Mythbusters bike flip

Anonymous

Just watched the episode of Mythbusters where they try and dis/prove the scene in Indiana Jones when a flagpole gets shoved in a motorcycle's front wheel, and flips the bike.
In the film, the bike shoots up into the air.

Right, I knew the bike wouldn't fly up, but I was expecting some serious endo action.

Anyway, in their test, all they achieve is to make the front wheel skid, the bike doesn't flip at all. In fact, the rear wheel never leaves the ground.

Now, what I don't understand is, I HAVE pulled the front brakes so hard on a bike that it flips over, and slams me into the floor (haven't we all, when learning to ride?) so how come a motorcycle's front wheel coming to an IMMEDIATE stop, just results in a front wheel skid? :?:

Any thoughts?

The Northern Monkey

Possibly to do with weight? No idea how much a motorcycle weighs tho a i've never ridden one!

Does seem odd tho... always figured if you got a stick stuck in your spikes you'd go arse over.

Anonymous

bigbenj_08 wrote:

Possibly to do with weight? No idea how much a motorcycle weighs tho a i've never ridden one!

Does seem odd tho... always figured if you got a stick stuck in your spikes you'd go ars* over.

I don't think it is weight. I've done the endo-faceplant thing by accident on a CT-125!

Whytepeak

The centre of mass of a motorbike + rider is a lot lower down than on a bike, so the weight is pushing behind the front wheel when deccelerating. On a bike the centre of mass is a lot higher because of the weight of the rider. So when a braking force is applied, the weight isn't pushing behind the front wheel, but above it, this is why a sudden snatch at the brakes results in these outcomes.

Anonymous

Whytepeak wrote:

The centre of mass of a motorbike + rider is a lot lower down than on a bike, so the weight is pushing behind the front wheel when deccelerating. On a bike the centre of mass is a lot higher because of the weight of the rider. So when a braking force is applied, the weight isn't pushing behind the front wheel, but above it, this is why a sudden snatch at the brakes results in these outcomes.

That does make sense, definitely. But I have flipped over the bars on a motorcycle as well! granted, only a little 125, but I've endoed much bigger ones.

Whytepeak

Yeah, when you endo a motorbike, you lean forward, and pull the brake lighly, you don't just pull on a handfull of brake.

Anonymous

Hmm, yeah, I see. I can understand that.
It's just so strange to see it - It's the last thing I was expecting!

It's like touching an electric fence. You know it's only low voltage, and isn't actually going to hurt, but still, it's surprising when it doesn't!

Nick Dastardly

My thinking is it's to do with the friction between the tyre and the road. If you're on your bike and overdo the front brake a bit, the brake grips the wheel solid but the tyre doesn't necessarily lose traction. So the tyre stays where it is and you pivot around it and smash your nuts on the stem.

On a motorbike you have a lot more momentum, so when you slam on the front brake (or someone shoves a flagpole through your wheel!) the brake grips the wheel, but there's so much forwards momentum that the front tyre loses traction and skids out.

Try riding down a slippery hill and slam your front brake on*. All that will happen is your front tyre will lose traction and you'll skid out.


* DON'T

Daz555

Yep. It is very easy to overload a motorcycle front tyre if you grab too much lever too quickly. Grabbing loads of brake (or sticking a pole in the wheel) will send you down the road everytime, not flip you over the bars.

To get the front wheel to grip hard on a motorcycle you have to introduce braking progessively in order to shift weight forward and load the front end. Once the front is loaded it grips like a bugger - at this point a trip over the bars can be arranged if you wish!