Windows 7 - Slow Bitlocker File transfer

wasnt sure where to put this, so this will do,

basically iv noticed that if im copying files from a non Bitlocked drive to a Bitlocked one, it goes ridiculously slowly, Ie. normal transfer is 20-30MB/s Bitlocker is 4-9MB/s

now im assuming that this is simply because Windows is encrypting it as it goes, i just wanted to check that there is not actually something wrong

Encryption is a slow slow process. Where are you transferring the file? Two different HDDs? Separate partitions? External USB drive?

Seems about right to me. Obviously the encryption is going to add quite a bit of overhead and will slow down the process. Personally, I prefer using True Crypt for my encryption needs as it works across more OS's and offers more flexibility. But what you are seeing I think is totally normal and based on your normal speeds of 20-30...seems about right to get 5-10.