September is on (2018) and there’s news to share. Up in Port Townsend, WA a new cycle school is getting underway and I taught Wheelbuilding 1 last weekend—twelve diverse students, a beautiful location, and 12 excellent wheels built.
Nice workstations.
The goals of wheel building and racing are the same—speed and efficiency. I am not a fan of most side stressing schemes for wheelbuilders because I believe they add time but not quality. The intention is noble—to make wheels more stable by relieving pent up stress in the freshly assembled structure. This is often done with the wheel supported at the rim on a table and a piston applying side load to the hub or all spokes facing the piston. This isn’t a cheap or compact tool. Granted, some of their users are very smart but… Read more →
A severe side (lateral) load on a bicycle wheel is bad news. Wheels are strong for radial (vertical) and torsional (twisting) loads but vulnerable for lateral. Fortunately, high lateral forces are uncommon with single track vehicles that lean through turns. Still, they account for most wheel failures and the actual dynamics remain poorly understood by many.
Let’s examine an extreme lateral load and discover how a wheel responds. How can a tensioned structure with balanced, triangulated bracing warp instantly into an unrideable potato chip shape?
Familiar shape with a bit of frost.
A lateral force usually arrives from the tire-ground contact, perhaps from skidding. The load moves the tire to one side which, in turn, pushes the rim to the side. The rim resists the force with both bending and torsional stiffness. The force is felt by spokes in the immediate region.
A spoke on the the force side tends to maintain its tension. A spoke opposite the force loses tension. The rim does not budge until the opposite side spoke reaches zero tension. At zero tension (all within milliseconds) all forces still balance out, and the rim is undeformed.
lateral load sequence
Once the opposite side spoke buckles, the rim begins moving. Would be helpful if the force side spoke, tight from the beginning, could increase its tension to resist the force. However, due to the low relative strength of bicycle rims, the rim begins moving away from the load in an arc whose radius is the force side spoke. The rim section swings at the end of the force side spoke as a yo-yo swings on its string going “around the world.”
Bent!
In practice, the force side spoke cannot increase tension to keep the rim stationary. The rim is too elastic and swings rather than remaining the same distance from the wheel’s theoretical center. In this example, the lateral force is extreme and our wheel now has a pronounced side bend at the site of impact. Neighboring off side spokes are unloaded as the rim moves their way. Their reduction in tension makes for a positive push that creates two bends that are reverse of the side load. Such “wings” also occur next to broken spokes.
Depending on the magnitude of lateral force, the flexibility of the rim and the amount of spoke tension; a sine wave can propagate around the wheel, driven by the reduction of spoke tension in half, or more, of the spokes. All energetic states seek a lower potential. The loss of spoke tension drives the sine wave, bending the rim into a potato chip shape. This has been triggered by the initial extreme lateral force, but the eventual collapse is an implosion of the tensioned structure.
© The Bicycle Wheel, J. Brandt
This potato chip shape, also known as a pretzel or taco, is technically a hyperbolic paraboloid. You can trace the edges of one on the Dumbo ride at Disneyland. When Dumbo swings low, its radial arm acts like a spoke that is maintaining tension. Swinging high is the same, but like an opposite side spoke.
Dumbo rises and falls as the ride rotates.
Hyperbolic paraboloid—Wikipedia
In wheels with extremely springy rims that do not easily take a permanent set, a potato chip wheel can sometimes be fixed by banging sideways on the ground. A reverse extreme lateral force can cause a sine wave that neutralizes the deformation. It’s a chancy strategy but if you witness one, you’ll know it was special. Steel and wood rims are better for this than aluminum or carbon.
If you travel around the rim like a bug (or Dumbo) it will be obvious the rim is deformed left and right but also twisted. It’s a torsional deformation, not simply left-right. Rims with great torsional rigidity resist taco shapes much better. Torsional rigidity increases as the 4th power of the radius of the largest inscribed circle that fits in the rim section.
