Oh man, there are a lot of wheel sizes to chose from nowadays. For mountain bikes you've got 3 choices, 26" 27.5" and 29" and on the road you've got 2, 650c and 700c. The mountain hype machines for each size are so loud, it's hard to decipher what's real and what's just loud noises. While the road debate is barely existent. How does one decide on a wheel size? Does it even matter?
Yes, wheel size does matter. I think we can agree that the purpose of the bicycle machine is to efficiently turn human power into the maximum amount of forward zoom. It has been proven that bigger wheels do equal bigger speed. SO it's settled, but the debate rages on. So what's the answer? The answer is that you should ride as large a diameter wheel as your body will allow. We would argue that if you have a 28" inseam, you shouldn't be riding a 29"wheel.
Think about it. When we go buy a bike for our kids, they are sold by wheel size. The wheels and frames grow in proportion to the rider. Now when we got to buy bikes for ourselves, that's all out the window. We see that when the size of the wheel drives the bike design, fit, handling and comfort suffer. Everybody's cramming big wheels in small bikes, so what's the issue?
The issue is that the efficiency of a bicycle benefits by being in proportion to its rider. We always think of body position first and that is the first thing to suffer at the expense of a proportionally too big wheel for your height. The head tube of a bicycle frame can only be soo short and still perform as expected, so at some point the handlebar height will stop decreasing at a certain frame size, but your demand for a lower H-bar will remain the same. At that point, design and fit tricks are employed to Tim Gunn (the "Make it work" guy) the wheel size. Disproportionately big wheels also cause more toe overlap as rider height decreases, so cockpit length is frozen, even though you need those handlebars closer than they are. A poor fitting bike hinders your bio-mechanics, meaning you can't effectively power your bike anymore and the advantages of the bigger wheel are negated by the loss of power from your pedal stroke. This isn't even to mention the out of scale weight and modified frame angles that hinder the bike's handling. However, When everything is in proportion, it looks right, feels right, and fits right. Making it the best solution for you.
So we'd like to offer our ideal progression of wheel sizes by rider height. First let's talk road bikes. No one under 5'4" should be riding 700c wheels. Yes, it can be made to work, but to make it happen, both your handling and fit are increasingly compromised as height decreases. We suggest a 650c wheel bike for riders 5'4" down to 4'10" and 24" wheels for riders shorter than that. We'd even like to see a larger wheel diameter for riders over 6'2", perhaps a 30.5" wheel!?
On the Mountain side it's the same deal, wheels for the rider. However, to accommodate a suspension fork, the wheel size ends up stepping down from the road equivalent. so If you're 4'6" - 4'10" We'd recommend a 24" wheel. 4'10"- 5'4" 26" wheels, 5'4"-5'9" 27.5 wheels,5'10"-6'2" 29" wheels and over that a 30.5" would be appropriate. You could and should run a size up if you're riding a rigid bike. This idea holds true for folks that pedal there bikes over a distance. If you're a gravity rider, don't listen to any of this.
Basically, don't be afraid to ride something that's off trend as long as it's right for you. Your fit on the bike is the most important factor in how fast you can be on it. As long as your equipment choices serve that, you can't go wrong. Remember, It's not a good deal if it doesn't fit.