Over the last 20 years, we have been building road bikes and tandems with 700c, 650c, and 26 inch wheels. A 26 inch, or a 650c wheel is about 1 inch smaller (about 2 inches smaller with road slicks) in diameter than a 700c. On smaller bikes, that 2 inches is a big help in building the perfect size without sacrificing performance. 26 inch wheels are not exclusively for small bikes though, I am 6 feet tall and I ride a tandem with 26 inch wheels. Often, a customer will ask for the larger size wheels, even when the smaller wheels would allow us to build the bicycle to a more optimum geometry. It seems that some people believe that larger wheels mean faster wheels. Some people think that because 700c wheels are the 'standard' for road bikes, they must be better.
In our shop we've been building bikes for over 30 years. Over this time, we've seen the rise and fall of many standards; Down tube shifters, center pull brakes, U-brakes, Suntour componentry, dual articulation derailleurs, side pull brakes and 27 inch wheels just to name few. These features were 'must haves' in their day. A sales person wouldn't dream of even showing a new bike to a customer unless it had at least some of these features. But now, one would have to search to the ends of the earth to find a current, 2004 model, high quality bike offering any of these features. These features were standards in their time but gave way to either newer technology, or, in some cases, the standard fell back to the predecessor. In any case, the standards took a long time to change. One standard that has more or less held for the last decade are wheel sizes. The 'standard' road bike has 700c (the successor to 27") wheels. The 'standard' mountain bike has 26 inch wheels (inherited from the old balloon tire cruiser).
It seems that many people make a connection that goes something like this......
"Mountain bikes are slower than road bikes, and mountain bikes have smaller wheels, therefore, 'smaller' wheels equal 'slower' bikes, at least on the road." Using this same logic, we could assume that a monster truck is faster than a Porsche, or a School bus is capable of higher speed than a Jaguar E-type. Do these assumptions sound ridiculous to you? If not. I've got a swamp I'd like to sell you. The engine in the monster truck is more powerful than the Porsche's engine. The wheels are certainly larger (2 to 3 times larger). What makes the Porsche faster than a monster truck? For one thing the Porsche is lighter. It is designed with more responsive handling. But most of all it has gears that will accelerate the car to higher speeds even with the smaller wheels. Can the same be true with a bicycle? The answer is yes. Road bicycles, regardless of their wheel size, are designed lighter, more responsive, and they are geared for the road.
Wheel size has nothing to do with the speed of a bicycle on the road. A road bike, or tandem bike with 26 inch wheels is geared to travel at the same speed as a bike with 700c wheels. The answer lies in gear inches. Gear inches is a means of measuring the relative number of inches traveled forward per crank revolution. The higher the 'gear inches' the more distance traveled per crank revolution. A road racing bicycle in its fastest gear, is usually geared to about 110 'gear inches'. This is true no matter what size the wheels are. My road bicycle has 26 inch wheels, and my top gear is 112 inches. If I have a 112 inch gear, and I'm pedaling at a cadence of 90 revolutions per minute, I will be traveling forward at about 31 miles per hour no matter how big my wheels are....same cadence, same effort, same calories burned, same panting and wheezing, no more or no less fun. Below are a few standard gearing patterns that are used for 700c and 26 inch road wheels;
700c wheel 52/39 X 12-24 (116 inches high gear) (43 inches low gear)
26 inch wheel 54/40 X 11-23 (122 inches high gear) (43 inches low gear)