The rim above (from 15yrs ago) can fit a large circle in its cross section, giving it extraordinary torsional rigidity. It is nearly impossible to twist into a taco shape. It’s not just the little dude inside making this rim strong. Many deep carbon fiber rims have high torsional rigidity. Pushed by an extreme lateral load they either bounce or break. Notice how many of today’s more enlightened rims feature large open space in their profiles? Good design!
A taco wheel often displays four lobes, two in one direction, two in the other; and one is usually larger than the others. Safe to assume the extreme side load was delivered at this spot and the other three lobes formed as a consequence. Trying to true this wheel is wasted time if the rim has taken a permanent set.
Loosening spokes will reveal how extreme the bend is. Once de-tensioned, the true rim shape appears. If you must use the rim again (think: remote location expedition) try and make it as straight as possible without spoke tension. Be very careful to not introduce kinks or dents as you lever the rim to flat. Once the rim is flat, it will support spoke tension again and have no residual tendency to return to a taco. Truing without first bending the rim makes an unbalanced structure prone to deform again.
Before we leave the world of tacos, pretzels, and potato chips, let’s notice one further way a wheel can assume a multi-lobed deformation—excess tension. A rim can only support so much total tension, in proportion to its mass and shape. We used to build a favorite rim to 100kgf per spoke, with 36 spokes. The same rim with 48 spokes could not support 100kgf on each spoke.
An over tensioned wheel can “pop” suddenly into a wavy pattern. It’s the same principal as extreme side loads. Such a deformation will have many (not just 4) lobes, each small deflections. If you lower the tension total, with luck, the rim may behave as if nothing happened. It was just trying to reach a lower energy level. In its wavy state some spokes lost tension, others maintained. The total was lower.
Whether you ever undertake such truing, it is important to understand the forces involved. A wheel can suddenly become a taco shape with an extreme side force. In slow motion, this begins at one spot and a sine wave of deformation travels around the wheel often leaving a 4-lobed taco shape.
When it comes to metal bending and tension, most everything is reversible so, even if impractical, such wheels can be repaired. With these principles in mind, try your hand at it. You may not succeed but the exercise is always informative. Experience at the fringe of possibilities is what makes developing world bike mechanics so resourceful. Hone your own skills, don’t let them have all the fun!
A 1970’s image of a bicycle was so rare in US media that I clipped and collected every one I could. That would be absurd today but this early habit brought me an appreciation for New Yorker magazine cover art. They’re a throw back to an earlier time when original art was created for covers rather than the splashy newsstand bait that today’s covers have become.
For over 90 years, New Yorker covers have celebrated the changing seasons of nature, culture, and national events. More than their share feature bicycles and I began collecting these (with the help of Richard Sachs, similarly smitten). To date, there are at least 100 such covers, many are among my favorite cycling images of all time. Collectable all. Last week’s (May 7, 2018) cover, Biking in the Rain by Jean-Jacques Sempé is a wonderful addition to this charming tradition. New Yorker covers can be bought here.
A serene cyclist floats through the urban scene. © New Yorker
This latest issue profiles Sempé, my all-time favorite cartoonist. He has done 111 covers for New Yorker and, at 85, lives and works in Paris. His art, especially NY covers, has been a lovely background theme to my life. Like a musical tune that captures a time and place, his renditions seem timed to my career.
In 1979, this cover showed a pair of tandem riders scooting through the countryside with knowing aplomb.
Dwarfed by the world, but unflappable! © New Yorker
Six months after that cover my wife and I were married and honeymooned on our tandem. In 1983, Sempé drew Cycle Shop for the cover. Wheelsmith was our crowded workshop in Palo Alto. His image captured perfectly the context, the customer, and the mechanic.
Homage to the bike shop. © New Yorker
So, caps off to this gifted artist and the timeless style of New Yorker magazine.
Perhaps no builder epitomizes the intense, eccentric inventiveness of mountain biking’s inception like Charlie Cunningham. And we now have a superb glimpse of his unique contributions by the like-named but unrelated, Richard Cunningham of Pinkbike. Both, by the way, living examples of eyes-wide, bold cleverness in the pursuit of 2-wheeled dirt. Please check it!
