Calculating Gear Inches

If you would have asked me about gear inches a few months ago, I would have said, “what? Huh?” After going on a search for the perfect bicycle to take on my tour, I found a lot about “gear inches.”

Not all bikes are the same. There are road, road touring, adventure, gravel, hybrid, MTB, and cyclo-cross bikes. There are others to be sure, but none that would fit into the group of bikes that concern me. To narrow down my choice, I will have to choose a bike that will give me the tire capacity and gearing of a mountain bike, the ride of a gravel bike, and a frame of a road touring bike. It so happens that most touring bikes have MTB gearing, however their tire capacity is on the thin side. Gravel bikes have a larger tire capacity, but sometimes the chainstay is too short for panniers and is usually set up in a backpacking format.

So, how do I figure out the gear inches that I need? A respectable low gear for touring with a heavy load should be as close to 20 gear inches as possible. The high gear should be a respectable 110+ gear inches if possible. I am not saying that these are your magic numbers, but they are mine. That being said, most tourists look for as close to 20 gear inches when purchasing a bike. I have read about many having bikes as high as 30, but never read about the negative climbing results they had, if any.

So how would you go about calculating your low gear inches. It is quite easy. Lets say you have a 29 inch tire. Take the smallest gear on your cranks chainrings (front) and divide by the largest in the back (cassette), then multiply it by your tire size.

26/36×29=20.9 (21 gear inches, low)

Now let’s calculate for the high gear. Take the largest chainring on your crank and divide by the smallest gear in the back (cassette), then multiply it by your tire size.

43/11×9=113.3 (113 gear inches, high)

It’s that simple. Remember to adjust for you tire size. 26, 27, 27+, 29, 29+, 650B, and 700c all are different sizes.