Gear

Technical Q&A with Lennard Zinn – Shifters and more ceramic balls

Dear Lennard;I wrote you this question right after I saw the downtube shifter onLance's bike last July, but I'm guessing it got lost in the flood of TDFe-mails, so here it is again:During one of the mountain stages, I saw an old-school front derailleurdowntube shifter on Lance's bike, and then in a later stage, I saw oneon Ullrich's bike. What is up with that? Were they really front shifters,or for something different?TedDear Ted;Yes, they are front shifters to save the weight of the STI or Ergopowerlever and extra cable and housing.LennardDear Lennard;I was intrigued by your statement that

By Lennard Zinn

Dear Lennard;
I wrote you this question right after I saw the downtube shifter onLance’s bike last July, but I’m guessing it got lost in the flood of TDFe-mails, so here it is again:During one of the mountain stages, I saw an old-school front derailleurdowntube shifter on Lance’s bike, and then in a later stage, I saw oneon Ullrich’s bike. What is up with that? Were they really front shifters,or for something different?
TedDear Ted;
Yes, they are front shifters to save the weight of the STI or Ergopowerlever and extra cable and housing.
LennardDear Lennard;
I was intrigued by your statement that “Shimano has not changed thecable pull per shift for the rear derailleur” (Tech Q&A Dec, 2nd).I had measured the cable pull of 8 and 9 speed systems and concluded thatthey weren’t compatible.Inspired, if only by the prospect of proving Zinn wrong, I put a Shimano105 STI lever on my winter hack, hooked it up to it’s old RSX 7-speed rearderailleur with an 8-speed cassette and lo and behold, it works just fine.Only get 8 speeds of course but the limit stop handles that. The shiftfrom 6th to 7th is a bit ‘lazy’ but, given that 7th to 8th is fine, I’llput this down to the derailleur’s age and condition. Bye bye down-tubeshifter.So, top tip and full marks to Shimano for backwards compatibility.
StanDear Lennard;
I was reading about the new Campy carbon cranks (both Record and Chorus):
“These new products have been developed using Unidirectional CarbonFibre, a new composite material technology that originated in the aerospaceindustry.” For 2004, this replaces Campagnolo’s previous 90-degree carbonfiber lay-up for cranksets. This new technology distributes carbon fiberin all directions to produce mechanical resistance in any direction.Furthermore, Campagnolo’s Unidirectional Carbon Fiber has been placedto further enhance the already outstanding performance of the Record andChorus cranksets.”Is this carbon fiber that much different than the “traditional” carbonused on Giant bikes or even my Easton monkey light carbon riser bars? I also thought about another friend who just bought a new 2004 Trek carbonbike with a “nude” finish…in other words, you see the carbon insteadof paint.The carbon on the Trek looks unidirectional like the carbon on the newCampy cranks. So….finally…the question……Is this “new” unidirectionalcarbon the wave of the future or just an alternative? I am thinking ofbuying a carbon frame this year, either Giant or Trek and I am wonderingif there are advantages or tradeoffs that I am not really considering.
MikeAnswer from Trek:

We believe that Mike may have accidentally mis-worded his question.The consumer stated that the new carbon fiber (that Campagnolo is using)is a “unidirectional” carbon fiber, when in reality it is a “multidirectional”carbon fiber material (www.Campagnolo.com).In 2000, Trek was the first company in the bike industry to introduce a frame component using multi-directional carbon fiber. This new material, called OCLV MC (Optimum Compaction Low Void Molding Compound), was used for the rocker links on the Fuel 98 and 100 suspension frames. OCLV MC is a proprietary material that uses the same carbon fiber as traditional unidirectional carbon fiber, but rather than having the fibers all oriented in one direction, it has shorter (50 mm long) randomly oriented bundles of carbon fiber. The randomly oriented fiber bundles cause this material to have nearly identical mechanical properties in all directions.While traditional carbon fiber works well in many tubing applications (where a high strength to weight ratio) is desirable, due to molding difficulties, it doesn’t always work well for molding parts with ribs, tight radii, counter bore holes, and other complex 3D features. OCLV MC however, while still having a high strength to weight ratio, works very well for molding parts that are not hollow (like tubes) and that have complex 3D features.At Trek, we look at OCLV MC as a material that compliments our traditionalOCLV unidirectional material. It will not replace it. Both materials willalways have their place in our product line-up. Regarding the questionof “Trek vs. Giant”, both companies have similar materials available tothem so the main difference is the process used to create the bike frame.Trek uses a patented process called OCLV (Optimum Compaction Low Void)to produce our carbon frames. The OCLV process allows us to produce compositeframes that are virtually free of voids (which weaken the bond) in thecomposite laminate and that exceed aerospace standards. We believe thisprocess sets us apart from our competition through the high quality partsthat it produces.
Brian Schumann
Trek carbon engineer

