Buyer’s guide: bicycle geometry

A step-by-step guide to the tubes, angles, and profiles of the chassis of your next bike


We touched upon headtube height and its typical deployment on so-called ‘sportive bikes’ (taller) and racing bikes (shorter) in our consideration of the top-tube. We also described the torsional forces exerted by the handlebar.

Steward argues the that the profile of the headtube can be used to dissipate some of that twisting force. His work with the Madison Genesis UCI Continental team can be seen in the flagship Reynolds 953 Volare, a machine revised three times in response to feedback from the team before being brought to market.

Tapered headtubes are increasingly de rigueur, offering greater real estate for a more effective junction with the downtube – an area subjected to torsional forces from the handlebar

“We downsized,” Steward recalls. “The feedback from the team was that the original tube was a little bit too fatiguing.  Stiffer isn’t always better.  You want the front end as stiff as possible, but you also want the rider’s body to be as far removed from that stiffness as possible. It’s a difficult balancing act.”

The aeroprofiled road bike is an increasingly common sight and Gribaudo’s Lapierre Aircode is set to be the latest to debut in the peloton. The importance of aerodynamics in the bike’s frontal plane places additional emphasis on the profile of the headtube on carbon frames. Like Steward, Gribaudo has also reduced the headtube diameter on one of his designs, the Xelius EFI, but with the purpose of reducing drag, rather than rider fatigue.

For frames of all materials, the tapered headtube is increasingly common, and its purpose is not only to accommodate the equally popular tapered fork steerer (more of which later), but to place additional real estate at the foot of the headtube and so provide a better junction with a similarly oversized downtube.

“The tapered headtube is the sum of its parts,” Steward says. “The larger surface area allows you to run a bigger downtube and also gives room for experimenting with shape, and that’s true I think of any material you use. The forks are a little lighter, a lot stiffer, but it’s also how you use that extra breathing space that a tapered headtube gives you, in terms of the top tube and downtube.”

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