Hi I just bought a hybrid bike btwin riverside 3. It has 28 inch tires and weights 15kgs. My weight is 75kg. How much should I inflate my tires. And how often should I refill?
For the correct tyre pressure, you should have a look on the wall of your tyre.
Obviously different tyre manufacturers will mould their tyres differently, but here is an example (one of my tyres, I have raided the flour cupboard to make the marking stand out!):
So we have: Max. LuftDruck / Inflation: 4.5 Bar / 65 PSI
These tyres are Continental, a German manufacturer, and the word LuftDruck means (surprisingly) air pressure.
Note that this tyre is on my offroad bike (26") so will probably show different values to those on your hybrid (I'd expect 75psi or thereabouts, but you should check).
For the frequency you should check the pressure: some people will say every ride, I generally go for every week or two for the bikes I ride regularly, every ride for those I don't.