turn, and you end up falling off when the board stopped because the turn was so tight. Well, I looked at the board and the front truck was still in the turned position. I picked it up and the trucks would turn, but wouldn't come back to center after the turn.
It wasn't a big deal. We were done skating for the day, so I just threw it in the trunk and left. Actually, I hadn't taken the board into the skatepark. Even with red bushings, I think eXkates are too sketchy for a skatepark, where stability on kickturns and control when dodging little kids on rollerblades are factors.
Anyway, a couple of days later, I took the trucks apart to see what was wrong. It turned out that the urethane on the bushing had broken away from the metal plate on the bottom that locks into the base plate. Has anyone else had their eXkate bushings fail this way? It's not a big deal. I've been wanting to get the green bushings anyway. Now I guess I have to.
Later,
Chris
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F-14
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On 1/6/1999 Lee
wrote in from
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If you would half the turning radius of an F-14 and keep the speed the plane doesn't get speed wobbles, the G force would simply tear it apart.
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wobble woes
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On 1/5/1999
Scheckey
wrote in from
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Im not discouting anyone at all in this but I think wobbles are caused by the turning radius of the truck. We all know loose trucks wobble and tight ones dont. Think about this, if truck A has a turning radius of 10 feet, it is going to have the SAME turning radius at ANY speed. Now go that way real fast and tell me you want a truck that turns on a dime. I have heard that an F-14 makes a 90 deg. turn in 15 miles. Think if you halved the radius but did not half the speed. Wipe out Maverick. I also think (Tannis) that a flexy deck would add to the problems. If Dan is right all your doing is adding more to the equation to start oscillating. But, hey, maybe Im wrong cause Randals havent wobbled yet.
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Wobble trouble
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On 1/4/1999
Pierre
wrote in from
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Well i may be wrong but i always felt that speed wobbles are
caused by the time delay between a pressure of the foot (accidental or not) and the reaction of the brain to place our center of gravity at the right place, by the time we adjust our balance, we should be at the opposite and its
the adjustement period that is the reason we wobble. By lowering your center of gravity and having a longer wheelbase (or less turning radius) you give yourself more room for error. Or maybe its just the speedier we get, the stiffer our body is. Well thats what i think. If you can ride in January, thank god you dont live in Montreal.
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Wobble trouble
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On 1/4/1999
Pierre
wrote in from
()
Well i may be wrong but i always felt that speed wobbles are
caused by the time delay between a pressure of the foot (accidental or not) and the reaction of the brain to place our center of gravity at the right place, by the time we adjust our balance, we should be at the opposite and its
the adjustement period that is the reason we wobble. By lowering your center of gravity and having a longer wheelbase (or less turning radius) you give yourself more room for error. Or maybe its just the speedier we get, the stiffer our body is. Well thats what i think. If you can ride in January, thank god you dont live in Montreal.
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WOBBLE MANIA
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On 1/3/1999
Rich @ SOUL CARVE
wrote in from
()
Ok heres my final take :
You want speed, I mean real speed and no wobble trouble .... you have to go with RANDAL and his race trucks, there is NO option on a standup board.
However how many of us want to go that fast ?
So then you have the option of Randal and torsions with stiffer bushings and then you get to the realms where the torsions only turn as well as the Randals (esp the RII which are not far behind to start with). Even then the RII's are more stable for the occasional short sharp bomb. At slightly lesser speeds though the medium/medium hard bushes of the torsions types means they turn like no other and still down give you brown trousers if you wnat a little bomb.
If feeling stable is what you want then go with Randals, if you want speed and carving and sliding then hit RII's, carving and medium speed then hit the torsion trucks with harder bushes and if you want flatland manouverability then torsions with softer/medium trucks (or mix and match). RII's are great in parks as are medium bushed torsions.
So to wobble or not to wobble (so much) is the question and you have to choose the answer oh consumers of new trucks !
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Randal and Siesmic
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On 1/3/1999
Tannis
wrote in from
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Randal and Daniel,
I'm curious about your thoughts on what roll the deck plays in high speed stability. Does having a torsionally stiff deck, allowing the trucks to do all the directional and stability work, lend it self to high speed stabilty? Or would a torsionally flexible deck have advantages working in conjunction with the current speed trucks to maintaining high speed stability?
