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!

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!

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!

As gravel beckons, where are we with disk road wheels?

Disk brakes have come late to road bikes and, until recently, have met a cool reception. Two questions arise:
1/ Will the feel and response match the best rim brakes?

2/ How well will road wheels support disk brake loads so fundamentally different than rim braking?

Read more →

As we northern climes head into damp weather and cyclocross, issues of corrosion deserve attention. Corrosion cannot be ignored but, for cycling, most of its challenges can be addressed.

Yum, yum!

Beware viewing extreme cases of corrosion on the Web. An incident only matters in terms of frequency. Being one of 1,000 witnesses to a wild case may not have statistical validity. Shape your practice around incidents that are representative.

Corrosion ~ oxidation ~ redox ~ rust
Beware, I’ll be interchanging these terms, most unscientific! To begin, corrosion is universal. Everything oxidizes under some conditions, life depends on this chemistry. It simply must be controlled and limited to an acceptable rate so we get good use from our wheels.

In general, corrosion is not a main driver of component failure, but is always present at the scene and often a player. Where a failure has occurred, note all the detail you can but be cautious assigning relative importance to each factor. A badly rusted hub bearing may show extreme wear but as it takes time and/or negligence to blow bearings, the coincidence does not define causality.

Corrosion is related to both material and environment. Warm, humid, coastal areas with onshore breeze and mist are hugely more corrosive than elsewhere. Components designed for average conditions need more care (rinsing) in FL or HI. In those areas, brass nipples can turn black with corrosion and crumble to dust. If you respond by cleaning and lubricating you might not feel aluminum is such a bad nipple material. Its corrosion is similar to brass and, maintained, can be reliable.

© bostonbiker.org

Hubs
Corroded hub shells are ugly. Chalky stains and pits can be impossible to remove. Anodizing provides a first line of defense. For hubs that are uncoated, a high polish is more corrosion resistant. Campagnolo’s early hubs were polished and builders cleaned and shined them before a build so subsequent maintenance was easier. Surface treatments like original WD40 go beneath water, clinging to metal surfaces. A light spray or wipe can minimize corrosion.

Spokes
Today’s better spokes are made of stainless steels, corrosion resistant enough to not require protective coatings. These steels can corrode so don’t be surprised to see a light haze of rust. Wipe it off with an oiled rag. The black color applied to many stainless spokes is decorative only and not as corrosion resistant as the underlying metal. A light haze of rust on a black oxide coating is easily wiped off with an oiled rag and will not rust again until the oil is removed.

Remember that multiple stainless alloys are used for spokes, each with different metallurgy and corrosion resistance. Likewise, there is no single black or color coating. Integrity of a coated spoke is difficult to predict without access to manufacturing details.

For non-stainless spokes, galvanizing is a common corrosion prevention. It begins as a shiny, attractive layer, quickly becoming dull, industrial gray. This is normal. On show motorcycles and antique bicycles we see chrome or nickel plating. Neither has much corrosion resistance without regular wiping and application of a protective polish. I’ve seen bad rust on non stainless spokes but rarely breakage for which the rust could be blamed. Of course, it happens but is rare on in-use wheels.

Rusty spokes…

Wiping spokes with a rag lightly soaked in an oil of your choice is good practice. Pressure washing removes dirt but dirt doesn’t cause corrosion. Washing removes the protective coatings all components need. We’re in a modern world of materials and coatings but superficial oils and waxes still play a key role for weather resistance.

Nipples
The debate over brass vs aluminum nipples is eternal. The issue should be decided on mechanical attributes, not corrosion resistance (IMO). Both are quite similar and a well anodized aluminum nipple can equal brass with a nickel plated finish. Brass is more ductile and self lubricating. High grade (2024 and 7075) aluminum is stronger, can be brightly colored, and a bit lighter.

Check this chart for comparable corrosion. The first two columns are aluminum and brass. For exposure to sea water, the two metals are similar. For distilled water, aluminum is excellent and brass is bad. For vinegar, aluminum is better. For boiling whiskey, brass is better. Two metals with different outcomes depending on environment. I’m for the whiskey.

In navigating the “controversy” remember that much unwelcome behavior by any single batch of nipples may depend on specific conditions. What, if any, lubricant is used? What process shaped the nipple (forged, cast, machined)? What plating and specification (depth, penetration) was used? Silver nipples are not necessarily anodized. Are yours? Notice also that many millions of aluminum nipples have been used on production wheels over the past 20 years; most outlasting their spokes, hubs, and rims.

Brass contains lead for formability. Recent law restricts the amount but the historic presence of lead in brass taints its otherwise classical charm. Regardless of nipple material, regular lubrication is key. If you soak nipples in heavyweight oil prior to building, the coating can last years. If your wheels see pressure washing, relubrication is required.

To lube a built wheel, touch a drop of light oil to the spoke as it enters the nipple. Watch it wick down the bore. A second drop belongs at the nipple-rim contact, applied from the same side. Spinning the wheel creates centrifugal force to drive lube into the assembly. Many of today’s chain lubes are ideal for this as they are thin for application and penetration but as their carriers evaporate the remaining formula becomes dense and long lasting.

Rims
Cracking of aluminum rims under tension at nipple holes can be accelerated by corrosion. After anodizing, rims are purged of liquids used in the electrochemical process. Inadequate flushing can leave seeds of corrosion deposited inside the rim. Anodizing can be too deep and hard, leading to surface cracking where the rim may be deforming from spoke tension.

