I am currently trying to create a dramatic introduction for one of my characters, John Smith. The current iteration of the idea has him suddenly colliding with a solid wall on a motorbike, which sounds lethal at high-enough speeds.

My question is as follows: with the right protective gear, what kind of speed does the vehicle have to be traveling at to achieve the effects I am looking for? I am specifically looking for a numeric answer.

I would appreciate some feedback on how to tweak or tone down the accident if it's still difficult to survive. I haven't been able to find a lot of info online, as it deals with traffic accidents only and I'm not convinced that these scenarios are comparable.

Detailed scenario

Time period: early 2020s - early 2040s

  1. John Smith, a 20 year-old, is riding home on a motorcycle during dusk time. He is wearing all the proper safety gear:

    • A good helmet
    • An electronically-controlled suit jacket with airbags and spinal column protection that engages when the jacket detects that an accident is imminent
    • We can assume that this protective gear is built out of much better materials than today, but unfortunately still no miracle carbon nanotubes, applied phlebotinum linings, or force fields.
  2. John loses focus for a second, doesn't realise he accidentally drove through a portal.

    • Portals work using the plain old "speedy thing goes in, speedy thing comes out wormhole" principle of operation, but are much harder to see, and are not colour coded. Certainly harder to spot in limited light conditions.
  3. John suddenly emerges out of the other portal, while maintaining most of his momentum.

    • The portal exits 1-1.5m above ground in a confined space
    • The confined space consists of an enclosed room (a scientific research lab), sized 12x20x20m
    • He is now hurtling towards a smooth, flat wall that reaches all the way to the ceiling
    • There isn't enough time to steer or make an emergency stop that would avoid the accident completely
  4. John crashes into the wall, which can be made of anything between bulletproof glass and concrete in terms of hardness. Fortunately he is not impaled or otherwise by the wall itself, just a simple impact. He may or may not impact the wall separately from the bike.

  5. He is immediately found by the lab staff who have rudimentary medical training. They are just about trained enough to establish that he can be moved to the hospital safely (i.e. no spine/skull damage), and know how to do so themselves. They cannot call the ambulance.

  6. John may have to spend anywhere between 6 weeks and up to 6 months in hospital to recover physically, while in a medically induced coma (for reasons that I'm willing to handwave or work around). He is otherwise mentally and physically unimpaired after a maximum of 8 months pass from the accident.

Possible mitigations

  1. The bike already decelerated to a safer speed due to passing an intersection earlier.
  2. Wall partially absorbs the impact, like an inverted crumple zone. I think that the right kind of reinforced glass (or similar material) should stretch out the length of the impact to make it more survivable.

Bonus: how do John's chances of survival change with his age, or the speed of impact?

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – James
    May 17, 2018 at 17:32
  • $\begingroup$ OK! With the edits I believe we have a question that leads to a specific answer that fits within the on/off-topic rules for the site, so I'm going to VTR. On a side note, I don't know if the industry does crash-test-dummies for motorcycles. If they do, that would be a direct reference. $\endgroup$
    – JBH
    May 22, 2018 at 4:11

6 Answers 6


Is it more important that John Smith hit the wall, or that the motorcycle does?

If the latter, he could hit the top of the wall with his motorcycle, and be thrown over the wall - survival would then depend on what was on the other side.

If it was, say, a large flat roof or garden, then, sure, tumbling and bouncing along until he slows to a stop will cause bruising at best, more likely several broken bones and a nasty concussion. However, his helmet should prevent his skull from being split open, and his biking leathers should protect him from having his skin scraped from his flesh as he skids along the ground.

(Both helmet and protective clothing are now tattered and wrecked beyond salvage, but that's what they're designed for - to take damage instead of you)

  • $\begingroup$ Hi, I've expanded a bit on the question to clarify that the wall reaches all the way up to the ceiling. Unfortunately he doesn't have much in the way of tumble/slide room. The biking gear is made out of something twice as strong as current leather, so scraping shouldn't be an issue. Having his gear take damage without killing the wearer is one of my goals here. $\endgroup$
    – John Smith
    May 15, 2018 at 9:57

Airbags are the way to go. They are available today: google "motorcycle airbag vest". By 2020, they can be made to form a 10 foot ball around the rider.

In addition, collision prediction technology on the bike can detect the impact, and deploy further airbags, eject the rider backwards, align the bike so it absorbs some impact, etc.

  • $\begingroup$ Thanks, added airbag to his protective gear. This should be near-future, so adequate protection by 2020 sounds good. $\endgroup$
    – John Smith
    May 15, 2018 at 9:56

You might be surprised by how much physical damage can be recovered from in 8 months. Broken hips can typically be recovered from with 6 months, and this guy is young enough that most of his bones will mend much faster than that, although surgical intervention will be required to prevent him from being badly disabled for the rest of his life. For reference, my own wife was put in a body cast due to having most of the bones in her body broken by a person who was actively assaulting her with a baseball bat (ancient history upon which I shall not expound) - she was out of that in 4 months and moving on.

Really, though, it's a matter of tone. Provided the head and vital organs remain intact, he could suffer multiple amputations, minor traumatic brain injury, a sucking chest wound and internal bleeding, and if a trauma surgery team was right there and had his blood type in stock, he could possibly survive and keep his limbs. But that's dark. Like Grey's Anatomy dark.

The real question is this: what, exactly, are you willing to subject him to? How desperate does the situation need to be in order to convey this story the way you see it? How far away is the trauma team from this surprise portal room? Then you can set the balance between technology level and the speed he was traveling at.

