Triathlete - Wheel Comp - Oct10.pdf - Zipp - Speed Weaponry

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Ge ar BagWind CheatingWheelsReviewedBy Aaron HershRace wheels are not the most cost-efficientway to improve your bike split, but they maybe the sexiest. However, those deep rims aren’t justfor looks: The rim is the most critical componentof an aerodynamic wheel. Triathlon race wheelsreduce wind drag by converting a standard tireand rim into an aerodynamically efficient shape.Designing race wheels with deep rims is the mostcommon way manufacturers reduce drag, butthe rim’s shape is just as important as its depth.The first aero wheels utilized narrow V-shapedrims but aerodynamicists eventually figured outthat certain wide and deep rims actually createless drag than narrower alternatives.Zipp and Hed have dominated the racewheel market for many years because theyshared a patent on the most aerodynamic rimshape—the toroidal rim. This bulged rim shapecreates less drag than a deep-V rim even whenthe rider is in a gentle crosswind. The patenton this valuable rim shape just expired, leavingthe race wheel market open to serious newcompetitors. No one has grabbed this opportunityyet, but Zipp has already designed andpatented a new shape that it asserts is even moreaerodynamic than a toroidal rim.The Anonymous Aerodynamicist on the topic of Rim DepthA wheel with a deep rim is not necessarilymore aerodynamic than one with a shallower rim.There are two types of aerodynamic drag:pressure drag and frictional drag. Frictionaldrag is the resistance created by air rubbingagainst an object as it passes over. Pressuredrag occurs when air separates from an objectas it passes over it, which creates a large airpressure difference in front of and behind theobject. This difference creates a force on theobject in the direction of the wind.At the speeds bicycles travel, pressuredrag is the predominant form of drag so aerowheels are designed to keep the flow attachedto the surface of the wheel to minimizepressure drag. The shape of the rim, not justthe depth, determines if air will stick to thesurface or flutter off to the sides. A deep rimthat is the wrong shape will still see flowseparation in even minimal crosswinds and,consequently, will create a lot of pressuredrag. A rim that is shaped to allow air togently transition from the tire to the braketrack and onto the rim body reduces thewheel’s aerodynamic drag more effectivelythan any other characteristic.Photos by Nils NilsenThe evolution of race wheelsTraditionalCutting edgeBox rim deep V straightwalledtoroidalwide brake tracktoroidalwide brake trackwide ID1 4 0 t r i a t h l e t e . c o m o c t o b e r 2 0 1 0
Ge ar BagZipp 404 Carbon Clincher $2700Ride quality: 130/140.6 (Our product ratings are depicted as a fraction of 140.6, thenumber of miles in an Ironman. ) It corners like a tubular but the carbon brake trackisn’t as grippy as an aluminum rim.Usability: 125/140.6. The clincher tires make changing a flat simple, but the widerim requires a brake adjustment when going from a standard training wheel to these.Value: 128/140.6 Cutting edge aero profile and carbon clincher rims make it aphenomenal piece of wheel technology, but it is still really pricey.Aero profile: Truly the next generation.Despite the name, the biggest differencebetween the Zipp 404 Carbon Clinchers andcompetitors’ race wheels is not the fact that theyare carbon clinchers. Other manufacturers have, infact, been successfully producing carbon clinchersfor a couple of years. The 404 CCs are a milestonein race wheel design because of their evolutionaryrim shape and unmatched combination of speed,weight and usability. Like the Hed Jets, the 404CCs have an ultra-wide brake track to improvewheel aerodynamics, but Zipp has taken thetoroidal rim shape one step further with its newFirecrest rim profile.The rim of the 404 CCs is not only incrediblyaerodynamic, but the wide brake track also createsa silky ride experience that can only be matched bytubular tires and other wide clinchers. Wideningthe brake track increases the amount of air heldin the tire and lets it absorb little bumps in theroad that would normally skip the rider off thepavement. This buttery ride quality, combined withthe incredibly light rims, make the 404 CCs a thrillon the road. Even with the carbon rim they are stillheavier than comparable tubular wheels, but the404 CCs are more nimble and eager to acceleratethan any aero clincher wheel I’ve ever ridden.Hed Jet 9 and Jet disc clincherJet 9 Front $800, Jet Disc $1050Ride quality: 120/140.6 Aluminum braketrack grips perfectly, and the spoked disccorners better than any rival, but the deepfront rim can feel twitchy in the wind andthe Jet wheels’ relatively stout weight makesthem slow to accelerate.Usability: 130/140.6 Clincher tires. Aluminumbrake track. Solid cornering characteristics.The only issue is spreading thebrake calipers to accommodate the wide rimand handling the front wheel in a crosswind.Value: 133/140.6 Best aero profile for theprice in the industry, but the flexible fairingsgive the wheels a cheap feel.Aero Profile: Hed Jet wheels are simplystandard aluminum rim wheels covered withcarbon fairings. The fairing is flexible andfeels a bit chintzy. Despite their low productionvalue, the Jet 9 and Jet disc are near thepinnacle of wheel aerodynamics. The key totheir aerodynamic efficiency is the smoothintegration between the rim and the tire.Its 23mm wide brake track, as opposed toa conventional 19mm wide track, turns thewheel and tire combination into one smoothtoroidal unit.Until just three years ago, even the most aerodynamic wheels in the world had an obviousdesign flaw. The rims themselves had an efficient toroidal profile but, with a tire on, the wheelsbecame a figure eight because they had a narrow brake track that formed a waist betweenthe wide tire and wide rim. Mad scientist Steve Hed was the first to solve this problem bybuilding an aero wheel with a wide brake track that smoothly transitions from rim to tireand makes the entire system, rather than just the rim, fully toroidal.Not only is the Jet disc aerodynamic, but it rides better than any other disc because ofits construction. It has sheets of carbon covering a conventional spoked wheel to give it theaerodynamic properties of a disc. Foam core discs transmit more road vibration than spokedwheels and this makes the ride feel harsh and compromises cornering because the wheelbounces off the pebbles in an asphalt road. The Jet disc rides like a spoked wheel because itis a spoked wheel.o c t o b e r 2 0 1 0 t r i a t h l e t e . c o m 1 4 1
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Triathlete - Wheel Comp - Oct10.pdf - Zipp - Speed Weaponry

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