The section on your main page that discusses how you make a small bike ride big erroneously states that "Gear inches" is the distance a bike will move (in inches) for one revolution of the crank arms (pedals). It's actually correct to say "Gear inches times 3.14" is the distance a bike will move (in inches) for one revolution of the crank arms (pedals).
In the days before bikes had sprockets and chains, one would purchase a penny-farthing based on the diameter of the drive wheel. When safety bicycles came in, bike shops had to come up with a way to sell them based on the metric that customers were already familiar with, hence "gear inches". See https://en.wikipedia.org/wiki/Gear_inches
I'm simply suggesting you add the words "times 3.14" to what the website already says in order to make it a true statement. Let's work a simple example (not on your chart). Say the front chainring is 48T, the rear cog is 12T, and the wheel diameter is 20". Substituting into the formula d x (fc/rc), we get a result of (20 x (48/12) = 80) gear inches, which is to say the effective *diameter* of the drive wheel is 80". Now, if we turn the crank arms through one full revolution with this 1:4 gearing, the drive wheel will rotate four times. The distance the bike will move is the actual circumference of the wheel (20" x 3.14 = 62.8") times four (62.8" x 4 = 251.2") or 80" times 3.14. Even this is an approximation. If you were setting up a bicycle computer on your ZiZZO, you'd want to measure the circumference of the inflated tire (not the wheel) with a tape measure and enter that value.
Granted, it's a very minor point. You could also change your explanation to read '"Gear inches" is the effective diameter of the drive wheel for a given wheel size and gear ratio' and that would also be a true statement.
Thank you for your input and insight. It sounds like you really know your stuff!
The formula we used to calculate gear inches is:
wheel diameter[d]/ (front chainring/[fc]back chainring[rc])
What you are saying, "It's actually correct to say "Gear inches times 3.14" is the distance a bike will move (in inches) for one revolution of the crank arms (pedals)." is correct if you are measuring the "actual" distance each bike will roll per pedal revolution.
When speaking in terms of comparing one bike to another, especially two very different models (a road bike vs a mountain bike, for example) you would use the d/(fc/rc) formula. This method converts every gearing combination of a modern bike into what a "penny-farthing" or "original" bike's drive wheel would be. So, the numbers we used in our website basically says if EVERY bike was a Penny-Farthing, this is what the diameter wheel it would have (could you imagine what it would be like to ride a bike with. We make gear inches available for customers so they can gauge how a ZiZZO bike will ride when compared to a mountain or road bike.
Thank you again for your feedback!