Anyway, later in the evening I decided to change the inner tube, so I could use the bicycle tomorrow (today). I knew that I had a spare tube at home, so it should have been a task of 10-15 minutes. But then I noticed a problem - the old tube`s valve was in the bicycle standard, while the new one - in the car standard (that is - significantly wider). And the hole where the valve should go on the rim of the wheel was also in the bicycle standard, so my new inner tube just didn`t fit in. What options did I have? I decided to repair the old tube, yet it proved to be impossible as its problems (so it appears at least) were not because of a hole but because of a malfunctioning valve, and there`s no way for me to repair a valve. So I could either buy a new matching inner tube the next day or make the valve hole bigger. As I hate going to work by public transportation in summer, I chose the first option. With the help of a big screwdriver and a hand-drill over 20 minutes I managed to make the hole big enough for the valve to fit in. So now I have a car standard inner tube on the rear wheel of my bike, and I`m happy about it.