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| Q&A: McKendry on Speed (1810 Posts)
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oh yeah
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On 10/7/2005 herbn
wrote in from
United States
(152.163.nnn.nnn)
another question that's been bugging me (just a little) ,when do you use 97mm wheels? I liked the accelleration of 76mm wheels over 83mm wheels and 70's are even quicker, 97a's whould take either a really big hill(how big is big) or maybe a heavier rider,turns? seems like 97mm wheels would be full of problems on turning courses, as if bigger riders don't have enough problems with turns. I might be inclined to thinking that wheels that big might just be a gimmicky marketing thing,but your company is so racing orienting.
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That distortion thing
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On 10/7/2005 herbn
wrote in from
United States
(152.163.nnn.nnn)
I use a set of 78a gumballs too,i have posted before that one session when i was using the 78a in the front they felt grippier while carving really hard,i egotisticly(sort of )took my board set up for cruising around on flats and small hills, onto a hill that would be 50mph in helmet and leathers(47 in baggy jeans and a t shirt)the asphalt is really pretty smooth but kind of wavey. There are some little wheels that are available in triple compound;a very hard core,a hard hollow tyre ,and a 78a "tube" in the tire,to raise resilience. Now , you could apply that to long/slalom board wheels. I think a 80a-84a tube in a 72a tire ,around a 100a (54d whatever) core would be interesting but very critical in the chunking/durability aspect. But perhaps a real hard small core,with a 86a soft(for a core) big core then a 75 or 72a core tire. To bad there isn't a way to make a progressively softer tire in one or two pours.
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Hard vs Soft
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On 10/6/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
Here's my analogy:
Hard wheels are faster than soft wheels when the surface is exceptionally smooth, like polished concrete, plastered pool walls, and wooden ramps. The wheels are like balls and the surface is like the race of a bearing. The less the balls distort from being round and the more polished the surface is, the faster you'll spin. The contact patch (and friction) are often minimized because traction is not the biggest concern. Quick acceleration is. Rebound in a hard wheel can (and does) help in the speed of the wheel, but as the hardness goes up, the rebound goes down. The rebound helps the wheel to return stored energy after running into/over the imperfections in the surface.
Once you get out onto the ashphalt however, things are different. Even the smoothest asphalt is an inherently pourous surface. And it tends to be softer too. Many of the wheels with the fastest roll speed are between 72a and 76a. Psychologically, it's difficult for most people to believe that these duros are that fast, because they feel so smooth. "Smooth" doesn't feel or sound fast, but the wind going through your helmet does. Even if the road is smoother, I resist the tempation of moving up in durometers and take faith in my 75a wheels. If you are pumping a board (like in slalom), you need the firmness and control of a wheel from about 80a to maybe 88a, with 84a being a happy medium. The roll speed is slower, but the traction and control is better in a wheel that doesn't deform too badly in the (many) tight turns. I'm developing a wheel in the 80's with more rebound than we currently have. Initial tests are somewhere between "big smiles" and "oh my god".
I wouldn't be surpised to hear that a 78a Grippin feels quicker than a 75a Gumball at moderate speeds. Especially if you're pumping at all. Gumballs have a lot of massive by comparison, and it takes a bit more to get them up to speed. The 75a Gumballs will feel a big "sluggish" at low speeds, but will start pulling away from a 70mm at higher speeds. People really like 78a - both the duro and the number. It does last a bit longer and doesn't distort as much, but for pure roll speed, 75a is kind of a sweet spot for rebound, and it doesn't go any slower when the asphalt is smooth. If the temparature is about 96 degrees or more, the 72a and 75a compounds start to run into some wear problems. They almost feel "greasy". I'd go with 78a or maybe even 81a when that happens.
Stay tuned though. Our new 81a formula has the rebound and feel of a softer wheel, without the distortion. I think that you're going to like it.
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good surface
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On 10/6/2005 herbn
wrote in from
United States
(205.188.nnn.nnn)
a few posts back you suggested 75a urithane for a "good" surface ,good is a relative term, good in nj may be mediocre when compared to the fine grain asphalt on the frostless,unsalted,streets of cali. harder urithane should be faster on really smooth streets, 78a or 81a ,especially with the new smaller cores.On the old wheels i thought the 75a was definitely the way to go but i'm using a set of 78a grippins and they seem quicker than 75a gumballs on my short local daily hill carves. I'm pretty sure the gumballs will be faster on bigger hills.
