B
Byron Sheppard
Guest
I recently read Sheldon Brown's intriguing proposal for a universal system of gear comparison which
he calls "gain ratio" (name attributed to someone else. see http://www.sheldonbrown.com/gain.html).
What do others think of it and why hasn't the system gained more "traction" in the cycling world.
Or has it?
As an engineer, I am attracted to the unit-less-ness of it, though I haven't yet figured out whether
that is actually useful, for reasons mentioned below.
It also raised some other interesting questions. In my own little cycling universe, I have always
compared gear combinations by calculating the front/back ratio and multiplying it by the wheel
circumference, usually in inches. Thus I have discovered that I reinvented the notion of
"development in inches" rather than meters. Contrary to Sheldon's claim that this method is
cumbersome because it involves multiplying the wheel diameter by an irrational number, I found it
easy because the wheel circumference is usually in my notes having been directly measured and
entered into my computer (though usually in mm's). Then I whip up a spreadsheet table that allows me
to compare the number of inches traveled per crank revolution with each ratio, which is then easily
compared between bikes with different gearing, tire, and wheel combinations.
Sheldon raises a valid technical point about the error introduced by ignoring differences in crank
length, but I only have four bikes and they all have the same crank length, whether on road or off.
So this would seem to be a problem only if you have as many bikes as Sheldon does, a problem I'm
sure we'd all love to have. (or perhaps for those naïve enough to have road and mountain bikes with
the same crank length)
I always thought I must be calculating what everyone else called "gear inches" and was baffled to
discover that that term actually refers to the gear ratio times the wheel diameter. What the heck
good is this number, except purely for the sake of comparison, and why did it become so popular? It
seems only vaguely related to inches actually traveled (through a proportion of pi) which doesn't
give it much intuitive value.
I guess I like comparing inches traveled, rather than gain ratios or gear inches, because then I
know the magnitudes of the numbers compared have some physical meaning.
So my question to the group is: what method of comparing gear ratios have others found
useful and why?
fire away, byron
BTW, for the record, I love Sheldon's site. I have learned a great deal about cycling from him
(including especially how to build my own wheels; the last great mechanical cycling mystery solved)
and always promote the site to others. It is a great service to our sport. Thanks, Sheldon!
he calls "gain ratio" (name attributed to someone else. see http://www.sheldonbrown.com/gain.html).
What do others think of it and why hasn't the system gained more "traction" in the cycling world.
Or has it?
As an engineer, I am attracted to the unit-less-ness of it, though I haven't yet figured out whether
that is actually useful, for reasons mentioned below.
It also raised some other interesting questions. In my own little cycling universe, I have always
compared gear combinations by calculating the front/back ratio and multiplying it by the wheel
circumference, usually in inches. Thus I have discovered that I reinvented the notion of
"development in inches" rather than meters. Contrary to Sheldon's claim that this method is
cumbersome because it involves multiplying the wheel diameter by an irrational number, I found it
easy because the wheel circumference is usually in my notes having been directly measured and
entered into my computer (though usually in mm's). Then I whip up a spreadsheet table that allows me
to compare the number of inches traveled per crank revolution with each ratio, which is then easily
compared between bikes with different gearing, tire, and wheel combinations.
Sheldon raises a valid technical point about the error introduced by ignoring differences in crank
length, but I only have four bikes and they all have the same crank length, whether on road or off.
So this would seem to be a problem only if you have as many bikes as Sheldon does, a problem I'm
sure we'd all love to have. (or perhaps for those naïve enough to have road and mountain bikes with
the same crank length)
I always thought I must be calculating what everyone else called "gear inches" and was baffled to
discover that that term actually refers to the gear ratio times the wheel diameter. What the heck
good is this number, except purely for the sake of comparison, and why did it become so popular? It
seems only vaguely related to inches actually traveled (through a proportion of pi) which doesn't
give it much intuitive value.
I guess I like comparing inches traveled, rather than gain ratios or gear inches, because then I
know the magnitudes of the numbers compared have some physical meaning.
So my question to the group is: what method of comparing gear ratios have others found
useful and why?
fire away, byron
BTW, for the record, I love Sheldon's site. I have learned a great deal about cycling from him
(including especially how to build my own wheels; the last great mechanical cycling mystery solved)
and always promote the site to others. It is a great service to our sport. Thanks, Sheldon!
