Motorbike crashes: highside and lowside crashes explained | Hacker News Reader

Motorbike crashes: highside and lowside crashes explained

driverknowledgetests.com

66 pointsmolteanu66 comments

This is an oversimplified assessment of these crashes. You can overload the front just by pushing on the bars too hard. You can unload the rear and high side by letting off the throttle. You can do either or both by shifting your weight while holding maintenance throttle (no throttle or bar input.)

Tires in general, but especially motorcycle tires pushed to the limit of traction behave differently depending on how they are loaded, it’s a very non-linear system. If you suddenly put 85 units of force into the tire (ignoring what these units are, doesn’t matter for this discussion) you can overload the tire and break traction. If you load the tire progressively, you may be able to put 105,106 units of force in and have the tire hold. You may be able to push the tire to 107 and get a little drift but maintain traction.

Different parts of the tire heat and cool differently, you may have been through 4 rights and 1 left, and the second left can only handle 95% of the force the last right can take. A cold tire can just slide out with no warning, no feel. Even the best riders in the world get nailed by cold tires on a regular basis.

The other component of these crashes in the video is stiff suspension and poor body position. These videos are almost exclusively knobs that bought more bike than they know how to ride. If you want to see what a bike can do, check out motard riding, they aren’t using magical tires… they have squishy suspension and they push the bike down lower than their body and use their legs as part of the suspension. You do that and you can drift a motorcycle at angles that would be impossible on a street bike. Same tires. Nothing magic.

Every crash on that site could have been recovered with better body positioning and some pre-planning. If you’d like to learn how, come join me at AFM racing and Pacific Track Time. I’ll happily run a couple laps with anyone from hacker news. I’m #413. See you out there

I used to ride a motorcycle. Once in Palomar mountain i was riding with a group and saw this guy who brought race tires. He was at the bottom of the mountain and I saw him getting ready with his group at the bottom of the mountain.

We turn around, head back up and head back down the mountain again... A group of bikes raced past us going way too fast. I had just exited a corner (they were about to enter). All of a sudden after they passed, I hear all hell on earth break lose of a crash.

We turn around and one of the guys was pinned in between the guardrail and his bike, sandwiched and totally stuck in the middle. On the other side was a typical Palomar dropoff... I don't know how big but you ain't surviving if you go over the edge. You're going to turn in a slinky.

We eventually pull the guy out and he's totally concussed with broken shoulder/arm. Otherwise he was fine.

Turns out, he didn't warm up his tires enough (race tires need to be warm) and had a low slide crash as soon as he hit his brakes.

The other crazy part what was when we got his helmet off, he was one of the mechanics that I brought my bike to! And I had just brought my bike in a few weeks before so I immediately recognized him.

fun times.

I almost had a high side accident after i locked both my brakes at midnight coming home from my girlfriends place. There was a notorious intersection with cameras in it that you came downhill to. And it was one of the intersections that has a shorter yellow lights than any other light, you know, just so they can get more tickets.

It was cold af outside and my visor was fogging, so I will not forget that moment speeding down at 60mph, hitting the yellow and realizing I wasn't going to make it, hitting the brakes, and seemingly locked up so bad I was doing 45 degree turns in both directions for a second or two before gaining control.

> Turns out, he didn't warm up his tires enough (race tires need to be warm)

Brakes too.

I was sitting on the couch yesterday, trying to figure out what happened the day before, when I found this article explaining it clearly.

It was a fast descent on my road bike, followed by a tight corner. There was gravel and dust on the road, as the article mentions. I hit the brakes at the wrong time, right in the corner, at high speed, over the gravel. I've lost control in a fraction of a second. The front wheel slipped and I was on my feet in what seemed to me no more than a second.

My first bicycle crash and my knee damaged. I haven't seen these things explained until now. It might be that crashes are a rite of passage for bikers and cyclists. Incidentally, I'm not sure why road cyclists don't wear knee pads. At least they are not promoted.

Wear your helmet (I got that damaged, too), wear something underneath your jersey to avoid road rash, protect your knees and wear gloves. It all happens in a fraction of second, you don't have time to think about anything. You don't need protective gear and an understanding of the road and bike physics (this article) until you do!

> Incidentally, I'm not sure why road cyclists don't wear knee pads.

