How fast do you need to go for a drop?

Here’s a great question from our remote coaching student Stefan in Switzerland.

One last question to the drops and speeds: Is this reasoning right: given all things equal with the drop except its height,  I could approach all drops smaller or higher with the same speed I‘ve been using now? With higher drops I‘ll land longer with smaller drops I‘ll land shorter? but other than that it‘s the same?

Stefan


First of all, here’s the drop Stefan’s been hitting.

Regarding our remote coaching, Stefan says:

This is so awesome. I‘ve been working with you for about a year now and have reached skills I thought would take me 2-3 years if at all (at my age you never know how fast you progress. – turning 44 tomorrow :-)). And I always felt safe with you. So Kudos to you for breaking things down so well and being a great coach!!!!!!!!”

Now my response:

—   —   —

Stefan,

This is such a great question. I’ve been thinking about it all day (including when I was doing a sweet ride). 

Let’s assume this drop has a smooth, infinite landing. 

In the simplest of terms, a drop is rollable if it is not as tall as your arm is long. You can ride a rollable drop at a full range of speeds from very slow (walking speed) to as fast as you want.

If a drop is taller than your arm is long, it is not rollable. If you’re coasting and not doing some permutation of a wheelie drop or a hop off the end, you need a certain amount of speed. This speed prevents the front wheel from dropping too much before the rear wheel takes off, and it gives you a somewhat flat flight trajectory. 

Basically, the faster you go the more level and flat the bike will stay, and the easier/safer the drop will feel. The speed you’re using now is appropriate. 

I agree that “non-rollable” minimum speed is the same whether the drop is 3, 4, 5 or 6 or more feet tall.

In your video you’re hitting the medium drop. As long as you execute with the same perfect technique, I think you can ride the large drop. 

But how fast is correct?

I can’t just say “Hey Bro, just ride at some random speed and send it” or even “My intuition says 8 mph is about right; go for it!” That’s not how I roll, so how about this logic:

When you leave the takeoff, your bike is angling down about 22 degrees. You’re able to handle this angle well. For this sort of drop, once you have the muscle memory, you can let the bike do what it wants and let your hands follow the bars. 

Assuming a “normal” wheelbase of about 1,170 mm, that means your front wheel is dropping about 44cm.

When you account for acceleration due to gravity, it takes 0.3 second for the front wheel to fall 44cm. 

If you’re traveling 1.171m in .3 second, you’re going 3.9 meters/second or 14 kph or 8.7 mph.

So that seems like a good minimum speed. About 8 mph. Pretty crazy how well the intuition works!

Does that make sense?

Lee

2 replies
  1. moose says:

    Love the math you put in to this one! Some great ‘back of the envelope’ calculations that maybe a few of us nerdier readers (caught me) might have to start thinking about when not out at the trails. Soon my wife will be finding even more index cards with random math on them around the house and have to laugh when she realizes what I’m up to.

    Reply

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