Abrasion resistance

[Horse]

Google says ...

[The Spin Doctor]

If you want to find out how MotoCAP tests clothing, tune in tomorrow (Mon 27 April) at 11 for my Elevenses live webcast... www.facebook.com/survivalskills

[Hot_Air]

If they provide a hard edge against which the leather can fold up that could cause accelerated wear.

Spin, I see Alpinestars agrees with you because it's thought about avoiding this hard edge: the plastic elbow, knee and shoulder "sliders" are softer round the outside.

[Plastic sliders] are dual density – harder in the centre and slightly softer round the outside – and have a gel pad and protector built underneath too.

And they do more than merely slide. According to Alpinestars: the plastic is designed to dissipate some energy before it gets to the (regular) impact protector underneath.

The idea of these special [plastic] protectors around the shoulders, elbows and knees is that they help dissipate the energy of an impact, and spread it over a wider area. By doing that, the energy received through the protector is less.

I wonder if this dissipation could be significant? Some race suits - even in top level racing - appear to focus more on the "energy dissipating" slider than the impact protector underneath. I'm curious about the physics.

Getting leathered with Alpinestars’ MotoGP suits

[Horse]

[Plastic sliders] are dual density – harder in the centre and slightly softer round the outside – and have a gel pad and protector built underneath too.

In the early days of arrmour (1988) the UK pioneers Pro-Tek (there were others abroad) used very simple foam construction, a harder layer over softer. Their back protector had a more rigid carapace over foam. NB this wasn't the soft 'padding' foam often sewn in 'armadillo' or x-hatch patterns on the elbows etc of leathers.

About the same time, 'cups' of thin rigid plastic were sometimes fitted.

And they do more than merely slide. According to Alpinestars: the plastic is designed to dissipate some energy before it gets to the (regular) impact protector underneath.

The idea of these special [plastic] protectors around the shoulders, elbows and knees is that they help dissipate the energy of an impact, and spread it over a wider area. By doing that, the energy received through the protector is less.

I wonder if this dissipation could be significant? Some race suits - even in top level racing - appear to focus more on the "energy dissipating" slider than the impact protector underneath. I'm curious about the physics.

The idea of spreading the load might well work to avoid a point loading. But, as always, what injury does the layering seek to mitigate?

[Horse]

Following your link ....

The idea of these special protectors around the shoulders, elbows and knees is that they help dissipate the energy of an impact, and spread it over a wider area. By doing that, the energy received through the protector is less. The first contact with the tarmac should be a glancing blow, so we try to control that initial contact and reduce the friction. When the rider is then sliding the energy from the impact is dissipating.

So does the bolded 'dissipating' refer to the impact absorber rebounding gradually?

Also, they talk about first impact being a glancing - not direct - impact, possibly emphasising what Spin has often proposed, that typical body armour might not be able to mitigate against impact injury, but are beneficial to act as a sacrificial layer during slides.

[Hot_Air]

It's not entirely clear, is it?

Perhaps you're right that the metal helps protect against a point impact: 65mph crash result - Dainese Racing 3 leather jacket

[The Spin Doctor]

And as always, we need to know the numbers.

It's all very well saying "it's a moon rocket" but you can SAY what you like. If it can't get a dozen feet into the air, it's a poorly-performing moon rocket.

And then the numbers that ARE provided by the manufacturers of body armour are extremely difficult to interpret. It's like saying "my moon rocket produces x thrust". It's meaningless unless you know the mass of the rocket, how long it can produce thrust and the velocity you need to achieve. You need at very least mass, impact velocity, and the work down as the object compresses the 'crumple zone'. I think you also need to know how a point impact is spread over a bigger area for rigid protect. I sat down with the CE2-beating figures from a UK manufacturer, Google and a calculator some years ago, and calculated that the brand-new (then) chest protector could just about absorb the impact of a chicken hitting it at 30 mph.

Based on observation of results, aside from the reduction in abrasion injuries, body armour protects reasonably well against the kind of impact resulting a fall from the height of a highside - which results in an impact of around 6-7 m/s.

But Liz de Rome's work found little difference in broken bone injuries between riders wearing / not wearing body armour. Some of that would have been the built-in kack that's just foam padding, but presumably some riders had CE1 or 2 armour in place. So the assumption has to be that once you're up around the urban limit - around 13 to 14 m/s, it doesn't provide much protection.

Until someone shows me REAL figures, that's the best interpretation I can come up with.

[The Spin Doctor]

It's not entirely clear, is it?

Perhaps you're right that the metal helps protect against a point impact: 65mph crash result - Dainese Racing 3 leather jacket

That is NOT a 65 mph crash... it's a crash at whatever velocity that the ride acquired falling from the bike to the ground from acceleration due to gravity.

The rest is the result of abrasion in the slide.

[Hot_Air]

But Liz de Rome's work found little difference in broken bone injuries between riders wearing / not wearing body armour.

As expected. Bianca Albanese's work found that the CE standard for body armour is too low to be effective:

The allowable transmitted force of EN 1621-1 may be too high to effectively reduce the probability of impact injury [...] However, there is scope to reduce the EN 1621-1 maximum limit of 50 kN transmitted force. A reduction in the maximum force limit would improve rider protection and appears feasible

Bianca Albanese et al. Energy attenuation performance of impact protection worn by motorcyclists in real-world crashes

[Hot_Air]

Spin, I agree with your interpretation. Though protection from the height of a highside could matter – let’s compare two of my (unlucky) motorcycling mates: Donald and Boris.

