When you pick up a club, you feel the club’s weight and, depending on where you’re holding it, you can get an idea of its balance.  Swingweight is a measure of the club’s balance about a point precisely 14” from the butt end of the club.  However, when you swing the club – especially at the transition from the backswing to the downswing and during the uncocking of the wrists – the resistance you feel is due to the club’s inertia, or more specifically, its moment of inertia (MOI). 

Let’s consider a common scenario.

We replace a standard grip with a midsize or jumbo grip.  When we do, the club gets roughly 10-15 grams heavier, but the swingweight actually goes down –  probably by a couple of swingweight points.  That’s because swingweight is a measure of balance, not total weight.  More weight at the grip end lowers the swingweight.  But we don’t want D0, we want D2.  So we add a little weight to the head and, voila, our club is D2 once again. 

Now let’s take that club to the range and swing it.  Does it feel the same?  Of course not, it feels heavier – perhaps much heavier!  That’s because the club with the larger grip and extra head weight takes more effort to swing.  The club’s MOI has increased significantly – just a little due to the heavier grip, but mostly because of the extra weight at the head.  In fact, if we’d just swapped grips, we probably wouldn’t even notice a difference in the way the club feels when we swing it.  That’s because the MOI is affected very little by changes in weight close to the butt end.

The bottom line: Constant swingweight does not mean constant swing feel.  If a set of clubs all have the same swingweight but different lengths (which all traditional sets do), they will not, they cannot, require the same effort to swing.  As a result, your swing must compensate slightly for each club in the bag.