Dear Lennard,
Was there any official report as to why David Millar's rear wheel fellapart during the stage 19 time trial at the Tour de France. I have neverseen anything like that. He seemed to have multiple wheels with the sameproblem right up to his mechanic riding a new bike out to him. How weirdwas that?
Christopher

Dear Christopher,
Yes, I saw that, too. We tried to find out that day what happened,but didn't get any official word as the team handed off the wheel to themanufacturer for analysis. Fortunately, we contacted Mavic to see whatthey had learned.
LennardAnswer from Mavic:

As you are aware, we use the World's best athletes in worldclass competition to validate and test new technologies in our products.David was using a prototype Carbon Comete. Much different and lighterthan a regular stock version. I'm told the extrusion totally separatedfrom the carbon flanges of the disc wall. At this time it hasn'tbeen determined exactly why it happened, but it was some sort of failureof the bond between the surface of the aluminum extrusion and the insideof the carbon flange. Not something we see with that product.While a lightweight prototype, I don't think the occurrence was necessarilyfrom any new technologies that were used. It just appears to be moreof a freak isolated incident with the preparation of the surfaces or thebonding process on his particular wheel and not a common failure with ourcompetition prototypes or our production Cometes. Mavic prides itselfon the quality and durability of our products and while we like to pushthe limits of technology for our racers benefit, we would never put anyracer on a wheel that we thought might have a catastrophic failure of thisnature and it's horrible that it happened.This incident happened right out of the start gate after the slightimpact from hitting the pavement off the start ramp, which then uncoveredthe flaw in the bond in this particular wheel. David rode the samewheel with no problems in the Prologue.It's terribly unfortunate for David to have this happen during sucha critical stage of the Tour on a day where he was sure to do very well.
Yours in Sport,
Sean Sullivan
Marketing Director
Mavic Inc.

More rolling resistance
Dear Lennard,
You may not be aware that Bicycle Quarterly tested the real-road rolling resistance of a number of tires. We compared the results with those from tests conducted by Germany's TOUR and reported on this in the Fall 2006 and Spring 2007 issues (Vol. 5, Nos. 1 and 3). We also tested the influence of tire pressure on resistance. We found that on real roads, higher pressures beyond a point do not provide great performance gains. The reason is simple: harder tires bounce or vibrate more on surface irregularities, and that energy is absorbed by the rider. On steel drums, these "suspension losses" are negated. A steel wheel (such as a railroad wheel) would have the lowest resistance on a steel drum tester, but we all know that on real roads, it is far from efficient.The "suspension losses" also are the reason why tires with hard rubber compounds, like the Michelin Pro2 Race, perform well on steel drums, but less well on real roads.
Coincidentally, we used your testing of ceramic bearings in VeloNews together with analyticcycling.com's models to evaluate the true on-road performance improvements available with ceramic bearings, and reported on that in the Spring ‘07 issue. Thanks for doing those tests. We compared them to Bicycling's claims of "one gear higher on certain climbs" and "especially fast on downhills."
Jan Heine
Editor
Bicycle QuarterlyRolling resistance on wet roads
We saw how treacherous the rain made the cornering traction for manyriders in the stage 13 time trial, taking down good bike handlers likeCancellara, Klöden, Gusev, and Popovych, among others. But many ofthe riders who did well in the Albi TT had wet roads. In many cases, theroads were wet and rain was no longer falling.So when the riders are not contending with curves, do their tires rollas well on a wet road as on a dry one? In my June26 Tech Q&A column on rolling resistance, one of the issuescovered was whether a tire rolls faster on a wet road than on a dry road.I think it does, and that the rider can consequently go faster, at leastas long as they are not plowing through raindrops in the air. I receiveda number of responses to my theory, of which here is a sampling:Dear Lennard,
Certainly I have also always believed that rolling resistance is reducedin the rain. I had never considered that water filling voids in the roadsurface thereby smoothing the surface could be a cause. Instead I consideredthe following cause.A local segment of the tire obviously deforms from a round to a flatsurface when in contact with the road. I would assume during this deformationthat there will be sliding of the tire surface against the road. If true,there would obviously be dissipative losses. If friction were reduced duringthe deformation then rolling resistance would be likewise reduced. Giventhat static and dynamic friction is reduced when the road surface is wet,this mechanism for reduced rolling resistance is conceivable.
SteveDear Lennard,
I'm an engineer, and I just read your response on wet rolling resistance.
While there may be some truth to your "road smoothing" theory, I thinkit's more a result of shear. Water has low viscosity, and shears easily.The shear is much less in water than it is with rubber on a dry road.
JasonDear Lennard,
I just don't agree with you on the rolling resistance of bicycle tireson a wet road.My experience has always been that it is much heavier going in the wetthan in the dry. I'm prepared to accept that a large part of this may bepsychological - it's just plain miserable in the wet. Even so, considerthat on a wet road there is much more work to do:The tire has to push surface water out of the way.Water is carried up off the road on the tire, breaking contact againstsurface tension.Water on the tire is sprayed up into the air - more energy expended.Water on the tire increases the weight of the wheel.Armstrong and Ullrich may have gone faster in that 2003 TdF TT, but Ithink there were other factors at play there.
Stan

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VeloNews technical writer Lennard Zinn is a frame builder (www.zinncycles.com),a former U.S. national team rider and author of numerous books on bikesand bike maintenance including the pair of successful maintenance guides"Zinnand the Art of Mountain Bike Maintenance" and "Zinnand the Art of Road Bike Maintenance" as well as "Zinn’sCycling Primer: Maintenance Tips and Skill Building for Cyclists."

Zinn's VeloNews.com column is devoted to addressing readers' technicalquestions about bikes, their care and feeding and how we as riders canuse them as comfortably and efficiently as possible. Readers can send brieftechnical questions directly to Zinn (veloqna@comcast.net)Zinn's column appears each Tuesday here on VeloNews.com.