Donald rides home one evening and, in the dusk light, doesn’t see the darned diesel that topples him. He hits the deck from, oh, 20 mph. ("Fake news, I was riding faster," claims Donald.) His CE1 knee armour takes the brunt. Unknown to him, the impact damages his cartilage. It causes a full-thickness lesion in his knee cartilage, hence Donald's arthritis in late middle-age. But he's elected President of the IAM.

On the Boris bike, diesel also takes him for a tumble at 20 mph. He’s wearing fancy SAS-TEC armour that surpasses CE2 by 40%. The bump causes trifling cartilage damage (he never notices it). And he continues his career as a trampoline performer until a ripe old age.

The point of this thought experiment is that, sometimes, impact protection can matter beyond fracture risk.

[Horse]

However, you ignored your third mate Vlad. His combat trousers are baggy, so the armour doesn't stay in place

[The Spin Doctor]

But people don't buy - or wear - body armour with the understanding that it may reduce some soft tissue damage.

Many fully expect it to work when they hit a car at a junction or a telegraph pole on a bend.

And there are still a big range of crashes that armour can't mitigate. My back injury was a crush injury from landing on my coccyx from a highside and my knee injury was rotational, after my foot got caught in the foot rest hanger and twisted my foot 180 degrees in the wrong direction.

Few people understand those limitations, and frankly, the manufacturers are loath to admit them.

[Hot_Air]

My back injury was a crush injury from landing on my coccyx from a highside

And (you may remember) there's evidence that the design of back protectors should be reconsidered to protect against this very injury. It's the main type of fracture for a motorcyclist's spine, and the current design of back protectors doesn't protect against it:

the design of back protectors should be reconsidered to better protect riders from what are referred to as compression fractures (craniocaudal force), which remain the primary form of fracture

Afquir et al (2020). Descriptive analysis of the effect of back protector on the prevention of vertebral and thoracolumbar injuries in serious motorcycle accident.

[Horse]

My back injury was a crush injury from landing on my coccyx from a highside

And (you may remember) there's evidence that the design of back protectors should be reconsidered to protect against this very injury. It's the main type of fracture for a motorcyclist's spine, and the current design of back protectors doesn't protect against it:

My 1988 ProTek Elite jacket had a coccyx pad ...

https://www.knox-lab.com/knox/

[The Spin Doctor]

And (you may remember) there's evidence that the design of back protectors should be reconsidered to protect against this very injury. It's the main type of fracture for a motorcyclist's spine, and the current design of back protectors doesn't protect against it:

Which is precisely why I said what I said... and have been saying the same for years.

[The Spin Doctor]

My 1988 ProTek Elite jacket had a coccyx pad ...

https://www.knox-lab.com/knox/

But AFAIK whilst that might prevent you from breaking your bottom (a mate of mine did exactly that, carrying something down stairs, slipping and sitting down very abruptly and fracturing his coccyx) it won't prevent crush injury to the spine's softer parts, which is what I really meant.

I damaged a couple of discs. And as it happened, I tweaked my back on Thursday bending down to investigate an interesting pebble whilst walking, and am suffering the stiff back / sciatica consequences this morning.

[Horse]

My 1988 ProTek Elite jacket had a coccyx pad ...

https://www.knox-lab.com/knox/

But AFAIK whilst that might prevent you from breaking your bottom (a mate of mine did exactly that, carrying something down stairs, slipping and sitting down very abruptly and fracturing his coccyx) it won't prevent crush injury to the spine's softer parts, which is what I really meant.

Simply pointing out that it was considered an area worth protecting over 30 years ago. I did a real test of it once, 'sitting down' after the bike went sideways on a patch of ice, at walking speed.

Especially in a one piece suit or longer jacket, it would be a relatively simple matter to extend air cushioning around the shoulder/upper arm, hips and base of spine.

[The Spin Doctor]

Simply pointing out that it was considered an area worth protecting over 30 years ago. I did a real test of it once, 'sitting down' after the bike went sideways on a patch of ice, at walking speed.

Especially in a one piece suit or longer jacket, it would be a relatively simple matter to extend air cushioning around the shoulder/upper arm, hips and base of spine.

So we're back to body armour only protecting against minor impacts. But until the stuff is marketed in a way that explains that, people will continue to have unrealistic expectations.

I know I sound like a broken record on this, but the message isn't getting over.

[Horse]

Especially in a one piece suit or longer jacket, it would be a relatively simple matter to extend air cushioning around the shoulder/upper arm, hips and base of spine.

So we're back to body armour only protecting against minor impacts.

Actually I meant that further, potentially effective, development may be possible.

However, it would require extensive investigation of crash outcomes (injuries) and causes ('mechanism of injury'), then design and implementation of accurate testing of prototypes against accurate data for impact forces likely to be sustained in real-world crashes.

In other words, it probably won't happen, particularly for road riders.

[Hot_Air]

I agree that further (potentially effective) development should be possible.

it would require extensive investigation of crash outcomes (injuries) and causes ('mechanism of injury'), then design and implementation of accurate testing of prototypes against accurate data for impact forces likely to be sustained in real-world crashes.

Oscar Ballester et al have done this work for torso injuries in road riding. And while their work was aimed at informing airbag R&D, it could apply to body armour too. But perhaps only an airbag, not old skool armour, could absorb sufficient impact to make a difference in many crashes?

Here's their paper (unfortunately all the good stuff is hidden behind a paywall): Analysis of trunk impact conditions in motorcycle road accidents based on epidemiological, accidentological data and multibody simulations