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I always thought that OTB is caused by deceleration if the rider stops too abruptly. But I've found an article that says:

Jobst Brandt has a quite plausible theory that the typical "over-the-bars" crash is caused, not so much by braking too hard, but by braking hard without using the rider's arms to brace against the deceleration...

And also I've found an answer, that supports this argument.

On the other hand, there are also people who say otherwise.

I'd like to read opinions, supported by actual practice or science, on that topic.

P.S. Personally, I only use the front brake while standing on the pedals and never when I'm sitting on the saddle, so I'm more able to control my balance, shifting my weight to the back more or less and bracing against the deceleration with my arms.

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    Are we trying to stop really quickly, or literally "always" which includes coming to a leisurely stop over the course of 100 feet? – whatsisname Sep 8 '16 at 0:27
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    I have seen a video of someone going head-over while front-over braking. It happens so fast there is no real opportunity to, in a reactive mode, change one's posture. So if you're going to brace with your arms you need to do it before you begin to brake, not when you feel the bike beginning to levitate. – Daniel R Hicks Sep 8 '16 at 2:12
  • @DanielRHicks, I actually agree, do you see anything contradictory to that in my post? – Gill Bates Sep 8 '16 at 9:53
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    What are you looking for that you don't already have? You have 5 answers, one from a very strong contributor and one from one of our top 6 members, the most thoughtful of our MTBers. If you're looking for a cut and dried answer then it would not be of any use to anyone else, because very little in cycling is cut and dried. – andy256 Sep 13 '16 at 5:35
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+150

What is the fastest possible way for you to stop?

For me, it's pulling hard on the front brake, with my rear end well behind the seat. Ideally my rear wheel will be a couple inches off the ground the whole time. Actually achieving this is virtually impossible, but it should be the goal.

The braking technique you should use is a "light" version of whatever can haul you to a stop the quickest. Every time you come to a stoplight, or are reducing speed on a descent, use your front brake and push your rear end a little further back (or whatever technique works best for you). You don't have to brake hard. Just connect those motions in your mind by doing it every time.

The benefit of this is that when you suddenly have to do an emergency stop, you will instinctively do the best possible thing.

So to answer your question, yes, you should shift your weight back when you brake (along with bracing your arms, of course). Because if you don't, you will fail to do so in an emergency stop, when it really matters.

I completely disagree with Jobst Brandt's theory. Bracing your arms against hard braking is of course necessary, but it's completely instinctive, and therefore not a problem. What's not instinctive is 1. using your front brake, and 2. shifting your weight back. Your goal should be to make those instinctive too.

On top of this, you could further hedge against going OTB by practice stoppies (lifting the rear wheel under hard braking). If you do this, you will be much more in control during emergency stops.

  • This answer assumes a lot about riding style and conditions. I wouldn't recommend it in wet/icy conditions, or in technical off road riding. – Deleted User Sep 14 '16 at 18:02
  • @SuspendedUser Under normal situations, doing a "light" version of whatever is most effective for you holds true for off-road too, right? I edited the post to make this a little more clear, it was poorly worded before. It sounded like I was telling everyone to do what works best for me. – BSO rider Sep 14 '16 at 21:48
  • Not for me, no. All winter I rely heavily on my rear brake because > 80% of my time is on snow or ice from October to April. I rarely use my front brake because doing so means probably washing out the front wheel. The same goes for when I am riding roots and rock gardens in the summer; more heavily reliant on the rear brake. I could try to develop a front brake instinct for my summer road rides, but then the rest of my riding would likely suffer. You advice is excellent for a subset (or even majority) of riders, but certainly not appropriate for all. – Deleted User Sep 14 '16 at 21:59
  • @SuspendedUser Good point. Switching instinctive reactions when you switch bikes or terrain would be pretty hard :) – BSO rider Sep 14 '16 at 23:00
  • I agree - some people advice to not use front brake in emergency situation, but it's obviously false, because in emergency situation you need to stop as quickly as possible and it's impossible without using the front brake. So learning how to use the front break is essential. – Gill Bates Sep 17 '16 at 6:55
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As this is tagged MTBing, the simple answer to your questions is it depends, but moving weight back will almost always be preferable when MTBing.

I'll explain this looking at the extremes of the kinds of OTB accidents. At one extreme, high speed smooth surface slamming on the brake and going over the bars. The other is a steep descent and topple over the bars - can happen when stationary.

