MAKING THE BEST POSSIBLE BIKE FRAME CHOICE
Do I Need Custom Geometry?
It’s hard to quantify how many people need custom geometry (custom frames). How many would like to have them is probably an easier question to answer. Only a very small percentage of the riding population actually needs a custom frame, and of that population we can identify two types of persons:
1. Those who need a 650 (smaller circumference wheel) bike
2. Those who need a custom 700 (standard circumference wheel) bike
While they may seem unfashionable, 650 bikes fill a much needed niche in the world of cycling. 650 bikes were popular in the early to mid-90s among triathletes but became extremely passé among road cyclists. In fact, for road riders, 650 bikes didn’t become unfashionable for any reason other than the industry as a whole found it too costly to manufacture a bike that a smaller percentage of the population would choose to purchase. Moreover, with the advent of sloping top tubes and so-called compact geometries, it became easier (and cheaper and more profitable) for manufacturers to fit a greater number of riders on a smaller selection of frame sizes. As manufacturers stopped offering 650 frames, parts manufactures—in particular wheel manufacturers—cut back or stopped production of 650 wheels altogether.
All these economic considerations trended towards the fate of the 650 bike, and along with that fate came a stigma: the 650 bike became seen in some sense as inferior or for less-than-capable riders. Nothing could be further from the truth. In fact, in the 80s and early 90s, it wasn’t at all uncommon to see even diminutive European professionals (like Chiappucci) riding a 650 bike.
So why ride a 650 bike? In principle (and as a matter of a very high-level explanation), smaller riders tend to be candidates for 650 frames. By smaller, we mean persons in stature under 5’5”. Certainly, not every person 5’5” or under needs a 650 bike, and in fact we’ve seen persons 5’10” for whom a 650 was the best option.
A 650 bike enables two things for the rider whose physiology demands such frame qualities: a shorter top tube and a steeper head tube angle. One problem with 700 bikes for smaller riders (or even medium sized riders with very short torsos) is that the top tube can only be so short (circa 51 centimeters) before the rider will start to experience toe-overlap. Toe-overlap occurs when the axle of the front wheel is sufficiently close to the rider such that the rider’s toe in the 3 o’clock position is susceptible of rubbing the front tire. With a top tube length in excess of ca. 51.5 centimeters, the possibility of toe-overlap is diminished, so long as the rider’s physiology and the head tube angle of the frame are pretty standard. However, some manufacturers try to accommodate smaller riders by making their bikes with 51 cm top tubes or shorter by slacking the head tube angle, which effectively pushes the front wheel away from the rider. While intuitively this may seem feasible, the result is a bike that handles like a chopper, not a high performance machine. It also makes for bikes that are unstable at high speeds, which do not descend well, and are not agile.
As there are very few frame manufacturers building production 650 frames, custom 650 frames have become very popular. But why would one need a custom 700 frame?
Candidates for custom 700 frames are, like those for 650 frames, restricted to custom geometry because their physiologies cannot be accommodated by standard frame options. For instance, medium height to taller individuals with extremely short torsos may need a 650 bike with a top tube short enough to accommodate their upper body. Additionally, the head-tube height on a production 700 frame that otherwise has the right dimensions may be too short. In such cases, “stack height”—a series of carbon or aluminum spacers placed on the steer tube of the fork between the bottom of the stem and the top of the head tube—is an option to raise the front end. But, there are limits to this, typically 3 or at the very most 4 centimeters is acceptable.
Of course, other considerations may drive a consumer towards a custom frame. For instance, a tall but lanky rider may prefer a frame that is not as stiff as production options; conversely, a more petite rider may opt for a stiffer frame than is offered by production options. For professional athletes who focus on one discipline, e.g., the time trial, a custom geometry frame is sure to enhance the rider’s performance by precisely positioning them for optimized muscle usage, critical prolonged power output, maximized oxygen intake and blood circulation, and reduced chance of joint damage.
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