Originally Posted by alfajeffster
It's very much like good pitching in baseball- Steffi had the Nolan Ryan fastball and great and mostly unreadable placement and consistency. Like so much else about her game, it's not something that can really be taught. Her serve was basically a variation on her forehand.
To add to what Alpha said:
From a technical standpoint, Graf's impeccable control and placement on the serve were the result of serving very much like the top men do. In other words, she didn't so much serve with her arm fully extended as she served with an arm that seems bent at the elbow as her shoulders rotate over the ball. This type of motion gave her amazing leverage at the top of the service motion and accounted almost entirely for the precision of her serve.
I tend to disagree with Alpha somewhat on how flat Steffi's various serves were. Her best serve to the AD court was the Twist serve out wide. The spin on that serve is a combination of top spin and slice, top spin to make it kick and slice to take it out wide. This serve was practically indefensible. And, Steffi hit this serve better than anyone in the history of the game.
To the Deuce court, Steffi hit two kinds of slice serves. The first was a more conventional one that landed short in the box and curved out wide; the second one was a ball that she placed in the right corner of the box and that tended to skid through its bounce. While technically the second serve could be described as a flat serve, an examination of the technique that produced it often revealed that Steffi in hitting the ball would slightly come around the outside of the ball.
The only serve that Steffi didn't hit much at all --- I've only remarked on a few instances --- is the topspin serve to the center of the court. When going to the center, she usually preferred to hit flat.
With today's technology, Graf would certainly have as fast a serve as any of the top women. She had better technique and leverage than many of them. A lighter, more powerful racquet would simply have enhanced that advantage. But, even without knowing how many more mph she might have hit, this much is certain. Her ability to serve to the extremes (outwide and down the T) is sill largely unmatched in today's game.