Safer cycling? Don't get a helmet and cross red light

[stevieb]

i also have a collection of helmets dating back to the 1980,s
i have checked them and can confirm what d8veh is saying.

 

[Deleted member 4366]

They had a bit on the TV today on Watchdog Testing about bicycle helmet testing. The main test of interest was the impact test, where they simulated the head hitting the edge of the curb at 10 mph. They showed side-by-side tests of high and low-end helmets. The test measures the deceleration. The results were between 50G and 100G. 250G is the maximum allowed. The low-end one had the lowest G.

Let me put some numbers to this:

a = ((v1*v1) - (v0*v0)) / 2d

Say you are travelling at 20 MPH v0 = 9 m/s

d = 2 mm of foam (say for a cycle helmet) a = 20250 or 2025G (most likely fatal even though the G force is for a very short duration)

d = 50 mm of foam (motorcycle helmet) a = 810 or 81G (most likely survivable)

I hope this illustrates that it is mainly about the value of (d) and a bicycle helmet gives you very little.

As TREF says above, these bike helmet need a re-think. I believe that the way forward is a lightweight aluminium honeycomb outer shell which distorts on impact (giving a greater value of (d). The current polystyrene ones are a con (very little (d)).

It looks like your maths is correct, but your assumptions about helmet construction are off by quite a bit.