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.
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.
I once called tensioned wire wheels “the most ingenious contrivance in all of human engineering.”
Extraordinary claims must be based on extraordinary evidence (Carl Sagan) and tensioned wheels have it in spades. Think, more than two billion nearly identical wheels see daily use on our planet. There is no widely used structure with such astounding strength to weight, and they conquered gravel on the moon!
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.
One of the most memorable characters in our cycling scene of the early 1970’s was Phil Wood who, with his wife Vada and manager Bern Smith, pioneered the modern use of cartridge bearings in bike components. Here Bern recalls some of the special challenges:
Here’s an introduction to the complexities of specifying, testing, purchasing, re-testing, lubricating and assembling bearings. Some of this will be pretty pedestrian to folks with working knowledge of bearings, but there’s plenty other facets to it.
In the earliest days of Phil Wood & Co. circa 1972, once Spence Wolfe had convinced Phil to manufacture some maintenance-free hubs, and they agreed that 50 pairs would be the most they could ever sell, Phil started testing bearing and lubricant samples. He settled fairly quickly on a single domestic manufacturer of bearings, but the grease samples were…disappointing…
He found ‘waterproof’ grease that dissolved in water, grease that absorbed water, swelled up and forced itself out of the bearings past the seals, and other oddities. Eventually he found a product from a local (Bay Area) supplier that was something of an oddity itself – the manufacturer produced only very small batches of this particular grease, and only occasionally. It was somewhat inconsistent in texture and color. But after Phil consulted with them a little, they changed the mix, and after that it worked really well in full immersion salt bath tests.
And it was green…
So we were off and rolling…
We specified that grease to the bearing manufacturer for lubing at their factory. Then the fun began.
A tangent (and a quiz) are required here.
• What is the highest rpm a bicycle bearing is ever likely to spin?
• How many rpm’s is a regular radial-contact industrial ball bearing typically tested to maintain without burning out?
• How hot do you think bearings get at max rpm?
• What causes that heat?
• What exacerbates it?
…and what is the maximum percentage fill of grease in the bearing assembly cavities (those gaps between the bearings, their retainers, and the seals) that most any manufacturer will agree to?
Back to the early bearings. We found soon enough that our idea of how much grease a bearing should have in it was vastly different from what the bearing suppliers were willing to provide. Typical over-the-counter industrial bearings are filled ~25% full with grease. That’s because those bearings, in a normal installation (an electric motor, say) might run as high as 10,000 rpm – 10 times higher than a bicycle bearing will ever spin. A bearing running at 10,000 rpm gets hot – really hot – from friction, and hotter still if it has too much grease in it (retaining heat in the assembly). Too much grease meaning anything over about 25%.
We specified 95% fill because our tests showed that provided satisfactory water resistance in the extreme tests we put bearings through. But the suppliers refused, citing product liability, and other not-pertinent reasons. So we had to lift seals and add grease to each bearing. That probly doubled our bearing cost.
At least we were getting good bearings…until…batches started arriving from the factory with large grit, wood chips, crystals and other unknown stuff. We rejected lots of bearings. It got so bad that, in the final batch we rejected from the original supplier, most of the bearings would not rotate. Now, there’s a handful of things a bearing needs to do, but above all…
Eventually we found a (foreign) company that produced consistently good bearings for considerably lower cost than the others. Were they eventually prosecuted for dumping bearings in the U.S. to put domestic factories under? Another story for another time…
Then the grease started to get weird…
As you might have guessed, as we grew more comfortable with the grease we chose, we had an idea that maybe we could use that grease for other purposes, and maybe other folks might like it as well. In particular, we felt that the lovely deep green color itself could help sell the stuff, and we settled on a slogan – ‘It’s Green!’. Anyway, we asked the manufacturer about making larger batches, that we could repackage from 55 gallon drums into 3oz tubes. They asked how much we might ever sell…
Each time we got ready to order grease for repackaging, I went to the lab at the lubricant plant and inspected samples. They had a few minor problems and we rejected some batches – turns out that the grease mixing vat was used for several different products and occasionally did not get cleaned out completely between product switchovers. Eventually the plant assigned a mixer for this grease alone, and things smoothed out.
