By Lennard Zinn
It’s fall and, as is usually the case, some folks’ hearts turn to cyclo-cross.I often get questions about brake selection on ‘cross bikes, so I am offeringtwo recent examples.
Let me start by saying thanks to your magazine for making me a fanof cyclo-cross. I primarily ride the road with an occasional trip ontothe dirt on my mountain bike but have never owned or ridden a cross bike,my question is; why do cross racers prefer cantilever brakes over V-brakes?Mountain bikes changed over to V-brakes and/or disc brakes years ago forbetter brake performance, I don’t get it.
Why is it that cyclo-cross bikes seem to use old-style (by mountainbike standards) cantilever brakes in lieu of a linear pull V-brake? Isthat just a UCI rule, a¹ la no disc brakes for cyclo-cross? I alsonoticed that Ti forks seem to be de rigueur, even with carbon fiber frames.Why not carbon fiber a¹ la a road bike? I saw one bike tested thatdid have a carbon fiber fork with post mounts, so they are clearly available.
SteveAnswer from Stu Thorne of Cyclocrossworld.com:
One of the reasons that most cross bikes use “older” stylecantilevers over the newer linear pull or “v-brakes” is that the cantileversretract from the rim further thus allowing for better mud clearance. Whilelinear pull brakes are very powerful they don¹t have the best clearancewhen the conditions are muddy. Many of the current cross brakes Empella,Spooky, Avid and the new Shimano BR-R550 – are designed to work with roadbrake levers. Linear pull brakes will work with road levers, but requirean adapter. This is another reason for the use of cross specific brakesas an adapter can complicate matters and also become clogged with mud.There are no UCI rules that outlaw linear pull brakes.In regards to your question about forks; it is quite common to findcarbon forks on cross bikes these days. I have only seen a few titaniumforks. There are many reputable forks on the market today that can handlethe rigors of cross. Carbon forks are favored by almost all of the topriders today.
Compact or triple
Given the recent discussions around the advantages of using doublering compact cranks to improve climbing efficiency on road bikes what optionmakes more sense; use a compact double ring crank 50/34 with an 11/23 or12/25 cassette or switch to a long cage XTR rear derailleur with an 11/34cassette and a standard 53/39 crankset. I¹m presently using a 12/27rear cassette with my Dura-Ace 53/39 crankset but am looking to improvemy spinning cadence and take the load off of my knees on climbs. I¹malso looking for the best combination of climbing and big ring descendingperformance, which set up would you recommend?
Good question. This is something I have done with customers who didnot want to get a triple. You have a bigger range with the 53-39/11-34XTR derailleur setup. A 39-34 is a lot lower than a 34-23 or 34-25 (it¹sas low as a 34-30 combination), and obviously a 53-11 is bigger than a50-11 or 50-12. However, you will have a lot bigger jumps from gear togear. If you want that much range, go for the 11-34 setup, but if you aremore interested in closely-spaced gearing, don¹t do it.
Warhawk industries www.chainrings.comoffers a 37 tooth chainring for 130mm BCD crank.
JoshA happy Bebop-er
In your 12/2 column you answered a question about free-floating off-roadpedals. One you didn’t mention is the BeBop. This is a well-thought-outpedal that is tough, simple, and has a very generous non-centering floatsimilar to Speedplay. I think they ace Speedplay with their smaller, lightercleat, and the engagement surfaces are all steel-on-steel. I won’t spendmy money on anything else; for the combination of cost, weight (includingcleat), durability, stack height, cornering clearance, solid retention,platform, and ease of entry/exit, (there, did I miss anything?) nothingelse is even close.
Nope, I’m not ‘with’ BeBop, I’m just a satisfied customer.
EricAre ceramics really that good?
Could you explain the advantage(s) of using ceramic bearings in bicyclehubs as touted by Campy and Zipp in the latest generation of carbon fiberhigh end racing wheels? I assume from reading the sales literature thatthe new ceramic bearings have far less friction than steel bearings. Isthis assumption true? Assuming that ceramic bearing do create less friction,are there other reasons to recommend the use of ceramic over steel bearingsfor high end bicycle hubs? What is the durability data for ceramic bearingsin bicycle hubs? What explains the extreme price differential of ceramicvs. high end steel bearings. In your experience is the price differentialjustified? Have you ridden wheels with ceramic hub bearings? Have you workedon wheels with ceramic hub bearings? When you were at Interbike did youattend a Campy seminar that discussed the new Hyperon wheels with ceramichub bearings? Are you aware of any studies that test the rolling resistanceof hubs with ceramic bearings vs. hubs with steel bearings?
