Adjustable geometry frame technology and the quest for the perfect mountain bike
Push-button on-the-fly geometry adjustment on the Bionicon Golden Willow (picture poached from BikeRadar.com)
The evolution of mountain bike designs:
As mountain biking evolved from riding modified cruiser frames downhill into a highly diverse sport with various disciplines, a
One of the early mountain bikes, circa 1976
similar evolution followed in bike designs, frame types and suspension technologies to cater for the various riding styles and disciplines. One of the most interesting aspects of such evolution can be see in in the areas where the riding styles overlap. That is, while purpose-built bikes serve the goal of optimizing frame design, suspension technology and build spec to a very specific type of riding (such as ultralight bikes for endurance racing, burly big-hit rigs for downhill and freeriding), the widest spectrum of recreational mountain bikers mostly ride ” a bit of everything”, and as such would like to have a bike that rides a bit of everything (almost) equally well. Nowadays, there is a strong trend in the industry to build such bikes.
Understanding frame geometry:
Frame geometry affects two things: bike fit and handling (and both are interrelated). You will want to get the correct frame size for your own 
height and other measurements, but you also need to think about the type of riding you mostly do and choose a frame design that most closely matches your preferred style (most beginner riders won’t give much thought to this initially, since they have not ridden enough to define a “riding style” yet”). On a spectrum of riding technical/endurance difficulty that goes from light trail riding on relatively flat and smooth terrain to super-technical, shuttle-assisted downhill runs or day long all mountain combat rides, most of us are somewhere in the middle. We want to earn our descents by riding all the way up, we want to enjoy the way down and take technical lines with confidence, and we want a bike that allows us to do both things well.
Component specs and riding gadgets vs. truly adjustable frame geometry:
It is possible to change your bike’s ride characteristics and handling with parts that do different things to elements that affect how the bike 
handles. For example, modern forks and shocks now offer adjustable travel, lockouts, and various other suspension tweaks. There are seatposts that allow you to change saddle height at the touch of a button or the push of a lever, no dismounting needed. Stem length and handlebar height and width can be changed. Parts that allow you to play with your bike’s behavior have been around for a while now, but real “on-the-fly” adjustable frame geometry is something that is relatively new.
Two good examples of bikes that use such technology are the Bionicon Golden Willow and the 2010 Kona Cadabra. I won’t write about the bikes and the technology since you can get all the information you want about them, and others, elsewhere online, but for a quick primer on the adjustable technology features on each, watch the two short videos below:
The Bionicon Golden Willow
The Kona Cadabra
Update (10/8/09): Cannondale demoed Simon, a very interesting electronic fork travel adjustment at Interbike 2009.
Cannondale’s “Simon” concept explained by Stanley Song, their advanced projects guy:
Final thoughts: Adjustable geometry and The Perfect Mountain Bike:
There is no such thing as a perfect mountain bike. Not yet at least. However, adjustable geometry technologies are getting us closer to such perfection where the riding disciplines converge. Mountain bikes are getting simultaneously lighter and tougher. Advancements in components and suspension technologies are gradually mainstreaming “do-it-all” rigs.
Regardless of suspension technology and component bling, it all boils down to enjoying the sport with whaever rig you can afford. Ride more, ride often and develop your mountain biking skills. When the time comes to upgrade your bike or buy brand new one (with adjustable geometry!), you will have the skills and endurance to enjoy riding it to the most.
