TriRig’s Nick Salazar knows a good design when he sees it. So do bike manufacturers, and Cervelo, Scott, Advanced Sports (makers of Kestrel and Fuji), Ridley and BH all use Ritchey’s seat post motif for their triathlon bikes. This seat post clamp hardware has a 10mm hole drilled longitudinally right through it. Along with a couple of other companies (XLAB's Delta Sonic, Profile's RM-10) TriRig uses this thru-rail hole for its new Beta bottle carrier.
There’s nothing beta about the Beta, it’s ready to go right now, just in time for Kona. There is a number of holes in the Beta, at set increments, allowing the user to extend the beta further out the back of the system, or closer in, to conform to the rearward protrusion of the saddle.
Mounting this system may take a little doing because you can’t mount it after the saddle is affixed to the seat post unless you’re lucky enough to have a saddle offering vertical access to the bolts that hold the Beta in place. Dash, Adamo and other split-nose saddles often give you access. You'll know as soon as you try to gain access to this pair of vertical bolts that mount down through the top of the Ritchey seat post hardware. If you don't have access, hold the Beta up to your bike in profile and take a bearing on how far that thing needs to stick out the back of the seat post. You want the Beta's clamp, with cage(s) attached, as close to the back of the saddle as you can get it.
You decide on either the 63° or 45° carrier, and what you choose might depend on the bottle size you’re going to carry. A big 25oz bottle might require the 45° unless you want to hike your leg way over some tall bottles when mounting and dismounting your bike.
The Beta isn't simply a nice system, it's the only system (to the best of my knowledge) that works with this Ritchey post that is made to accept two cages. You can't use this system without the Ritchey post, but 700 or so of the bikes in Kona will have this seat post system.
The Beta sells for $68.99 and is available from TriRig.
One thing that makes me not like behind-the-saddle carriers is the propensity for bottles to fly out the back of them like depth charges. The way to keep that from happening – and make me like those carriers again – is a cage that securely grabs the bottle like it’s the last water on earth. TriRig’s Beta is nice, but only if it’s paired with a cage like TriRig’s new Kappa. This cage joins XLAB’s Gorilla as the cage you want if you’re resorting to rear bottle hydration.
TriRig says the Kappa is the "The strongest-gripping cage on the market” and at $52.99 compares well to the XLAB Gorilla, which sells at a variable price (depending on the store) but is in that general vicinity.