If he was going more than, say, 40 mph into this flat wall, and hits it head on and airborne, you have to mitigate somehow. I recommend having him hit the wall at an angle and continue upwards away from the bike, maybe hitting the ceiling and another wall on the way down. Each hit takes away kinetic energy; every year surprised riders bounce off of things at weird, terrifying angles and speeds that look like they should be fatal, but aren't. If that's not an option, the wall is going to have to be awfully convenient (and yet, somehow not convenient enough to prevent all injury).

Plain old wood and drywall is a decent choice, because it has a believable amount of give. If that's not the feel of the world you want, some current architects are playing with layered cardboard for better insulation and renewability. Aircrete is also a thing that might have enough bounce to be believable, provided it's the thinner stuff people are experimenting with in South and Central America, not the enormous blocks they make houses out of in the UK.

  • $\begingroup$ Hi, thank you for your personal perspective. I find it really valuable and hope that your wife is feeling well. I want the tone to be realistic, but not too dark. Broken limbs are all right, as is anything that can be corrected with a surgery, but no amputations. Ambulance cannot be called, but John can be transported relatively safely to an ER department at the local hospital by the lab staff in 1h. The idea of hitting the wall(s) at an angle to reduce speed sounds great, I'll use that. Awfully convenient I am OK with, as long as it's not a deus ex machina (because nobody is that lucky IRL). $\endgroup$
    – John Smith
    May 15, 2018 at 10:44

If he hits the wall while still in the air, the series of impacts is as follows.

  1. Front wheel hits the wall
  2. Front fairing hits the wall
  3. Rider's face hits the wall
  4. Motorcycle hits the rider in the back and drives him into the wall

I'm assuming something like a BMW R1200 GS, it's currently a popular style of bike, and conveniently someone has calculated its centre of mass which lies considerably above the front axle.

The simplest way to resolve the issue without having him wearing cutting edge safety gear is to let him land, fall, and hit the wall at an angle bike wheels first. Tyres and suspension absorb the bulk of the force, with decent leathers it's reasonable he could walk away from such an impact with nothing worse than having smacked his helmet against the bike and a bit of shock to his spine.

Against future tech and safety equipment, the bike would probably be a self drive with gyroscopic stability systems and automagic braking at the point of detecting an obstacle.

Safety gear update

All safety gear is sacrificial, the energy of the impact is dispersed by the destruction of the equipment.

Airbags are one shot kit, once it's been deployed the airbag must be replaced. This will probably be a replaceable inserted unit.
Helmets are destroyed on impact, if there has been an impact the helmet must be replaced. If you so much as drop the helmet on the floor you should replace it.
Leathers are generally ok as long as the surface is intact, they're mostly friction protection with a certain amount of inserted armour to protect vulnerable areas (joints and back). If the surface is particularly rough or there were sharp edges involved in the collision, leathers could also be damaged to the point of needing replacement.


Younger people heal faster
Impact force is relative to the square of the speed, every 1kmh slower significantly increases his survival chances.


I used to work inspecting airbag control modules. Airbag deployment alghoritms can be compared in complexity to things like orbital mechanics. There are some generalizations and simplifications that I've seen in this field, though. At least one european maker stated that, for deployment purposes, hitting another car with relative speed $x$ is roughly equivalent to hitting a hard wall at speed $ \frac{x}{2} $.

So, hitting a wall at 10 miles an hour should feel like being roadkilled by a Mercedez going on 20 mph. Imagine a collision between a car and a motorcycle... The motorcycle driver should survive if wearing at least a helmet. Protections for elbows and knees, and a leather jacket would be good to have too. From the question it seems that John has better protection than that, so he's good. How bad the damage will be and how long the driver will take to recover depends on how well he can brace for impact (hitting a vertical wall with your feet and forearms is generally better than hitting it with your shoulder or back).

If the wall is low enough that John Smith can go over it, rolling post impact will keep him from going paraplegic too.

Last but not least, luck plays a factor too. Check out this guy who had no protection at all, got his bike totalled by a car, but came out walking and without a scratch: https://youtu.be/VrjCbAf9g3c . In a collision against a wall, a "critical save" could be something deflecting the bike before the impact and causing the driver to roll against the wall, like the guy in the video rolled on the car.


Alternative - have the receiving chamber partially filled with water. You said its raining on the other side, perhaps a gradient is funneling stormwater through the portal where it pools.

Or the staff at the far end have done this on purpose, to slow down fast-moving things while minimising the damages.

Of course driving into a wall of water at 40 mph (60 km/h) is going to be exactly like a brick wall. So the water is shallow, about 100mm deep (4 inches) which puts it below the front axle height.

To your rider, it will feel like an unseen puddle or localised flooding (which will disguise passage through the portal.)

The bike will do one of two things depending on the depth of the water and the angle+height of the tyre. Either the bike will:

  1. aquaplane where it rises and tries to "skim" over the surface but looses momentum fast. There's an instant loss of steering too because the front tyre left the road. The bike will fall sideways and slide, normally in front of the rider until they diverge paths. OR:

  2. rotate as the front wheel digs in, the front suspension loads up, the bike slows down reasonably fast and the rear of the bike rises. Since the rider is not secured to a motorbike, they tend to fly Over the Bars (an OTB) or if the bike is not straight on, the bike falls to one side and everyone slides. In this case, the rider often slides in front of the bike.

Can you enlarge the room? Or slow the bike a little? 40 mph is the same as 17.9 m/s so your rider has just over 1 second to transit the length of the room.

If he'd slowed to 22.3 mph at the portal, then that's 10 m/s so 2 seconds to impact. And if the chamber was 50 metres long then he has 4.5 seconds which would feel like a very long time. "Altered phenomenology" during an accident is a known but poorly-researched topic, I've experienced it once.

During this reaction-time window, your rider might kick the sliding bike forwards to slow and reduce his own momentum.


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