Having recently picked up a copy of "Five Summer Stories" and watching the Guy Grundy, 55 MPH speed run segment, I think it's intresting to note that he was using Bennett trucks on a 5' flexible board, which, needless to say, he experienced speed wobbles on! Of course that was 25 years ago, today we wouldn't even consider going that fast on standard equipement, thank goodness for the speed trucks we have today! Those guys had some big cajones for sure! We should also note that the world skateboard speed record has only been uped by 7 MPH since then, 25 years!
How come there has never been a national, or better yet, international downhill and slalom racing association? I can't think of a better way to come together and advance this speed technology than to share our ideas with each other and prove our theories in racing conditions. What are your thoughts on this? Tannis
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Speed Wobbles
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On 1/3/1999
Randal
wrote in from
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All right...one more time. Stability is what the Randal trucks are all about. Understanding "No-Speed-Wobble" geometry is the original reason I did trucks. This subject is too important for any confusion. Many people have been hurt and even killed by speed wobbles at high speed (I once saw a guy die in front of me). Bombing hills is a serious business and false claims by other truck makers regarding "no-speed-wobbles" should not be tolerated. The Randal trucks are way more stable than any other truck - there is really no comparison. If you don't believe me then talk to the Pro Downhill Skateboard racers. Speedboard competitors in the U.S. and Europe ride the Randals; Sector-9 Downhill Team, Gravity Team, Team Dregs, Madrid, TVS, Chronic, etc. all race on Randal's; the last two world speed records were set on Randal's (current: Gary Hardwick @ 62.55mph). If you want to break bones and lose skin that's your choice, but if you want to bomb with confidence then there's only one choice.
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More About Speed Wobbles
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On 1/3/1999
Daniel Gesmer / Seismic Skate Systems, Inc.
wrote in from
()
In the late 1980's and early 1990's I had a number of in-depth conversations with two professors of mechanical engineering who are apparently the only academics in the U.S. ever to have systematically studied the dynamics of skateboard steering. Based on those conversations, I can offer the following conjectures regarding high-speed wobbles on skateboards:
Wild theoretical speculations aside, there are probably at least three possible ways that resonant oscillations can begin in a real-world skateboard-skateboarder system:
1) Surface irregularities initiating resonant vibrations within the truck;
2) Looseness or sloppiness at the ankle joint, or in one or more other parts of the body;
3) During high speeds turns (where the steering geometries of available trucks force skaters to lean at angles much greater than the deck¹s degree of tilt), skaters' resultant force vectors might create unwanted return-to-center forces.
The predisposition to high-speed wobbles may also be a property of the system as a whole, a frequency ‹ or set or range of frequencies ‹ at which system-wide oscillations can occur. Analogously, pendulums have frequencies at which they naturally oscillate, and pendulums with multiple degrees of freedom of motion have several potential frequencies or modes of oscillation.
A related conjecture is that speed wobbles (or shimmies, as they are called in the cycling world) are oscillations that are, in a sense, waiting to happen ‹ a single bump can set them off. It is interesting to note that a car with a trailer hitched to it can swim even on a glass-smooth road.
According to one of the professors, a bicycle made of a single piece of solid material could not, theoretically, shimmy. Therefore, speed wobbles are most likely the result of the behavior of joints and connecting points. (Duh, eh?)
We can probably solve the physical problem of speed wobbles more quickly and easily than we can scientifically explain the phenomenon of speed wobbles. Most technological advances are achieved through inspired guesswork, and this may be the best approach to take vis-a-vis skateboard speed wobbles. Truck engineers, start your engines!
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What About Speed Wobbles?
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On 1/3/1999
Daniel Gesmer
wrote in from
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High-speed wobbles are an amazingly complex phenomenon that even professors of mechanical engineering can¹t fully explain. They¹re simply a fact of life if you¹ve got moving joints of any kind, whether you¹re talking bicycles or skateboards. Any truck that can turn will also be subject, under certain conditions, to speed wobbles. It may never be possible to totally eliminate the possibility of speed wobbles using trucks that have the capacity to turn. However (as is well known), the tendency for skateboard trucks to wobble at high speeds can be minimized by tightening the suspension elements (grommets or, in the case of Seismic trucks, springs), or using stronger ones. In addition, slowing down the trucks' steering response with angled risers can help.
