After work, practice round. As usually, Christos Politidis from Ludwigsburg is in his garage and takes his stand pump to shortly check the tyre pressure. With the forth pump stroke there is a loud fizzling, then the pump head fell down. When putting the pump head back on the valve the passionate cyclist was quite amazed. The valve was actually sticking to the pump. It had completely loosened from the inner tube.
A few weeks agao TOUR editor Manuel Jekel erected a newly mounted wheelset next to his desk, when a tremendous bang made the colleagues startle. The explosion was so great that the plastic covers of the hub cracked and were thrown several metres through the office. The search for the causes revealed a rim with a minor oversize and a thick rim tape as well as a tightly mounted tyre. The latter had been forcefully mounted by Jekel, thus weakening unconciously the inner tube. You don’t even dare to imagine what could have happened, if he had set off immediately.
Maybe something similar as happened to Reinhold Grewe from Berlin. At the spring training camp the 48-year-old racing cyclist took a bend at about 50 kmph, when the tyre suddenly lost air making the bicycle including rider slid over asphalt. The inner tube had burst on the rim side at the seam of the reinforced valve area. Grewe rode a rim without spoke holes and thus without rim tape as well as an about eleven year old, probably outdated inner tube.
Three examples of many proving that tyre punctures firstly occur still frequently and secondly can have manifold causes, besides the thorn or the broken piece of glass piercing the rubber from outside: defective designs, sloppy mounting or bad quality assurance, i.e. sharp valve hole edges that have not been deburred, too narrow rim tapes or rim tapes made of unsuitable material as well as rims and tyres of improper dimensions. Defects as a result of too big valve holes, of rims without spoke holes and of asymmetrical rims are relatively new.
With rims having a closed base a rim tape seems superfluous at first sight, indeed. For this reason many manufactures do without this part weighing only a few grams. For this reason, however, there is no protection of the inner tube at the edge of the valve hole. This bears the risk of the valve being actually cut out or of the inner tube being overextended in this area during inflation, which can make it burst later on during the ride.The disadvantage of strongly asymmetrical rim profiles is that the spoke holes in the rim base are so close to the edges that they are not reliably covered by the rim tape, the sharp edged spoke holes being thus a risk for the sensitive inner tube. In such a case an exactly fitting and glued rim tape would be absolutely necessary. Furthermore, we have observed that this problem becomes even more acute by old inner tubes that have become brittle. TOUR recommendation: For safety reasons do change even sound inner tubes, especially light butyl tubes at less than 65 grams, after three to five years.
This inner tube was mounted on a smooth rim without rim tape and is burst in the transition from valve reinforcement and valve.
A too big and sharp-edged valve hole in the rim cut out the valve from the inner tube.
A too narrow rim tape has shifted to the side. The inner tube pushed through the spoke holes until it burst in one area.
Author/Photos: Dirk Zedler