ONLINE Speed Trainer
When asked, most great guitar players can tell you that the best way to develop speed is to start at a low tempo and gradually increase the number of BPM (beats per minute). Below is a speed trainer which increases the tempo by 1bpm from 40 to 320bpm after every four beats. The reason why this works well is that such small changes of tempo are hardly perceptible, so you can start playing whatever that is that you're practicing at a tempo that feels comfortable and after a while hit some serious speed while preserving that comfort and control that you had at the beginning.
Below there's another version with double bass playing 16-th notes.