On The Road
by: Bill Oetinger 9/1/2011
Gear Inches!
My wife is not a cyclist. Well, okay, she does own a bike and occasionally even rides it. But she is not a cyclist: not steeped in the lore of cycling, not deep into the cycling subculture. She can hardly avoid it, being married to me, but she doesn't live and breathe it.
Many of my cycling friends are her friends too, so when my buddies drop by after a ride for some chips and beer, she happily joins the group. Ditto when we have some of the biking gang over for dinner. She won't run away and hide in a back room while we tell our old war stories one more time. She's quite good at maintaining at least an appearance of interest in topics that involve nothing but bikes. However, even with the patience of a saint, she does have her limits, and I discovered many years ago that the dividing line between polite interest and eyes-glazed-over catatonia arrives with the mention of gearing or, worse yet, gear inches.
Whenever anyone says, "so…I was in my 38-23," you can see her enter a sort of zen state of suspended animation, all systems shutting down until the conversation becomes less minutely esoteric….kind of like a Prius sitting at a stop light.
Over the years, some of our better (bike) friends have noticed this, so inevitably, these days, they will deliberately interject gears and gear inches into the conversation, just to watch her eyes roll back in her head. It's become something of a standing joke around here. So I have come to think of gearing and gear inches as the edge of the continental shelf, where the bottom falls away and we descend into the dark abyss of biker madness.
Gear inches are the secret handshake for the brotherhood (or sisterhood) of hardcore, over-the-top cyclists…the ones who really do live and breathe cycling; who have chain lube flowing in their veins. This level of obsessiveness does not embrace all cyclists. It of course excludes sometimey riders like my wife, but it also probably excludes at least half and possibly much more than half of all the riders in the average pay-to-ride century.
You have to be pretty far gone down the rabbit hole of bike life to even have heard of gear inches, and you have to be all the way 'round the bend to know what gear inches are and how to calculate them. Okay…so what are gear inches and why should you care about them?
To best answer that question, we have to consult with the late, great Sheldon Brown, the arch-druid of bike-tech trivia…
In his encyclopedic glossary of bike terminology, he defines gear inches thusly: “One of the three comprehensive systems for numbering the gear values for bicycle gears. It is the equivalent diameter of the drive wheel on a high-wheel bicycle. When chain-drive ‘safety’ bikes came in, the same system was used, multiplying the drive wheel diameter by the sprocket ratio. It is very easy to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket. This gives a convenient two- or three-digit number.”
Hmmm… If you ask me, that definition is opaque to an almost tautological degree. You pretty much have to already understand gear inches to understand the definition. But let's let that go. Let's assume it makes at least some sense to the novice.
When Brown refers to the “size” of a sprocket--a chain ring or cog--he means the number of teeth it has, not its diameter. For a conventional road bike, the diameter of a wheel is--at least nominally--27". So, for instance, a typical rolling gear that the average rider might use on a flat road could be calculated from a 50-tooth big chain ring, a 21-tooth cog, and that 27" diameter wheel: 27 X 50 / 21 = 64.3 gear inches. (Note that I used a 50-tooth or “compact” chain ring, which is all the vogue these days. More about that later.)
Brown says the calculation is easy to do. Maybe, if you can divide a four-digit number by 21 in your head, or if you can even remember the formula for the calculation. I can't, so I bookmark a page on the 'net that offers up a nice gear inches chart…
There are many gear inch charts out there. If this one ever goes off the air, just google “gear inch chart,” and you'll find others. I like this one because it has a nice spread of numbers. It has chain ring sizes on one side, from 22 teeth to 53 teeth, and cog or cassette sizes on the other, from 11 up to 32. That's going to cover pretty much any front-rear sprocket combination that would be likely to appear on a conventional road bike. Go to the 27"-wheel chart, scan across to a 50-tooth ring, then down to a 21-tooth cog and, voila: 64.3. (They have a chart for 26" wheels too, which covers most mountain bikes.)
Alright then…so we have this number, this gear inch figure. What does it mean and what can we relate it to in the real world? What bearing does it have on riding a bike down a country road? On some levels, it means absolutely nothing. You could spend a long cycling life without ever knowing--or caring--that riding in a 50-21 adds up to 64.3 gear inches. But in a geeky, nerdy, pointy-head phred kind of way, it can be fun and even illuminating to mess around with gear inch data.
