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By Lennard Zinn
On one of the tech segments during the OLN coverage, they interviewed someone from CSC and he talked about a different type of chainring they were using for the time trials. But they didn’t explain what the differences were. Did you hear anything about this?
Those chainrings are called Harmonic, and they offer a larger gear ratio when the crank is horizontal than when it is vertical (the opposite of Biopace). I asked Bobby Julich about them, and he referred me to the company’s website. And lest you think they are a revival of the old Biopace design, Julich says “they are the furthest thing from what Shimano had!”
What was Ullrich riding in the prologue?
I remember reading a response in your column to a question about Jan Ullrich using spoked wheels in the prologue. The response was that he used a disk in the rear, but I’ve seen several images of him riding a spoked rear wheel. By spoked, I mean something like a Spinergy Rev X type of spoke. Care to comment? I’m not sure if it’s been corrected on your column. I’ve tried not to miss them as I love the technical stuff.
As I said in a Tour posting, they are made by Xentis in Austria and imported by Storck USA into North America.
FSA explains its latest and greatest
Is it true that FSA is coming out with its own cranks with integrated BB just like the new Dura-Ace? I was planning to order an FSA compact crank from our LBS but according to them they were told by their FSA supplier to wait for an upcoming integrated BB version, which will be coming out anytime.
First, I will refer you to my posting from day one of the Taipei bike show in March. Second, I will let Dave Anthony from FSA’s design, research and development department field that question.
Let me give you the long and the short of it:
“Just like?” The short answer is, “No, FSA’s external bearing integrated cranks will be better, lighter, and of course, carbon.” The working name is “MegaExo,” and they will be available sometime in early 2005.
The decision to wait should be based on your current needs. It sounds like your main consideration is gearing, so let that guide you first. Do you need to ride your bike now or can you wait until ’05? As much as we love breaking new ground, we love riding. If a current compact crank can get you riding sooner, our suggestion is get out and ride.
Consider that FSA compact cranks in ISIS-Drive are no slouch and are such a significant improvement in weight, stiffness and gearing over what came before. CSC is doing okay on them! External bearing BB’s do have some advantages, but they are incremental gains.
The long answer requires the question: What is driving the development of integrated-crank systems? The answer lies in the success of ISIS-Drive, which FSA has been a major proponent of, and the strengths and weaknesses of the ISIS-Drive BB. ISIS-Drive came about because the owner of the Octalink patent would not license it. Several other component manufacturers cooperated (the ISIS-Drive Committee) to develop this alternative spline BB standard, which is superior in most respects and offer it as an open-standard for all manufacturers. This led to a lot of advantages for crank makers, BB makers, bike manufacturers and consumers, because as a result there was greater competition and choices. The Octalink owner was, however, less happy.
ISIS-Drive vs. Octalink
ISIS-Drive BB’s with 22mm diameter axles have superior strength and stiffness compared to Octalink BB’s (also 22mm axles), which in turn were already an improvement over square-taper BB axles (17mm diameter axles). In our testing, ISIS-Drive BB’s are typically at least 20 to 30 percent stronger and stiffer than Octalink, for comparable BB’s (i.e., we weren’t using M12 DH ISIS-Drive BB’s). Strength and stiffness of ISIS-Drive set the bar high in those categories. Going to the 24mm diameter axle used in integrated BB’s offers a marginal improvement, only a 9 percent diameter increase. In comparison, the 22mm axle is already 29 percent larger diameter than the old benchmark 17mm axle.
Currently, FSA ISIS-Drive BB bearing life is acceptable, although in the past, many ISIS-Drive BB’s suffered from short bearing life. The same oversize axle that is great for strength and stiffness presented engineering and manufacturing challenges to fit bearings with a high enough load capacity inside the BB shell. (High-end Octalink BB’s had similar problems.) The difficulty of engineering ISIS bearings can be evidenced by the fact that one of the three members of the ISIS-Drive Committee never produced an ISIS-Drive BB, while another member was the first to follow with an external bearing BB.
FSA has used its bearing know-how to develop long-lasting ISIS-Drive bearing BB’s. Last year, CSC was on ISIS-Drive with good results (ridden to three stage wins in the Tour de France). We have taken the feedback from CSC and have continued to improve our ISIS-Drive BB’s by introducing high-end quadruple bearing versions with improved sealing, under the designation “MegaQuad.” Next year, we will introduce an external bearing ISIS-Drive BB for MTB cranks.
Alternative systems – oversize integrated BB’s
That said, over two years ago we started new developments looking beyond ISIS Drive. We looked at all the novel systems that came before, such as integrated cranks like Bullseye and Sweet Parts, etc. as well as external bearing BB’s such made by Magic Motorcycle. But the conclusion we came to was that the weakest point in the system was the small diameter BB shell and that the best system was to enlarge the BB shell and integrate the BB into frame. The oversize integrated BB in the frame offers the greatest absolute system (frame + BB + crank) stiffness at the lowest overall weight. Cannondale previously proved this point by switching from the Magic Motorcycle external bearing system (which they owned) to a frame-integrated BB. More recently, Pinarello is headed this way.