At one point, after about 3 years without a single problem, I asked Phil if maybe we didn’t need to go to the plant to check the samples first. We looked at each other for a moment and said simultaneously “Check the grease”…So I drove to the plant and met the project manager in the lab, where he pulled out the latest sample. It was a beautiful, deep black. Lesson learned the easy way for once.
Years later, after the project manager had retired, I related that story to his successor, who laughed, and said “Oh, yeah – he was colorblind!”
Alex Singer (Paris) bicycles were sold by Spence Wolf at Cupertino Bike Shop. I was nearby and idolized them. There’s plenty written about these gems, no need to add to the legend. Suffice to say, I still have a musette from Spence with the historic and romantic address.
Here is great tribute by Jan Heine about the Singer tradition and Ernest Csuka; proprietor-builder, 1962-2009. Who better to embrace the Csuka vision than his son, Olivier? Photographer-wheel builder Corey Mihailiuk is in Paris and provides us with a thoughtful portrait of Olivier in the old workshop. Corey lives close by and drops in to chat with Olivier who runs it today.
According to Corey, “The tools in that place are truly ancient. I took a look at the wheel stand the last time I was in there and I could hardly believe what my eyes were seeing. I think they made it themselves during the second WW and it was put together from scraps of metal. It is by far the most primitive device I have ever seen. Somehow they have built every wheel that has come out of that shop for the last 75 years. You won’t believe it…” I hope Olivier lets you photograph it for us!
Corey is updating his website (5/15) and less of his oeuvre is displayed but the haunting, provocative portraits he shows are special. People are unique; like bicycles, complex, no two the same.
After 20 years in the Toronto bicycle scene (BicycleSport, Mike Barry/Mike Brown; Mariposa; etc.) Corey followed dreams to Paris where he has previously lived. Now an interest in wheel building is again rising. With 40+ years experience, we expect to hear more from “Cognoscenti Hand Built Wheels” in the near future.
Thanks, Corey; and hello to Olivier!
Jobst Brandt; the legendary rider, mentor, theorist, and engineer; died yesterday May 5, 2015. Many around the world and, particularly, on the San Francisco Mid-Peninsula are now reflecting on the incredible influence he had on us all, while living a cycling-centric life without compromise.
Ray Hosler, journalist formerly with the SF Chronicle, comes closest to anyone for sustaining a personal yet detached and lengthy relationship with Jobst. Here he offers us elegant and accurate retrospection. Thanks, Ray. Read more →
Clinchers are the primary pneumatic wheel system of our time. Cars, planes, high speed trains all use forms of this proven approach to suspension and travel. In cycling as well, clinchers are the bedrock tire system. Today’s topic concerns the high pressure clincher (HPC) for road racing and performance pavement riding. Who would question The System??
When did HPC’s arise?
Before the ’70’s, bicycle clinchers had maximum pressures of 80psi and most depended on 30-65psi. They served the needs of everyday riding from commuting, to commercial delivery, to touring and recreation. Racing to win was another form of cycling. Competitors used narrow (18-25mm) tires at high pressures (7 bar/100psi+) to make wheels light, yet resistant to dents, and hopefully win races. Since the dawn of pneumatic tires, racing needs were not met by clinchers but, instead, by tubular (sew up) tires.
The mass of riders on modest pressure clinchers were well served and racers had little problem gluing sew ups or hiring mechanics to do it. For both systems, rims and tires were simple to design and flats were rare and easily fixed. What ended this happy, stable era?
In the mid-1970’s, America experienced a sudden bicycle boom, fueled by alternative thinking and, especially, a nationwide gas shortage with soaring prices. Suddenly mobs of young Americans wanted to ride bikes. Cycling didn’t have much of a role in the US besides besides grade school commuting and news boys. To get out on the roads with cars was intimidating, but less so if you rode fast. Going fast was fun and the boom focused on speed. European racing was inspiring.
Unexpected Boom Crisis
Importers found supplies of racing bikes and soon everyone was hunched over skinny tire racing bikes, riding as fast as they could. Despite some problems (neck pain, sore butts, safety, etc), one threat loomed largest: better racing bikes from Europe came with tubular tires. Few in the US knew what to do with them, no old timers in the neighborhood to mentor beginners. Tubulars were misunderstood, miss used, and became the bane of lightweight riding. They weren’t, after all, intended for general use.