I mountainbike, started with trail and am now doing more XC. When I ride either type during training (or just fun rides), I always wear knee pads. But when I race XC I don't, even though often we'll do the same downhill sections (not black diamond obviously, but certainly rocky blues).

I think it might be that, at least in racing, knee pads restrict your movement a little. Though I've been wearing them for so long I don't even notice them anymore, and certainly if you wore knee pads on a road bike they would be less restrictive than even lightweight MTB knee pads.

For mountainbike, yes, I've seen a more "aggressive" approach towards protective gear. But even in that area, the feeling I get is that you get that equipment only if you're really into jumps and high-speed. Other than than, it's just a walk in the park, as the saying goes.

One gets better at crashing the longer they mountain bike (joke, but also true).

I’m similar philosophy. Usually in pads early season and when riding casual. Once it gets hot, I’m not riding as hard and heat exhaustion is the main threat, not crashing, and the pads take a break until the fall.

If you are going to wear knee pads, you should also wear elbow pads, shoulder pads, padded gloves, and a spine protector.

Road cycling is stupid dangerous even without cars. People descending at 70km/h wearing nothing but Lycra and a bit of polystyrol on their head...

Right?! And still, "lycra only" seems to be the standard, and not only for competitive rides.

GCN has over 3 million subscribers on youtube, they post highly informative road bike videos, often with people who competed professionally at the highest levels. Still, they don't wear any protective gear rather than the helmet. For someone who just starts biking and wants more info about the sport, will look at these videos and don't even know about the existence of such a gear or the need for it.

That's just one example, but literally all articles I've read in the past 10 years or so are picturing slim, fit, cyclists wearing just lycra.

It's still a big question mark for me.

I think the problem is that riding with protectors is uncomfortable when you ride for hours. I ride a road bike too, and I don't wear protectors, I just don't ride that fast because it scares me.

For downhill mountain bikers, full protective gear is standard, but I guess they don't ride for hours, and they crash more regularly.

You spend at least 3 times as long going up the hill as you do going down it, and a reasonably fit person will be putting out the equivalent heat of an 800w-1000w heater during that period. This makes wearing protective gear impossible. If you look at downhill mountain biking the gear worn is very different.

That’s the reason!

I got my motorcycle license in CA back in 2007... assume this is still true, but the driving test was nearly impossible with anything but a small cruiser bike (which no one owns) due to the required turning radius on the cones section. In lieue of that you could take a day long motorcycle safety course where they hammer into you the dangers of high/lowsides and how to prevent them. It's generally held belief amongst riders that this is on purpose.

While I had a lowside (low speed loose gravel coming out of a turn by a construction zone), never had a highside. That said, I would occasionally have nightmares about them when I was an active rider. I feared them as much as getting clipped by a car running a red light.

Still the same. Got mine a few years ago. Driving test still impossible so you do the class instead. Both written portion and training have this info on it.

This test? https://www.youtube.com/watch?v=E9hE8GUVUWM

... could you explain why this is nearly impossible on anything but a small cruiser? I'm having trouble understanding what you mean.

I’ll guess that anything other than a small cruiser is going to be some combination of higher center of gravity + more weight, which just gets harder and harder to learn farther (accurately) at very low speeds.

Also gearing and turning radius. Putting along at 3mph is much harder on a liter bike.

Sports bikes in particular don't have much steering angle to work with, so at slow speeds - on a course designed to test slow speed manouvering - they can have wide turning circles.

It is possible to turn more tightly but it requires leaning much more into the turn. That needs a lot of skill and confidence to do smoothly at low speed when the bike has a high center of gravity. The bike will crash if you brake or stall, and on a sports bike there often isn't a huge amount of torque at low engine speeds, so you need to be very adept at clutch slipping and modulating the rear brake.

The course in the video isn't that bad though. A U-turn on the road, a mandatory part of the UK test, is done with a tighter radius than anything on that video.

Maneuvering at low speeds is all in the rear brake. It smooths out the power delivery and reduces latency when you need more/less power. I took the test on an SV650 and barely passed. Years later, once I learned to use the rear brake, I did it on my 848 easily.

Interestingly enough my bike was a SV650 as well (and came very close to purchasing an 848 as my next)

Ah. You were saying that it was nearly impossible which didn't seem right at all. Needs a few weeks of practice to become competent at yes certainly, but nearly impossible on anything but a cruiser just seemed wrong to me.