In his April 11 post, Richard explores Charlie’s 1978 CCproto that includes so many years ahead ideas, he could barely fit them into 1,500 words. None of us who’ve shared this era can deny Charlie’s many influences on each of our work, a true Hall of Famer.
Sloping top tube, 1X gearing, oversized rear cogs, extra wide rear hub, dropped bars,… 40yrs ahead of its time. © Cunningham bicycles
To many in the day, Marin seemed a fantasy land—tinkering with dirt cycling, consciousness, rampaging around various watersheds, light shows at house parties, a bit unhinged. The joy of taking cycling down a somewhat different path was too much fun. For kids, like visiting a chocolate factory.
Chocolate, that mesoamerican delight, nearly addictive for many, health enhancing (in moderation), never out of season; seems an apt metaphor for the playful indulgence of mountain biking’s early years.
For his part, writer and inventor, Richard Cunningham packs a career of surprises and discoveries. Wish I had an image of him on his horse, but here’s another typical scene.
WWI Fokker Eindecker-inspired airplane, a machine hand-built by Richard.
Thought I saw RC the other day. Nah, maybe Eddie Vedder.
Sadly, Charlie’s inventive career was interrupted several years ago when a bad crash left him with brain injuries. Now, with the care of his wife, legendary racer and writer Jacquie Phelan, and many friends, Charlie works hard every day to recover and enjoy what he can. He needs your help. Consider contributing to Charlie’s recovery fund.
While mentioning Jacquie, let’s remember one of her more famous fashion statements from the era—a mud covered RockShox moment. Funny how much that mud looks like chocolate!
Maybe it was chocolate?
We’re having some fun up here on the Olympic Peninsula. A small group of lifelong cyclists are inspired to start a school, Port Townsend Cycle School. Website coming soon.
A permanent home is proving hard to find and we may decide to build ours. In the meantime, I’m going to start by teaching wheelbuilding classes for the first time in a few years:
Wheel Building 1, Introduction to Lacing and Truing
Anyone can build a bicycle wheel. Obstacles are few and mostly self imposed. Learn a mistake-proof method along with important wheel and component theory. Each student will build their own wheel, receiving one-on-guidance. All tools and parts are supplied for this 2 day adventure. Class size is limited to 12. Dates: Sat-Sun, April 21-22 and Sat-Sun, July 14-15. Cost: $300.
Tried and True.
Wheel Building 2, Attaining Proficiency
Intended for those currently building (prereq of WB 1 or equivalent), to take your skills to the next level. More sophisticated tools, experience, and measurement is necessary to build professionally and profitably. Each will build a wheel and analyze the results. Focus is on process refinement for greater quality and speed. We’ll be using P&K Lie truing stands and digital tensiometers with download! Class size is limited to 6. Dates: Sat-Sun, June 23-24. Cost: $400.
No shortcuts for these guys.
Wheel Building – Level 3, Wheel Design and Engineering
Decades of manufacturing and building experience are distilled into a 2 day intensive for established builders and students of the category. Wheel mastery can be difficult to attain because data on how and what works is seriously scarce. Join us for 2 exciting days of demystification and full disclosure. Lecture and presentation plus hands-on with special tools, class size is limited to 20. Date: Fri-Sat, May 24-25. Some of you will recognize this as the sort of material shared at the PBMA’s Portland Clinic in February. Cost: $300.
Same as it ever was!
These will be hosted at the Port Townsend School of the Arts at Fort Worden in Port Townsend. It’s a spacious and lovely facility but only available to us through July.
While there are as many ways to build as builders themselves, information and examples add immeasurably to a learning curve. A beginner needs access to a trouble free method and examples from which to build a style that works. These classes are full disclosure from someone who loves the task and has spoken to as many builders as perhaps anyone else. Join the conversation!
Send questions to me (ric@wheelfanatyk.com). For registration, contact Nora at ptcyclingschool@gmail.com.