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MR. WOBBLY
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On 1/2/1999
SOUL CARVE
wrote in from
()
MMMMmmmmm the old wobble curse.Everyone has a way to beat it but no one can explain fully why it happens. That's probably because it is dependent on a number of factors. The main one being the geometry of the truck itself. Move a standard truck in your hands and you notice it moves in a number of ways. One is the way it has to to turn, but they will also move in a horizontal plane unless you tighten the kingpin down onto super hard rubbers which almost stops it. It is that movement plus sometimes a worn rubber where your truck connects to the front of the baseplate (slight memory lose to tthe name there). Welding the trucks and using super hard bushings were two ways we used to stop the wobbles for speed runs. Another factor is the angle of the king pin and the associated turning radius thats why old indies with an almost vertical king pin hardly got speed wobble when tightened (mind you they hardly turned either). Thats where wedge risers came in to originaly steepene the kingpin angle (put on the opposite way then we have them now) and thus make it turn less and eliminate the wobble slightly.Also the actual dynamics of the way the force from your weight bears on the set up of the kingpin and bushhings, it bipasses them and goes straight to the front of the truck thingy (still have an attack of memory loss) makes it wobble around that point.
It's easy to see why conventional trucks are crap with regard to speed wobbles. Then comes RANDAL and his trucks, by altering the geometry you don't have to overtighten the trucks to eliminate the wobbles. People used to say to me that there loose wedge induced Indies turned as well, which they did but when going down any simple slope they had to tighten the trucks and couldn't turn any more ! The Randals were solid and still turned as well. The newer Randal II's have a steeper kingpn which may mean they wobble in the end if going real fast, but then at those speeds you'd be racing and thus have the downhill version.
So Exkates they say they don't wobble, well they DON"T they can't in the conventional sense. Yet anyone why bombs on the softer bushes knows they bloody well do ..... well they don't ! But what they do do is respond to any single twitch you do. So your first ankle movement sets off a turn, you compensate which sets of the opposite turn (as you will overcompensate) and then it's like a snowball effect. SO get harder bushes or just try doing it controled. When the wobbly bit starts just stand damn still and ride it out, then start the wobbles then ride them out. We made a game of it to see who could look like they had the worst speed wobbles. Not recommended down a bloody big hill of course. Another way to stop Exkate form feeling wobbly is to not go damn straight but link nice carves together.
I am sure there will be more to add by people !
Rich
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speed wobble
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On 1/2/1999
Sandy M
wrote in from
()
Can somebody explain the phenomenon of speed wobble? We ALL know what it is, but where does it come from? does increasing your wheelbase help stave it off to higher speeds? why do some trucks claim to be "wobble proof" (ie exkates, randals). I tested this claim on my G&S Fiberflex with Exkates and blue bushings. They definetely DO wobble. (I ate pavement.) what's up?
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Randal II's
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On 1/1/1999
Tannis
wrote in from
()
Thank you Randal for educating us on truck dynamics, your explanation makes alot of sense. I have a couple of sets of your traditional speed trucks and just acquired a set of Randal II's and it is clear to see that the pivot point through the bushing mid point angle from deck surface, coupled with truck spacing is the key to establishing turning radius. Your new trucks are really awesome, I loved them from the first time I tried them! Thanks, Tannis
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Seismic Trucks
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On 12/29/1998
Daniel Gesmer
wrote in from
()
Nice to see such a dynamic forum here! We've been preoccupied with other endeavors for a while but have never stopped offering Seismic trucks. We're stoked to see more and more carving-oriented trucks on the market. While this is not meant to be a promotional forum, we believe our product still offers unique performance advantages. Look for more (non-self-promotional) contributions to this dialog from us soon...
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Stuff
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On 12/27/1998 tz
wrote in from
()
To TC. Allt his debate about disageeing trucks and projection angle sounds like a crock. There's this wonderful set of tools at the bottom of our legs called ankles. I use them with my Exkates to make infinite adjustments so back doesn't disagree with my front and that my projection agrees with my carve. Like the Randall guy said, "there are no rules" with longboards. Customizing a board is a personal thing that transcends rules but more conforms to the style of riding you do your weight, build, strength and experience. For instance, who's to say the European guy who won a tight slalom championship on a stiff slab much like Tony Alva's Earth ski is superior to John Hutson's 30" graphite, Indy combination that won more races than any slalom racer ever. Or look at the old Bones Brigade of Stacy Peralta and pals sliding for 50 sixty yards throughout a several mile downhill on dare I say, a shortboard.
