|A Terry Classic in the wild.|
Here's my opinion in a nutshell...They're good quality bicycles, but the two different wheel sizes? Come on.
Lest you think I am among the uninitiated mouth-breathing masses, I will claim that I have a great understanding of exactly why Georgena Terry et al did this to their bikes. Smaller frames, which tend to get bundled under the label of "women's frames" but the same could be said of any small frame, are difficult to design well around your standard 700c road wheel. Think about it...as the frame shrinks, the wheels stay the same size. At the ludicrous end of the spectrum you end up with a tiny frame and monstrously proportioned wheels in relation to the frame. If we were to be more realistic we would be more interested in how the increasing size of the wheels in direct relation to the frame affects frame geometry. The big concerns that you hear about relate to seat and head tube angle. In order to get the bicycle to fit right, and retain a short-ish wheelbase, the seat tube of a small bicycle equipped with 700c wheels needs to become steeper, which affects fit along the top tube. As the frame shrinks toe overlap with the front wheel becomes a concern, which leads to manufacturers using slacker head tube angles. This in turn affects steering and handling. And all because you, ignorant designer of women's/small person's bicycles that you are, felt somehow beholden to the 700c wheel size. Enter Georgena Terry and her unique brand of bicycles which use two different wheel sizes on a single bike; a 700c wheel in the back and a smaller wheel (typically 650c or 24-inch) on the front. Terry also manufactured a line of bicycles that used two smaller wheels. I've seen both a touring bike and a mountain bike designed by Terry that used 24-inch wheels and they were both really nice bikes, just built for a very small person.
This solves a lot of the problems associated with building smaller frames but it introduces obnoxious maintenance and bike-ownership issues, like having to carry two different tube sizes. Not a huge issue, but kind of a pain. Another longer term and more expensive issue arises when you either ruin your front wheel or get it stolen. There aren't a ton of options out there for high-quality 24-inch road wheel, or even 650c road wheels. This set of circumstances means that you are almost certainly buying a custom, hand-built wheel from someone like me. I'm happy to do this for you, we have the tools and the technology, but it's going to cost a bit.
I will stake my claim and alienate thousands of people when I say that a smaller frame is better designed when it uses a pair of smaller wheels. Everything in proportion, right? There is absolutely nothing wrong with a small road bike using 650c wheels, and it most likely means that there is a greater chance that the frame will be designed well and have the correct angles and sizing that will make it handle like a road bike should. This even has a more recent application to the field of bicycle design when you start considering the steadily growing field of 29er mountain bikes. 29-inch wheels are gigantic and, I'm sorry to say this, they have no place on a 15" frame. This is essentially the same issue (giant wheels on a tiny frame), but using an even bigger wheel and trying to fit it onto a similarly tiny frame.