Ryan Cousineau a écrit:
> If the NuVinci catches on, cyclists will start to think of their gearing
> in terms of ratio of the lowest to highest gears (ie, 305% gearing
> indicating that the top gear has about three times the development as
> the low gear).
That's one way to calculate it, but I don't think it's the _best_ way
to calculate it.
My gear calculators provide not only values for the individual gears,
but also show the percentage difference between adjacent gears. There
has been some confusion about this, so here's the skinny:
The percentages are mainly of use with derailer or hybrid gearing,
where they help the rider determine the most efficient shift pattern,
where there are two or three different shifters to be considered.
The algorithm is pretty simple. Look at two adjacent gears, then
express the higher one as a percentage _increase_ over the lower of
the two.
For instance, if one gear is 80 inches and the next gear up is 88
inches, that's a 10% increase. The higher gear is 110% of the lower
gear, but the increment is only 10%.
Manufacturers of internal gear hubs tend to tout the total gear range
of their hubs, but they commonly calculate it in a different way. For
instance, if there was an internal-gear hub that only covered a range
from 80 inches to 88 inches, the manufacturer could say this was a
range of 110%.
This is a legitimate way to represent the overall range of a gear
system, though I prefer the incremental approach, and would call it
10%.
Using the overall percentage is not really a good basis for
comparison. For example, take this hypothetical gear that gives 80
and 88 inches with some particular set of sprockets. Compare it with,
say, a SRAM 7-speed or Sturmey-Archer 8-speed. If you use the
"overall" gear to express the range, they're 110% and 305%, so it
seems that the 7- or 8-speed has a bit less than 3 times the "range"
of the other system.
My algorithm would list these hubs as having "ranges" of 10% and 205%
respectively, which I think is a more reasonable expression of the
gear ranges.
I have a work-in-progress Web page that shows the ranges of various
hub gears and derailer systems expressed graphically. Check it out at
http://sheldonbrown.com/gear-range.html
Sheldon "Numbers" Brown