I have a Centurion Ironman Expert and I was wondering what the drop out screws are for and is there a specific adjustment or position that they should be?
With a derailleur equipped bike I have always set the the screws to allow maximum rearward positioning.
You can use the screws to make up for any misalignment.
The use for screws is if you have a single sprocket (fixed or 3 speed hub etc.) is, you can set the screws to position the wheel to give the best chain tension.
Older bikes with horizontal dropouts sometimes had more variation in how well the two dropouts were aligned. So if you just pull the wheel all the way back into the dropouts, it would end up at an angle in the frame. The screws let you set where the wheel sits when you pull it in so you don't have to tinker with alignment. As cyclerUK says, as far back as possible is a good general rule of thumb, though as long as the QR skewer is getting a good amount of dropout under it, it doesn't matter too much where it sits.