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Bob's Burn Quest
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On 10/5/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
I think that Bob is using 90mm Flywheels and going around 100mph. So what is the circumference of a 90mm wheel? Hmmm. Well, 90mm is about 3.5433 inches and C=Pi*D or 2*Pi*r, right? So I get 11.1316 inches every time that the wheel rotates once. There are 5280 feet per mile and 12 inches per foot, so a mile is 63,360 inches. That wheel would rotate 63,360/11.1316 times to travel a mile which is 5691.9 revolutions. 60 miles per hour is 1 mile per minute, which makes 5691.9 revolutions per minute. Therefore:
60 mph = 5,692 rpm
70 mph = 6,641 rpm
80 mph = 7,589 rpm
90 mph = 8,538 rpm
100 mph = 9,487 rpm
105.41 mph = 10,000 rpm
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Tire Sauce
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On 10/5/2005 EBasil
wrote in from
United States
(63.206.nnn.nnn)
Jeez, Bob. Just tell those motorheads to stop using tire sauce and to hose down the track before you run...
Nice looking wheels! yuck
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Fish Oil
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On 10/5/2005
Bob
wrote in from
United States
(132.250.nnn.nnn)
Hmm thanks for the tip on cleaning the wheels.. where you implying I get smaller whels and they will just fling the sludge off? Now just one question for you. Who ever said anything about 83mm wheels?
bob
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Omega
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On 10/5/2005 Skeptic Skater
wrote in from
United States
(207.200.nnn.nnn)
I believe that 10,000 rpm works out to 97.2 mph with an 83mm wheel. My math shows that yours are turning around 9206 @89.5mph. Chris?
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Cleaning Flywheels
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On 10/4/2005
Bob
wrote in from
United States
(69.251.nnn.nnn)
Hey Chris, Here's a question for your Top Secret Chemist and it is not one you will get from many..
What kind of solvent can I use to clean the VHT and burnout rubber from the dragstrip from the Flywheels??? Something that won't attack the magic green mix and turn it into green goo please.
It is some kind of ride with this stuff stuck to the wheels when they are turning over 10,000 rpm. A ten year old spectator suggested that I spray them with PAM before I get on the track.
this is a serious question by the way..
bob
Dragstrip sludged Flywheels
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Spacers for JimZs
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On 10/4/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
If JimZ uses a bearing with a 10mm bore (0.3937"), the axle will a little less than that. McMaster-Carr (McMaster.com) has some 1/2" (12.7mm) OD steel tubing with .049" wall thickness, which could be used to make some spacers. The part number is 89955K26, comes in a 6' length, and is $19.33.
I'd cut .402" (+/- 0.001") spacers. The .012" chamfers are a luxury. You should be able to get two spacers per inch, which is 144 spacers out of a 6' tube. If shipping is less than $10.00, the cost per spacer is under 20 cents. Now try and find some machinist who won't break the bank...
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Short, Steep and Straight
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On 10/4/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
To be perfectly honest, I hate "short" and I hate "straight", so "steep" just means that it will be over sooner, which perhaps is a blessing. It's nice that the surface is good. It sounds like a better Slalom or Slider hill than one for Downhill.
To answer your question though, it sounds like a pushers dream hill. A short hill with smooth pavement and without any technical turns means that whoever can push out in front might not be passed. A quick, low, narrow, lightweight setup would be ideal for getting a good jump, and a huge wheel won't provide any real advantages. The 76mm or 83mm Flywheels in 75a would be a good call. If the surface is bad, the Gumballs (although heavier) would smooth it out.
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wheels for short steep straight dh
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On 10/4/2005 brad
wrote in from
United States
(155.229.nnn.nnn)
Chris,
What wheels would you choose for a short, steep, straight dh (bombing)with good surface?
maybe a better question: do you think a short, steep, straight (bombing) dh has any merit?
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spacers for 10mm axles
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On 10/3/2005 droid
wrote in from
Sweden
(83.250.nnn.nnn)
Any idea where to get some spacers that would fit JimZ 10mm axles on his hanger?
