What are Gear Inches?
Gear inches are the unit of measure
that we use when calculating the various gear ratios
on a bicycle, to determine the relative ease or difficulty
of pedaling. This calculation is done using the number
of teeth on both the chain wheel, to which the pedals
are attached, and the gear cluster, or cassette, mounted
on the rear wheel. Also the effective diameter of the
rear, or driven wheel is entered into this calculation.
A larger number is a harder ratio to pedal and you travel
a greater distance for each pedal stroke.
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Bikefold.com > Airnimal
Travel Bikes > Airnimal Geometry and Gearing
The Airnimal
Chameleon bicycle comes in two
frame sizes, 52cm & 56cm,
that caters to riders with different build and needs. Both
sizes
have a wide range of adjustability.
| |
52
cm frame |
56
cm frame |
| Wheel Size |
24" (520) |
24" (520) |
| Wheelbase |
38" |
39 1/2" |
| Top tube length |
20 1/2" |
22" |
| Stem length |
8cm to 14cm |
8cm to 14cm |
| BB height |
27.9cm (11") |
27.9cm (11") |
| Head tube angle |
72° |
73° |
| Seat tube angle |
74° - 73° |
74° - 73° |
| Chainstay |
41cm (16.1") |
41cm (16.1") |
BB to seat:
300mm seatpost
350mm seatpost
400mm seatpost |
Adjustable 22.4" - 28.3"
Adjustable 24.4" - 30.3"
Adjustable 26.4" - 32.3"
|
Adjustable 22.4" - 28.3"
Adjustable 24.4" - 30.3"
Adjustable 26.4" - 32.3"
|
| Head tube diameter |
1 - 1/8" |
1 - 1/8" |
| Seat post |
27.2mm diameter, 300mm, 350mm or 400mm
seatpost length |
27.2mm diameter, 300mm, 350mm or 400mm
seatpost length |
Below are gear
ratio charts for various chain ring and nine speed sprocket
combinations
calculated
in GEAR INCHES, for the Airnimal ISO 520-25 wheel size.
Touring:
| |
11 |
12 |
14 |
16 |
18 |
21 |
24 |
28 |
32 |
| 52 |
106.4 |
97.5 |
83.6 |
73.1 |
65.0 |
55.7 |
48.8 |
41.8 |
36.6 |
| 42 |
85.9 |
78.8 |
67.5 |
59.1 |
52.5 |
45.0 |
39.4 |
33.8 |
29.5 |
| 30 |
61.4 |
56.3 |
48.2 |
42.2 |
37.5 |
32.1 |
28.1 |
24.1 |
21.1 |
Road:
| |
11 |
12 |
13 |
14 |
15 |
17 |
19 |
21 |
23 |
| 53 |
108.4 |
99.4 |
91.7 |
85.2 |
79.5 |
70.1 |
62.8 |
56.8 |
51.8 |
| 39 |
79.8 |
73.1 |
67.5 |
62.7 |
58.5 |
51.6 |
46.2 |
41.8 |
38.2 |
Triathlon:
| |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
19 |
21 |
| 56 |
114.5 |
105.0 |
96.9 |
90.0 |
84.0 |
78.8 |
74.1 |
66.3 |
60.0 |
| 44 |
90.0 |
82.5 |
76.2 |
70.7 |
66.0 |
61.9 |
58.2 |
52.1 |
47.1 |
Calculating
Divide the number of teeth on the chain ring by the number of teeth
on the rear wheel cluster, for which we are making the calculation.
Then multiply this by the wheel diameter.
Example: A 52-tooth chain ring
driving a 13-tooth rear cog. So 52 divided by 13 = 4
Now multiply this number by
the wheel diameter, which for a standard 700c wheel is approximately
27 inches. So,
4 x 27 = 108 Gear inches.
This number is not the distance traveled for each revolution of
the pedals. But is the gear equivalent of a high wheeler with a
108 inch diameter wheel. This is where all this gear inch stuff
started, when in the early days cyclists needed a way to compare
ratios of various geared bicycles to the high wheelers of the day.
So how can we make use of these numbers except as a way of comparing
one set of gear arrangements with another?
Well, we can multiply the gear inches by pi (3.1416) to give us
the circumference of the wheel and this will give us the distance
traveled for each revolution of the pedals. From this we can determine
our speed for a given pedaling rate.
So now if we were to pedal that 108 inch gear at 70 revolutions
per minute, then we would travel 108 x 3.1416 x 70 = 23,750 inches
per minute or 22.5 mph.
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