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tpleskinen57
12-16-1991, 06:49 PM
Dear Biomch-l readers,

As an active cyclist and a former victim of an accident I read with
interest Heinz-Bodo Schmiedmayer's inquiry on deceleration of bikes,
though my accident was rather caused by the acceleration of the car
than the insufficient deceleration of my bike.

As I remembered that some standards exist on the safety of bikes I
phoned to the Finnish Standards Association (SFS), and received some
information:
There is a Finnish standard SFS 5200 from 1985 based on an international
standard ISO 4210 from 1982 on the safety requirements of a standard bicycle.
According to these standards the breaks of the bicycle must be such that
the bicycle can be stopped safely under dry conditions from the
velocity of 24 km/h within a distance of 5.5 m. (Under wet conditions
from 16 km/h within 15 m). The 5.5 m from 24 km/h means that the
deceleration is just above 4 m/s^2, which is just on the limit to
cause tipping over the front wheel according to Heinz-Bodo's
calculations which confirm my own calculations a few years ago when I
first read about the standard.

But the standard defines the requirements for bicycle construction only:
The breaks must be good enough to achieve the maximal safe
deceleration in good surface conditions. So the use of maximal
breaking capacity is already dangerous in traffic at least when
cycling downhill when the c.g of the body is more forward.

After my own unfortunate empirical trial (using only "I felt that ..."
type of transducers), the forces acting on the head when it hits the
street are far higher than the inertial forces when breaking. I
recommend all of you to wear cycling helmet whenever cycling.

Happy cycling!

--
Timo P. J. Leskinen
Institute of Occupational Health
Biomechanics Laboratory
Topeliuksenkatu 41aA
SF-00250 Helsinki
Finland
E-Mail: tles@occuphealth.fi
Telephone: +358 0 4747 505
Telefax: +358 0 4747 503