There are a lot of different shapes out there, to suit different preferences. We tend to prefer S-type extensions.
So now it comes down to it. Beyond shifter height and hand width, there's one another preference each rider will have, which is the actual shape of the extension. Mostly, this is a matter of how much of the extension's "curve" you want to have in hand at any given time. We discussed this a bit when talking about the VukaShift extensions. Some riders like the pistol-grip of an S-bend, which puts a little curve in your hand, and puts the rest of your hand over the flat part after the S. Some prefer the sharper upturn of a J-bend, which fills your whole hand with the upturn. And some prefer a straight extension, which requires you to lay your whole hand down on the flat extension.
There's no reason that one shape is preferable over another simply on account of the volume of riding you do. Ironman-distance athletes and sprint-distance athletes alike have been successful with all kinds of shapes. Chris McCormack won the 2010 Ironman World Championships using straight extensions, which are often misconstrued as too uncomfortable for longer distances. Look at how he holds the bars. His wrist is cocked down, but not at an extreme angle. Much of his hand is actually resting on the top of the bar, but the flat shape provides a good point of leverage when needed. The same sort of dynamic can work with an S-bend shape. Personally, I ride S-bends for those reasons. My hand mostly rests on the top of the bar, while my finger wraps around the front of the shifter body in a kind of pistol grip. There's plenty of leverage if I want to pull up on the bar, say for a rolling hill. But most of the time my hand is very relaxed on top of the extension. There's a good picture of Julie Dibens in the gallery below holding her extensions almost exactly as I do.
There's one more piece to this puzzle that I want to illustrate here. And it's a big one. And that's the way in which extensions ought to be gripped. In the neutral position - when you aren't choking up, and just riding comfortably - your hands should wrap around the front of the extension. The fingers wrap around the front of the shifter body in such a way as to produce a bit of a pistol grip. This is ideal regardless of the extension shape. Without that wrapping grip, the wrists often rest at a strange angle, or feel constricted. Take a look at the pros pictured in the gallery at the bottom of this page. Macca, Crowie, and Dibens are all using different extension shapes, on different bar setups with different stack heights. But they ALL wrap their hands around the front of the extensions for a much more natural feel. You can do this no matter what shifters you're using, but the SRAM R2C shifters are a blessing here, because they always stay put, and never end up at a strange angle that could make that grip feel awkward.
Macca, Crowie, and Dibens are using different extension shapes, but they all wrap their hands around the FRONT of the extensions for a more natural feel.
Julie Dibens uses S-bends, which lend themselves well to a little fore-aft movement.
But here's where it gets tricky. If you move forward or backward at all during your ride (let's say you slide back a bit to climp uphill), what happens with your hands? Some extensions are much better suited to "choking up" than others. Straight and S-bend extensions do well at choking up, because their curves (or lack thereof) are gentle. Your hand can easily slide up or down a bit, no problem. J-bends are much worse at this, as they don't have a very comfortable "intermediate" hand position. You're basically locked into one spot. If you slide back, your hands sorta have to stay where they are, which stretches your body out a bit. Some riders have no problem with this compromise, or don't shift around on the bike enough for it to matter.
One attempt to marry the steepness of the J-bend with the adjustment of the S-bend is the so-called Lazy-S-Bend shape. Felt's F-bend is similar. Both of these shapes end with the extensions pointing up rather than horizontally, but they still offer some nice intermediate positions. However, both of these shapes are better-suited to bars with some extra pad stack to put the shifters in the right place. Not the best choice for a Brezza or a Ventus, but perfect for a Zipp Vuka.
So this is a lot of information to take in, and hopefully it wasn't TOO confusing. In summary:
That's the Cliff's Notes version. And obviously every athlete is different, and some people don't fit into well-defined boxes. But in general, the formula above is pretty good, and should work for most athletes.
- Keep your shifters close to the same height as your pads. Up or down a small amount as desired.
- Your aerobar determines what shape(s) will accomplish number 1 above.
- You might want to roll your hands in, just be aware of how this changes your shifter height.
- If you like to shift around while riding, get an extension shape conducive to that.