The Myth of Rotating Weight
 Share
The version of the browser you are using is no longer supported. Please upgrade to a supported browser.Dismiss

View only
 
 
ABCDEFGHIJKLMNOPQRSTUVWXYZ
1
Rim Weight (kg)12
2
Rim Radius (m)0.6720.672
3
Rim moment of intertia (I = MR^2)0.4515840.903168
4
5
conversion from kph to Hz0.13164324470.1316432447
6
Speeds (kph)
7
101.316432447
8
405.265729788
9
506.582162235
10
607.898594682
11
709.215027129
12
13
Energy required to spin (J) (1/2 I w^2)0.78259253751.565185075
14
12.521480625.0429612
15
19.5648134439.12962687
16
28.1733313556.3466627
17
38.3470343476.69406867
18
19
Power required to accelerate from 0 to given speed in 1.5 seconds (W)
0.52172835831.043456717
20
8.34765373316.69530747
21
13.0432089626.08641792
22
18.782220937.5644418
23
25.5646895651.12937912
24
25
Let's say in a crit you slow down to 35 kph and re-accelerate to 40 kph, in 1.5 seconds, how much power does that take?
26
(Ignoring all air resistance, the dominating source of power draw)
27
Light RimHeavy Rim
28
Initial velocity (kph)3535
29
Final velocity (kph)4040
30
Time (s)1.51.5
31
32
Initial kinetic energy (J)56.84756105113.6951221
33
Final kinetic energy74.24987566148.4997513
34
Difference17.4023146134.80462922
35
Power11.6015430723.20308614
36
37
Power required for 80kg rider + bike
38
3780.864198
39
4938.271605
40
1157.407407
41
771.6049383
42
43
So it takes 10 W more to accelerate the heavy wheel, but it *already* takes 771W to accelerate the rider + bike, ignoring air resistance.
44
45
So that's a 1-2% difference, even before you consider aerodynamics.
46
For an average rider with a CdA of 0.3, at sea level, with normal Crr and normal drivetrain losses, 200W gets you about 35 kph, 300W gets you 40 kph
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
Loading...