@Uho: Nope, sorry. Hate to be the bearer of bad news, but as Ghol, opalo, and JGMcI have said, 'demand' is singular.
You say 'There are a number of bicycles' because 'a number (lot, variety, etc.) of' is a fixed phrase that means 'some,' 'several,' or 'many.' It might help to think of such phrases as being special invariable or indefinite counting expressions, somewhat like 'ein paar.' You construe them as an adjectives answering the question 'How many/much?' rather than as nouns answering the question 'What/Who?'
However, you say 'There is a demand for bicycles' because 'demand' is not a special counting expression, just an ordinary noun that happens to be singular. So, for example:
• There was much demand.
• There were many orders.
• 40% of the demand was for wine, 30% was for beer, and 30% was for soft drinks.
• 40% of the orders were for wine, 30% were for beer, and 30% were for soft drinks.
BTW, note that English, unlike German, doesn't put a space before symbols of measurement that aren't alphabetic abbreviations: 40°, 30%.