An alternative to the tubular was needed quickly or the biggest American bike boom of the century faced an untimely end. Mountain bikes were still 10 years away so a new machine was not an option.
Enter the HPC. The dawn of tires and rims attempting to hold high pressures, for example IRC High Racer tires on Araya rims, was scary and loud. Tires could be mounted crooked, rims could expand with pressure, standards for fit were inadequate, tire levers bent and broke, pumps were not strong enough. HPC’s, the bastard child of an awkward historic moment?
However, the goal was clear: a system to equal the performance (pressure, weight, speed) of racing tubulars but be easier and cheaper for the masses to maintain.
40 Years Later
Where do we stand with high pressure clinchers?
(1) They are heavier and less strong by weight than tubulars.
(2) They are not cheaper, rather equal or more expensive than tubulars.
(3) They get more flats, especially pinch flats, than tubulars.
(4) Rim-to-tire fit standards are so vague one can buy a top-of-the-line tire and be unable to mount it to a top-of-the-line wheel. I would estimate 70% of riders of HPC’s do not repair their own flats. They call home. Prying off the tire and making the patch or tube insertion is complicated, requires too much hand strength, and often fails. Mechanics, like the readers of this piece, have noticed the difficulty but are not in the 70% helpless category. We are busy helping our less-able customers and riding companions. Fact is, more tubular riders with punctures ride home than their HPC counterparts.
(5) “Tubeless” systems aim to fix this but is it worth the trouble? True, fewer flats, but the rim interior is often invaded with sealant that can NEVER be removed. Bead fit is so tight that only experts can mount them. Tires cannot be inflated without compressed air. And the suggestion you can insert a tube if you flat during a ride is bogus. Putting tubes in a road tubeless system is a task virtually no one can accomplish.
(6) Making light rims in any material for HPC’s is complicated. Outward pressure of tire beads is gigantic. To withstand this force carbon rims add mass to equal the weight of aluminum rims. Huh? The circumferential pressure of HPC’s (tube or tubeless) on rims is 10X that of tubulars due to the different physics. Tons of constricting force shrinks light rims, lowers spoke tension, and deprives wheels of much strength. Is it worth it?
High pressure clinchers have had 40 years to accomplish the goal: equivalent performance, improved convenience, and lower price than tubulars. They have failed. It’s over. Good try but no win. 40 years is long enough. Believe me, I’m not alone among industry veterans puzzling over this situation.
This is not a call to return to tubulars. That’s the system that needs replacing. A new system is needed for the narrow, high pressure, racing pneumatic. Don’t stop using HPC wheels. Until there is a better alternative, it’s the best we can do.
Nor does this apply to moderate pressure clinchers as in BMX, MTB, utility, and randonneur riding. Larger casings, lower pressures, and a wide variety of rims are delivering great function and value. It’s also important to note that efficiencies of narrow, high pressure tires have been exaggerated. Fast, competitive riding is often better with lower pressure and larger cross sections. Jan Heine’s Bicycle Quarterly (among others) has really driven this point.
Here is also not a criticism of the modern HPC tire. Taken alone, todays’s HPC’s are remarkable technology and quality. Complex and refined, tough and impressive. Same with rims. It is the system that is at a dead end for high pressure.
What to do?
(1) Separate yourself from deniers who claim HPC systems (especially tubeless) are perfect. They’re not.
(2) Think hard about alternatives. Study tubulars. Study HPC’s, both tube and tubeless. Cycling innovation begins with you.
(3) Don’t hold your breath. Innovation requires motivation (we have plenty), technology (it’s out there), and courage (well…). Structural obstacles also seem insurmountable. Tire companies are some of the largest corporate entities in cycling. Michelin, Hutchinson, Continental, Innova, Cheng Shin, Kenda, these are global chemical giants. Cycling products are trivial for them.
Why does this spill from the mouth of a wheel person? We are über proud of wheels. Anything seriously limiting their beauty and usefulness gets our attention.
Rest assured, a fearless young bicycle thinker is reading this and in due time will engineer the needed solution. I’ll bet it’s a wheel builder.
If my tongue-in-cheek leaves you confused or annoyed, make a comment. Then hug your bike and take a ride!