Take for instance the differences between a conventional, “old-fashioned” chain ring set of a 52 and a 38 and a trendy new, compact chainring set of a 50 and a 34. (When I bought my current bike, a few years ago, it came with a compact set-up, so I switched from the former to the latter.) It was instructive for me to learn--by consulting the chart--that my old, kindest climbing gear of 38-28 (36.6 inches) was almost exactly identical to the way I set up the new bike: a 34-25 (36.7 inches). That reassured me that I wouldn't have to make any serious or painful changes to my basic climbing efforts.
(In fact, when I first got the bike, it had a 36-tooth little ring, and those two extra teeth made a big difference for this tired old plugger. Two little teeth translated to two gear inches (38.9), and on our steepest hills, I was working way too hard to get on top of that gear. Doesn't seem like much, and for stronger riders, it might not be much. But for me, it was significant. After a couple of weeks and some tough rides, I swapped the 36 out for the 34 and got back inside my comfort zone.)
In a sense, gear inches are a way of expressing effort or energy output or efficiency. Every cyclist is different and every one of us has a different comfort zone where we are pedaling and moving the bike forward most efficiently. If you cycle long enough, and if you pay attention to what your heart and lungs and your muscles and hip and knee joints are telling you, you will eventually figure out where your own sweet spot is, where you are producing your best power in a sustainable way. Obviously, most of this is going to be intuitive or seat-of-the-pants: if you feel like you're working too hard, lift it up a cog or two in back or drop it down into the little ring in front. Duh… But spending a little time looking at a gear inch chart can help you to a logical, quantifiable understanding of that intuition. I can help you articulate the subtleties up in the front of your brain.
Back when I got my first road bike, 45 years ago, the cog sets in back had only five gears. (With two in front: a “ten-speed,” as all road bikes were called in those days.) With just five gears in back, the increments between them were substantial, so the question of when to shift was sometimes cause for a heated internal debate. Plus the old friction shifters didn't always work that smoothly, so shifting might also be a finicky pain, in addition to being a big, chunky jump. Now, with ten cogs in back, the jumps between speeds are tiny. (And the index shifting usually works so smoothly…) If you're even thinking about shifting, just do it. No point in debating the matter.
These advances in shifting and gearing technology may have rendered gear inch lore even more esoteric and irrelevant than it used to be. Of course, in the perversely contrarian way of obsessive maniacs everywhere, that tenuous, arcane irrelevance only makes such trivia more valuable to those who understand it and are privy to the inner sanctum of its secrets. It's like a knowledgeable stamp collector understanding why one old stamp sells at auction for $50,000 while another one that looks almost the same isn't worth ten cents. That, I suppose, is the charm of such off-beat pursuits: to really get into gear inches--to understand them and to make sense out of them and even to enjoy them--is to know yourself to be one of the chosen few, even if those chosen few are just a demented subset on the fringe of the already ragged fringe of bike nuts.
Sheldon Brown grumbles that the classic gear inch calculation fails to take into account crank arm length, which will affect the final figures to some slight degree. (Needless to say, he has an even more abstruse formula for taking this into account…called gain ratio.) His complaint is certainly valid, but then, you might as well also consider the length of the rider's upper and lower legs, which are just extensions of the crank arms…all of them being parts in the engine that drives the bike. After awhile, it becomes like the baseball statisticians, trying to come up with one universal yardstick that can compare the relative merits of Ty Cobb, Ted Williams, and Albert Pujols. It probably can't be done--to account for all the variables--but it's fun to try.
At some point, each of us reaches our limits on how much data and detail we want to kick around when it comes to understanding the mechanism of making a bike move. For a certain kind of cyclist, it can be fun to play with the figures, to parse our pedaling out into its minutest metrics…to pick it apart and then put it back together. But for others, it's all silliness. They are like the zen monk who said, “I ride my bike to ride my bike.” They've thrown their cyclometers away. They don't have any use for power taps or heart rate monitors or cadence counters or altimeters or GPS data dumps.
I suppose it doesn't have to be an either-or proposition: the same cyclist who can enjoy poring over a gear inch chart can also let all that go when actually rolling down the road, in the moment. The road and the chart both have their charms. Both fall within the general rubric of riding. Both are part of why we like being cyclists. Not only do we like cycling on its own merits…the magical, kinetic dance of it…but we like it because we believe being a cyclist makes us an initiate in a special, semi-secret society, like rosicrucians or masons; we believe we know something of value that the rest of the folks out there don't know.
If the simple act of riding a bike doesn't confirm you in your feeling of membership within this select society, then a skull session with the intricacies of a gear inch calculator ought to do the trick: yes indeed, you are not like other people! You've gone way 'round the bend…and doesn't the view look good from here!
Bill can be reached at srccride@sonic.net