I got this because I'm lazy and didn't feel like hand pumping my indoor bike that I have on rollers. To keep the resistance uniform from ride to ride the tire pressure need to be the same. This screws on and inflates quickly. It's a little noisy (okay, it's a lot noisy - but slightly quieter than the one I have for the car) but it inflates at about 0.3 psi per second to it's not on for very long to top me up (bike tire...it would probably take quite a bit longer for an auto tire).