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Helmets.org

Calculations for Understanding Standards



1, Drop Heights vs Joules

Calculated with a 5 kg drop mass.

  Drop Height        Energy       Falling Speed*
===============      ======      ================
Meters     Feet      Joules        KPH      MPH

 0.8       2.6         39         14.3       8.9

 1.0       3.3         49         15.9       9.9

 1.2       4.0         59         17.5      10.9

 1.4       4.7         69         18.9      11.7

 1.5       4.9         74         19.3      12.1

 1.6       5.2         78         20.2      12.5

 1.8       5.9         88         21.4      13.3

 2.0       6.6         98         22.5      14.0

 2.2       7.2        108         23.7      14.7

 2.4       7.9        118         24.7      15.3

 2.5       8.2        123         25.2      15.7

2. Joules vs Drop Heights

Calculated with a 5 kg drop mass.

    Energy         Drop Heights        Velocity        Falling Speed*
==============     =============     =============    ================
Joules  Ft-lb.     Meters   Feet     M/Sec  Ft/Sec      KPH      MPH

 40     29.5        0.8      2.7      4.0   13.1       14.3      8.9

 50     36.9        1.0      3.3      4.5   14.7       16.1     10.0 

 60     44.2        1.2      4.0      4.9   16.1       17.6     11.0

 70     51.6        1.4      4.7      5.3   17.4       19.0     11.8

 80     59.0        1.6      5.3      5.6   18.6       20.4     12.6

 90     66.4        1.8      6.0      6.0   19.7       21.6     13.4     

100     73.7        2.0      6.7      6.3   20.7       22.8     14.1

110     81.1        2.2      7.4      6.6   21.8       23.9     14.8

120     88.5        2.4      8.0      6.9   22.7       24.9     15.5

130     95.9        2.6      8.7      7.2   23.7       25.9     16.1
                 

* Note that KPH and MPH relate primarily to the speed of the helmet hitting the pavement, not to the forward speed of the bicycle or rider, unless the rider hits a concrete abutment. The typical bicycle crash impact occurs at a force level equating to about 1 meter (3 feet) of drop, or a falling speed of 10 MPH. The rider's forward speed before the crash may be considerably higher, but the speed of the head moving toward the ground, plus a component of the forward speed, less any energy "scrubbed off" in other ways, normally average about 10 MPH.



We are indebted to Jim Sundahl for the Excel spreadsheet to calculate these numbers.



This page was reformatted on: April 28, 2015.
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