Should have worded as very difficult for a new rider.

Around that time I took the test in NJ. Not having a bike yet, I rented one from a Norvegian woman who specialiezed in this for some reason. Before the test she showed me the test setup in an open area with cones. This was good because I hadnt ridden in 10 years. I protested that the cones could not possibly be that close. She said they are the right distance apart and demonstrated how to do it - with only one hand just to rob it in.

I was able to then do it and also do the same in the test and pass.

I think it makes a lot of sense to rent a more comfortable bike, even a scooter, for the test if it's allowed. I actually wanted to do thr MSF course which is like a luxury that does not exist anywhere else but the demand for them was huge and they were all booked, even the expensive ones.

The same was recommended in CA if for some reason you didn't have time for the safety course.

> actually wanted to do thr MSF course which is like a luxury that does not exist anywhere else but the demand for them was huge and they were all booked

I got lucky and bought a slot on craigslist from someone who decided to bail. Not sure, how often that occurs (and in my case that was 20 years ago). Well worth it imho (while the instructors do stress that they teach you only the very basics). I can't imagine going out in traffic with little more than the skill to ride around cones (as challenging as that is, particularly on a large bike).

(actually, I just remember that I was riding before w/o either on my "learner's permit", in fact, I rode to the training on my CB750F, but I wouldn't say that it's a good idea to do so)

Low slides are the best and kind of fun… when wearing a race suit on a race track. It was most often the case that my racing motorcycle and my protective gear was still in one piece after a low slide. Race tracks typically have a mixture of grass, sand, and rocks that you slide into.

Fortunately I’ve never experienced a high side. Those can be dangerous for a person, as the head or shoulders are the common impact points.

It seems so, indeed. You are closer to the ground and slide on the road rather than hitting something with your head or shoulders. I often complained to myself with "who put the rocks there right beside the track?" when I was little and watched the sport. In my mind, the racers got hurt by those stones when they fell off their bikes.

The higher end sport and sport naked motorcycles make high sides almost next to impossible. They have lean angle sensitive traction control which allows you to literally be full throttle out of a corner, with the actual power to the rear tire will be modulated based on the setting (which can have an intermediate value and allow you to pretty much hold a drift without it getting away from you.

The top of the line models from Ducati and BMW also make braking lowsides (where you slide the front from too much brake and tuck it) very rare, because they also have lean sensitive ABS where the solenoids distribute the braking force between front and rear brakes depending on how much you are leaned over.

If you are leaning that much in the street you're a hazard to yourself and others. In the street lean with the body, not the bike, to reduce the angle. You never know if there's oil or a new hole in the tarmac. Can always do track days to have fun.

This is incorrect. There is literally nothing a motorcycle’s electronics can do to prevent you from putting too much input into the bars, fix your stupid body position, or save you from a decreasing radius or off camber turn. Say nothing of dirt, gravel, moisture, leaves, etc.

Yep. If the only thing you have to deal with is a ham fisted input into the throttle, the bike may prevent that. Most crashes aren’t from that. Rider aids are just that, aids. You see skilled riders with top tier aids crash all the time during racing.

Don’t trust the Nannies. Learn to control your motorcycle and you will only have them to nudge you in the rare case you need it. That’s what they are for.

That's completely false and dangerous to think. Even said manufacturers of motorcycles equipped with six axis IMU for ABS and traction control specify this in their user manuals.

You have configurable levels of TCS on modern motorcycles, because what the electronics can't know is the current difference between static and dynamic friction. That depends on what tires you have, what pressure and temperature they are at, the road surface composition, temperature, water presence. There's also suspension and road imperfections and other things.

The difference between static and dynamic friction is critical in deciding when the electronics need to intervene. For dry perfect asphalt the maximum traction is at 14% (if I remember correctly, exact figure not important) wheel slip. Meaning the wheel is accelerating/decelerating 14% more than the bike. Any less and you lengthen the stopping distance or losing acceleration. Any more and you risk crashing. On water though the difference between static and dynamic friction is very large. Once a slide begins the available traction goes to almost nothing compared to before (I think 30%) and you are in for a bad time. An simpler example is road bumps. There's nothing the electronics can do if you wheel leaves the ground because your suspension can't cope.