In the first, particularly with road bike brakes, just bracing will usually work as you won't generate enough braking force from the brakes (not the tires/road interface) to stop quickly enough to be able to go over (If you have a MTB with 200mm rotors and dual piston callipers think before jamming the front on full). If you are not braced, the bike stops very quickly when brakes are applied, you keep going, weight comes forward, you straighten your arms to brace, as your shoulders have moved forward all you are doing is lifting them higher rather than backwards, raising the CoG making things worse.......

The other extreme is the steep descent where the CoG is already close to tipping you over. Bracing is probably the worst thing you can do. You need to be in the Attack position, arms and legs bent, elbows out so you can move your body and maintain balance. You move weight backwards far enough to keep the back wheel loaded and lower you body weight - dropping your bum as close to the rear tire as you are brave enough to go. This may cause you to have straight arms but is not the brace position, and with straight arms in this situation, a crash from loss of control and balance is imminent. In this situation, the concern is maintain control then control speed.

  • Ordinary MTB v-brakes will easily raise the rear wheel while riding on a paved road at any decent speed. You don't need disc brakes for braking to be limited by CoG rather than available braking force. (I don't understand why typical hybrid / commuter bikes have such bad brakes that they can't even raise the rear wheel at all, even when you don't drop your butt behind the seat. It feels dangerous not to be able to stop quickly when I've borrowed my brother's bike, for example.) For me, it's normal for the rear wheel to lift if I stop quickly, as speed approaches 0. I have good balance. – Peter Cordes Sep 8 '16 at 0:12
  • "f you have a MTB with 200mm rotors and dual piston callipers" and 180mm forks with slow rebound and zero compression damping. – Vorac Sep 8 '16 at 7:26
  • @PeterCordes In a road situation the last thing you want is to lock a wheel. If you skid or raise your rear wheel, you've lost the ability to swerve whilst braking. It's the same reason we have ABS in cars. – mikeagg Sep 8 '16 at 14:38
  • @mikeagg: It only happens right as speed approaches zero, when my bike will stop within about a bike length anyway. It's not like I do a front-wheelie for many meters approaching a stop sign at the bottom of a hill! (And BTW, this is a nearly 20 year old bike with no suspension (Peugeot Dune)). And of course I don't lock the front wheel, that would be really dangerous! Anyway, I don't think having brakes too weak to achieve minimal straight-line stopping distance is much of a safety measure. IDK, maybe these bikes are mostly intended for riders that wouldn't know how to manage good brakes – Peter Cordes Sep 8 '16 at 14:59
  • you won't generate enough braking force from the brakes (not the tires/road interface) to stop quickly enough to be able to go over -- Untrue. Once the rear wheel levitates the entire weight of the bike and rider (plus some redirected momentum) is on the front wheel. If you have enough momentum at that point you're going over. – Daniel R Hicks Sep 11 '16 at 0:32
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Both explanations are true under different circumstances.

Situation 1: you brake hard using the front brake and don't brace against the handlebars. The bike will slow down and, unless you are bracing against something else (seat, pedals, etc) you will keep going forward. You will probably flop over the handlebars. This will happen with relatively minor braking forces.

Situation 2: you brake hard using the front brake and do brace against the handlebars. This will work pretty well until the braking forces are large enough, at which point you will pivot up and over the top of the handlebars anyway.

The better thing to do, of course, is to brace against something lower, usually the pedals. The aim is to stop yourself pivoting up. You can most easily do this by pushing yourself back and low behind the seat. You can then withstand much greater braking forces without going OTB.

  • How can I brace agains the pedals when my centre of mass is far above the pedals? – Crowley Sep 8 '16 at 14:28
  • @Crowley: Push yourself behind the seat. – Ian Howson Sep 8 '16 at 19:47
  • But still I am bracing more against handlebar than the pedals. – Crowley Sep 9 '16 at 9:23
  • Well, you could move back enough, brace your crotch against the rear of the saddle and use your back muscles to keep your upper body steady. I trust everyone can figure out why it's usually not done. – ojs Sep 10 '16 at 21:41
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    @Crowley: Handlebars are still involved, and it's unusual that they limit you. Like everything else in cycling, you'll have a better time if the big forces are going through your legs and arms. You'll be able to brake harder and be more in control. Heels down, butt back, stay low. Google 'mtb attack position'; it's very useful in road traffic too. – Ian Howson Sep 11 '16 at 19:45
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Standing on the pedals raises your center of mass, which is bad and makes it more likely to go over the bars. Keep your feet on the pedals and sit lightly on the saddle, but don't stand.

Moving your weight back as much as possible is good, also helps to make the back brakes work better. When you break using the front wheel, this will add a downwards force onto the front wheel and an upwards force on the back wheel, so you try to counteract that.