Trick procedures are as important to your tool box as the individual tools. Please share them whenever possible. In that spirit, check these:
Proper dial indicator use
Plunger dial indicator
Indicators magnify movement and provide numbers to better judge trueness. However, your standard dial probe indicator is not made for rapidly moving surfaces. Even when an indicator is fitted with a bearing, the measure surface (rim brake track or edge) should only move slowly for two reasons:
1/ The probe is not designed for sideways force. Its accuracy is wrecked if the probe bushing wears.
2/ The probe return spring is as weak as possible. Consequently the probe can jump off the test surface with a tiny bump and vibrate with a pattern of roughness. To navigate a rapidly moving surface, the probe would need a strong spring and a dampening mechanism to maintain contact.
Spinning a wheel on a truing stand is normal when a light gap is used to watch trueness. A gently spun wheel can turn at 60 rpm. With a full sized wheel, this is 4800”/min, the same as a 1/4” drill at 6,000 rpm. This is not slow speed!
So, move your wheel at any speed for visual truing but turn it slowly with dial indicators. Don’t let your measuring instrument use cause machinists to cringe!
Bearing play
Builders deal directly with hub bearing play. Play interferes with truing, even when it’s too little to bother riders. In some hubs, play can be adjusted to zero for the build and then returned to the recommended amount for use. In most cases, however, it must be tolerated.
How to measure play? Axle play is magnified 10X at the rim but quantifying is delicate work. Hold the rim where a dial indicator is located. Give it a slight lateral force, left then right. The wheel is easy to flex so your finger force must be extremely light to reveal bearing play only.
What is reasonable? No single answer exists for all wheels. One number many experts would approve is 0.008” (0.2mm) at the rim (TIR—total indicated runout). Such a reading at the rim can be produced by less than 0.001” (0.02mm) movement at the axle. These numbers are at the very extreme of manufacturing tolerances for consumer products. More accuracy may be needed by NASA, but not us.
Heat Guns rock
Trusty heat gun
A must around any shop is your standard 1500W heat gun. Like anything with voltage and heat, special care is important—flammables must be far away and good ventilation present. Some of my favorite uses:
1/ Removing adhesive vinyl stickers from nearly anything. Vinyl stickers lift off effortlessly with the right heat. Use less until you discover the perfect amount. Be careful not to damage your surface.
2/ Heating metal so stuck screws or bearings can be removed. Heat makes metal expand, each material with its own CTE (coefficient of thermal expansion). Aluminum expands much faster than steel. But even in steel-to-steel assemblies, a larger unit will expand faster than a smaller (like a stuck screw). Frozen nipples are a good example.
3/ Drying touchup paint, adhesives, spoke prep, rinsed chains, etc.
4/ Removing old sewup glue from metal rims. Heat then scrape or wipe with steel wool.
5/ Lubing old leather saddles. Apply a preservative cream or wax, heat the area and watch the saddle inhale the lube. Be sparing, it’s easy to make a crispy old saddle way too oily.
6/ Paint removal where the substrate can take the heat. This works on metal or wood. Paint softens before burning and can be scraped or wiped off.
7/ Applying shrink wrap. Handy shrink wrap is available is many colors and diameters, used extensively in electronics. Find ways to employ it on bikes—bar tape or cable end finishing, for example.
Got some other tricks? Wheel specific? Please share!
A Zen teacher saw five of his students returning from the market, riding their bicycles. When they arrived at the monastery and had dismounted, the teacher asked the students, “Why are you riding your bicycles?”
The first student replied, “The bicycle is carrying the sack of potatoes. I am glad that I do not have to carry them on my back!” The teacher praised the first student, “You are a smart boy! When you grow old, you will not walk hunched over as I do.”
The second student replied, “I love to watch the trees and fields pass by as I roll down the path.” The teacher commended the second student, “You eyes are open and you see the world.”
The third student replied, “When I ride my bicycle, I am content to chant nam myoho renge kyo.” The teacher gave praise to the third student, “Your mind will roll with the ease of a newly trued wheel.”
