Originally Posted by Circa 1762
I think you're misconstruing travlerajm's argument. Each person, the theory goes, has an ideal MgR/I, but this ideal MgR/I depends on things like arm length. Therefore, each person's ideal MgR/I is going to be slightly different. Travlerajm has looked at the specs of pro's rackets, and based on the assumption (I think) that pros are likely to have MgR/I's close to their ideal, found that the pros cluster around an MgR/I of 21.0 (although again, there are variations due to things like height). As a result, he's suggesting (travlerajm, correct me if I'm wrong) that you might want to start with your search for your ideal MgR/I around 21.0. He is not saying that your ideal will necessarily be 21.0.
Based on a series of blind tests - for example, setting up two rackets with the same weight and swingweight but different balance, leading to different MgR/I's - I've concluded that my ideal MgR/I is around 21.2. I'm shorter than the average pro (5'8"), so this isn't too surprising. And these were blind tests with the exact same racket model and on the same day, so I'm pretty sure the differences I felt were real. So basically, don't just set your racket up to MgR/I = 21.0 and call it a day. If you have two rackets, set one to 21.0 and one to 21.1, and see which you like better (you should feel a difference). Say you like the 21.1 racket better. Next, leave that one the same, but set the other one up to MgR/I = 21.2. If you still like the 21.1 racket, you can be pretty sure your ideal is around 21.1, and almost positive it's between 21.0 and 21.2. You can continue to do blind testing like this until you zero in on your ideal.
That's nicely stated. Note however that this is no different than saying that each person has ideal mass of the racket, balance and swingweight - which very well may be true. In fact, as stoneage pointed out, combining those three values in some sort of equation (like MgR/I) and implying that that particular equation should result in some sort of particular number (or range) for the racket to be perfect is counterproductive. This is because even though one may have a particular optimal racket, balance, and swingweight (as in one optimal value for each) you lose that fact when you multiply the values. Please read this post by stoneage http://tt.tennis-warehouse.com/showthread.php?t=352140
when he nicely explains (with numbers, not feelings) that there are (quoting) "infinite number of very varying solutions making it impossible to use [MgR/I) as a design criterion". There was also a post somewhere that noted that $15 Walmart racket has MgR/I~21.0 while Head Prestige, widely regarded as one of the best rackets ever, was nowhere close to that value.
But again, you can read into it whatever you believe.