Mobility is Work
The more efficient the mobility, the more successful is the organism. Salmon and gulls rate highly but humans aren’t far behind. Our ability to move with relatively low energy expense is key to human history. Bipedal motion, sweating, a springy foot, and other physiology made it possible for indigenous hunters to simply walk their prey down over a period of days.
We demand similar efficiency from bicycles and they deliver. After all, look who made them. Bearings, of course,are key. Keeping their friction low is one of our highest priorities.
Rarely seen anymore, some early bikes used bearings with spherical races that would continue to spin even if the axle was bent. Today we try and keep axles from bending but there’s no denying this is a clever idea.
Before cartridge bearings, adjustable loose ball bearings ruled bikedom. Shimano and Campagnolo still use them in many of their high-end hubs.
A cup and cone system features angular rather than annular contact.
Most think it is because of regular side loads that a hub must see. True on a 3 or 4 wheel vehicle but single track side loads are relatively tiny and statistically rare. The best reason is how much easier it is to get the bearing to a sweet spot of adjustment where friction and side play are low.
Side play is important not only because of noise and squirrelly handling but the potential for harmonics. Vehicles that are light (like bikes and planes) are vulnerable to harmonic vibration. That’s why test flights, before the era of computer modeling, were so suspenseful. Many planes (and helicopters) failed because harmonic vibration that could not be dampened shook the structure to pieces. Cars and locomotives are less risk because it takes so much energy to vibrate larger masses.
We’re all familiar with bicycle speed wobbles. They rarely cause a nasty crash, but take worrying concentration to control. Bearing play will aggravate, if not promote, speed wobbles. So we want it minimized. The angular contact bearing can be adjusted whereas the annular is manufactured to a given fit and cannot. Today’s annular bearings are made so well that when located at either end of a hub, there is often no play to be detected. Small play can be made invisible by slightly side-loading a pair of annular bearings with only a small friction consequence.
None of this compares with the friction from grease and seals. Chester Kyle conducted tests that should have woken the world to this factor. In one case, he swung a 1o-pound weight on a pendulum from a hub with sealed-cartridge bearings. He then removed the seals and grease, and performed the test again. The pendulum swung 20 times longer. He estimated seals and grease were responsible for a 3 to 5-percent increase in total bike rolling resistance. Clearly our choices affect performance; bearing friction is not negligible. Since we all use similar bearings, the subject is overlooked; like complaining about air density which is pretty much a given. But bearing friction is no longer taken for granted.
Look Out Ceramics
The latest chapter in bicycle ball bearings has begun. And it is being ushered in by the widespread adoption of ceramic bearings by professional racers. These spheres of silicon nitride, not a true ceramic, are lighter, harder, smoother and rounder than the best steel bearings. Combined with high-grade chromium-steel races, they’re known as hybrid bearings and are huge news throughout cycling and in other sports. Invented nearly 25 years ago by Swedish bearing giant, SKF, these units are now ﬁnding their way into bikes.
Whether the expense is warranted for your own riding is not the issue. They simply illuminate how important bearings are. A perfect object lesson.
The ceramic bearings hiding in this bottom bracket offer huge performance gains – reducing rolling resistance by up to 4 percent. That’s like doping without the crime.
lnline skaters, whose wheels revolve thousands of times per minute, were some of the earliest adopters of ceramic bearings. Next came F1 (up to $250K per car), and now cycling. Ceramic bearings are everywhere in top UCI road and off-road competitions. Retrofitted to hubs, bottom brackets and pulley wheels, the bearings represent the latest performance enhancement, and unlike many injected “enhancements,” they are completely legal.
The benefits are twofold: first, the actual ceramic ball is three times harder than steel. While this leads to greatly extended life spans, it also reduces friction. Believe it or not, all balls deform slightly under load. This is the major, microscopic source of friction in a bearing. Less deformation equals lower friction.
Like the proverbial truffle in cooking, however, it’s a waste to use ceramic balls if the other ingredients are inferior. So the second benefit stems from the better seals, grease and retainers that harder, smoother ceramic bearings allow. For a higher price, you can use extra—low—friction seals that aren’t available on industrial bearings. At the same time, weatherproof grease can be replaced with extra—low-viscosity lube. Most bearings use a retainer to separate the balls from each other. If balls bump, there’s extra friction because they’re rotating in opposite directions at the moment of contact. Compared to metal retainers in traditional bearings, some ceramics have low-friction retainers made from special polyamides.
