Many things can slow down the burning speed of a disc.

• The firmware of your burner can be out of date or faulty, causing a slower writing speed. Go to the firmware page and download the latest update for your drive.
• The software can determine that the maximum writing speed could cause problems and therefore reduces the maximum speed. Update the software by going to the manufacturers website.
• The disc or the laser could be dirty, in which case you can use a drive cleaning kit.
• The drive itself may not be able to write at the speed of the disc, check the manual to see the maximum burning speed of the optical drive.

Try all these things and invariably it will improve the results and speed that your discs burn at.