Gearing demystified: Put mechanical advantage to work
April 26th 2016
By Bob Forgrave
Often, we try to reduce quality measurement down to a single number. A 2.4 liter engine is more powerful and “better” than a 2 liter engine. A 64 GB USB drive is “better” than a 32 GB drive because it has more capacity. So with bikes, we get locked into a numbers race for more and more gears. Better, right?
Not as often as you’d expect. To see why, it’s important to dive one level down and think about what those gears actually do. And that requires a quick photo trip through the 200-year history of the bike.
Step 1: The Draisine, 1817. No mechanical advantage.
The first mass-produced two-wheeled, human-propelled vehicle, invented as a replacement for horses in 1817, had no pedals, no gears, and a top speed of about 8 mph on level ground.
Step 2: Penny Farthing, 1889. Mechanical advantage on flat ground.
70 years later, the addition of pedals freed riders to build increasingly large wheels in search of a longer distance with each pedal revolution. Mechanical advantage at last. But don’t fall off on uphills!
The “safety bicycle” replicated that ability to go further with each pedal revolution by having a large gear drive a small gear, using a chain. It’s the mechanical equivalent of this concept:
This development created some interesting perspectives. In the US, safety bicycle riders wanted to know how big a penny farthing equivalent they were riding, while European safety bike riders wanted to know how far they were going with each pedal revolution. In essence, one group cared more about the diameter of a circle, and the other the circumference!
Step 4: Early 1900’s. Mechanical advantage up hills.
Still, none of this helped anyone get up a hill. But this next development would.
Great in concept, but how do we get there? Early 1900’s efforts were just for racers, like taking off the rear wheel mid-race (!) and flipping the wheel over to a larger cog, or the delightfully easier system of leaving the wheel on and using a gloved hand to physically move the chain to a larger cog.
Step 5: Today’s super-responsive, hill-leveling derailleurs.
Derailleurs like the Shimano Acera gear system on the CHANGE Bike ruggedized hybrid combine hill-optimized gearing with quick-action thumb-shifters for the best gear for every situation. That’s why this bike is able to conquer a 22% grade with a one-handed rider.
Let’s do the lowest-gear and highest-gear math on my CHANGE Bike, both US-style and European-style:
US-style: How big a penny-farthing bike?
- Lowest gear = 26 inches x 22/34 = 16.8 inches. A very tiny bike, and easier to ride up hills than any other bike.
- Highest gear = 26 inches x 44/11 = 104 inches. That’s an 8-foot, 8-inch wheel for level and downhill speed!
Euro-style: How far with each pedal revolution?
- Lowest gear = 0.66 meters x 22/34 = 0.427 meters per revolution. Not that different from walking up a hill.
- Highest gear = 0.66 meters x 44/11 = 2.64 meters per revolution — over six times as far, for a massive gear range.
Getting back to the premise that opened this article, yes, number of gears is an indicator. But far more important is the gear range, and why a CHANGE Bike outclimbs bikes with even more gears. The more important question is, what can you actually do with the bike?
With a CHANGE Bike, the answer is simple: Fear no hill.