It is easy to buy a bike because your salesperson says it is “right for you”, but what does that really mean? What it means to me, is that your bike can be positioned to provide a comfortable, fast ride for YOUR body. Every triathlon bike manufacturer and many road bike manufacturers provide geometry specifics via the web, which vary between makers/models.
If you want to be sure that a road bike or a Triathlon bike is going to enable the most optimum performance, comfort and minimal chronic stress on the body then get a professional sizing done prior to purchase and then buy with confidence. This is even more crtitcal if you are getting a custom frame built. Any reputable frame builder would require a sizing be done and the establishment of stack and reach as a mimimum to work with. For the best in professional sizing we recommend 3D Bike Fit of San Francisco. You can get a Pro Sizing for a custom bike build or utilize their in studio custom 3D Sizing protocol for a road bike and Tri/TT bike and each will provide everything you need for an informed decision.