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Abec Differences
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On 10/2/2005
Bola
wrote in from
United States
(206.53.nnn.nnn)
Shaner:
Going from abec 3 to abec 5 or 7 should not affect the ability of the bearings to withstand loads and shock, if you are within the same bearing family (same manufacturer). The abec rating is based on toleracing (balls and race, no pun intended) and directly related to surface finish. As for the biltins, 7 is the way to go.
Bola
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best wheels, bushings for "downhill" bomb race
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On 10/1/2005 brad
wrote in from
United States
(216.233.nnn.nnn)
Chris,
Best wheels, bushings for "downhill" bombing race, short, steep, good surface?
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Biltin abec differences.
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On 9/30/2005
Shaner
wrote in from
United States
(66.235.nnn.nnn)
awesome forum. and by the way, you should make some more videos like the one on your site of you riding that "waterski longboard." youve got style, (although the shirt was a bit much)
i want more speed in bowls and parks and i'll take it anyway i can get it. so was thinking of using abec 7 biltins, as opposed to the abec 3 biltins. but i was wondering if the abec 7's can take as much punishment (ollie'n, flat landings) as the abec 3's or if they would break. or any abec 7 bearing for that matter.
thanks, Shaner.
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Biltins on Exkate Cherry Bombs or Turbo
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On 9/27/2005
DeMitt Rutledge
wrote in from
United States
(12.110.nnn.nnn)
Yikes - this forum is THE BEST thing around . I TRULY appreciate the most informative and expeditious response ! ! Some little voice told me this might be the case - but I just wasn't sure. The information provided is such a help ! For now though - I'll stick to bombin' with my Greenies, and as far as the C.B.'s and Turbo's - never hurts to have wheels available for street ridin' 'eh? ? Thanks again for the great info folks.
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Spaced Out
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On 9/26/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
This picture is a few years old, but the numbers are the same except for the newer eXkates. The newer Cherry Bomb/M80 hubs have been converted over to the .400" standard. The older ones had this very strange proprietary spacing, and there's a good chance that the wheels DeMitt owns have the older spacing. To fix up the old wheels, two washers that are 1/32" thick will work perfectly between Biltins. So will one that is 1/16".
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2mm spacers
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On 9/26/2005 herbn
wrote in from
United States
(205.188.nnn.nnn)
find some washers or one thick one that add up to 2mm, you may need a caliper, electonic ones are getting real cheap and you can convert metric to universal decimal american.
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Regarding the note below....
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On 9/26/2005
DeMitt Rutledge
wrote in from
United States
(12.110.nnn.nnn)
There appears to have been some type missing on that last post....What I was saying is that I own quite a few different sets of Abec 11 Wheels,Satori,Exkate Wheels, and Sector Nine wheels...but Exkates just doesn't seem to take a bearing set with 10 mm bearing spacers...it looks like they take a 12mm bearing spacer. Anyone else notice this....Both my Turbo's and Cherry Bombs appear to have this problem...they don't spin freely when using 10mm Biltins with the axle nut even slightly tightened..but my Abec 11's can take biltins with the axle nut cranked hard as HE**
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Biltins on Exkate Cherry Bombs or Turbo
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On 9/26/2005
DeMitt Rutledge
wrote in from
United States
(12.110.nnn.nnn)
Say cool cats - I love longboarding and breathe it in deeply as often I breathe in air...I've been fortuante enough to own new sets of 76mm Gumballs , 83mm Flywheels , 82mm Cherry Bombs..76mm Turbos..Sec' Nine 72mm Nineballs with the 'racecore', NoShoolz, Cliff Sliders....etc. I have a few sets of Randal DH's and 180's...here's my question. My Biltins work great in my Green Wheels - but they don't work as well in the Exkates...I've even noticed a 2mm gap between the bearing races and inner race of actual bearings when the wheel is sitting against the end of the hangar arm.....it looks as though they take a 12mm bearing spacer ? Any answers to this dilemma would be helpful. Just to be clear,when using my Biltins in Abec 11 wheels - I can crank the axle nut until it bleeds,and the Abec's just roll and roll and roll forever...but when using the biltins on Exkates - I tighten the nut just a bit, and it drags and spins like like 3 revolutions per spin. any answers ? Oh - and is there any truth to there being a 82-85 mm Gumball coming out ? ? I use my Greenies for all riding now - but now I have 2 sets of wheels that seem kind of worthless not being able to use them efficiently....