Corrosion and cracking at once.

Tire sealants can also be corrosive agents and leak into rim interiors, especially those with ammonia.

Carbon rims are neutral for corrosion but can act as anodes when in contact with metals, stimulating corrosion. It is relatively easy to isolate and protect such galvanic combinations with anodizing, washers, and lubricants. For better or worse, the vast majority of carbon wheels are built with aluminum nipples, showing the combination is not automatically bad news. Enve’s recent switch from aluminum to brass for internal nipples does not indict all use of aluminum. Many of the problems they observed are owed to ammonia from tire sealants and poor anodizing on nipples. Substantial numbers of carbon wheels show no aluminum nipple corrosion. There is often more to the story than simply nipple material.

Storage batteries in use or awaiting disposal can create electrical fields that produce very corrosive conditions. When you see an “impossible” corrosion example, wonder about the context. With growth in e-bikes, e-cars, and home energy storage, we can expect more such cases.Electrical fields…?

In following corrosion, make careful observations and notes, utilize magnification and photo images, and use components with highest material and coating properties.

This upcoming La Niña winter should be fun, not corrosive!

Nipples aim from their rim holes in order to align with spoke angle. The goal is to have no bend in the spoke as it enters the nipple because threading there is a weak spot. Spokes can fracture in thread roots after many loading cycles. Nipple and rim shape determine the amount of spoke angle that can be accommodated. The angle is a product of hub and rim size, spoke number, and crossing pattern.

Today, rims are frequently smaller (650 instead of 700, 20” for folding, cargo, and e-bikes, etc.). Hubs can be larger (generator, internal gear, e-motors, etc.). These combinations produce spoke angles that are more concerning.

e-motor wheels are here

A perfect spoke angle is 90deg with no bend in the spoke. Side angles generated by hub width and dishing are rarely below 80 and most nipple-rim combo’s handle them. The angles we need to address are in the rim plane and a function of rim and hub size.

Different wheels, different spoke angles. Adapted from Grin spoke calculator.

Grin offers a great spoke calculator, among many valuable resources. It will determine the spoke-rim angle and, incidentally, works with paired spoking (another topic). Nipples can easily aim for entries of 80-90 degrees. Less than 75 may be accommodated. Below 70 is beyond most components and requires special attention. Solutions:

1/  Kink the spoke with a plier or wrench so it enters the rim at the nipple’s angle, a slow but effective process.

2/  Drill holes larger so nipples are freer to pivot, not an option or advisable on many rims.

3/  Reduce the lacing cross number to make an angle closer to 90. Despite sub-optimal torque geometry, many builders are doing it. As Grin says, “In spite of the popular wisdom not to use radial lacing on drive wheels, empirical experience has been that this isn’t really an issue with the large hubs in small rims.” The burgeoning e-bike scene cannot be slowed down even though appropriate rims are not available.

Radial motor wheel, they are in use!

4/  Rims could address this issue, for example, with a bulge at each nipple. Motorcycles figured this out 100 years ago. Drill the rim to accommodate the required angle. Here is a solution with optimal spoke angle and torque transmission. Cycling will certainly figure this out soon.

Rim drilled to match spoke angle.

Anticipate spoke angles and plan accordingly. An engineered solution to the situation requires initiative from rim makers. Let’s hope it is sooner than later so I can stop envying motorcycle wheels!

Start a blog! The number out there is well past the point of discouragement. Like a micro-organism in the ocean, just do your thing!

Justin VanAlstyne is adding to his wheel building skills, acquired a P&K truing stand, and shares it with us in one of his first posts. You don’t need to be a 30yr veteran to be a keen observer, capture amazing images, and produce a good read.

Please check it out. Like Spring flowers that now grace so many hills (north hemisphere 2017!) the blue P&K is a masterpiece of high craft, blossoming with care to detail and passion for wheel building.

Thanks, Justin!

Triumph of Collaboration
PBMA continues to gain members, supporters and influence. So great to see mechanics network like never before, debate important issues, and clearly begin to gain in stature and resources. Both the FB page and the organization are open for applications and eager to share the growing list of benefits.

Another great mechanic story hails from Rwanda where the National Cycling Center is taking shape.

From ashes to elite cycling in a decade.

Read more →

A good primer on basic wheel building is hard to find. I’m regularly asked to create one since the articles in our library address wheel building subtleties, concerns past the initial challenge to assemble a rideable one.

Here is part of the solution, four articles (10k words!) written in 1986 for BICYCLING magazine. Many of our present day concerns (extreme dishing, carbon fiber rims, tubeless systems, disk brakes, etc.) are missing. The fundamentals have not changed so this series is still useful.

Dour but persistent!

It is a good, basic primer on wheel building that is still relevant 30 years later. After all, the tensioned wheel remains at the heart of cycling and the laws of physics are unchanged.

The link is here. Hope you find it useful. I am working on an updated version of this instruction but it keeps getting delayed. Go figure.

In Part 1 we saw rims deform from tire pressure causing spoke tension drop and discussed the role of tire dimensions, noticing road tubeless clinchers have the most potential to amplify tension drop.

In Part 2 we established that design, not manufacturing inconsistency, makes for odd matches and extreme tension drop situations.

Here in Part 3, let’s ask what builders can do to minimize negative influences of tension drop. After all, builders invest spoked structures with tension and answer for wheel performance. Read more →