Tyre

Most people believe they have to put much air into their tyres which is not right at all every tyre has its own maximum air size and its own expiring date also.
Tyre have up to about 5 to 5 ½ years to expiry after they are manufactured so either they are used or kept in a store once the 5 years is up they are expired and should be replaced. Also every tyre has its own maximum pressure (PSI) it must contain and this is written by the manufacturer on side of each tyre.
Different vehicle manufacturer ask for different maximum pressure (PSI) for their vehicle so if a manufacturer ask for 42 PSI on a particular vehicle you should not exceed the specified. If you go beyond the maximum pressure (PSI) for the tyres, it could burst the tyre when you are on motion.
If you have a tyre of size 205, 65, 15 and the maximum pressure (PSI) is 42 the PSI the tyre should contain must not be more than 32 or 35 PSI because the minimum space in the tyre must 6 before the maximum PSI so that the air in the tyre can expand. If you have the right 32 PSI in your tyre and you are driving the PSI will increase from 35-41 so this space difference will make your tyres last.
BALANCING OF TYRE
Every tyre whether new or old needs to be balanced because when you buy a new tyre and you mount it on a rim the weight on the left side of the inner side will be different from the outer side unless you balance it.
When your tyre are not balanced properly you will be feeling a lot of vibration and the entire steering wheel will be shaking and this happen when you are driving at 60k/hr and 100k/hr so when you feel this that means your tyres are out of balanced.