17

Throughout the entire Kranked series, riders are doing insane jumps and drops. What puzzles me is that, despite beginner advice to land both wheels (nearly) simultaneously, about half of the landings are as seen on the first several seconds of the linked video:

  1. Land on rear tire
  2. While the front tire descends to the ground, perform a disproportional movement with the body - the hips move little, the upper body moves a lot.

I very much doubt those drops look like that, because the riders are unskilled. So - what is the usefulness of landing rear-first, provided tire placement precision is not a concern (i.e. not hopping around)?

  • 1
    Another thing to remember about beginner advice, is it relates to popping a foot in the air off a small lump, or riding off a kerb. Not jumping a road gap or falling 6 feet to flat. :-) – Grimm The Opiner Aug 14 '15 at 8:17
  • Is this conclusion correct? Most important before landing is to keep the center of mass high and centered above the bottom bracket. Landing on the rear tire absorbs more energy from the impact and a chance to regain traction on evil terain, while touching down provides more control (necessary in high speeds). – Vorac Mar 29 '16 at 17:53
12
  1. Landing on the rear wheel is a safe bet when you are not sure about the landing zone.

    For example a small tree root would be catastrophic if you are landing with both wheel. What happens is that since the downwards force from the fall is applied to both wheels, it is much harder to roll over the obstacle. If the front wheel cannot roll over, you basically flipped.

    But it is ok for the rear wheel to struggle to roll over an obstacle, as you can always drop the front wheel, balance the weight and roll easily over.

  2. After the initial landing, there is always a bounce-back where all the tyre and spokes compression/tension is released.

    It is better not to lose traction on the front wheel upon landing and thus landing on both wheel is also not a good idea.

What actually happens is 1) they are not exactly landing on rear wheel, it is an initial touch-down to reduce the falling momentum, 2) the body still continue to fall but decelerates thanks to the rear, 3) critical step to distribute the remaining falling momentum onto two wheels: too much on rear you will break something (minor) or even worse it will pump all your weight to the front wheel (see video at 34:54), too much on the front you will either flip or lose traction as previously discussed.

Having said all the above, what is important, perhaps a lot more important than whether you land on rear first or front first or both at the same time, is that you can extend the duration of impact as much as possible. This reduce the bounce-back as discussed in 2. Landing rear first is one way to prolong the impact and is also safer than landing front first.

  • That comment about the root doesn't make much sense. If it's a rooty terrain (roots everywhere) then no matter how you land, you'll have to deal with roots. If there is only 1 root, and upon landing it lies between your front and rear wheel, then hitting it with the rear wheel while the front one is still in the air will only increase the force with which the front wheel will land afterwards, reducing control. – cherouvim Aug 14 '15 at 14:14
  • small root is an example, in general any small obstacle is what I mean. Reducing control at later stage is still less hazardous than the initial landing and having obstacle in the front. As I said, you and your bicycle would easily do a 180 degree flip. – Nhân Lê Aug 14 '15 at 15:29
10

All those riders were doing a very specific of rear wheel landing where you land into a momentary manual (finding a balance point on the rear wheel by shifting your weight backwards and pulling on the handle bars with your arms and upper back). This lets you absorb the impact with your upper back and legs (the two biggest muscle groups in the body) as well as using the bike's suspension. This is essentially a modified trials technique (watch how Danny MacAskill lands drops to flat). If you have ever landed this way and you nail the balance point, you feel like you can extend the time of impact by quite a bit, reducing the peak forces you experience. When done right it feels like you have an enormous capacity to absorb huge hits (especially when landing to flat). Miss landing into the balance point and you can end up in a lot of pain.

Historical context of the linked video series

The video series you linked to (the Kranked series; early 2000's) came out in the infancy of the big air/free ride movement in the North Shore and interior BC (time and place I learned to mountain bike). Being able to absorb hits like this was useful as most of the trails at the time didn't have big run outs or fast lead ins (we built them when our bikes were hard tails with 3 inch suspension forks). As a result riders tended come into these insane drops at a slower speed that is done today. The drops also didn't have kickers and the transitions were not groomed or tailored. The style evolved to handle these natural drops at a slower speed. (Personal I never did anything above 10 feet on these trails, though a couple people I used to ride with did do some of those insane road gaps and were even featured in the video series you linked).

Today many of the trails are much different, more groomed and much faster with tailored launch rams and big transitions at the proper angle to land on. This necessitates a different style than the one in the video series.

7

I can't watch the video now, but there are two reasons to land on the rear wheel first:

  • The first wheel to touch down is more likely to suffer a loss of control or traction. It's a common two wheel maxim that "most rear wheel slides recover, most front wheel slides crash", so you want that wheel to be the rear.