Many of these non-ceramic improvements (better/fewer seals, lighter grease/oil, etc.) are available to anyone and as Chester Kyle pointed out 25 years ago, they greatly reduce friction. But when they are combined with ceramic balls, the bearing is taken to a whole new level.
The next and final chapter of this bearing excursion details how they affect wheel building. Understand what the hub is doing and don’t let bearings interfere with your building.
There was a time when bicycle racing was transformed. In the early 1980’s a sudden, dramatic turn towards technology brought us a largely re-invented sport. New equipment, new players, new media, a new experience.
In three subsequent decades, despite new materials and rules, the Euro road scene is much as it left the ’80’s. Faster and more expensive but fundamentally the same. That seminal period also saw the rise of electronic music driven by pioneers like Kraftwerk, fueled by futuristic themes and accelerating change around the world.
Kraftwerk released an LP in 1983 called “Tour de France.” A copy in my archives surprised me the other day but our recent move from Seattle to the Olympic Peninsula has opened many boxes and memories.
The ’84 US Olympic Team, Greg LeMond, and Francesco Moser started using tri-bars, funny bikes, disk wheels, clipless pedals, carbon fiber frames, Oakley glasses, bladed wheels, aero helmets, cycle computers, and more.
The ’80’s saw a new generation of US riders, many on the 7-Eleven Team, who busted into the European peloton. No rider so arrested the scene as Greg LeMond and his first Tour win (1986). Australian Phil Anderson was the first non-European to lead the Tour (1981). Andy Hampsten won the Giro (1988). Canadians Alex Stieda and Steve Bauer wore the Tour’s jerseys many times.
Breaking Away (1979) and American Flyers (1985) brought the sport to a wider audience. Before US television networks covered the Tour, we waited outside Mac’s Smoke Shop (downtown Palo Alto newsstand) to grab the early edition of the London Times and clip out the latest Tour results to post at the shop. All day long we’d receive visits and calls. No more!
A new style
Graham Watson has explained how visually painful it was for photography when riders all began using Oakley-type glasses and aero helmets. No longer could exertion, anger, desperation, and exhaustion be readily caught by camera. It was as if the peloton’s members morphed from unique personalities to droids.
Eventually, of course, technology brought us aerial, helmet, wattage, and 3D map images, all universally accessible. The sport evolves and thrives.
In time, today’s events and changes will be fond memories, just have to wait. Still, for many of us, the 1980’s were an incomparable period for cycling and Kraftwerk captured it well.
[Note: this is #2 in a series of 4 about bearings]
Ball bearings are everywhere in your bike (you’d be surprised) but their greatest impact comes from four positions: hubs, headsets, bottom brackets, and pedals. Each is a different situation but low friction trumps other considerations.
IN HEADSET WE TRUST
Headset loads are huge and sideways to the bearing. But at the same time, a single-track vehicle requires low steering friction. Why? One of the most intriguing aspects of bike function is steering stability. To remain upright, it’s necessary to steer gently in the direction of a lean, creating a gradual turn. The centrifugal force that appears with the turn is enough to support and even undo the lean. Ka-ching, stability.
To make staying upright nearly automatic, we have an autopilot system to initiate that turn that relies on:
(1) Gyroscopic force of the front wheel
When the bike leans, the wheel’s wants to turn in that direction. Instead of falling, we turn. But this urge would be useless if the headset interfered.
The relationship between the steering axis of rotation and ground contact of the wheel is called trail. In a bicycle, as with casters on a shopping cart, ground contact is behind the rotational axis of steering. With forward motion, the wheel automatically prefers to stay straight.
(3) Moment of mass
It has recently been proved that the mass of the bike that is forward of the steering axis, induces a turn in the direction of lean. I touched on this topic here. We owe Jim Papadopolous and Andy Ruina of Cornell for the insight. More recently researchers at Holland’s University of Delft have provided physical testing.
