Helmet evidence could of course be used in court and also considered by insurance companies providing for cycling events. If the claims for those not wearing are likely to be lower than for those wearing, they should not specify that helmets should be worn to take part in an organised event.
With this in mind a list of advantages v disadvantages may be of benefit.
1. Helmet adding to the rider profile, estimated at 3% increase.
2. Helmet providing protection, preventing injury, resulting in fewer accidents being reported.
1. Extra impacts to the helmet that would otherwise be near misses for a bare head. http://www.cycle-helmets.com/au-assessment-2015.pdf
Robinson 1996 detailed the incidence of hitting their head/helmet in a cycling accident was "significantly higher for helmet wearers (8/30vs 13/476, i.e. 20% vs 2.7%, p 0.00001)". A bare head width of approximately 150mm may avoid contact compared to a helmeted head at approximately 200mm width.
2. Extra neck injuries.http://www.ta.org.br/site/Banco/7manuai ... helmet.pdf
Neck injury data indicates helmet use may not provide any benefit. Attewell stated "Three studies provided neck injury results that were unfavourable to helmets with a summary estimate of 1.36(1.00, 1.86), but this result may not be applicable to the lighter helmets currently in use". A combination of helmet factors increase the risk of a neck injury, size, mass, gripping the road surface, bending moment and overall accident rate
Elvik 2011 details a factor of 1.40 (0.97, 2.02) in a more recent study, ref http://www.cycle-helmets.com/elvik.pdf
3) Rotational injuries to the brain due to increased helmet impacts and helmets gripping the surface, compared to a bare head loosing hair and skin. http://www.cycle-helmets.com/au-assessment-2015.pdf
McIntosh et al results indicate a rotational product of approximately 8 krads/s² for 8 ms for helmeted (Fig 3), (64 krad/s²-ms) vs for non-helmeted (Fig 4),13 krad/s² for 3 ms (39 krad/s²-ms). In effect, their results show that helmeted may be more at risk from rotational acceleration by the extended time involved. Consequently their conclusions may not be reliable. The research also fails to take account of a major report by St Clair and Chinn  who conducted tests showing that helmeted can experience rotational acceleration levels up to 20 krad/s² by impacting a central vent position. McIntosh et al failed to test for central vent impacts.
3. Slightly higher centre of gravity (0.2% - 1%)
4. Extra weight on the head contributing to increasing the forces for going over the handlebars when braking very hard.
5. Extra wind forces on head (30%-40%) adding to riding instability. Refer http://www.ta.org.br/site/Banco/7manuai ... helmet.pdf
and ‘Effect of crosswind on bicycle with and without rider control
N. Sharma, R. Happee, A. L. Schwab.
6 Up to 10g forces (60N) due to high impact accelerations, by hitting deep pot-holes, affecting balance and riding stability. http://www.bmj.com/content/346/bmj.f381 ... -responses
‘A rider travelling at about 12mph (20km/hr) or 5m/s and hitting a pothole, for example 300mm wide, may take about 0.05 seconds to cover the distance. A typical reaction time may be about 0.1- 0.2 seconds, so the rider would not have time to react to any forces from the pothole impact. Reportedly up to 10g forces to helmets can occur from hitting deep potholes (ref 6). Helmets may add 5% to 10% extra to the bare head mass. The forces on the head would likely be higher for a helmet wearer and in random directions and the out of balance forces from the impact on the rider and bicycle may vary in direction. As a consequence wearing a helmet increases the risk of falling by incurring extra forces that the rider may not have time to react to.’
6. Increased risk-taking at times, or being slightly less cautious, by some helmeted cyclists.
7. Helmets making young children look taller giving drivers the impression of an older child.
8. Drivers passing closer when overtaking cyclists wearing helmets.
9. Riders being distracted by comfort aspects, straps rubbing, ventilation holes catching flies, wasps or by adjusting their helmet.
10. Riders feeling warmer/hotter at times, affecting concentration and increasing fatigue.
11. Helmet or strapping affecting the sound pattern reaching the ears.
Given the fact that helmets are not tested for rotational accelerations and designs vary, any cyclist choosing not to wear a helmet is making a reasonable decision as they cannot be assured that the product is safe. Insurance requirements to wear helmets are not justified with the uncertainty about the safety aspects of helmets.
A number of reports details a higher accident rate can occur following helmet use, refer;http://www.cycle-helmets.com/au-assessment-2015.pdf http://www.ta.org.br/site/Banco/7manuai ... helmet.pdf
The BMJ reported the findings of; Ben Goldacre, Wellcome research fellow in epidemiology, and David Spiegelhalter, Winton professor for the public understanding of risk.http://www.bmj.com/content/346/bmj.f381 ... =ref#ref-9
In any case, the current uncertainty about any benefit from helmet wearing or promotion is unlikely to be substantially reduced by further research. Equally, we can be certain that helmets will continue to be debated, and at length. The enduring popularity of helmets as a proposed major intervention for increased road safety may therefore lie not with their direct benefits—which seem too modest to capture compared with other strategies—but more with the cultural, psychological, and political aspects of popular debate around risk.