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August 31, 2013 2 Comments
Do you know aero spokes were once unknown? Sounds unlikely, they're so fundamental to today's wind slaying cycling. Modern aero spokes begin with Claude Lehaneur's, in his visionary Roval wheels of the late 1970's. That work deserves a chapter of its own. Coming. The mass appearance of aero spokes coincides with technical excitement running up to the 1984 Olympics in Los Angeles. Never before was such a concentrated effort made in the USA camp to quantify and optimize the design features of racing bikes. Francesco Moser had just set an hour record on oversized disk wheels. The Pandora's box of aerodynamic tricks was opening.
Aero spokes infect the field
At this time, Scott Gordon (Aerosports), Andrzej Bek (US National Sprint Coach), and Wheelsmith (yours truly) began making aero blades from 14g blanks. Not so easy. Stainless with such small dimensions strenuously resists rolling, curling up, bending sideways, showing uneven surface finish. Even so, Andrzej got good results and some really sharp edges. Ken Carpenter's spokes sliced through a competitor's twin Binda toe straps in one brush during a World's sprint qualifying heat.
The alternative, pressing 14g wire into aero shapes, was also challenging. The thinnest section we could manage was 0.9mm. This made a width of about 3mm. No standard hub hole would fit. In addition, steel dies capable of flattening stainless wire need hardness of almost science fiction grade. Mystery metal and 250 ton presses. One spoke per press. Costly passion in action.
Simultaneously began a tradition of hub slotting. Many styles emerged but, for years, each builder did the slotting. Few hub brands offered aero-friendly holes. Eventually, the economic pressure of mass distribution forced bladed spokes and slotted hubs out of the scene. Major players like Zipp embraced a semi-aero spoke that fits standard hubs without slotting.
I never bought the premise these smaller blades were genuinely more aerodynamic. They have the same minimum thickness (around 0.9mm) so their aspect ratios (width divided by thickness) is lower. Likewise, claims that full blades generate unacceptable resistance in side winds are suspect.
Punching holes for blades
So, it's with some nostalgia that I revisit hub slotting. First widely used method was a hand-held punch. The die enters a hub hole and creates notches at the hole midline, allowing a bladed spoke to be threaded through.
A hand-held punch plier with special tooling enabled notching. I recall it originated with Frank McKeown, the original importer of DT spokes to the US. He and his Swiss wife, Christine, introduced American wheelbuilders to a new level of spoke integrity. Proud to say, at one time Wheelsmith was the largest single customer of DT spokes in the US. Here's the plier.
A custom punch, receiver, and travel limiter made it a quick solution to hub slotting.
Slotting a hub.
Grinding the slot
In spite of the speed and effectiveness of punching, a superior solution was grinding a single slot from the spoke hole bottom towards the hub center. This was better for hub strength as the hole was untouched throughout the area of spoke contact and pressure.
A hand Dremel die grinder suffices for the slot. While the work is boring, the speed is impressive. By far, we slotted the most hubs this way. Use Dremel bit #113.
(1) Mask the hub to prevent scratches, grease, and contamination from metal shavings.
(2) Mount in a TS-2 stand and fasten tightly.
(3) Put a spot of grease into each hole to catch cutting residue.
(4) Rub the 113 grinding bit on a block of beeswax before each hole.
(5) Hold the hub from rotating with one hand. Hold the grinding tool with the other. Use very light pressure. No forcing. Replace the bit after every few hubs. They're under $5, so don't economize.
(6) Take care to control the bits tendency to drift with its rotation. Keep the slot radial.
(7) Use a spoke to test how short the slot can be. No deeper than necessary.
(8) An air gun will clear out debris.
Bladed spokes make a great look, offer tremendous aero benefits, and are the province of hand builders. You'll never get a mass produced wheel with blades and a special hub like Chris King or Phil Wood. Not to mention disk compatible.
Wheelsmith was so devoted to blades, we made hundreds of thousands. These ruled the competition world for almost 20 years. Thousands of wheels are still out there, reliable and special. The ACE3 spoke was one of our best creations. It featured a 2.3mm (13g) elbow, a 3x0.9 blade, and 2.0mm (14g) threading. Any slotted hub would receive it (hub holes are already over 2.3mm so rolled 14g threads will pass).
Use your ingenuity. Build a fixie wheel with blades. Be artistic. Put a 21st century carbon rim on a clever hub (think Powertap) with bladed spokes. Don't know where to find them? I have many thousands rescued from USA Cycling's team shop. Drop me a line with needs. They're ready to race.
Know more and think different!
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