In MotoGP in addition to the six axis IMU they also have GPS and the values in the electronics are set manually for each turn depending on what the conditions they expect to find there at that time. And they still have both highsides and lowsides! Reality is extremely resistant to being perfectly modeled in computers.

I've done both of these (on dirt and ice). "A lowside crash is usually less damaging than a highside crash" is one hell of an understatement. With a lowside and wearing the right gear you might end up a bit dizzy from tumbling, with a highside you are launched into the air and as soon as you land you have your entire 200 kilogram bike tumbling towards you. I've been lucky and been uninjured every time but you can really picture a lot of damage being done by having the thing land on top of you, even if you dont hurt yourself when you hit the ground

Can't help but think of Wayne Rainey.

https://www.youtube.com/watch?v=7QDDaymJHYA

In the highside crash video the motorcycle wobbles shortly before the crash. This reminds me of the death wobble in which the steering goes out of control.

They're effectively the same process occurring to different degree. A high side is what you get when you arrive at a point of unrecoverable inflection in such a wobble.

Not sure that’s true. My understanding is the lowside happens when the tires lose traction while cornering so the bike skids along the road on its side with rider often beneath it (or hopefully behind it).

The highside happens when the bike is cornering in a skid and the tires regain traction but he angle of the bike is insufficient for the speed and the radius of the corner[1]. This regaining of traction causes the bike to flip towards the outside of the corner, throwing the rider over the high side.

A death wobble happens on any road (ie not just when cornering) and you hit a bump that the suspension can’t recover from which also causes a deflection in the steering. The action of the bike attempting to gyroscopically self-correct, coupled with the rebound of the suspension causes the bike to go into the wobble from side to side (if the bike has a steering or suspension flaw). You eventually get thrown off the bike either side.

[1] Given the speed of the bike, the angle of lean and the radius of the corner I would think it is often the case in a high side that if the tyre had not regained traction that the bike would have skidded out and the rider would have had a low side crash instead.

> They're effectively the same process occurring to different degree. A high side is what you get when you arrive at a point of unrecoverable inflection in such a wobble.

Simply not true? Lean a bike in a turn and jam on the brakes will give you a low side. No wobble.

Loss of friction holding the bike up through the turn. Went from static to kenetic.

I don't disagree, but I also didn't mention low sides at all so I'm unsure of what you're trying to express here.

My point is that a high side is what happens if you lose and regain rear traction, landing you in an unstable death wobble that immediately flings you out. It's possible to regain traction after losing it in a corner and not high side, you just get some wobble which you (more, the bike's suspension) can hopefully correct for. It's a matter of degree.

Nah. Incorrect. The wobble can happen when you’re 100% straight up and down. Highside needs a lot of yaw force to get the flick.

Well, yes. How 'high' the side is depends on many factors, but it's a gradient. A death wobble when going in a straight line happens to be relatively weak with regard to how much force the rider is ejected with should it fully destabilize / lose contact w/ the road in either direction, but you still get ejected in the same way.

As you increase wheel misalignment with the direction of travel (and speed), more energy goes into the fling. As you increase lean angle (more lean means more time for the wobble to accelerate you) the fling gets more violent on one side and less violent on the other (the 'high' and 'low' sides).

Hence, the observation that high sides are what happens when you enter a death wobble that is already past the point of stability.

Do you have sources to prove this?

I race motorcycles, I have a mechanical engineering degree and build race motorcycles, spent a lot of time researching motorcycle suspension dynamics to improve my systems and I think you’re basically making this up.

We can chat about it more, but I’d like to see your sources so I can see what you’re basing this on.

Prove what, specifically? I'm honestly unsure which part is a controversial enough claim as to require sources.

It seems trivial to me that in both cases a perpendicular force applied at the road acts to fling you, and that said force comes from wheel misalignment with the direction of travel.

Is that not the case?

Prove that the dynamic instability that causes a speed wobble is the same thing that causes a high side.

