DVD recorders do not have recording speeds, like a VCR, but Recording Modes. DVD Recording modes can be used when recording from outside sources, such as a VCR or Camcorder. The DVD Recording Modes enable the user to put more video time on a DVD disc by increasing the amount of compression in the video signal, not changing the rotation speed of the disc.
The downside to putting more video time on a DVD disc is a loss of quality in the recorded video and possibly decreasing playback compatibility on other DVD players.
Disc Writing Speed, on the other hand, has no relation to how much time you can put on a DVD disc, but refers to how fast you can dub from a computer or DVD recorder hard drive, or from another disc to a recordable DVD disc. Disc Writing Speeds are used when making copies of video or data from internal pre-recorded sources, residing on a PC, DVD Recorder hard drive, or another disc.