growisofs / -speed

[Bernhard]

hi everyone.

i want to burn a dvd with growisofs and set the writing speed manually.
i read the man pages and know that this parameter should be set via the
-speed option.

however, each time i try to burn my stuff with growisofs -Z
/dev/hdc=/path/to/myiso.iso --option,... -speed=1

the dvd gets burned, however not with single speed but with the standard
speed (4x).

anyone who has a hint for me where i should or could start looking?
thanks a lot in advance.

bernhard