More weight = harder landings
In the comments for “Can big riders jump?” someone asked about the effect of body weight on landing force. You know I love this stuff, so …
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Said Patrick:
Being a big guy who wants to jump better, I found Can big riders jump? 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.
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Hey Patrick,
Landing force is directly proportional to weight (aka mass). Twice as massive = twice as much landing force (everything else being equal).
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 suspension to spread the impact over the longest distance possible. The more leg travel you use, the smoother the landing. Check out the snappy chart: a smooth landing can be 1/5 as hard as a stiff landing.*
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 |
Compared to the 5’6″ 150-pounder, the 6’4″ 200-pounder has about 16% less body suspension per pound. That translates into a noticeably harder landing.
If you simply gain 60 pounds, it gets way worse:
| Height | Weight | Height in inches/weight |
| 6’4″ | 200lbs | 0.38 |
| 6’4″ | 260lbs | 0.29 |
Compared to your medium self, your heavy self has 30% less body suspension per pound. That’s a big difference, whether the weight is fat or muscle. (But muscle is way more useful!)
Conclusion
If you’re a big rider:
– Minimize your weight. Especially fat.
– Get as strong a possible. Plyometrics help you handle impacts.
– Hone your technique. Use your entire range of motion.
You can argue with the math, but lean, strong and skilled always destroys fat, weak and sloppy.
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*Read this: Drops: Don’t get bucked
**More about Body Mass Index: www.consumer.gov/weightloss/bmi.htm
Range of motion! I am 6’3″, 215 lbs., and I love to jump. Range of motion is key! I used to feel that my size inhibited me, but I learned that it could really help. Nathan Rennie and Peaty don’t let the little guys do all the jumpin’!
Ah Wise One,
On behalf of Clydesdales everywhere: “oh man… you’re killing us”. Your argument is very solid. There’s no doubt that increasing BMI and weight are more than just counter-productive. I think you’ve also focused on a key component, namely the ability to put the bike and your legs through a maximal range of motion to absorb the energy of the impact.
However, I would suggest that the development of sufficient eccentric leg strength to absorb impacts is a far more complex task than just doing plyometrics. Most authors would suggest an established base of leg strength, somewhere in at least the 1.5 bodyweight squat range, and more optimally greater than 2-2.5 x bodyweight prior to doing exercises like plyos. As with all off-season conditioning, it is optimized if it is approached in a periodized schedule, but especially for eccentric training, sufficient leg strength is mandatory (you’ve got to decelerate that body, before you go hurtling off in another direction).
Thanks for another great topic, Scott
Right on Scott.
You’re right about the complexiy. It’s too much to explain in few words, and too much to explain in a few hundred words. I want to do an ebook on training for gravty racing — it’ll be the first to cover the topic.
Squat 2.5x your bodyweight??? Wow, I better man up!
“Squat 2.5x your bodyweight??? Wow, I better man up! ” Don’t sweat it too much man, we’re all working towards real numbers (currently about 1.20 x BW).
Ebook would be great, there’s a lot of info out there, but little directed towards the specific needs of gravity racers.
I’ve been pondering the weight per height argument, you know me, can’t come up with anything original, but happy to try and shoot holes in other’s arguments.
What about suspension design?
You, oh man addicted to motos can probably answer this. Aren’t big bikes(i.e. Greater than 250s) the faster, more capable machines?? They also proably have more weight for a given amount of suspension travel. Do they make the suspension on bigger bikes that much longer??
I realize some of the answer lies in the physical requirements of a motorcycle suspension: coexisting with steering, coping with torsional forces, etc.
It may be that the dominant factor is not how long the levers involved in the human suspension are (i.e. your height), but how good your springs are (how much muscle you packing). There is probably some optimal ratio???
Unfortunately it doesn’t get us too far away from all race machines whether human or mechanical have to be as light and strong as possible (horsepower to weight is too good a predictor of outcome). Oh well…. back to the diet AND the exercise. Scott
Thanks for the response, Lee. Yeah, looks like I’m at a disadvantage at every turn. I’m heavy (270lbs) and not very tall (5’11”). So lots of impact force and not much “body suspension”. Also, I’m not very smooth, which is probably my biggest problem, but I am working on my technique (your book is helping 😉 . The good news is that I’m pretty strong and explosive, especially for a guy my size (although I’m not yet squatting 675lbs…maybe sometime soon). Plus, I can afford to lose 30-40lbs, and would be pretty damn lean at 230lbs (with the same amount of muscle).
Well, thanks again for “doing the math”, and here’s to hoping the 5″ of travel of my RFX is enough to cushion my drops.