One of the most popular exercises in the early days of Slowtwitch was matching you to your ideal tri bike. Geometries of these bikes have really changed over the last half-dozen years. Certain geometries are just gone. Vanished. This leaves riders of a specific type without options formerly available. But there are workarounds.
What you're reading today is the intro to a series of installments matching you to your optimal tri bike. I'll describe the "you" I'm writing about in each installment and then help you narrow your choice of bikes. This is similar to the process I go through during a fit session, like the sessions which occurred over the course of Slowtwitch Road Shows.
My idea of a proper, complete, satisfying fit session is one that replicates during a session what you see, feel and experience out on the road; and then prescribes the bikes that will precisely fit, and that will handle well. Your long or short torso; your fore/aft posture aboard the bike (forward or less so); riding lower in front or less so; all inform the bike that is ideal for you.
There is a conundrum in tri bike fit however. Road and tri bikes makers have changed their approach to geometries. Road bike makers who used to make one road geometry now almost without exception make two or three: so-called gran fondo geometry; middling road geometry; and perhaps a more aggressive road or criterium geometry. You want a road bike? The road bike world is your geometric oyster.
Triathlon, not so much. Here's a data point for you. Felt's IA in size 56, Quintana Roo's PR5/6 in size 54, Cervelo's P2/3/5 in size 56, Dimond's size M and Trek's Speed Concept in size L are virtually identical geometrically. They are all roughly built with a stack of 540mm and a reach of 425mm. This is Trek's geometry, that is Trek is the company that first chose this geometry for its Speed Concept in 2011. You can see in the chart above how certain bikes coalesce around this geometry in size M and L, and as you can see you can throw Argon 18 and Orbea into this mix.
How did this become the de facto geometry? Trek. Its engineers plotted size runs of all the tri bikes on a Cartesian graph, drew a line through the middle, chose equidistant dots along that slope, the stack and reach of those dots were design inputs. A chart showing this is just above. All the other bike companies fell into line and you no longer see these slopes to the left and right of the Trek slope. If you ignore the sizing nomenclature of these tri bikes, and you simply look at their geometries for the purposes of fit, you'll find the opposite of what's been going on in the road bike market: instead of more choice there is less.
What is much less often written about is how to achieve positions that are lower and longer, or taller and less long, using a combination of frame geometry, aerobar geometry, and the things that connect the two (stock or proprietary stems, pedestals and so forth). We also don't talk much about the other elements of the tri bike: pursuit position, for example. I will spend the next several days and even weeks moving through the list of rider cardboard cutouts. Memes. Stereotypes. When you think you've identified yourself, that's the article where I'll describe the bikes you ought to be looking for most closely.