I received a lot of mail about the reply on ceramic bearingslast week from Zipp’s Bill Vance. Here is a sampling:Dear Lennard,
The quote, “Any technology sufficiently advanced is indistinguishablefrom magic,” by Zipp’s Bill Vance on his thorough reply about ceramic bearingsis actually by science fiction author Arthur C. Clarke, who is best knownas the author of “2001: A Space Odyssey” and “Childhood’s End.” Clarkeis also responsible for founding the concept of the geosynchronous communicationssatellite in the late 1940s.However, Robert Heinlein is not without his own notable quotes, themost famous being, “Ninety-nine percent of anything is s**t.”
(Please accept this as a paraphrase.)
RexDear Lennard,
I wanted to write to add a minor correction to Bill Vance’s excellentdiscussion on ceramic bearings. He states cryogenic heat-treatingis performed to “…harden and align the crystalline structure…”; thisis not rigorously true. Cryogenic treatments are typically performedon highly alloyed steel (such as the 52100 and 440C alloy commonly usedfor bearings) after the first tempering operation to complete the transformationof any retained austenite to martensite. A subsequent second temperingoperation is typically performed.The main benefits of cryogenic treatment are more controlled materialproperties and dimensional stability. Any retained austenite in thesteel microstructure can transform under mechanical loading to martensitewith a resulting increase in volume. The effects of this volumetricchange can be dimensional changes (this would be critical in ZIPP’s applicationof high tolerance ceramic rolling elements), internal microcrack formationand an increase in residual stress; all of these could lead to reducedservice life.
Keith
MetallurgistDear Lennard,
On the recent subject of bearing friction, I think it’s worth takingclaims of increased performance with a grain of salt. The amountof power dissipated in even a standard steel ball bearing hub is quitesmall. I’ve always believed this but decided to calculate it for kicks.In case you’re interested, the calculation is below.Typical coefficient of friction for a ball bearing is about mu=1.5e-3 (for example, http://www.ntnamerica.com/Engineering/PDFs/2200/frictemp.pdf)
Power dissipated in one bearing is

P1 = mu * (m/2) * g * V_bearing where mis mass of rider+bike V_bearing is linear speed the bearing rotatesat.
P_bearingloss = 2*P1 total power lost in two wheels
V_bearing = V_bike * d/D d = bearing race diameter= wheel diameter
P_bearingloss = mu * mg * d/D * V_bike
P_bearingloss = C_bearingloss * mg * V_bike where C_bearingloss= mu * d/D, can be compared to C_rolling resistance of tires
For a bearing race diameter of 20 mm and wheel diameter of 668mm (700×23) C_bearingloss = 4.5e-5
for comparison, C_rolling resistance is supposed to be 4e-3for smooth pavement (e.g. from www.analyticcycling.com),or 100x higher.

For a rider+bike of 75 kg traveling at 10 m/s, I get that the powerdissipated in wheel bearings is 0.33 watts. I suspect this vergeson negligible. A major technological breakthrough that cut bearingfriction in half would only gain 0.16 watts. It might be significantin hourrecords or even the pursuit world record. At my low levelof competition, I think the sleep gained in not worrying about it has agreater performance benefit.
BenDear Lennard,
I think Mr. Vance of Zipp has vastly over-hyped ceramic bearing frictionreduction.
Given a typical 250 watt output, the rough breakdown would be:

80 percent, 200 watts is aerodynamic friction15 percent, 37 watts is tire rolling resistance 5 percent, 12 watts is mechanical losses of which75 percent, 9 watts is drivetrain(bottom bracket, chain, derailleur)25 percent, 3 watts is wheel hubs/bearings.

You can adjust the percentages somewhat to your personal preferences butthe end result will always be a wheel bearing total loss much less thanMr. Vance’s vastly overstated claims of 10 watts reduction. Evenan estimate of a 1 watt reduction, from 3 to 2 watts, is possibly too large,since most hub losses are due to the seals.Put a tiny drop of Teflon based lube on the inside surfaces of yourhub seals, save more watts, and hundreds of dollars.
SteveDear Lennard,
I concede that ceramic balls may save 3-4 percent over regular bearingsas stated by Zipp.However, that most definitely does not translate to 30 watts of savings,as the regular wheel bearings may at most scrub 1-2 watts of energy. Ceramic bearings cannot save energy that is lost to wind resistance andgravity. At most they will save 3-4 percent of the 1-2 watts usedby the wheel bearings, which would amount to about 30 MilliWatts–roughlywhat you would get drafting behind a flying wasp. The anecdotal evidenceof better performance may easily be explained by the lighter-wallet syndrome.If that is what your readers need, yours truly will be happy to supplythem with boron-impregnated scandium wasps.I am all for tighter tolerances and better bearings. But unliketurbines, bicycle wheels do not need to spin at 300,000 rpm and high thermalloads. I suspect the plastic bearing carriers all but negate theadvantage of ceramic balls because of their higher friction. So inthe absence of scientific measurements, I consider the statements fromZipp regarding ceramic bearings, just so much marketing hype.
Shawn


VeloNews technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of several books on bikes and bike maintenance including the pair of successful maintenance guides “ Zinn & the Art of Mountain Bike Maintenance” and “Zinn & the Art of Road Bike Maintenance.”Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.