Good notes from the Randall guy. Conventional design trucks are one of those goofy things that won't go away. Let's just hope the newer designs won't go away like the metric system or their predecessors: Power Paw, Radical, the 1st Variflex and Gull Wing trucks, etc. They were all designs that made more sense but lot of skaters didn't have the balls to buy them. Support new and better designs.
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Truck Turning
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On 12/27/1998
Randal
wrote in from
()
There has always been a lot of confusion on how trucks work. I've talked to many people over the years that should understand this stuff, but no one really does. To begin with, conventional skateboard trucks evolved from roller skate trucks, and the basic design really hasn't changed since. On roller skates, to get the wheelbase longer designers were forced to move the kingpin and cushion set to the inside of the axle. This may be ok for your sister, but not for skateboards - especially not for longboards. The basic problem with skate trucks is inherent instability - they feel 'sketchy' and speed-wobble. This is because of 'leading caster' geometry; the distance from axle centerline to pivot axis. Now, let's be clear on what pivot angle is; it's not the angle of the kingpin - this has little to do with it; it's also not the angle that the hanger tip comes out of the pivot bushing at. It is the angle from the horizontal (a line down length of deck) to a line through the center of the pivot bushing/hanger tip through the center of the cushion set/hanger clearance hole. This angle is what makes a skate turn. You tilt the deck, the truck pivots, and the wheels turn, ok? So, more pivot angle = more turning (the 'lean-to-turn' ratio increases). Another important factor in turning response is wheelbase. The farther apart the trucks are, the slower the turning is. Conventional trucks have a pivot angle of about 37 degrees. This may be about right for a shortboard (about 20" wheelbase), but when you put them on a longboard (about 30" wheelbase) they turn too slow. This is why longboard completes come with wedge risers (this adds about 5 degrees of pivot angle). This turning 'crutch' helps but the trucks still do not turn enough and wedging them makes the trucks more unstable and 'sketchy' feeling (the kingpin also now hangs up on grinds, etc.). Our R-II truck is designed to deal with all this at once. It uses a near 'neutral' castor geometry for stability with just a slight 'lead caster' for 'snap'. The design incorporates a 'no-hangup' kingpin arrangement. And we use a quick turning 50deg pivot angle in this truck for responsiveness. There is no "magic" pivot angle - it all depends on wheelbase and how you want the board to work. Our Downhill truck uses a slower 35 degree turning angle and 'neutral' geometry for high speed work. And our Luge trucks are available in 28,35,50,60deg baseplates. Even with 60deg trucks on a short wheelbase luge setup (50"), the trucks are stable well into the 70mph range and respond quickly. It's all about tuning for performance; we recommend using wedge pads for the R-II on decks over 50" long. This is 55deg of turning on a longboard! This works for the Randal trucks but other trucks don't have the stability to run such a responsive pivot angle. While it is possible to have a setup that turns too quick, the real problem can be trucks that turn too far. This is what Rich is talking about. If the trucks turn too far then the front end can 'crab under' and spit you off - usually backside! You want your trucks adjusted so that there is increasing resistance the farther you lean the board. You don't want the trucks so loose that they 'flop' all the way from one side to the other. Also, adjust your trucks depending on what kind of skating you're doing; both loose for gyrating, pumping, and slalom style; tighten the rear more than the front when using a longboard in skateparks and working it 'from-the-tail'; and both trucks tight when running hills. One cool thing about longboards is that there's really no rules about what a longboard is supposed to be - anything goes! So, have fun and play around with your equipment!
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Truck action:stiff board
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On 12/26/1998
tc
wrote in from
()
I've always found a stiff board to be more responsive. You may not get the "pop" associated with a flex board in slalom racing, but for other purposes, I let the trucks do the work. FYI back in '77, Tony Alva won the tight slalom world championship on a Logan Earth Ski (wood-no flex). He beat Bad H, Henry Hester who was the man for Gordon & Smith FibreFLEX boards. So this is nothing new.
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