The ABCs of tire size
Dear Lennard,
What does the c stand for on a 700c rim and or tire? What unit of measurement is this and how is it determined?
BWDear BW,
The “c” is not a unit of measurement. It merely designates a certain international rim/tire standard. A 700C rim has a 622mm bead-seat diameter (diameter of the tire bead circle), and you will often find this number imprinted on 700C tires and rim strips. Obviously, there is nothing you could measure on the wheel or tire and come up with 700 units of anything (the outer diameter of a 700C X 23mm road tire is about 668mm).To illustrate the arbitrary nature of the “c” you are asking about, you may be aware that there are a number of different “650” standards that one can still buy. There is 650A, 650B, and 650C, and the letter does not designate measurement units with them, either. For instance, 650A is a road 26-inch rim/tire size, and 650B was a popular size for mountain bikes in 1981 or so and has been periodically carried forward by small companies. I believe Rivendell recently made bikes with this wheel size. In 700, 700C is really the only remaining one, but I believe that there were 700A and 700B sizes at one time as well, and there certainly was a 700D size, which had a 587mm bead-seat diameter.
LennardWhen do threads count and how to count them
Dear Lennard,
Please explain the value of "tpi" when choosing a clincher tire. What would make a 300tpi tire better or worse than a 350? Veloflex makes them and I have tried both. Both are excellent and roll super fast, but the 350 costs 15 green backs more, 10 on bulk buys.
KarlDear Karl,
The higher the thread count as long as they are only counting the number of threads per inch in a single ply of the tire, the thinner the threads are (in order to fit that many threads lined up next to each other into an inch, they obviously have to be thinner).The thinner the threads, the more flexible each is, and hence the more supple the casing will be, since the individual threads can move with less energy loss to absorb imperfections in the road surface than could thicker threads. This results in lower rolling resistance and better cornering grip. Continental has recently muddied the waters by claiming much higher thread counts for some of its tires than they actually have, simply by adding together the thread counts of all of the different plies in the tire.This is like falsifying the ingredients on food in the grocery store, as far as I am concerned. Just as with ingredients, the consumer does not have the ability to verify the claimed thread count. However, you can see the difference between a high-thread-count casing and a low one, at least between, say, a 130tpi casing and a 290tpi one. And you can definitely feel the difference in your hand by bending the tire around.
LennardOut with the old?
Dear Lennard,
I recently had to build up a new frame with a bigger seat tube, requiring me to purchase a new derailleur (34.8). Upon doing so, I discovered that Shimano does not seem to be producing Ultegra 9 components any longer. I had to purchase the braze-on. As an alternative, one shop said I should purchase the Ultegra 10 and modify it. I am not purchasing a component that needs to be modified! If you look in the catalogs under Ultegra, everything is listed as “new”, new being Ultegra 10. If you try to order Ultegra 9, you will probably find a limited, if non existent supply left. As a customer, I do not like being forced to upgrade!I hope I am wrong about Shimano not producing Ultegra 9 components and forcing customers to upgrade.I think the bike shops are going to be the fall guy when the customer that purchased a bike from them comes back to replace a component and the shop owner has to tell them they have to upgrade. That just isn’t fair to the customer or the shop owner. If you remember last year, a vast majority of the high end bikes came with Ultegra 9.Could you check out Shimano’s policy on supporting very recent legacy (2004!) equipment? Shimano has been vague on this matter.
EricaDear Erica,
Since I can do it with Zinn Cycles (I still have customers ordering 9-speed Shimano parts), I am sure that local bike shops can do the same.
LennardHere is what Shimano has to say in response to your question:

Yes, we still support Ultegra 9 (and Dura Ace 9, for that matter). In general, we support any past product until demand drops off or until there is a compatible new version. So, it might be tough to find Deore XT seven speed thumb shifters (unless Rivendell or Euro Asia still have some!), but Ultegra 9 and Dura Ace 9 will be supported for the foreseeable future.
Jasen Thorpe
Shimano American Corporation

A dimple, a dent or....
Dear Lennard,
I started road riding about two years ago. After a short search I ended up purchasing a Trek 1000. After a full season I tore the bike down completely in order to clean and overhaul it. Much to my amazement (horror) I found what looked like a pretty serious dent on the seat tube under the front derailleur. At first I was very upset, thinking the dent must have been caused by the local bike shop, or that the factory tightened the front derailleur too much. I reluctantly ignored it as I had already put over 2000 miles on the bike. Last fall my wife surprised me with a new Trek 2100 road bike for my birthday. It’s a beautiful bike and I’ve been very happy with it. Yesterday I began disassembling the frame for a good spring cleaning and noticed a nearly identical “dent” in the seat tube (same location, size, etc…)! I was mortified! I couldn’t understand how this was possible; the bikes were purchased from two different dealers.After calming down a little and speaking to the LBS, I am beginning to think that this “dent” may not be a “dent” after all. Is it possible that Trek shapes their tubes below the front derailleur to allow for the full swing/shift to take place? Or am I just some type of seat-tube-dented magnet?
PatDear Pat,
This is a question best left to Trek's very own go-to-guy, Dean Gore.
LennardAnswer from Trek

Lennard,
This is a perfect example of support for my personal mantra: Never clean your bike!Seriously, as your writer guessed, that ‘dent’ is quite intentional and necessary.As aluminum became the material of choice for many performance road bikes, the tubing diameters (in comparison to steel frames) increased. This has crowded into the space required for the drivetrain. In this case, that ‘dimple’ in the tube is necessary to allow the cage of the front derailleur to drop the chain to the inner chainring of the crankset. This is especially necessary for bikes with triple chainrings.
Dean Gore
Trek Bicycles

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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.