Here is an article on the physics of wobble:

https://en.wikipedia.org/wiki/Speed_wobble

A high side happens when the rear tire breaks traction at lean, and is no longer able to hold the arc it’s trying to turn on. The forces in the tire, suspension, twist and deflection in the swingarm and the frame of the motorcycle rapidly unload, and the bike turns around the z axis if x and y are the flat plane of the road surface. Then catches traction, and that z axis rotation and gyroscopic forces becomes a violent flick to stand the bike up straight.

These things are totally different.

> Prove that the dynamic instability that causes a speed wobble is the same thing that causes a high side.

This is a broader claim than the one I made.

> A high side happens when the rear tire breaks traction at lean, and is no longer able to hold the arc it’s trying to turn on. [...] Then catches traction, and that z axis rotation and gyroscopic forces becomes a violent flick to stand the bike up straight.

How much lean? And how much traction loss / for how long? What if there's just enough to where a high side doesn't occur and the bike/rider don't fly off? Will the bike instantly right itself with no overshoot, without any sort of steering column oscillation? If there is an oscillatory response, what do you call it? What do you call it as you gradually reduce the lean angle to 0?

At near 0 lean angle, is this oscillatory response meaningfully different from the oscillation of a speed wobble?

My understanding is that the highside always has that wobble. This is the tyre losing and then (fatally) regaining grip just before the crash. It’s the regain of traction that causes the vector of force towards the outside of the corner that throws the rider over the high side of the bike.

This is the death wobble for people who don’t know. https://youtu.be/eoc1EM6yUSc

In this video the rider handles it perfectly and doesn’t crash but you can easily see how this has caused many crashes. As I understand it, it is a harmonic wobble after hitting a bump that intensifies and is due to a flaw in the design of the rear suspension on some Harley Davidson models that they have chosen not to fix to keep the designs authentic. Make of that what you will.

Another terrifying variant on the “death wobble” is the “tank slapper”. This is typically caused by a flaw in the front steering (specifically having the steering geometry too vertical). Having the front forks close to vertical makes the bike handle very fast so is favoured by sports bikes however if the bike steers too quickly and hits a bump the steering will veer uncontrollably from side to side eventually causing the riders wrists to hit the sides of the petrol tank as the bike careers down the road weaving uncontrollably. The most terrifying part of all is slowing down makes a tank slapper worse so pretty much the only way it’s possible to recover from a tank slapper is to accelerate hard, get the front wheel off the ground and put it down straight. As a rider even thinking about the prospect of accelerating hard when in that situation makes me feel sick. Tank slappers are prevented by fitting a steering damper. I had a (crazy) friend[1] who bought a bike that was infamous for tank slappers[2] and then remove the steering damper to “see what would happen”. He had a tank slapper on the West Side Highway in Manhattan.

[1] Hi Kirat!

[2] Old Suzuki TL1000s

Accelerating enough to be always spinning the back wheel is also the way to avoid high-siders. Perhaps only very powerful bikes can do this predictably at any speed. It's the same technique as a speed way bike, but on bitumen and far higher speeds.

Mick Doohan was a master at this. https://www.youtube.com/watch?v=Bs0Kg-niVk8

On the 'supermoto' side of things: https://www.youtube.com/watch?v=6SXtaUQxsWk&t=27s

Yeah that controlled drift thing at speed is completely terrifying and amazingly skillful. Not for me, though. I was always taught to set up before the corner with the bike still vertical "in slow, out fast". I guess that's why on the one hand I could never be a racer but on the other hand I never crashed.

Mick had a much different body position than is standard now.

If you spin the rear while you’re hanging off like a current MotoGP rider, you’re going to get flung into the atmosphere.

I’m sorry but this is conjecture about how to save or prevent a highside, you shouldn’t actually try to put this advice into practice.

When you’re putting input into the bike at lean, it won’t wobble. The wobble is a progression that starts with a lightly loaded front tire, and every bike I’ve ridden with a good quick front suspension geometry will wobble in the right circumstance. A steering damper will kill the progression of a wobble, but if you’re accelerating the front can still give a wicked shake on a bike with a damper. Enough to loosen the front brake pads, smash thumbs, etc.

When racing, if you have a hill crest that you’re accelerating over and you set the front down after the hill, it’s common to get a good shake. You learn to ride through it.

