Can big riders jump?

/18 Comments/in , /by


Hey Lee,
First, I’d like to thank you for putting together a great book and website. I consider myself an intermediate dh rider, riding a couple of times a week and entering a few races a year. I know you get a lot of questions on jumping but I would like to know what effect rider weight has on jumping?




I’ll bet Brian Lopes can deadlift close to three times his weight. That translates into impressive pop off jumps.

From what I can tell, at least from a physics standpoint is that speed and ramp angle are the only factors that affect distance and height given the same technique and other variables. So I’m inclined to think my jumping ability is hindered more by ability to carry speed than by my mass. Then again I don’t see many 255 lb people spend that much time in the air in any sport. This isn’t really an overweight issue as my weight is more a factor of muscle density than flab. I guess what I’m getting at is that I want to become a better all around rider and as a better jumper I would be better at riding the jump laden courses out there. I’m just not quite sure how to go about that. Thanks!
John

Hi John.

Man, what a fun question. Fun for a nerd like me, anyway.

You’re right that being heavy doesn’t change the core dynamics of jumping. When you negate air resistance, cannon balls, bowling balls and BBs all fly the same. For that matter, so do feathers.

Catching air (literally)

When you jump your bike, air resistance is a relatively small factor, but a bigger rider is less affected than a small rider (because the ratio of weight to drag is higher). So, all things being equal on a windy day, a 255-lb stud will fly farther than a 140-lb spud.




Pound for pound, Bobbi Watt is hard to beat.

It’s all about the pump

The big variable here — and one you control — is the amount you compress into the face of the jump. The harder you load into the face of the jump, the more you rebound, and the higher you go. It’s exactly like diving off a diving board — the farther you compress the board, the higher it sends you.

Timid and/or weak riders don’t pump very hard, so they seldom jump well. Confident, strong riders pump VERY hard, and that’s the key to their jumping kung fu. A rider like Brian Lopes or Steve Wentz can bunny hop three feet on flat ground and get huge air of a tiny lip. I’ve seen Wentz gap 15 feet off a shovel.

Bigger is weaker

When we talk about pumping a lip, we’re not talking about the absolute downforce. We’re talking about the downforce compared with your body weight. When Bobbi Watt (~120lbs) and you (255lbs) each pump with 120 pounds of force, she gets more than twice the lift.

  Equal pump x 1/2 the weight = 2X the pop




A little infographic magic for the kids at home.

Pound for pound, larger animals tend to be weaker than smaller animals. Why? As you get larger, your volume (and weight) increase faster than the cross-sectional area of your muscles. Basically:

  2X as large -> 4X muscle cross section -> 8X weight

When you double your size, you can lift four times as much as before, but you weigh eight times more. So your strength/weight ratio is cut in half.

Here’s a cool explanation of size/weight/strength relationships.

We periodically do Feats of Strength in my basement. You weigh yourself on the spot, then you lift a percentage of your weight to failure. We bench half our weight, pull down half our weight, row with half our weight, military press one-quarter our weight and do dips. So far, Bobbi Watt is the champion. Lopes and I each managed 31 dips — she cranked out 32 then stopped just to make the point.

Bike riding is all about strength-to-weight ratio, and — overall — smaller riders have a distinct advantage there.

Let’s wrap this up

A big guy like you can definitely become a great jumper if you work on your timing and commitment. Just remember that for the same amount of lift, you’ll have to pump harder than the little guys. You’ll never achieve the pop of Lopes and Wentz, but I’d rather move a piano with you!

18 replies
  1. John says:

    Lee,

    Thanks for taking my question. I appreciate the thorough and nerdy answer (from one nerd to another). I didn’t realize how significant the strength to weight ratio is, but given the size and relative strength of athletes in other aerial sports, it seems to make sense. So, if your baby grand is giving you trouble, I’ve got your back!

    John

  4. scott says:

    Oh wise one, as one of the heaviest and oldest around this is a topic near and dear to me. Several thoughts come to mind.
    If you’re heavier you truly have to commit to dropping your body fat percentage. Big frames can hide a lot of fat, that does nothing but hurt your efforts to hoist it into the air.
    You have to use your power to Pump! I’m only getting glimmers of this, but when you’re on the money with well-timed and really explosive pumping the results are really cool! Despite your elegantly presented arguments for the relative advantages of body mass and cross-sectional area, in absolute terms, it’s us clydesdales that move the big tonnage! (not that there’s not an optimal body size to maximize this, remember the optimal male olympic gymnast is 5’4″ and thought to be huge at 5’8-9″).
    Lastly, remember that the ability of large muscle groups to address high-speed or high-load inputs has seen some larger athletes do very well in downhill events (as opposed to slalom). Steve Peat, Rennie, the Herminator on skis.
    Train explosively, get lean, listen to the sage!
    Scott

  6. Miller says:

    I am a bigger guy as well, 6′ 240. I ride dh/street/ park/ Ray’s mtb in cleveland. The only problems of being a bigger guy has on jumping is the beating both your body and bike take. Other than that, you can do the same things that the skinny guys do. What lee says here does make sense. Be aware that you will go through parts more quickly than others. If you are going to jump, get a steel frame(I ride an evil doc, I killed 4 aluminum frames before I figured it out) some strong wheels(I run halo 48’s), and a set of BMX cranks(I run profiles). Buying the right things the first time would have saved me some cash. Another thing to think about is what type of tire you are running. Don’t run Kenda K-rads. I blew the side out of 2 of them. Kenda kiniptions, maxxis holy rollers are much better ideas for bigger riders.

  7. Wayne Beavers says:

    I don’t ever allow any tire to leave the ground, but my son does.

