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The Backstory on Holey Spokes

In fall of 2008 I (Bruce, trikebldr) bought a 2003 Speed. As I hefted it up to put it in the rack on top of my car I thought I would just throw it all the way over the car, it was so light. When I got it home I weighed it at 28lbs, complete with fenders. It made me wonder how light I could make my 2007 Speed. Stock, it weighed 31lbs.

I have a friend in Los Angeles who runs the computers that control the earthquake shift equipment under a high-rise building in downtown. He asked for a lot of pics, dimensions and weights, then plugged them all into this computer to do a stress flow analysis. It gave us back hundreds of diagrams that showed where the trike’s frame, and other parts, were most and least stressed under load.

DF bikes are made from butted and double-butted tubing to reduce weight. For those not familiar with the term “butted tube”, this means that the center has thinned out walls while the ends are thicker walled. These special butted tubes can be made in approximate lengths and cut to fit precisely into a DF’s frame. All trike makers that I know of use pretty much generic, uniform-wall-thickness tubing. It’s simply a matter of economics, since trikes of various frame design require too many tube lengths to be able to provide butted tubing for all parts of the frame. The old solution to non-butted tubing was to drill across the tube in the middle areas to reduce the weight. Tubes under side loading cannot be drilled, but those in longitudinal compression and tension can be. Most DF frames are completely triangulated, meaning their tubes are all under tension or compression, but not side loaded, appreciably. Trike frames are not so lucky!

Holey Spokes was drilled in those areas shown to be over-built as far as tubing wall thickness. The main, one-piece frame was drilled exactly as the computer showed, but I took some liberties on some smaller, easily replaceable parts. In the end the only area that I would do differently would be not drilling completely through the boom’s internal “peace” webbing. A stock, undrilled boom gave me 1/16″ of twist under heavy loading measured at the top of the der post, but the drilled version now gives me 1/8″ of twist, measured the same way. By loading, I mean causing the rear wheel to spin slightly with the front brakes on. This would not be acceptable for all you pseudo-Lances out there, but for me it isn’t a noticeable loss of efficiency.

A lot of criticism has been heard about drilling the cranks. You cannot drill most cranks, but the older Truvativ Elita cranks have a dog-bone cross section to them and the main strength is along the edges. Small, 1/2″ holes can be drilled with no problems. The most stress that can be applied here is until the rear tire breaks free, and I have done that, as well a stomping on them hard.

I have about 200 hours of drilling and de-burring in the project, as well as other tweaks to make it handle quicker. The wheels were tightened up to the max recommended spoke tensions for each rim. Ceramic bearings are used everywhere except in the Frog pedals. I have one set of Stelvio Light tires that are over 11,000 miles old and are much lighter than new Stelvios. I keep these stored except for special rides. I normally run newer Stelvios. I dumped the stock seat mesh and made up a new sling from a single layer of the stuff POC sells. It’s laced inside the seat rails with some parachute cord.

The cost to build this trike (other than the stock trike) was $12.53 for the materials to make the seat, plus about $183 for the new XTR Shadow carbon-cage rear der. The der weighs just 181grams as opposed to the 495grams for the stock Deore der. I was already running Q-rings and hollow-pinned chains, so throw in a bit more money for those if you must. Ceramics for the whole trike run about $500 for everything, including BB and idler.

The base trike weighed 31lbs, 3oz when I started. Set up for final weighing, with the lighter tires, no headrest, mirrors, bottle cages, it weighs exactly 24lbs. I normally run it with newer, heavier Stelvios, one mirror, one cage and a POC headrest. Set up like that it weighs at 25lbs, 14oz.

Holey Spokes drew a lot of flak on the Catrike forum as it was being built. Comments like “fold up around his ears” were found often! The drilling was not done helter-skelter like so many bikes were in the old days. It was done carefully according to indicated high and low stress areas. It’s now three and a half years old, and I ride it about 3000miles a year. I almost always pull my dog in her trailer behind it, too (another 56lbs, total!)! If Cindy is pulling the trailer, I get carried away and take a lot of curves on two wheels. After all, higher performance in handling was what it was built for. I prefer to bicycle it rather than slide through a corner.

I  have weighed between 207 and 225lbs during the last 3-1/2 years, so it has endured a lot of heavy abuse from my riding style, with no failures yet. The reason is, those drilled tubes are not being BENT, but are under tension or compression. The seat side rails were not drilled specifically because they are being pulled sideways, inward from the weight of the rider in the mesh. There’s one short video in the link to my pics of this trike, showing me bicycling the trike as well as doing hard stoppies. This is pretty much normal for me while I wait for others to get ready to ride. It’s just a fun trike to play with like this!

About six others have test-ridden it and two of them have had me do this treatment to their’s. One is a 2008 Speed, and the other is a 2007 Pocket, called Piccolo Pockets. I consider the 2007 to be the very best Speed of all models, especially to do this with.


Bicycle Spoke Technology

Bicycle Spoke Technology

Spoked wheels have been around for millenia, and have reached a high degree of refinement in bicycle wheels.  Bicycle wheels must operate for years with no maintanance, support hundreds of pounds of weight, and be as light as possible.  There are a number of possible spoke configurations, but the one that is used on most bikes is the “triple cross” tangential pattern.  If you look at bike wheels, the spokes are attached to the hub tangentially, and each spoke crosses another spoke three times, hence the “triple cross”.  This tangential spoke pattern was invented by renowned bike designer James Starley, and was patented in England in 1874.

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When properly made, each spoke has a certain amount of tension on it when unweighted, pulling the hub towards the rim with a force of about 50 pounds per spoke.  When the wheel is weighted, by weight pressing down on the axle, the hub tries to move toward the ground.  When it is does this, the three spokes directly below the hub become unweighted, and the rim deflects a small amount, about .001 inches.  That is about the thickness of a piece of paper.  The tire around the rim deflects a good deal more than that.  Although the three spokes under the hub are unstessed, the other remaining spokes pull equally on the hub, and prevent it from moving in relation to the rim.  As the wheel is weighted and rolled, the rim is thus constantly flexing at the spot under the hub, and the spokes are constantly being unstressed and stressed as they come under the hub.  Below is an exaggerated view of the wheel under weight.

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These spokes appear to cross more than three other spokes because the spokes on both sides of the wheel are shown.  Each spoke only touches and crosses three spokes on its side of the wheel.  When a rider hits a hard object, such as railroad tracks or a curb, the spokes most likely to break are the spokes that are above the hub and closest to vertical, and they are most likely to break where the spoke head enters the rim hole.  The hub basically shears them off the head of the spoke.

This information has almost no practical value, but isn’t it fascinating! Of course some sites go into the physics of things like spoke strain and hub deflection, such as  Held by Downward Force by John Forester, and Henry P. Gavin’s paper on Bicycle Wheel Spoke Patterns and Spoke Fatigue.