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June 17, 2007 4 Comments
Tubular, or sewup, tires provide the ultimate ride for a modern road racing bicycle. Because the tire is sewn together around the tube considerable weight is saved in the tire’s construction -- no beads of sturdy wire or cord are needed to grip the rim, and in the rim -- simplified because the tire is bonded by cement. Its use is critical to the reliability and performance of the system. Over 100 grams are usually saved per wheel between equivalent tubulars and demountable clincher wheels.
Because the tubular wheel system predates our era of user-friendly, danger-free engineering there are numerous idiosyncrasies related to their use that you might not expect.
There is no adequate way to “teach” all the important practices and exceptions that one needs to fully utilize tubular tires. However, we wish to state some of the more basic and obvious do’s and don’ts. Just remember, only a lengthy and detailed “apprenticeship” to a practicing expert in a club or team setting will cover the many considerations you should know.
Few technical skills in cycling will bring you so close to the experiences of our forefathers than mastering tubular tires. And little else in equipment can so transform and invigorate your riding.
An inflated tubular grips the rim with a powerful contraction upon inflation but your security depends almost entirely on the integrity of the cement bond between tire and rim. Both the rim and tire must be absolutely clean before gluing so, if in doubt, use a strong soap with plenty of water to wash both. Let them dry thoroughly before the next step.
Pump some air, perhaps 5lbs, into the tire. The very first inflation of a latex-tubed tire should proceed very slowly. Otherwise there is a small risk the tube will become ruptured. Now mount it on your rim, beginning at the valve. The last little bit is a struggle, serving to remind you what lies ahead. Once mounted, fully inflate the tire and let it stretch for most of a day. When you are ready to glue, demount the stretched tire. It will now be much easier to mount a second time.
Make yourself a small bottle of lacquer thinner in which you can store an acid brush between tire gluing sessions. Put the pristine-clean wheel in a stand and run a bead of tire cement around the rim. Immediately after, use your acid brush, with a slight amount of the thinner, to spread the cement out across the entire concave surface of the rim. Step away and allow the cement to dry. Keep the wheel away from any unnecessary dust or smoke.
Now coat the tire base tape with cement. This is best done by putting enough air pressure in the tire to cause it to “roll over” on its side, exposing its base tape “belly” to the sky. Run a bead of cement around the tape following quickly with your brush. Stroke the cement into the base tape fabric covering the whole surface from edge to edge. This coat must also dry and only 15 minutes may be required in hot dry conditions.
Shortly before mounting the tire, add a second light coat to the rim but do not wait for it to dry. Let enough air out of the tire so it is round but soft. Carefully place the tire valve through the rim valve hole as the wheel stands on the ground before you. Now, with valve at the top, lean over the wheel grasping the tire to either side of the valve. Use your hands to place the coated base tape on the rim and your body weight to stretch the tire on each side of the valve, pulling it down.
By the time you reach the last difficult section of tire you should be directly opposite the valve with enough tire slack to easily roll the final section aboard. Put 60lbs into the tire and make minor adjustments to its position. Spin the wheel and admire your handiwork. It will be somewhere between one and five hours before the tire is safe to ride.
How will you know if you have done it correctly? Only by asking an experienced race mechanic to test the bond by hand. Basically, if you can demount a tire by hand without tools you do not have an adequate bond. That sounds crazy but the heat generated by braking, the side forces of cornering, and the uncertainties of adhesives mean you cannot trust anything less than a “total” bond. If you need to remove a tire use a dull pry bar, like a screwdriver, to very gently pry a section from the rim. Pass the lever completely under the tire and then force it carefully around the rim to break the rest of the bond. A round shaft screwdriver blade works best as it can be rotated as you force it around the wheel, separating the tire from the rim.
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