Is there any data available on ceramic bearings used in non-bicyclerelated applications that demonstrate the advantage of ceramic over steelbearings. For example, are ceramic bearings used in industrial applications?Any information you can provide on ceramic bearings is greatly appreciated.Due to the astronomical price of these new wheel-sets, and the fact thatthe wheel-sets cost nearly the same amount as the typical contested divorce,I want to do as much research as possible before I purchase a pair.
I have no experience with them, nor have I attended any technical seminarson them. I am familiar with ADA installing them inside many of the bearingsurfaces of bikes of top pros at great expense to said pros. Otherwise,I probably know no more than you, so I will defer to someone who knowsa lot about them.
LennardAnswer from Zipp:
The use of ceramic bearing systems in cycling is starting toaccelerate since the introduction of own ZIPP Z3 wheel set two years agoand now with the adoption ceramic bearings by Campagnolo I believe we willsee an inevitable increase in the use of this technology. Judging fromthe notes and phone calls I receive, there is quite a lot of both excitementand confusion out there so this is a great opportunity. I will try to answerall your questions, but please excuse me if I tend to go on too long: Ilove this stuff and I tend to get carried away.I believe it was the writer Robert Heinlein who said something alongthe lines of: “Any technology sufficiently advanced is indistinguishablefrom magic.” Ceramic bearing systems aren’t quite magic, but the technologybehind them seems to be getting closer all the time.I am going to talk about ceramic bearings, bearings in general and ZIPPbearings in particular as these are the bearings I am most familiar with.Other manufacturers such as Campagnolo will have faced similar challengesin adopting ceramic technology and will have addressed them in ways bestsuited their own needs.When speaking of ceramic bearings, we are really speaking of ceramicballs replacing the more common steel balls in the bearing assembly orsystem. Ceramic bearings do offer dramatic potential for significant performanceadvantages, but the key word is potential. Optimal performance is a resultof an entire bearing system rather than as a result of the ceramic ballsthemselves. What the ceramic balls do by their physical properties is raisethe bar of what is possible to achieve in the entire system.When you start talking about any material, you have to remember thatthere are steel battleships, bridges, “tin” cans and my favorite toy, theslinky, all made of steel. In other words, each material has a range ofproperties and it’s not the magic material, it’s what you do with it andhow you apply the material properties to a particular design solution.Modern bearings, any bearing ceramic or otherwise, are really prettyamazing technological objects. Steel ball bearings used in cycling havetolerances now measured in millionths of an inch. In top quality hubs,steel bearings typically will have a tolerance of between 50 and 60 millionthsof an inch between the balls of a 12 or 15 ball set. This is not easy todo, but by pushing the manufacturing envelope further (and spending a lottime and effort), steel ball bearings can achieve a precision of 10 millionthsof an inch total variance per matched set of 15 balls. Of course to takeadvantage of this precision in the ball manufacturing, the other partsof the complete assembly must also receive similar attention. This attentionto detail results in improved performance across a broad range of parameters,but the basic material properties become the limiting factor. Being theperformance fanatics (and that’s a nice way of saying technology geeks)we are here at ZIPP, all our hubs using steel balls are using ZIPP designedand custom manufactured bearings sets that achieve less than 10 millionthsof an inch total variance in roundness and size in a matched set. A similarattention of detail is applied to the remaining parts of the bearing assembly.Now in talking about the above it’s time to mention a key part of manufacturing:The more time, effort, and precision you insist on, the greater the cost.It’s pretty much a rule you cannot get around. The cost, by the way, increasesat an ever accelerating rate with each level of precision achieved. Byadopting new technology and materials (Ceramics!) new options become available.Dramatically greater precision and performance can be achieved and, ofcourse, the cost also accelerates along its ever increasing path. That’sthe answer to why the price differential exists between ceramic and steelbearings.Ceramics have been around for several years, but it is the new and rapidlydeveloping new manufacturing technology that allows the dramatic increasesin precision that were unthinkable until recently. They are used in numerousindustrial, military and aerospace applications where long life, high speed,heat, pressure and low rolling resistance are required. As with anything,a range of quality is possible…but it is the manufacturing technologyat the highest level that breaking new ground and offering unprecedentedperformance potential.How much benefit is possible from adopting this new