The portable tire pump does not just save you the inconvenience of going to the filling station or the few cents you may be charged for using the filling station pump. As would be expected, it is generally slower than its filling station counterpart due to the size of its motor. Those that pump quickly tend to drain the battery fast, and even if the engine is on the battery may not recharge fast enough. All things considered, it tends to give better accuracy for two reasons:
1. You have the luxury of checking your tire pressure in the morning before you drive off. A tyre that has been working or exposed to the sun tends to have higher pressure that a cold one.
2. It is better maintained. It does not go through the rough handling such as being banged, dropped and poorly stored as its filling station counterpart experiences.
Benefits accrued from having the correct tyre pressures are longer tyre life, better handling in adverse conditions, improved fuel economy, and most importantly fewer accidents. By the way, the recommended tire pressure can be found at the sticker on the driver's side door, the owner's manual and not on the tyre wall.
Here are some of the things you need to take into account while choosing a portable tyre pump:
Ease of use: The cable must be long enough to reach all tyres. While you think this should be obvious, not all pumps meet this basic criterion. A cable length of 9 feet would be sufficient. Still on this point, you should be able to use it without needing someone to hold the pump nozzle for you or help you remove it from the tyre valve. Quite a number of well known brands are not exactly user friendly and tend to be either too loose or too tightly gripped at the nozzle that keeping the nozzle on the tyre valve or even removing it becomes an unpleasant experience.
Capacity: It should have a pressure range of between 0 - 150 PSI. Another measure of capacity is how quickly it fills up the tyre. Just like anything else you buy do not take the seller's word for it. Search the net reviews about the product in places like amazon about its performance before you make a commitment.
Versatility: you do not just want a "one trick pony". Most pumps come with adapters for bikes, air mattresses and football. Make sure these come with your portable tyre pumps.