Check out some local bikeshops, and look for knowledgable folks who support the sport. Ride some bikes (lots), and discuss the type of riding you'll most likely do. Make sure the fitting process takes all that, and your physical dimensions as the primary concerns, not what bikes they need to get rid of. A good fit is the most important factor in bike selection, followed by appliction and budget.
Here's an opinion I found entertaining on the internet about 650 wheels:
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"It may be appropriate to point out the term "650c" is not a measurement of any dimension on the wheel itself. If you measure a 650c wheel you find it is roughly 58 centimeters in diameter. 650c wheels are also sometimes erroneously referred to as "26 inch". You may also discover the 650c ("26 inch") wheel measures 22&15/16ths inches. As you can see, the wheel isn't "650" of anything, and I have no idea what the "c" stands for. I've been in the bike industry 23 years and I've heard three or four different interpretations of what these numbers mean. In general, they aren't a dimension of the wheel or measurement of any kind. More so, they are a somewhat arbitrary designation for the size of the wheel. Interestingly, the so-called "26 inch" wheels on a triathlon bike are not the same size as the "26 inch" wheels on a mountain bike- which also don't measure 26 inches.
This opens a huge question: What size wheel is right for you and, what is the difference anyway?
Triathlon bikes originally had 650c wheels due primarily to mechanical considerations. It had nothing to do with weight or aerodynamics. On early examples of 78-degree seat angle bikes a larger 700c wheel simply wouldn't fit in the rear triangle. People often ask me what is "faster", a 650c wheel or a 700c. The only truly correct answer is "Neither is faster". Both have minor differences in aerodynamics, weight , rolling resistance and lateral stiffness that almost exactly cancel each other out. "
Review by Tom Demerly.
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So, in the end, since you're new to the sport, find a good bike shop and invest a bit of time in making sure you end up with a bike that's right for you, not a bunch of guys in cyberspace you'll probably never ride with.
Yes, lightspeed makes some very good bikes.