INTRO
...:::<<<PRODUCTION BIKES>>>:::...
KESTREL
ORBEA
FELT
QUINTANA ROO
CERVELO
SPECIALIZED
TREK
CANNONDALE
GIANT
...:::<<<CUSTOM BIKES>>>:::...
CALFEE
ELITE
YAQUI
GURU
...:::<<<INTRO>>>:::...
There are two overwhelming problems smaller riders face. First, it's hard to get the aero bars low enough relative to the height of the saddle. This problem becomes greater as the rider's position becomes more aggressive, that is, as the rider chooses a steeper seat angle and a lower amount of armrest drop.
This problem is considerably worse for triathletes than for road racers, because the bars must be lower for time trial positions, and the aero bars and their armrests sit on top of road or pursuit bars, raising the elevation of the handlebar yet further.
The second problem is the length of these bikes. It's typical for smaller riders to need short "cockpits," only to have a hard time finding them, because shortening these bikes causes shoe overlap (the back of the front wheel intersects with the rider's shoe when the crank is in its forwardmost position; while a little overlap might be okay, the problem can become quite severe).
The culprit in both these cases is the size of the front wheel. The easiest solution to both problems is to replace the standard 700c wheel with a smaller 650c wheel. This issue of 700c versus 650c has reached religious proportions in triathlon, but when you take the religion out of it and simply consider it as a practical matter, tri bikes almost have to be made with 650c wheels in sizes below 50cm if the bike is to be taken seriously.
What the appropriate cut-off point is becomes a matter of fruitful discussion. Perhaps 50cm bikes and up should be made with 700c wheels. Maybe it's 52cm, maybe 55cm. Reasonable people can disagree, but the newest generation of tri bikes bring with them an extra issue that must be solved, and that concerns the rear wheel cutout sculpted into the back of the frame's seat tube. If you want to maintain a longish chain stay for the purpose of smooth shifting and low friction between the chain and the cogs, that dimension is probably in the area of 38cm. But if you build the chain stay to that distance and place a 650c wheel on your bike, how deep will the seat tube need to be in order to still grant you your cutout? That's a design element tackled by a few companies, but not by many.
Most would concede that if you can't achieve your optimized position on your bike, the cutout isn't going to overcome that. So, obvious editorial preference is granted by us to the bikes which resist the temptation to be conservative, and boldly forge ahead with the 650s on their small-sized bikes.
The above having been noted, the steeper the seat angle the lesser the shoe overlap problem. Also, internal headsets help get aero bars a bit lower than otherwise. Spec'ing aerobars with low-profile armrests also helps to solve any problem getting the front of the bike low enough. So, a company spec'ing lower profile armrests on their steep seat angled, internally headsetted bike could make that bike with 700c wheels one or two sizes smaller than would a company not employing such design techniques. All that established, you're still paddling upstream if you're a manufacturer making a 700c tri bike in a 47cm or 48cm size.
