I've always used gear ratio and gear inches with cadence to set speed goals. I just ran across a newer term called Gain ratio. Athough S. Brown hypes it up, I don't see how it could do much to improve performance unless you're super tall. Anyone have insight on Gain Ratio?

Gain Ratio = wheel diameter / crank length

Source: https://www.sheldonbrown.com/gain.html

I looked at his site too and he seems to support it as a better way of understanding how far you go per pedal stroke as opposed to using the old term Gear inches. As he is inventing a whole new system to deal with the 3% difference between 175 mm MTB cranks and 170 road cranks I am not impressed. Once I hosted a transcontinental cyclist who thought extremely long cranks could solve many problems. He had some monster chainringsto balance the crank length. Net change zip, nada, zero.

It it ain't broke Sheldon, why fix it?

I think that one of the advantages of gain ratios is that they are universal pure ratios. There's no unit, thanks to the math. So you can use whatever unit system you want to. With a gain ratio of 5.3, for every inch that the pedal moves around the BB spindle, the bicycle moves 5.3 inches forward. Or for every angstrom that the pedal moves around the BB spindle, the bicycle moves 5.3 angstroms forward. For every mile... you get the picture.

I think that IF gain ratios were to catch on, they would be a more useful means of analyzing gear ratios for bicycles than the gear inch and meters development systems already in place. The problem is that they aren't terribly likely to catch on, simply because it's difficult to make the mental switch to something new. So the systems we use now are likely to remain pretty well ingrained. Still, never say never - there may be a sudden wave of practical inspiration in the bicycling world. Things could change.

That's only true for direct drive bikes.

Source: https://www.sheldonbrown.com/gain.html

It's not about "improving performance", it's about comparing mechanical advantage between different bikes with different crank lengths.

Sorry, you don't get it. That is one thing that it does NOT do that the traditional systems do.

Basically it's the ratio between foot speed (linear foot speed) and road speed. it's also the ratio between how hard you push on the pedal and how much driving force the wheel delivers.

Sometimes racers say gear inches are useless because all you need is the sprocket ratio. This is the result of tunnel vision that assumes every bicycle has the same wheel diameter. That is true in racing circles, but it is most definitely NOT true in the larger cycling world.

Ken seems to think that there are only two crank lengths, 170 and 175. It ain't so. My own personal fleet ranges from 160 to 175, but most of my bikes use 165 or 170. I used to have a pair of 180s but they made my knees hurt. I also own a pair of 150s that I was running for a while.

Actually the long crank fad seems to be running its course, and I encounter more and more cyclists looking for shorter cranks (mostly aging boomers who are trying to deal with aging knees...)

If you're talking about gear inches, it IS "broke" 'cause it's based on inches!

The gear inch system is only used in English speaking countries, and most of those have already switched over to metric units.

I admit that it's difficult to teach an old dog new tricks, and I still have a much better intuitve feel for gear inches than I do for gain ratios, but for younger cyclists who didn't grow up with gear inches that's not so much of an issue.

Sheldon "Gain Ratio" Brown
+-----------------------------------------------------------+
| Oh, my ways are strange ways and new ways and old ways, |
| And deep ways and steep ways and high ways and low, |
| I'm at home and at ease on a track that I know not, |
| And restless and lost on a road that I know. |
| --Henry Lawson |
+-----------------------------------------------------------+

I read this to mean that I could customize the cassette (and choose appropriate gear for conditions).

Source: https://www.sheldonbrown.com/gain.html (top of page)

Edited: And when you say that for every inch, the pedal travels in its orbit around the bottom bracket, the bicycle will travel N inches, I believe a commuter (or whoever) would not measure the inch...rather factor the number of inches for an entire RPM.

The most useful feature of gain ratios is letting you compare bikes of unequal crank length. It gives a more accurate understanding of how easy it will be to spin the lowest gear, and you can set 2 bikes to matched gain ratios before you test which feels better/fastest.