How does gyro ball work my steelix's speed is 49 and is level 65 but for some reason it is not very strong on the rhydon and gravler I face why. does it also have something to do with the opponents speed
It's based on your speed compared to the opponent. So using Gyro Ball against a fast opponent is way more powerful that against a low opponent.
Graveler and Rhydon are fairly slow as well so it won't do much damage (if they were the same speed it would only be power 25). When you have Gyro Ball it's best to make yourself as slow as possible. You would do this with a Speed-hindering nature and no speed EVs.
According to this http://pokemondb.net/move/gyro-ball the calculation is base power = 25 x target speed / user speed so, if your opponent speed is 100, you have base power 51... so small, I think!