Given the human condition of being a bony meat sack, we are not particularly well suited to brushing off impacts with the ground much in excess of tripping at a light jog.
When moving upwards of 32 times that speed inches above the roads in traffic, it might warrant augmenting our natural impact and abrasion resistance.
Enter motorcycle clothing and armors; where the former is typically intended as both functional clothing as well as a sacrificial layer before your skin, and the latter is generally billed as impact protection.
Coverage
Conventionally there are 5 typical locations that may receive armor in moto clothes or dedicated protectors, those being:- Elbow, Shoulder, Knee, & Hip Protectors - Which have a corresponding European Union standard[1] CE EN1621-1 defining expected characteristics and performance.
- Back Protectors - Having an associated standard CE EN1621-2.
Additionally some jackets, suits, and back-protectors may include options for chest armor (CE EN1621-3). While some pants/shorts, suits, and back-protectors may include sacral or coccyx coverage for the spine below the hip to the tailbone.
Materials
Armors will generally fall into one of these categories, or will combine multiples into a composite piece.
Hard plastic
Often made of thermoplastic polyurethane (otherwise known as TPU) forming plates and cups that resist abrasion, puncture, and deformation. Like the plate armors seen on knights of old, aside from potential to disperse point impacts across a larger surface area they do little to reduce impact energy. These are often backed with other materials to provide impact reduction and reduce wearer discomfort, they can be bulky and limit range of motion.
Foam
This can vary from stiff foams like you find in helmets that permanently deform to absorb one good hit, soft closed-cell foams which don't absorb much yet aren't one and done, and denser memory foams that offer more impact absorption yet slowly rebound after compression. The better options here will combine multiple densities of foam to find a compromise between impact dissipation, rebound, and stiffness. The main draw-backs tend to be bulk, heat retention, and some degree of stiffness.
Silicone gel
These can dissipate some impact energy and don't typically retain as much heat as foams, but they aren't generally as compressible for similar thickness leading to lower impact dissipation. More often these get used close to the body as a comfort layer in concert with foams and/or hard TPU armor. Along with MX jerseys and pants as buffer between you and dedicated external protectors.
Viscoelastic polymers
Operating on a principle similar to what's seen in a non-Newtonian fluid, like we see with corn-starch & water otherwise known as oobleck. Allowing the armor to be both soft and pliable at rest, then rigid in the plane of impact dissipating energy via the change in state along with the material's compression. While still spreading that energy over a larger surface area of the armor like more rigid options. Giving it advantages in impact reduction, bulk, and comfort vs. many other options.
The more state of the art viscoelastic options tend to be popular, as they do not overly encumber movement and once you're used to them you can almost forget it's there. Still some people prefer the more traditional hard plastic and foam, and in terms of externally worn protectors hard plastic shells do make a lot of sense for deflecting debris as well as their tendency to slide well on most surfaces.
Performance and Safety
No motorcycle gear is going to provide equivalent protection to a modern car's steel safety cage, with it's crumple zones and myriad of airbags surrounding you. Yet, I'll take some harm reduction over none as every little bit counts when you literally have skin and bone wagered in that gamble.
In theory if the manufacture creates and markets something as motorcycle protective gear, you would hope that it's generally safe and effective for that purpose. However, the equivalent of 'trust me bro' for what is fit for the purpose of motorcycle armor is only something well established brands with a long track-record should be able to get away with... And even then only so far.
So it would be very convenient to have some specific measurement criteria and independent lab testing of that criteria, to gauge relative performance of armor pieces with different combinations of materials for various manufactures.
Thankfully the EU seeing the need for some way for consumers to have some degree of minimal assurance and evaluate performance created a set of standards for that purpose.
The CE standard EN1621-1 for limb joint protectors uses a 50 joules (J) impact, and then measures transmitted forces in kilonewton (kN). To pass level 1 it must transmit less than 35kN, and for level 2 that is 20kN.
To put those transmitted forces into perspective, and as an American we'll use any unit of measure except the metric-system:
- 35kN - Approximately the bite force of a large crocodile[2]
- 20kN - Slightly more than the bite force of great white shark[3]
When you compare that to the average force required of 5kN to break a typical human femur it's not exactly confidence inspiring.
Some studies suggest the reduction in transmitted force to areas like the shoulder can range as low as 3-13% (averaging to an 8% reduction) using body armor, and generally there's no strong evidence to suggest association between body armor use and the risk of fracture injuries.
However, they did find fitted body armor significantly reduced risk of injuries in the form of open wounds (abrasions, cuts and lacerations) which resulted in a significant overall reduction in risk of injury[4], and hence secondary complications like infections.
Personally I think I'll take any reduction in force and injury vs. the alternative, and if you've ever had road rash or broke bones you're likely to agree.
References
[1] List of EN standards - Wikipedia;
https://en.wikipedia.org/wiki/List_of_EN_standards
[2] Erickson, Gregory M.; Gignac, Paul M.; Steppan, Scott J.; Lappin, A. Kristopher; Vliet, Kent A.; Brueggen, John D.; Inouye, Brian D.; Kledzik, David; Webb, Grahame J. W. (2012). "Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation";
https://ui.adsabs.harvard.edu/abs/2012PLoSO...731781E
[3] "Great White Tops List of Hardest-Biting Sharks". Discovery News. Discovery Channel;
http://dsc.discovery.com/news/2009/01/09/shark-bite-head.html
[4] de Rome L, Ivers R, Fitzharris M, Du W, Haworth N, Heritier S, Richardson D. "Motorcycle protective clothing: protection from injury or just the weather?";
https://pubmed.ncbi.nlm.nih.gov/21819816