You can't say you haven't been warned. Well, maybe not warned, but at least warmed up. In a series of articles written for this online portal and for Inside Triathlon's print publication, I've bitten off certain elements of tri geometry to write about.

Examples of these articles are the recent discussion of dual-use timed race bikes; an analysis of steering geometry; and if you don't include the recent articles, and don't mind going back a few years, there's an overview of tri bike geometry in general terms.

But I think it's time I stick my neck out a little and just print the danged geometries that I think bike companies ought to be using for the tri bikes they build. I'm neither brave nor contrary in doing this, because 2007 marks the year bike companies are coming toward F.I.S.T norms.

Without further ado, here's tri geometry the way I would do it if I were making production bikes.

Bikes that deviate from the geometries above will ride just fine, as long as the deviations are sound. A person might choose steering a bit more sprightly than that which is indicated by the steering geometry above. One might favor sitting slightly further arrears, or slightly more forward. But there are tri-specific truisms that are forcing their way into designs, and I'll demonstrate this further below.

First, though, there are some things I ought to point out. I'm assuming that bikes are going to have internal headsets. Those not employing this design ought to have head tubes about 2cm shorter than those listed above (to make room for the head parts).

Also, I should make a note about calibrating head tube lengths for aero bar styles. On paper, before you settle on a specific head tube length, you need to take a stand regarding what style of aero bar you'll use. Low profile armrests do not sit a large distance above the pursuit bar, high profile armrests do. You can lump aero bars into two categories. Profile Design, Syntace, Zipp and Easton all make aero bars with high-profile armrests. Hed, Oval, Blackwell, Visiontech all make low-profile armrests. The difference between the two themes accounts for about 3cm of head tube length.

My head tube lengths above about split the difference between high and low profile aero bars, and this would allow somebody to use the aero bar of his choice, and normalize his armrest height through the use of headset spacers and/or stem pitch. For example, I could simply employ a stem parallel to the ground instead of one angling 12 degrees up from horizonta. This would suck up most of the extra height that a Profile Design Cobra T2 gives me, were I to sub this in for the Visiontech that might come standard on the bike.

But I wouldn't fault a bike company that used head tubes up to 2cm taller or shorter than the ones I'm suggesting above, it's just that if you do this, you're closer to locking your customer into one style of aero bar or the other.

I've chosen 58cm as a bellweather size to use for comparison, and I'd like to show the geometries chosen for some new '07 bikes.

Note that certain of these companies allow for a forward and rearward placement of the saddle. Two geometries notwithstanding, I think what we'll see below is that the bikes are all built for the steeper position, and the rearward saddle placement is there for what I would term the stubbornly uneducated retailer. Accordingly, the geometries below assume the saddle's placement in the forward of two positions (Felt and Cervelo), or the center of the singular position, should only one position be offered (as is the case with QR and Giant).

ST = Slowtwitch geometry listed above
GNT = Giant Trinity Alliance
FLT = Felt's new '07 line
QR = Quintana Roo's new '07 Kilo and Tequilo geometry
CRV = Cervelo's existing P3C geometry

The reader will note an obvious convergence in geometric thinking. Head tube angles, trail, head tube lengths, top tube measures, seat angles, all are quite similar. Cervelo has a slightly shorter wheelbase, but that's due mostly to its shorter chainstay. I suspect that our "Slowtwitch" geometry shows a longer wheelbase than the others simply because we're using a different wheel radius input, that is, depending on the tire profile the radius might be anywhere from 333mm to 340mm and it'll impact your outputs for trail, front/center and wheelbase.

You can see the trend represented in the bikes profiled in this article and, trust me, it's the same regardless of the size bike I choose. Compare these geometries to those of some of the dual-use bikes to which I refer in an earlier overview -- bikes that are made in what one might call a more European mold. Keep in mind these dual-use bikes must serve both triathletes and the time trialers forced to conform to the UCI's rules.

It's debatable, though, whether the bikes need to change overmuch in their configurations to be ridden under the UCI's rules, since Cervelo's P3C is ridden to great success in timed bike races and its geometry is very much like these other newer-generation bikes profiled here.

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