Monday, March 29, 2010

Size Matters

One of the things that is confusing in the bike world is the fact that while bicycles come in different sizes, the way in which the sizes of bicycles are described is not very logical or consistent. For example, when talking about children's bikes, we tend to refer to wheel size. So we say things like "Suzy is riding a 16 inch bike now, but next year she'll move up to a 20 incher." In adult bikes, folks in bike shops refer to bikes by their frame sizes, where frame size is the traditionally refers to the length of the seat tube. In the case of the two bikes pictured above, while they both have 26" wheels, the black bike on the left has a 24" frame

While the much smaller white bike has a 13" frame.

And while a quality manufacturer and a good bike dealer will give you good guidance about sizing a bike, the big stores that try to sell everything fall back on just specifying wheel size when they sell their cheap Bike Shaped Objects. Poor fit, poor assembly, poor components and poor manufacturing all make the Bike Shaped Object something to be avoided. A good used bike is always a better deal than a new Bike Shaped Object. (My friends at Dirt Rag did a great article on BSOs a few years ago. You can read it here.)

But sizing of quality bikes is confusing. While we specify bikes based on seat tube length, wheel sizes and frame geometries factor in. Some manufacturers have longer top tubes and some kinds of bikes may have top tubes that are level while others may have sloping top tubes. Some bikes, like those designed for cyclocross, may have higher bottom brackets. Just because you ride a 52 cm bike from manufacturer A doesn't mean you'll be comfortable on a 52 cm bike from manufacturer B. And by the way, the US bike business is still schizophrenic with regards to the metric system. Road bikes usually have their frame sizes specified in centimeters, while mountain bike sizes are usually expressed in inches. And no, you can't just do a simple metric conversion to figure out your mountain bike size from your road bike size. That would be too easy. As the late, great Sheldon Brown noted, "Anarchy reigns!" But Sheldon's article here is a good guide map to some of the issues involved in sizing a bike.

With bikes, like shoes, fit is the most important thing. As a rider you are really only going to be happy if your butt, your hands and your feet wind up in the right spots. That means making sure the distance from the saddle to the bars is not too long and not too short. You want to have just the slightest bend in your knee at the bottom of the pedal stroke and have the position of the saddle relative to the cranks be such that you make the most of the power your legs can generate. (This can vary somewhat depending on the type of bike and style of riding; triathletes tend to have their saddles farther forward than folks riding beach cruisers, for example.) Peter White has an excellent fit article here.

At the top of this article I showed two 26" wheeled bikes. The larger bike would comfortably fit someone well over 6 feet tall and a five foot person would probably be comfortable on the smaller bike. Wheel size alone doesn't really tell you much about the bike, it is only one factor in the sizing.

Below I've included a picture of two of my own bikes, my Monocog Flight 29er and my Dahon D3. I'm 5'6" tall and I ride the smallest (15") frame that Redline makes for the Flight. I don't know if anybody much smaller than me could fit on a 29er but I'm perfectly comfy on my Flight. And despite a more upright position (the handlebars are closer to the seat) I also am completely comfy on my Dahon D3. The bikes feel very different but I ride them in very different environments. The 29" wheels take a bit to get rolling and then tend to roll over everything, so the Flight is a machine that just eats up the back country trails. The Dahon, on the other hand, has very little inertia in those tiny wheels, so it's quick off the line and is perfect for zipping around town. Both bikes fit me and fit into the environments where I ride them.

Size matters and so does fit. If you find a bike that is the right size for you and the right fit for you, you'll have fun riding and you'll ride more.

Keep 'em rolling,



Jill Homer said...

I too have wondered what the basement height is for 29" wheels. I'm 5'7" and am sometimes annoyed by the lack of clearance on my frame, as well as the occasional tire scrape on the wheel. But I have another friend who is 5'2" and loves her 29er.

Still, my Karate Monkey is well on its way to becoming a commuter, and I have a suspicion that my next mountain bike may be a FS 26er. I've heard all the rhetoric on the big wheels, but I can't say I've been fully sold (wide wheels, however, are another story. :-)

Qamuuqin said...

Loved it. Very well written and informative.

Mel said...

Some great points there, and an interesting read.

My greatest wish is that road bike manufacturers would allow for the fact that people - women in particular - might be under 5'6. I'm 5'1, (not unusually tiny) and Cannondale's smallest women's specific frame has a standover a good couple of inches longer than my inseam. I'm going back to my LBS today to try out a junior model, aimed at age 10-15...

Loving the Bike said...

Nice article. Yes, bike sizing is a complex thing, isn't it? Even when the right shape and size of bike is selected, getting a professional fit is also a great idea. No two bodies are the same, so a fit will ensure your bike is tweaked to fit you right.

Anonymous said...


Where can I find some coroplast to build some fenders in these famine times of sign hunting.....Thanks


Kent Peterson said...


If you can't find any campaign signs that fell by the wayside and lie semi-hidden in the weeds by the side of the road (my prefered source!), try calling around to local sign shops. They often have scraps or leftover bits that you can get for free or just a few dollars.


Skippy @ What Size Bike Do I Need said...

GREAT Post. I had to work through this bike size mess too when I bought a new road frame to build up last year.

I ended up with a great bike that I love, but...they sure don't make it easy, do they?

karmapics said...

A small diversion about BSOs. (first off, that link is broken.)

I always am thoroughly amused when the unenlightened take the ignorant and/or patriotic route when addressing those bikes. The derogatory 'Cheap Chinese' always figures somewhere into the rant, when A. 95% of bikes are made in China/Taiwan (as is everything else from computers to clothing) and B. the same companies manufacture cheap and expensive bikes.

The fit as you say, isn't poor, it's non-existent. If you don't fit the one size, you're SOL. Same with assembly. If the min-wage worker-du-jour who puts it together doesn't know about bike mechanics, the buyer's opinion will be clouded and their safety endangered.

It's easy to see how this plays out if you read reviews of bikes on sites like Walmart, Target etc. You see reviews that trash the entire bike with quotes like "Brakes don't work" because store employee or customer don't know how to properly adjust them.

And that's likely by design. Since the same companies make those bikes, it's in their better interest to steer you, the ignorant customer, towards a bike shop where the bikes cost more but you also get a better 'experience,' meaning personalized service and a properly-adjusted and tuned bike.

I've bought several BSOs over the years as projects, and the frames are just as good, the parts are definitely inferior but in the proper hands, serviceable.
Not everyone can afford a $500+ bike, so if people want to go the big-box store route, I always advise they start a relationship with their LBS, endure the momentary snobbery, and have them give it a proper once-over. That way it's a win-win situation in the long run for everyone.