A tube is not a tube. Airtightness. Schwalbe tubes retain air pressure considerably longer. The quality and the material purity of the rubber mixture directly effects the quality of the tube. Each Schwalbe tube is individually inflated and inserted into a mold. This ensures the even wall thickness and excellent air retention. Reliability. Consistent quality control brings with it the security of use: Each tube is inflated at the factory and stored under pressure for 24 hours in order to test the air retention. Group Tube System. The high elasticity and quality material used in our tubes allows a great many tire sizes to be covered. For example tube no.17 fits section widths from 28 mm up to 47 mm. Only an extremely high-quality and reliable tube is up to this requirement. The only tube marked "very good" by the Swiss consumer magazine ‚Kassensturz’. 29.05.2012. 12 tubes in the test. Test winner: Schwalbe SV13 Retains pressure longer! In comparative tests against other tubes (including named brands, own-label brands and “No Name“ products). The result was clear. Over a period of 30 days the other tubes lost nearly twice as much pressure than Schwalbe tubes. Possible reasons: Less butyl content, or lower quality of butyl. Schwalbe is uncompromising in its standards – despite ever increasing world market prices of butyl. All tubes were tested on the same rim with the same tire. Tire size 28” x 1.75” (47-622). Start pressure 5 bar. Loss after 30 days.