    While I was still paying for parts for him he used to practice jumping (a lot) on his Schwinn Homegrown full rigid. His thought was that if he learned to land it soft on the big jumps then it would be even easier to race the big jumps with suspension.

    Until recently I had possesion of a cracked aluminum frame to prove it. My wallet appreciates every sponser he has ever had.

    Point is, it seems to me, that the more mass you have the softer you will need to land. There is only so much sucking up that the suspension can do.

    I am amazed at the races by the big guys and the old guys. There are guys older than me and bigger than me that do things I will never get to do in my lifetime. Big John does pretty well, imo.

  8. leelikesbikes says:

    Wayne, your boy Curtis is tall, which helps smoothness, IMO. Longer legs have more travel.

    Light guy with long legs – great

    Heavy guy with long legs – OK

    Heavy guy with short legs – bad news bears

  9. Mark says:

    Lee, one thing you didn’t really mention is the relationship between bike weight and body weight. Don’t you think that while a smaller rider may be stronger than a larger one proportionally, the fact a bike will weigh almost the same despite rider size will influence the optimum jumping weight?

    Off the top of my head it seems like it would be something like 160# that would be ideal. Not too heavy as to where you loose strength, but the bike is also not heavy in comparison to the rider.

    Just a thought.

  10. leelikesbikes says:

    Great point.

    Bike weight evens things out, but based on some simple calcs a lighter rider still seems to have an advantage (all else being equal).

    160 is a pretty common weight for mountain bikers. I’m 180 now; at 160 I was a WEAPON!

    I’m loving this topic!

  11. mb says:

    I often wonder why people don’t focus more on reducing their body weight vs spending hundreds on lighter bike parts (assuming there is excess body baggage of course). Wouldn’t five pounds off your middle ride as good as five pounds off the bike?

  12. leelikesbikes says:

    Yes – From the standpoint of moving your bike and body from A to B.

    Taking weight off your bike makes it feel much faster — in the moment before your fat butt starts to move too.

  14. Patrick C. says:

    Being a big guy who wants to jump better I found this to be an interesting article. I know that when I hit a jump or drop “right”, with correct body position and proper body english, that the jump feels almost effortless.

    But I wonder about the other side of things…like when you have to land. How are the forces different for a heavy guy. If a 260lb rider drops 8′ to transition, how much greater are the forces (ground reaction forces, forces on the rider’s body/joints) than if a 160lb rider does the same drop? Of course, there are many other variables to consider, but assume we are using a hypothetical rider that is capable of gaining and losing 100lbs for our experiment, so rider skill (and bike) stay the same.

    Maybe this is a topic for a separate question? Either way, I’d be curious to hear some opinions.

  15. leelikesbikes says:

    Hey Patrick,

    The landing force is directly proportional to weight (mass). Twice as massive = twice as much landing force — everything else being equal.

    Kinetic energy = 1/2 x mass x velocity squared

    That’s the quick answer. Another post would be fun …

  16. leelikesbikes says:

    I can never leave this stuff alone!

    When you do a good sized drop, you generate a lot of kinetic energy. If you land a 5-foot drop stiffly, you can easily damage your bike and body.

    To land smoothly, you must use your legs and bike suspension to spread the impact over as long a distance as possible. The more leg travel you use, the smoother the landing.

    The thing is, as you get bigger, you add pounds faster than you add height. So you endure more impact with relatively less leg travel.

    For two riders with the same medium build (Body Mass Index of 24) …

    Height  Weight  Height in inches/weight
    5’6″  150lbs   0.44
    6’4″   200lbs   0.38

    The 200-pounder has about 16% less body suspension per pound.

    If you’re big: Get strong and dial in your technique.

    —

    Check out this story about landing drops:

    https://www.leelikesbikes.com/drops-dont-get-bucked.html

    —

    More about Body Mass Index:

    http://www.consumer.gov/weightloss/bmi.htm

  17. Mike Johnstone says:

    About bike to rider wieght.

    The following could be explained better but I’m not a writer so here goes. Both the rider and the bike have independant inertia when moving. The heavier a bike or rider is the more mass and momentum/inertia it will have as you go down the trail and these 2 masses must be dealt with when changing direction, as in jumping or cornering. A smooth rider lets the terrain move his/her bike under them like a mogul skier so that the body stays quiet and the bike moves with the terrain. This is done through range of motion, strength, and timing and coordination. If the bike is greater in wieght it will have more momentum when the ground moves it upwards. The rider is not attached to anything and has to rely on their own inertia and range of motion to not get kicked by the bikes momentum, but will also have a harder time pushing the bike back to the ground and will be more at the mercy of gravity. How this relates to jumping; when we jump we press through our bikes into the face of the jump. This force causes our bodies mass to change from a forward direction to a more upwards direction. Here comes the kicker. We don’t change the direction of the bikes momentum, the ramp does. As the bike comes to the top of the ramp the front wheel goes over the lip and the bike can now start to fall forward while the back end is still travelling up the ramp(the deadly rotation). If your bodies momentum is still too much forward instead of up your bodies mass will also start to fall forward and you will feel the back wheel come up towards you, ie the dreaded kick that turns into a dead salior. This can be dealt with by absorbing the bikes momentum and then pushing the bike back down once it has cleared the ramp. If the bikes rotating inertia is too great the rider will not be able to absorb the force from the rear tire coming up and that force will be transmitted to the body, can you say “DEAD SAILOR ROTATION”. The heavier the bike, the more momentum it will have. The lighter the rider, the easier they can be thrown.

    Working with many female downhillers I have found that keeping a bike to 25% of the riders wieght works best, but the lighter the bike the better. And I would not suggest gaining wieght to meet these numbers. ; )

Comments are closed.