These three effects are small compared to weight, energy, and outside influences when riding, so the headset must have very low friction to respond instantly. A free-running headset plus an ingenious system of stability makes riding upright easy. In fact, safer than walking for stablity. Falls while walking or running occur more often than when riding. An improvement to our evolved bipedal mobility?
A nasty test of the point is to over-tighten a headset. A wonderfully balanced and easy-to-ride bike becomes a jerky, uncooperative donkey. No, thank you. So, ball bearings are a good solution to the headset’s low-friction demands. But how do they deal with all that side force? The contact points for the balls are angled, rather than radial, as in hubs. This angle allows bearings to brace against side loads.
OPEN OR CLOSED
Bike mechanics all know the distinction between traditional “open” cup-and- cone bearings, and modern “closed” cartridge bearings. Today, the trend leans heavily toward the latter. But it wasn’t always so.
A cup-and-cone system has two big advantages, One is retaining the balls: they’re neatly captured as the cone moves toward the cup. The assembler can easily install them and then pick the amount of bearing play (looseness) by adjusting the inward movement of the cone. A modern cartridge bearing offers no such adjustability. To run with minimal looseness, the cartridge bearing must be made to very high precision, which is not an option for most bicycles.
The second big advantage of the cup-and-cone system is its high tolerance for misalignment. In the case of poorly made, bent, or worn elements, a cup-and-cone assembly can run smoothly where a cartridge system would seize. For 150 years, cup-and-cone bearings have proven their ruggedness and, for much of the world, they remain the best choice. In the hands of Shimano and Campagnolo, who continue to offer cup-and-cone hubs, this practical system approaches high art.
Why, then, are Cartridge bearings taking over? They have the advantage of mass production. By setting international standards, not only are ball sizes predictable, the entire mechanism is standardized. Mass production delivers huge economy as machine designers around the world share cartridge dimensions. For mid to high-level quality, cartridge bearings offer the most value and variety.
Maxicar (FR) and Phil Wood (US) were pioneers to install industrial cartridge bearings into hubs and bottom brackets. Chris King (US) was among the first with a sealed-bearing headset. Widespread use of cartridge bearings in the bike industry waited until the early 1980s with Specialized’s sealed hubs that came on many of the earliest mountain bikes.
SEAL OF APPROVAL
However, these early cartridge-bearing components weren’t exploiting their economy. Heck, these were products at the highest end. Ease of maintenance, “sealed for life,” weatherproof performance – this was the early dream of cartridge bearings. After all, they were known as “sealed” not “cartridge” bearings. Of course, such performance wasn’t always possible, but the dream lived on. WTB developed Grease Guard to enable weather-challenged users to replenish the lubrication in “sealed” components.
To retain lubricant, which tends to leak, and to repel contamination, which brings rust and abrasive wear, bearings need protection. Shields, labyrinths and seals are all employed to extend bearing life. Shields fit so that only a very narrow gap remains through which contamination can enter. That works for large particles, but not for fine grit or moisture. Labyrinths interlock without contact and effectively provide a tortuous path to keep grease in and contaminants out. But they can be heavy and still not totally effective. Shields and labyrinths work best when used in addition to seals.
The most popular bearing seals are contact type. A very thin lip of urethane material makes light contact with the bearing’s inner raceway. If the raceway finish is fine and the contact lightly lubricated, such a seal does a great job of repelling dirt and retaining lubrication. However, some friction is produced by the contact. But until recently, little attention has been paid to that.
For nearly a century, most engineers assumed that rolling resistance with ball bearings was negligible, about 1 percent. But bearings ran on oil when those early measurements were made. Modern bearings rely on thick grease, which adds rotational resistance. The efficiency estimate also fails to include bearing seals, since early bicycles used non-contact seals with the oil. In fact, this was a very effective system. Oil is a great, low-friction lubricant, but without contact seals, it leaks. That flow of oil did a fine job keeping contamination out, but it also made a mess of the bike’s exterior.
Modern riders are only too glad to break the cycle of oily bikes (and stained trousers). Grease was a first step, followed by sealed cartridge bearings. Unfortunately, no one did the rolling-resistance calculation. A huge change was on the way.
Next Dirty Secrets will delve into a long period of stiff, low maintenance bearing options. Stay tuned for Dirty Secrets #3.