The tri bike vs. road bike quandary. Before you even ask the road bike vs. tri bike question, you should have a couple sprint triathlons or duathlons under your belt. For your first couple go-rounds, use whatever you have available to you. Ride your kid's BMX, borrow a bike, buy a $20 garage sale bike. Whatever it takes. You're probably not going to win anyway, so you might as well try it out and see if it's going to be something you're going to enjoy.
When you make it to this point, it might then be the time to ask the question: tri bike or road bike?
There's not one fit-all answer here. Every individual is different. The first thing to consider is: What are you trying to accomplish? Do you plan to compete and/or train for triathlons on a continuing basis? Have you been bitten by the bug, or are you still just getting your feet wet? Are you primarily riding in an effort to train for multisport events, or do you plan to ride on a regular basis with your non-triathlete friends?
We'll get back to the above questions. First let's take a quick look at standard road geometry and tri bike geometry.
Road bikes are made to handle well in a wide variety of circumstances including climbing, cornering, or riding in packs of other riders where space is tight. The seat tube angle is generally 73 degrees and the rider's position is often upright. The hands are positioned on top of the hoods to allow for easy shifting and braking. This position allows for maximum power transfer when pedaling, especially climbing, and quick response time when in a pack of riders.
Tri bikes also handle well but in a different way. Tri bikes are made to go fast while utilizing rider energy efficiently and even conserving energy to some extent (remember - the bike is only 1/3 of the race ). In order to accomplish this, tri bike geometry has a steeper seat tube angle, usually 76-78 degrees. The head tube angle is usually a little less aggressive, the top tube is slightly shorter, and often the front end slopes. The chain stay is also often one centimeter or so shorter. This geometry allows the rider's hips to remain open while riding in the aero position.
Attaining and holding an aero position on a tri-specific bike vs. road bike with clip-on aerobars should be significantly more comfortable, especially for longer periods of time. The forward position requires more energy from the hamstrings when pedaling. Hopefully this will conserve some energy for the quadriceps when the bike leg is over and it's time to run. We also can't overlook the aerodynamic benefits of an efficient aero position.
So road bike or tri bike?
There's definitely a difference between a road bike and tri bike. Will the differences benefit your riding style and ability? Some people can read and relate to the differences between the two geometries and understand how the differences might affect their own riding / training immediately. It might not be so clear for others. It is always a good idea to meet with a certified tri bike fitter and have them evaluate you in person.
For most of us, if you've been bitten by the tri bug and you plan on training and doing triathlons and multisport events, get a tri bike. If you found that you really liked duck hunting, would you go buy a BB gun so you could target practice with your friends that like to do that on occasion?
For your question specifically, I would say consider the above points, evaluate your future goals, and definitely meet with a certified tri bike fitter and get evaluated. Would a steeper seat tube angle be advantageous? Probably. Remember, you still have to get off the bike and run with that 250 lbs. Any energy savings that your quads take advantage of during the bike will benefit you in the run. There's one in favor of the tri bike.
If you were just getting into triathlons and already have a road bike, then sure, by all means throw on a clip-on and go to town. But if you are buying a bike to train for triathlons specifically and that's what you enjoy, why even consider a road bike? You answered your own question. Train with what you are going to race with. Ideally.cross train. Don't trade in that old road bike. Save it...as a road bike. No clip-ons. It's not worth much. It's worth more to you as a bike to cross train on, ride with friends and as a spare
Backgroung image Cortesy of http://www.vo2maxracingevents.co.uk/