We introduced in 2002 the “MegaTech” integrated BB standard, open to all frame and BB manufacturers. The large-diameter BB shell offered frame designers a larger foundation to work around with lots of space inside for BB manufacturers to engineer better axles and bearings. However, bicycle manufacturers have been reluctant to embrace the MegaTech standard (which is surprising because they sure drive the experiments with headset standards), despite the great advantages of integrated BB’s.
Alternative systems – oversize threaded BB’s
A season after we introduced MegaTech, the ISIS-Drive Committee proposed another standard for an internal oversize BB, called OverDrive. The difference is that OverDrive is not integrated, but uses oversize threaded cups. OverDrive’s advantages compared to MegaTech are that frame builders do not have to hold as tight tolerances (a thread can have sloppier dimensions than the ream required for a press-fit bearing) and it is more “familiar” to dealers and consumers than a press-fit. It is significantly heavier than other BB systems, which is probably OK for the mid-end and heavy-duty bikes it is targeted toward.
Alternative systems – external bearings and integrated cranks
External bearing BB’s combined with integrated cranks offer some modest weight and stiffness improvement over ISIS Drive. For a given crankarm technology, the main weight savings is the elimination of BB bolts and thinner axle, but the larger bearings, external cups, and longer axle do limit the weight reduction compared to frame-integrated BB’s.
There are advantages to external bearings, which are different from the advantages of integrated cranks.
The advantages to the BB manufacturer of the Magic-type external bearing are that the bearings are both larger (last longer) and are common off-the-shelf cartridge bearings (cheaper), which are easier to produce and procure than custom bearings for Octalink or ISIS BB’s.
The advantages to the crank manufacturer of integrated Bullseye-type cranks are that they are guaranteed that the customer will always use the intended BB with the crank (and it doesn’t hurt that they will always sell a BB with a crank). The advantage to the bike company and dealers is that there are fewer worries about mismatched BB’s, faster assembly and compatibility with current threaded frame designs. For a bike company assembling tens of thousands of bikes a year, reduced assembly time is important.
When bike manufacturers and consumers are free to mix and match cranks and BB’s, there is the small chance that a crank will be installed on a BB it was not intended for, which can in turn cause problems for chainline (shifting performance), crank-arm clearance and q-factor.
There are two major problems with square taper BB’s in that (i) there is no standard axle length for cranks and (ii) their taper dimensions can be made to either Japanese dimension (which follow JIS) or European dimension (which follow ISO), so even if you get the right axle length then you may have the wrong taper size.
ISIS-Drive cleverly addressed this problem by assigning standard lengths (i.e., 108mm for road double, 113mm for MTB, 118mm for road triple, etc.), so you almost always know which length of axle you need for your cranks, and by using chainline control shoulders, so your chainline would always be as intended.
The great power of ISIS-Drive’s open standard is also its weakness – the tapered spline requires great care to produce and the ISIS standard leaves manufacturing open to interpretation in some respects. In some instances early on, manufacturers found that their in-spec products would not work with another’s in-spec product – exactly what was not supposed to happen with ISIS-Drive. Fortunately, many ISIS-Drive competitors have cooperated together to hammer out the manufacturing kinks.
So, external bearing BB’s offer some simplified manufacturing and some performance benefit compared to ISIS-Drive BB’s. They are compatible with most current bikes and frames. Integrated cranks reduce the possibility of mismatched BB axles and allow faster assembly.
FSA will introduce an external oversize bearing integrated-BB crank for next year. The code name is “MegaExo,” to reflect the trickle-down over-size bearing technology from our MegaTech effort.
The main reason is a need to keep our price and performance stable for our customers. Worldwide, the cost of raw materials is rising and we need to reduce costs somewhere – by saving cost on the bearing, we can continue to offer our famous carbon technology and performance.
We will continue to support ISIS-Drive well into the future.
As long as that answer is, it really simplifies and glosses over many points and details about the advantages and disadvantages about crank interfaces. It is not intended to be a definitive treatise, but just matter-of-fact for the interest of your readers.
Design, Research and Development, Full Speed Ahead
More on the fork
I have continued to receive mail on the broken fork steering tube on Ag2R sprinter Jean-Patrick Nazon’s bike that occurred on the descent of the Col de Portet d’Aspet during the 205.5km 13th stage to Plateau de Beille in the Pyrénées. As I posted on August 3, according to Time USA’s Doug Knox, the broken fork happened during the crash, rather than causing it. Knox managed to reach an Ag2R team mechanic during France’s August vacation who said that Nazon’s fork broke after hitting a low wall on the road edge. If I find out anything further, I will let you know.
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.