Technical Q&A with Lennard Zinn: Switching cogsets; Carbon sizes
One more gear? Dear Lennard, We have a 27-mile climb just outside of town that I ride up occasionally. My problem is that I tend to spin out on my way back down and find it difficult to keep up with some of my riding partners. A friend of mine told me that I could swap my 10-speed Shimano cassette (12-25) for a SRAM (11-26), which would give me both a better climbing and descending gear. Although I understand 45MPH is plenty fast, is the swap compatible? Brian Dear Brian,
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By Lennard Zinn
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One more gear?
Dear Lennard,
We have a 27-mile climb just outside of town that I ride up occasionally. My problem is that I tend to spin out on my way back down and find it difficult to keep up with some of my riding partners. A friend of mine told me that I could swap my 10-speed Shimano cassette (12-25) for a SRAM (11-26), which would give me both a better climbing and descending gear. Although I understand 45MPH is plenty fast, is the swap compatible?
Brian
Dear Brian,
The cogsets are compatible in terms of shifting. You may run into a problem installing the SRAM cogset, however, if you have a Shimano 10-speed wheel. SRAM cogsets, whether 10-speed road or 9-speed MTB, all fit onto 9-speed Shimano freehub bodies. Shimano 10-speed freehub bodies, however, are aluminum and have taller, deeper splines. A 9-speed compatible cogset will not fit on one, so if you have a Shimano 10-speed rear hub you need to get a different rear wheel before making this switch.
Shimano 10-speed cogsets also fit on 9-speed Shimano freehub bodies, so your rear wheel may already have a 9-speed Shimano-compatible freehub, in which case, you are good to go with the SRAM cogset. Mavic and many other hub manufacturers never adopted the 10-speed spline configuration (or the aluminum freehub body), so you could mount that SRAM cogset on one of those. And for 2008, even Shimano’s own high-end road wheels will have 9-speed freehub bodies, not 10-speed.
Lennard
An annual inspection?
Dear Lennard,
Do you have an opinion on whether one should re-glue tubulars annually? I glued my racing tubulars to their rims last year and the glue job still seems strong, but I’m worried about the risk of rolling a tire due to an old glue job.
Mark
Dear Mark,
You should at least try to remove the tire once a year. If it is still glued on really well, and you can’t peel it back at all, just stop and leave it. But if it peels off easily, be glad you checked, and re-glue it.
Samuele Bressan, Product Manager & Designer for Vittoria says, “It’s a good habit to check the glue annually. Humidity conditions (especially where the bike is stored) may make glue force weaker than thought.”
Lennard
Carbon sizing
Dear Lennard,
I have been doing a lot of research on carbon frames lately and most companies seem to be using a common theme. The frame sizes are offered in small, medium, and large. Occasionally you will find an extra small or extra large, but not all the time.
Why is this? All my life frames have been produced in 2cm increments and now all of a sudden 4 sizes are all we have to choose from? With so much emphasis on the fitting process these days you would think that there would be more geometries to choose from.
Rick
Dear Rick,
Indeed, you’d think that more sizes, not fewer, would be available in this day and age of boutique shops with high-tech fitting areas. But the short answer to your question is that the small size run is done for reasons of profitability.
The steel or aluminum frames of yore to which your question hearkens were made out of tubing that could be cut to any length with minimal additional expense. However, most carbon frames require a mold of the entire frame (for making one-piece, or “monocoque” frames) or molds of sub-assemblies that are then glued together to build the frame. While the multi-piece method often affords more manufacturing flexibility and hence allows production of more sizes and even custom sizes, the fact remains that only one size or very limited sizes can be made from the mold or set of molds of a frame.
Carbon molds cost a lot of money, as they are precision machined, often have heating elements built into them, and must be made of giant, thick pieces of metal (usually aluminum) so that they do not distort under the pressure and heat of the carbon curing process. That is why big manufacturers build frames in only a few sizes to serve the meat of the bell curve of human sizes. By only building the sizes for which there is high demand, they can increase profitability by amortizing the cost of the molds over more frames.
Sloping top tubes allow manufacturers to get away with a small size run more easily than in the days of level top tubes, too, by eliminating concerns about standover clearance. And manufacturers know that, with the sloping top tube, short and tall people outside of the bell curve will often buy a too-big or too-small carbon frame anyway and adapt themselves to it with super-short or super-long stems, bars and varying seatpost setback. People are so hot on carbon these days that many of them will forgo good frame fit and proper positioning in order to attain a superlight carbon frame.
Lennard
Correction: In a recent column, I said that Tom could interchangeably use a Shimano mountain bike rear derailleur or an Ultegra triple rear derailleur with a 12-34 cogset, but that is not the case. The Ultegra RD will not handle a cog that big; it is rated to 27 teeth maximum. A number of readers have tried innovative things to increase the capacity of an Ultegra triple RD, and here is an example.
Lennard
Dear Lennard,
I think you might be mistaken when you mentioned to Tom that he could use an Ultegra triple rear derailleur with an XT/XTR 12-34 cassette. The cages are long enough but something else about the geometry is different. I have got a few to work okay on cogs as large as 30 teeth by installing the B-tension screw backwards to get its tension a little higher but the capacity was pretty well maxed out.
I tried a 32 and the derailleur pulley was definitely bouncing off the teeth of the large cog when on the small chainring, especially when pedaling backwards. I suppose variations in derailleur hanger length might be somewhat of a factor and a smaller 10 tooth pulley might buy you a few more mm of clearance, but I think it would take some pretty creative wrenching to get an Ultegra derailleur to be happy on a 34 tooth cog.
Jeremiah
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”Zinn and the Art of Mountain Bike Maintenance” and “Zinn and the Art of Road Bike Maintenance” as well as “Zinn’s Cycling 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 ([email protected])Zinn’s column appears each Tuesday here on VeloNews.com.