Highsides are unrelated to tankslappers - it is a totally different concept, as discussed in another post. As stated in the article the highside is caused by rear breaking traction and then regaining it while the bike is crossed up, sending you either over the bars or skyward. My own recent highside (6 weeks ago) was caused by an engine seizure after a downchange from fifth in a third gear corner in qualifying. I had the bike leaned over, let out the clutch lever and because of the lean angle the bike rear kicked to the left, grabbed, kicked right and threw me over the bars. Well, so I was told - I do not remember the crash, waking up in the medical centre.

Highsides are particularly nasty, especially if you are knocked out so that you cannot control your crash and get rag dolled.

Glad that you are ok. Engine seizures/failures are a frustrating way to end a race.

For relative values of OK - right collarbone/shoulder/4 ribs, right knee ACL (fortunately micro tears, not snapped) and a traumatic brain injury (big bleed). I had lowsided the previous round after losing the front and that was fine, you slide along the track, controlling the fall and slide. In the last one was pitched head first into the track, knocked out and got severely rag dolled.

Maybe you should find a different sport...

Splashing about in reef breaks off the south coast is a lot a fun .. and water's soft, right?

https://youtu.be/xjHaFOGBPzk?t=144

( As a physics note, you don't often see a three lipped wave:

https://youtu.be/xjHaFOGBPzk?t=346

)

Ouch

You can highside by locking the rear, but the common highside you see on track is pushing the rear tire past its limit of traction, while having a heavy load on the rear suspension. As the tire breaks traction, the rear suspension unloads, the tire catches because the force the suspension was putting into the tire is gone and now it only has to support its grip, the rear suspension loads heavily now that the tire has grip and the spring reacts in the way you’d expect. Boing. The yaw angle induced is enough to fling the rider off. I’ve high sided off and then once the bike was free of me it just started riding straight. Happy it was free of the problem.

The rider into the video is putting some really ham handed inputs into the motorcycle. It’s not a wobble, bikes don’t “wobble” at lean, it’s a culmination of looking at the front wheel, forgetting where they are in the turn, surprising themselves about how close they are to the line, scaring themselves about the cliff edge, while being shocked about what the bike is doing. The person on the bike has stopped riding, the bike was riding them at that point. It’s a good example of someone way out of their depth on a capable motorcycle.

I'm confused about how a loose chain can cause the rear wheel to lock. Does the chain wedge between the rear sprocket and wheel?

It's hard to tell what's actually happening in that clip. To me it looks like the chain is actually fully off the rear sprocket just before the rear locks up (it appears to have come off around 1:12). At that point in time the rear wheel should just be free spinning. It also appears to be free spinning during the highside, which is strange because I would expect the most likely non-rider-error issue in this case to be the chain binding between the rear sprocket and the swing arm.

I'm almost inclined to call that one rider error. Their general body language and control of the bike don't suggest to me that they're an experienced rider, and it almost looks like they've just panic-braked and locked up the rear, except it's an odd speed and place to have done that too.

That is exactly what happened. You can see the rear lock and leave a black stripe.

i was once doing a racecar event at a venue with two racetracks. the other track had a motorcycle event and i think they airlifted three people out over the course of two days. i do not think i will ever be comfortable with riding a motorcycle.

It's indisputable that motorcycling is a relatively dangerous mode of transport. That said, where I live the required education and multiple exams for public road motorcycling are pretty comprehensive.

Most accidents involving multiple drivers/riders occur due to right of way errors. I've been motorcycling for around 5 years now (on a pretty slow bike) and used to commute that way exclusively. In my experience you're pretty safe if you ride like everybody's drunk and out to kill you.

I keep the fun stuff off road on a monster KTM dirt bike with a gearing that kicks up the front for the first 3 gears. :-)

I rode daily for a long time. Road hazards like diesel and ice were the biggest issues when I commuted, though you really have to anticipate what drivers are going to do. I've been down a few times, mostly from screwing around, once from worn tires, once from ice. You don't learn the limits unless you find them. I'm comfortable knowing exactly what I can and can't do if the need arises.

> i was once doing a racecar event at a venue with two racetracks. the other track had a motorcycle event and i think they airlifted three people out over the course of two days. i do not think i will ever be comfortable with riding a motorcycle.

For me it depends. I feel safer on a cruiser type bike - low CoG and easy to manoeuvre.

Fitting article given the IOM TT is happening right now.

A seriously nuts race if I ever saw one :)

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