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Footbraking
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On 9/25/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
Hey Dan, You want to set your foot down flat, close and parallel to your board, as if it was a ski. Just don't rub your shoe into your wheels. It's easier on low CG board because you don't have to bend your knee as much and "reach" for the ground.
Since there are two stances (regular foot and goofy foot)and 2 ways to brake (regular and mongo), there are four different ways to brake. I'm trying to "undo" 30 years of braking mongo by dragging my rear (right) foot (I'm a regular foot) but so far I only bust it out at the end of Slalom runs - I'm too chicken to try it in Downhill racing. So if you're just starting out, and you take your front foot off your board and drag it, maybe it's not too late to change. Usually whatever foot you push with, is also the foot that you brake with, and mongo is usually a disadvantage in controlled steering and setting up for turns.
Get some cheap shoes (or at least one "throwaway" shoe for the foot that you brake with) and practice. Try cruising along at a nice clip, setting up, and then just "tapping" the bottom of your shoe for a split second and returning it to your board. Keep doing this until until it feels like second nature. Then try doing it before both left turns and right turns. Steering left and braking is different from steering right and braking and both are different from braking in a straight line. You don't want to find yourself in a position where a high speed turn comes up and you've never set up for that direction before. Sometimes the road jogs to the left before making an abrupt right, and these are tricky as all hell. You may want to brake in the straights before the jog, or slide a turn that's too tricky to footdrag before.
Always be ready to slide if your braking isn't working as you planned. Sometimes you'll have just enough time to get your foot back on board and throw down a slide to save your bacon.
Remember that footdragging means that you are more upright, further from the ground, and is therefore more dangerous if you fall. It also incorporates airbraking which is less aerodynamic, and so it does slow you down very quickly. I never run off of my board, unless I would otherwise faceplant. What this means is that I'm constantly throwing down little footbrakes whenever I'm skating the bike path, on campus, the park, or at the end of a run. Replacing one shoe is cheaper than replacing 4 wheels, so find a "shoe buddy" and footdrag more often. The sound of a shoe scraping along the ground is the skater's equivalent of a horn on a bicycle. Comin' through!
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footbrake
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On 9/24/2005 dan@CSU
wrote in from
United States
(216.17.nnn.nnn)
hey chris just a quick ?. i have my pendulums down but want to learn to foot brake. what part of your foot touches the pavement? any other tips? thanks and i want some green bushings. -dan
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Kingpin Stress
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On 9/24/2005
Chris Chaput
wrote in from
United States
(66.116.nnn.nnn)
Imagine that your trucks didn't have pivots at the end of the hangers (I cut it off in the image above, and "pinned" the hanger to the kingpin to emphasize the point). The pivot cup couldn't help in supporting any of the weight of the rider. ALL of the weight of the rider and lateral forces are therefore placed on the kingpins instead. The kingpins in these trucks are cantilevered - unsupported at the end. Turn to the left, turn to the right. Repeat. This is a recipe for disaster. It's a bit like grabbing the metal from a coat-hanger, bending it back and forth until it heats up and breaks.
The problems with pressfitting a spherical bearing into the cushion seats are hard to ignore. Aside from being a royal pain in the neck to assemble, they prevent the pivot cup from relieving any of the stresses on the kingpin in every condition except for one. Two things must happen. The hanger must be designed so that it the pivot (or pivot shoulder) can "bottom out" into a hard (solid) pivot cup/pivot bearing AND the hanger must be perfectly perpendicular to the pivot axis (the axis of rotation). If you have a soft pivot cup, or one that doesn't support the hanger, it won't prevent the stress on the kingpin. We all know that the hanger is almost NEVER perfectly perpindicular to the pivot axis, and there are several reasons for this - undercompressing or overcompressing the cushions, too tall or too short of a bottom cushion, having one cushion which is harder or softer than the other. All of these conditions have the effect of "pulling" the pivot out of the pivot cup and putting the stress on the kingpin. There are ways of removing slop without adding stress to the kingpins. Stay tuned.
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truck ballz
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On 9/23/2005 sinned
wrote in from
United States
(216.9.nnn.nnn)
look up Jim Z speed parts
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