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Comment by bediger4000 | Hacker News Reader

What happens when you brake hard? I imagine some bicycle caliper brakes grabbing the wheel's rim, which if the coefficient of friction between tire and road is high enough, causes the driver to just go round with the still rolling wheel.

Seems unsafe.

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If you brake too hard on a bicycle, you flip over too, especially downhill. You can brake up until the point that you've popped a front wheelie. Bicyclists usually forgo most of the available braking force, by solely using the rear brake, for this reason. Same for monocycles. If you go past 90 degrees, there's no point in further braking force. If the brakes are electric, they would throttle themselves to that limit, so you have max braking force. Just like anti-lock brakes on a car.

All that said, the terrible wheel-to-rider leverage ratio dooms the design to always have poor stopping distance. Probably not any worse that a bicycle without a front brake, though.

It's my firm opinion, and that of many people who've looked at it, that flipping over the bars is caused by the rider not bracing themselves as they use the very powerful front brakes.

https://www.renehersecycles.com/how-to-brake-on-a-bicycle/ https://www.sheldonbrown.com/brakturn.html

If most cyclists don't use the front brake, that is their loss. Most advanced cyclists, in my experience, rely heavily on the more powerful front brake.

In a physics sense it would happen when the torque applied by the forward momentum is higher than the force applied by gravity - the higher you are above the contact point with the ground, the more torque you apply and the more likely you are to rotate around the wheel.

The lower and further back you can get your weight, the more force you should theoretically be able to apply (being wary of deweighting the front wheel too much such that a hard front brake causes a skid instead)

I'm a hardcore cyclist too. If you're bombing down a San Francisco hill at top speed and lock the front tire, no amount of crouching behind your seat is going to leverage it from flipping. The point is physics is physics, monocycle and bicycle follow the same simple kinematic diagram of pivot point x torque vs pivot point x inertia. If you use 100% of your braking ability you'd better be tall and heavy enough to torque it the other way, else the free body diagram rotates.

Bicycles are not a physics 101 problem. In practice this just doesn't happen. See the links I provided. You can also read more about this in the "Bicycling Science" book.

A unicycle or bicycle flipping is a Physics 101 problem. First you must lock up the wheel if you want to flip, meaning the complications of kinetic friction are irrelevant. There's a center of mass, a contact point, a velocity, and a force. You can make a free body diagram to accurately calculate if you have the speed and CG to rotate forward (flip). Newtonian physics isn't magic. Telling someone to "read a bicycle science book" just sounds like a flippant dismissive insult. You're safe to assume I'm already well studied. This is a conversation, not an insult battle. If you have a point in mind, then bring it to the conversation in plain english to be inspected under the light of day. What juicy morsel is contained in this book of yours - perhaps it will sell people on moving it to the top of their reading list. Until then it's meaningless.

The angle of a very steep hill makes it easier to do a front flip, but such steep hills are an exceptional circumstance. Most of the time, experienced cyclists can safety use a great deal of front braking.

There's a world of difference between locking up your front wheel and not using the front brake at all. A reasonably skilled cyclist is able to use the front brake effectively without locking it up.

We are in total agreement. I was illustrating my point that a unicycle rider avoids flipping because they never use the full braking power (lock up the wheel). The gyroscope controller won't let you - you can only brake as hard as you can counterforce (throw your entire body weight hard backwards). As soon as the gyroscope senses a change in angle, the P.I.D. motor controller compensates.

This is indeed true -- I try to get my wife to use front brake more, and I sure will teach my children to.

But it remains the fact that many cyclists don't use the front brake -- or are even aware of its advantages.

(If you want to find out yourself, step off your bicycle and move it gently either forward or back. Try applying first the brake in the direction of travel, and then the trailing brake. You may be shocked at the difference!)

Heck, most people I know have the kind of rear brake that applies when you pedal backward. They find it more important to have hands firmly gripping the bars than pulling levers in situations where they want to stop. (Not saying it's sensible, but it is what they report. It's hard to convince them to use the front brake when their lives have stacked them against it.)

I suggest u spent 5min on youtube to learn how motorcycles, bicycle and EUC's, brake.

I've been riding those daily for years. Today I am going to Alameda naval base where they've set up an EUC racetrack on the tarmac at noon. I don't know what part your'e taking issue with, but physics is best communicated with free body diagrams and equations, which are difficult to articulate in conversational english and interpret correctly as a reader. I'm sure there's countless ways to misinterpret and nitpick my comments, but I'm not going to squabble over those or spend too much time rewriting anything — I'll just say I stand by my arguments from years of experience, so try to read my comments in that light first. If you had an actual point to share, share that instead.

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