  • It can help absorb the impact. Imagine the rider standing tall on the pedals with the bars pulled up to their chest, the bike nearly vertical. As the rear wheel hits the ground the rider can allow the bars to fall away from them while they simultaneously transition to hanging off the back - rider and bike collapse like a scissor-jack absorbing the impact. This is particularly beloved of trials riders, it can be emphasised to varying degrees depending on the severity of the drop - and the amount of suspension you do or don't have!

  • 1
    The second bullet point here is the main reason for landing on the back wheel after falling any great amount of distance. It forces some of the linear momentum of falling downwards to be converted into angular momentum, as the bike pivots around the back wheel. This causes a vertical deceleration and an angular acceleration about the back axle. You need good shocks on the front to then take the final impact of the front tire hitting the ground even harder than the back tire. – Luke Hutchison Aug 13 '15 at 21:12
  • 2
    Most importantly though, Since the pedals are between the back and front tires, it gives your body (and especially your knees) a cushion time between the back and the front tires hitting during which your body can decelerate. If you landed hard on both tires, you could blow out a knee and/or slam down hard on the seat. Impulse = force times time. By lengthening the total impact time, you reduce the impulse (i.e. the shock) to your body. – Luke Hutchison Aug 13 '15 at 21:15
5

When none of the wheels of a bicycle are on the ground, the center of mass is going to accelerate downward at approximately 9.8m/s/s and there's nothing the rider can do to significantly alter that. If both wheels touch the ground while the center of mass is at the highest possible point where that can occur, there will be a severe limit as to how much further down the center of mass can move after that point without damaging something. This means that, if landing on flat ground, the wheels must transfer enough force to the ground to reduce the velocity of the center of mass to zero within that distance, or else the center of mass will travel further than would be possible without damage, and as a consequence something will get damaged.

While the rear wheel is on the ground but the front is not, any force with which the rear wheel pushes on the ground will help to reduce the downward velocity of the center of mass. Although the rear wheel alone cannot supply as much upward force as would both wheels together, the center of mass can be much higher when just the rear wheel touches than it could be with both wheels touching. This effectively increases the distance over which the velocity of the center of mass can be reduced to zero, and thus reduces the peak amount of force required to accomplish that.

If a bicycle is landing on a downward-sloping ramp, the downward slope of the ramp will reduce (sometimes significantly) the amount of velocity the bicycle will need to shed after making contact with the terrain, to the point that one may be able to make a comfortable two-wheeled landing after falling a distance which would make a two-wheeled landing on a flat surface injurious to the rider, bicycle, or both.

4

When you land you tend to go out the front rather than the back.

You pretty much never land in perfect alignment and even if you do you get pushed around.

If you land front wheel first the rear wheel is going to come around and only get worse. When the rear does touch it will be out of alignment. As you absorb with your arms you only get more forward and go out the front. If you extend your arms and put you weight back as far as you can you have to take the whole hit. Your body is not in a position to help absorb the landing.

Rear wheel first the font is pulled into alignment and front steers so the front (can be) in alignment when the wheel touches even if the bike is not yet in alignment. Also legs are longer and stronger than arms to absorb the shock and can stay in position on the bike. Even if you are way rear wheel early you can shift weight forward and your body is in a position to absorb the landing.

4

Landing with the rear wheel first is rarely a good idea nowadays.

The video, although very "ballsy" and really of great historical importance, is very old school in regards to bike technology, terrain and rider technique.

Landing with the rear first is only useful when you need to drop to flat from more than 10 feet where you need a way to absorb as much as possible without risking a failure (bike or body). This is common in trial and BMX riding. Modern MTB riding doesn't involve much "hucking" to flat nowadays. Every aspect of aggressive MTB trail riding (all mountain, "enduro" and downhill) which is done at high speeds and requires high levels of control, mandates that all landing are as controlled as possible, which is to land both wheels at the same time on the transition of the landing. Even in slope style and big mountain events, landings are always very very smooth so the rider can land both wheels at the same time and not risk losing control:

enter image description here

Have a look at those riders on how smooth they land both wheels at the same time. Doing anything other than that in those speeds would be really dangerous: http://youtu.be/UoKL_bKx3bw?t=53s

Also, have a look at another explanation by some pro riders why landing with the rear is not good: http://youtu.be/XJSaSod4AqA?t=1m35s

0

Landing on the back wheel is a technique used to offer greater control of the bike when landing or transitioning between bike maneuvers. When landing on the rear wheel, your positioning on the bike has a greater amount of control and stability. Say, for instance, you need to turn or pivot the bike in order to land safely or successfully transition into a different maneuver. If landed on two wheels, the process itself would be slowed down drastically and you just might find yourself falling off or hitting something with your bike. If you landed on the front wheel, the same hazards apply, but your control of the bike is vastly lost.

In short, the rear wheel gives you a fairly solid foundation on the ground to either avoid collisions, transfer into new maneuvers, or to simply just land a maneuver in a controlled and quick manner.

  • Landing on the rear reduces control and is dangerous. Not sure whether you ride MTB and doing jumps/drops. – cherouvim Aug 14 '15 at 13:53

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