Then there are probably multiple kinds of going over the bars:

  • when you've got good brakes and good ground contact (so you don't just start sliding and then fall sideways or something), your whole bike may flip over and the only thing you can do is brake less using the front wheel. Which might mean that you crash into something instead.
  • or you can brake without properly estimating how much braking force there will be, not brace against the deceleration enough and go over the bars.

Seems to me like the latter shouldn't happen when you know your bike/brakes and aren't a novice rider.

  • Your first bullet point also happens easily if braking when turning. Its more of a loss of grip caused by over-braking at the wrong time. – Criggie Sep 7 '16 at 22:07
  • @Criggie Yes, but then you don't go over the handle bars, do you? That's why I didn't elaborate such a case. – Nobody Sep 8 '16 at 10:03
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Think about how heavy you are compared to your bike, so when your braking most of the momentum is you! You have 3 contact points with the bike, the handlebars, the saddle and the pedals and the best one to put the forces generated when braking through is the pedals, if you put all the force through the bars then you'll go over them, if the saddle then your relying on friction between you and it (slippery when wet). If you put the forces through the pedals you get more traction and stop faster as you push the bike into the ground.

So in order to do this you need to get out of the saddle and drop your heels, as soon as your heels are below the axle on the pedals your momentum will be driving you down into the bike and then driving the bike into the ground. Moving back slightly can also help, especially if going downhill but it's the heel position that's important.

Dropped heels also helps when just riding along, if your off (or on) road heading downhill at any speed and hit an obstacle, if your heels are dropped you'll sink into the bike and the chances are roll over the obstruction. If your heels aren't dropped that same obstacle will send you flying! You pivot up around your ankle and it's 'game over'.

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TL;DR Technique is a lot like bikes. There is rarely something appropriate for every situation and it's important to understand where advice or input is coming from. Advice from a pro road rider may be great for road racing, but it isn't going to necessarily translate if you are riding BMX. Circumstances and situation are everything.

There are a multitude of factors that go into this, so I am not going to suppose there is a completely correct answer.

To start with different riders will have varying levels of arm strength, so the ability to resist forward forces will vary accordingly. A pro Slope Style rider with a better developed upper body (from hours spent shoveling dirt and throwing a "heavy" bike around) maybe able to resist far more force than a pro road rider whose arms are purposely underdeveloped to maintain a favorable power to weight ratio.

Beyond the fact that the individual rider differences, there are large differences brought on by the braking situation. Braking suddenly on a road bike (with road geometry) on dry pavement has a vastly different set of circumstances than braking on loose wet mud on a steep downhill on a full downhill race rig. The amount of traction available will dictate how quickly one can bleed speed. In favorable conditions, the braking period may be relatively short and resisting those forces briefly with just upper body strength may be a good option. In poor conditions, some slide may be assumed, some balance may be required, and an extended period of force resistance may dictate different technique. You may be able to press your body weight for 2 seconds or less to come to a complete stop, but can you do it for 6 seconds while sliding down a rock garden and maintain your balance?

Other factors include instinctual development of skills for braking (muscle memory). I ride a few different styles (some road, downhill in the past, lots of winter snow riding and some mountain as well) and almost all of those styles require different technique. I can't remeber ever trying to get behind the seat on my road bike. The geometry doesn't really support it and it just isn't necessary during any normal riding situation. I have had times on a downhill rig sliding down a long gravel hill where the rear wheel is spinning against my shorts and I was damn glad because I hoped it would slow me down just a bit more. I've had times on my snow bike that I couldn't get behind the seat on an icy downhill because I had an expedition seat bag and ended up laying the bike down instead because I didn't think I could maintain control without getting my weight farther back.

In some situations, it is actually better to lock your rear wheel and enter a controlled slide and leave your front brake largely untouched. Sheldon has those situations deliniated here at the bottom. Keep in mind that while those may seem seldom to some, riding in ice and snow or on mud in the rain can mean that "slippery surfaces" are the norm.

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For every action, there is an equal and opposite reaction. Newton's 3rd law. In braking - especially sudden braking - the opposing force acts to destablize the bike and rider.

Riding motorbikes you learn - your most effective braking is through the front wheel - bigger disk, better contact, bigger contact patch. An experienced MTB rider - before the back-end lightens up under braking will shift his body weight to compensate and stablize the bike under braking forces.

Explicitly, the centre of gravity is moved lower and rear-ward. Which makes it far harder to "flip" the object.

The idea of simply bracing one's arms prevents an OTB is therefore not entirely true on its own.

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