The more super superbikes get, the more problems are created. Let's consider Trek's Speed Concept. Anybody out there got one of these? Anybody try to slip some HED or Zipp race wheels in it? With the wider rim profiles?
It's not that you can't do it. It's that you have to adjust the brake pad width (as with any bike). But that's not so easy on a Speed Concept. The only way you can do this is by taking beveled washers that sit on the brake block out from the inside of the brake caliper, sticking them on the outside of the brake caliper. Do-able. But primitive.
Or, you can put an inline barrel adjuster on your bike, something like these made by Jagwire.
While these inline adjusters can be invaluable, they are not ideal for superbikes that do an exceptional job of hiding cables. Like the Speed Concept.
It helps to have a set of very competent engineers and industrial designers working in the next office over, for your captive house brand. Specialized has this, Trek has this, as do a few other companies. Bontrager is Trek's house brand, and it's Bontrager to the rescue.
The Bontrager RXXXL Aero brake lever has a barrel adjuster built in. This is the fruit of an 'Aha!' moment that I admire, and that drives me crazy because I didn't think of it. This is so simple. It already exists in MTB levers, for cripesakes. If you drew me by the nose and showed me, step by step, what the problem was, and showed me an MTB lever, and a pursuit lever, and asked me the logical conclusion, I just wouldn't have gotten it. There was plaque in my brain that kept the synaptic junction from happening. I did not draw the logical conclusion. I could not make the cognitive leap. Bad Slowman.
Fortunately, the young whippersnappers at Bontrager are not old enough to have that brain plaque build-up, and they did make the connection. Why is this brake lever useful? Because, as stated above, the Speed Concept does such a good job of hiding cables. You can't defer to an in-line barrel adjuster if there's no exposed cable on which to place it.
Furthermore—and even on those bikes where in-line barrel adjusters are possible—it's nice to have a second place where adjustments can occur, when you're looking at a wheel change (training to racing) that might represent a 21mm width to a 26mm or 27mm width. That might be beyond the reach of any single adjuster's capacity.
For those of you who have Di2 on your Speed Concept, well, tough luck. Join the club. I've got one of these in my garage, and my solution was to get some training wheels built that have a rim width matching my race wheels (HED Belgium rims built around 7900 hubs, typical 3X DT stainless spokes, are the training wheels; HED Jet 60mm front and disc rear are the race wheels. All the wheels have rims about 25mm wide).
The RXXXL levers tighten into the pursuit ends via your typical wedge mechanism, which you can only get to—with a 4mm Allen wrench—after screwing out the barrel adjuster entirely, until it falls in your hand. The cable runs through the center of the pursuit bar, not outside and adjacent to it. So, the brake cables will exit the bar near the stem if your pursuit bar can be internally routed, or they will exit a few inches after they leave the brake lever, on the underside of the bar—probably at the point of that last upturn—if that's your preference (refer to the manufacturer of the pursuit bar if you have any questions, and certainly before you break out the Dremel and commence free-lancing holes in your bar). In either case the cable housing makes the entire run, butting up against the lever.
These are not inexpensive levers at $129. But I think they're instantly the best levers going for insertion into pursuit bars. The barrel adjuster is the best thing that's happened to this style of lever since the return spring.
I have not weighed them, but they are light in my hands, the blade is of a comfortable shape, and it's designed to have enough throw so as not to bottom out against the bar.
Now that you're whipped into a buying frenzy, they are not as of this writing available. But I have a set in my workshop, so, they do exist and they do function.
The RXXXL lever will be available through Trek dealers and also through a limited number of non-Trek dealers authorized to carry Bontrager products.
LATE ADD: I'm told the levers are available now. This, as of March 1, 2012. Refer to the Bontrager website.