The fourth student replied, “Riding my bicycle, I live in harmony with all sentient beings.” The teacher was pleased and said to the fourth student, “You are riding on the golden path of non-harming.”
The fifth student replied, “I ride my bicycle to ride my bicycle.” The teacher sat at the feet of the fifth student and said, “I am your student!”
Plucking spokes while building is a time-honored technique for tension appraisal. It’s especially effective for judging if neighboring spokes on the same side of a wheel are at different tensions. The more even the tension, the more stable and long lasting the wheel. For more on the acoustic tension method, check here.
30 years ago, visitors to Wheelsmith would remark that we sounded like a harp tuning studio with musical notes in the air as builders plucked spokes to confirm or correct their hunches about the best adjustments to make. In those days we used fingernails to pluck and it wasn’t so easy for everyone.
Today, plucking continues in popularity among builders who want to make accurate adjustments and move faster through builds and, guess what, guitar/banjo picks are being used. Here, I show how to compare the tensions of neighboring spokes by plucking them.
After Jude Gerace told me she used banjo picks, I tested every finger pick I could find to determine the best for wheelbuilding. Here’s an assortment:
© Fred Kelly Picks
The winner was no contest: Fred Kelly’s delrin Freedom Pick does it all. They are the white one’s above. This pick can be fitted on your spoke wrench hand’s ring finger. There it is neatly out of the way for truing and handling. When you want to establish tone by plucking, the pick acts like a reinforced fingernail. Pluck as hard and as often as you want without strain. Delrin produces a clearer, more spoke-only sound than a metal pick, which invites harmonics into the tone.
The delrin Freedom pick.
This pick is just one of 58 pick styles Mr. Kelly makes in Grayling, Michigan. He’s been playing for 60yrs and making picks for 40. This one takes the place of your fingernail, has a comfortable yet secure fit to your finger, and is completely adaptable for a personal fit by exposing them to hot and then cold water.
We stock medium and large which fit 90%+ of wheel builders. Try one as soon as you can. Buy two and keep what fits best. You’ll never go back to bare nail plucking.
The eminent Fred Kelly.
Thank you Mr. Kelly!
First time ever, Jude Gerace (Sugarwheelworks, Portland) and I will lead a 2-day intensive wheel class for established builders, Jan 5 and 6 at United Bicycle Institute. Class is limited to 20, a few slots are still available. Enrollment details at PBMA.
Jude says: “If I would have had a class like this when I was first starting out, I would have saved myself years – and many nights of banging my head against the work bench. It is my pleasure to teach this class with Ric… Come join us for a weekend of geekery!”
Ric and Jude at her Portland workshop.
We’ll cover wheel components (tires, rims, nipples, spokes, hubs, complete wheels) in terms of tools, engineering, testing, and especially building. Plus introduce our work with shop systems to streamline otherwise complicated tasks. Most of this information cannot be found anywhere else.
Much tech detail is familiar to experienced industry designers but they cannot share their work for obvious reasons. Rarely, a veteran will open up. Josh Poertner (Silca, ex-Zipp), for example, has recently written very helpfully on testing and design issues from his heyday at Zipp. Otherwise, it takes builders many years to discover so much of what wheel function and construction entails.
It’s Judes and my wish to accelerate the learning track for builders. The world needs more of us at the highest levels to meet the future that’s coming our way.
We plan many hands-on experiences with tools and fixtures rarely seen outside development and manufacturing environments. You’ll gain valuable insight to guide building decisions and better interpret outcomes.
Unlike wheelbuilding 101, we will offer a solid and fairly vast foundation for an enlightened understanding of wheels. Tensioned wheel engineering is an obscure corner of mechanical engineering. Little of it is obvious even to those with ME degrees. As an industry, we develop systems and procedures obscure to the wider world and, needlessly, to many practicing mechanics and builders.
Fundamentally these are answers to questions that plagued us for years and which, once learned, helped advance our building. It will be a privilege to share so much, to have real time questions and discussion, and begin some networking to propel us ahead of the game!
Hope to see you among us, enjoying UBI hospitality and two days of geekery!