technology? Accordingto reports from real world testing done by ZIPP sponsored Team CSC an averagereduction in wattage of three to four percent under our standardbearing systems, already the tightest standard within the industry canbe expected. For an average trained cyclist developing 250 watts, that’sa savings of approximately 10 watts. At any level of competition, thatis significant. The key is every part of the bearing system has seen markedimprovements in precision resulting an a total benefit greater than thesum of its parts. Similar to current math theory, at some point numbersreach a point where the rules just don’t hold true any more.Anecdotally, one our ZIPP representatives recently became a world recordholder on the track. After numerous attempts and misses at the record bya few hundredths of a second, he broke the record after switching to theceramic bearings. He has since lowered that record again using the sameset up, but in several tries without the ceramic bearings has been unableto ever match his original record breaking attempt. Of course this wasnot a scientific test, but try to tell him the bearings don’t make a difference!Matched sets of ceramic balls used in ZIPP bearings exhibit tolerancesof LESS then one-millionth of an inch total variance in both size and roundnesswith a corresponding increase in surface smoothness. This is near the technologicallimit of measurement and worlds better than any steel bearing of any ratingor type. These bearings are currently exclusive to ZIPP and NASA.Ceramic balls of the highest quality are made of pure silicon nitride.(Earlier ceramic bearings of any type, possibly familiar to skaters orskateboarders, were often merely coated steel balls inserted into standardnon-specific races and offer no comparison to the current state of technology.)The critical issues of manufacture are purity of materials, chemistry andparticle size control, ability of the pre-manufactured material to floweasily, packing density, uniform compaction, micro-structural development,geometry, surface quality and finish.As mentioned earlier, ceramic silicon nitride balls exhibit much greaterhardness than steel balls resulting in at least 10 times greater ball lifedue to the ability to hold the surface finish longer. (Later I will mentioncryogenic treatment of the steel races. This is required to take advantageof this durability and prevent the hardness of the ceramic ball from destroyingthe race.) The ball has dramatically smoother surface properties than thebest steel ball resulting in less friction between the balls and bearingrace surfaces. Thermal properties are also dramatically improved over steelballs resulting in less heat build up at high speeds. To achieve the finalsurface finish, the balls are floated on a magnetic field and polishedwith plasma stream. They are rated to a spin rate of 300,000 rpm versusa spin rate of 33,000 for our steel balls.All the other parts of the bearing system and of hub design are directedat optimizing the potential of our bearing technology, both ceramic andsteel.The custom steel bearing races are designed and manufactured specificallyfor the loads and requirements of a cycling application. The races arecryogenically treated at minus 300 degrees Fahrenheit to harden and alignthe crystalline structure of the material. The races are then polishedto a surface smoothness 30-percent greater than an Abec 9 rating, the highestinternational standard rating level. Each bearing assembly also includesa thermo-plastic based waffle shaped seal that encloses and locates eachball to its optimal location in the race. Friction is further reduced bythis system as individual balls are kept at their optimal location at alltimes. Lubrication is provided via a depleted barium hydro-flex lubricant($650 per kilogram and used in all
ZIPP bearings!) that is also a product of the space program. The lubricantis actively hydro-phobic, meaning it repels water at a molecular level.The lubricant is also thermally stable and exhibits the same propertiesat -200 degrees as it does at over 2000. Most importantly, it exhibitsthe lowest friction coefficient of any lubricant available. Designed tomatch the bearing performance with modifications adapted to current use,the lubricant is rated to spin rates of 300,000 rpm and an expected lifeequal to that of the bearing.
As a final word, properly designed ceramic bearing systems do in ouropinion increase performance and will become more common, perhaps the futurestandard. Certainly at the top levels of the sport the difference is significantenough to change the out come of races all things being equal among similarlygifted athletes. For the time being, however, the cost of such technology,even the availability of the materials themselves remains a barrier towide application of such systems. Manufacturers like ZIPP and now Campagnolo(others to follow) will continue to push this direction, but ultimately,it is the individual rider who has to decide if the current state of theart is of value to them. In the auto racing industry there is an old saying:”Speed costs money; how fast do you want to go?”
National Sales Manager and Factory Guy
ZIPP Speed Weaponry
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.