elcruxio

I'm still somewhat unsure how motorcycle specific maneuvers would benefit me with a vehicle I can lift with one arm...

Also I don't see how stuff done in the air is relevant to steering inputs on the ground.

Daniel4

Don't know if it has already been posted.

Myth: Cycling is dangerous.

Jeff Neese

Well, it kind of was, tangentially. The supposed "myth" was that the difference in mass at the rim of a wheel has more of an impact (that many of us, including you, readily admit you can actually feel) on the way a bicycle handles and behaves, than the same weight on the frame. There are a few here who are claiming that adding a pound to each wheel is no different than adding two pounds to the frame.

Jeff Neese

Not a myth. I feel like every time we hit the road, we're taking a risk. The number of cyclists killed each year by motorists seems to bear that out.

Eric F 

Why do you think this is a myth?

icemilkcoffee 

I think most people simply misunderstand how Biopace works. A lot of people thought that it's there to lower the gear ratio when your leg has the most leverage at around 3 o'clock. When it's actually the opposite. It lowers the gear ratio near the 5 o'clock point. It's not there to let your leg perform more work when it has the most leverage. It's there to stop you from over-stomping 6 o'clock. The tendency for most people is to continue stomping downwards even when the pedal is at 6 o'clock, and this is obviously wasted energy. This is especially true when you are standing and pedaling. Another instance when this happens is when you are going down hill and spinning your pedals at a high speed. Sometimes you find yourself bouncing off the saddle- this is because you are over-stomping 6 o'clock. Biopace is designed explicitly to counter this tendency.

tomato coupe

Just trying to get an idea of how much physics you should be able to understand.

Eric F 

Not just the road. Trails and bike paths have dangers, too. Hell, I crashed in my driveway hard enough that the wounds on my knees and elbows are still healing 2 weeks later. If it wasn't dangerous, we (most of us, anyway) would not feel compelled to wear a helmet when we ride.

tomato coupe

That 1.85 factor is just a rough estimate if weight is added at the rim. You have to look at the where the extra wheel weight is actually located to come up with the real number. If you're considering the extra weight of a deep vs. shallow wheel, for instance, then the factor is likely 1.5 or less.
What you wrote does not make sense. What does "similar to the calculus" and "values will continue to digress" mean? Plot what? What two lines will separate?

Nope, no specific cases. In the most general case, the effect of the rotating mass is insignificant.

Quite the opposite, in fact. Most of what you write is nonsense from a physics and math perspective.

MeganCook

I had always thought that the gear ratio would be lower at the 3 o'clock point, so it's good to know that it's actually at the 5 o'clock point.

It makes a lot of sense that Biopace is designed to counter the tendency to over-stomp at the 6 o'clock point, which can lead to wasted energy. I can imagine that this would be particularly useful for standing and pedaling or going downhill at a high speed, when it's easy to lose control of your pedaling technique.

FBinNY 

Possibly the best arbitrators of whether bicycling is dangerous or not are those who do these calculations professionally. Specifically life insurance actuaries.

Just about every life insurance company, not only considers bicycling safe, and will not deny their best rates to cyclists. Moreover they not only say that bicycling is safe, but can show that the health benefits more than offset the risks.

So, to those who say bicycling is dangerous, I say not bicycling is more dangerous.

This isn't to say that it's absolutely safe. Like just about everything else, it's not about statistical risks, but how we manage them.

Eric F 

In summary...Everything will kill you. Die doing something you enjoy.

base2 

Trying to demonstrate the forces involved have little to do with the weight of the rider & everything to do with the riders manipulation of those forces.

When looking down the steer tube at the rotational motion of the wheel, inputing a force 90 degrees to the rotational axis (turning the bars) forces a perpendicular force at the top of the wheel to drive the bike over into a lean. This is how a steer is started. Now that the bike center of gravity is no longer under the rider, a fall inward towards the ground is the consequence. The rider cleverly turns the bars the other direction causing an opposing force at the top of the wheel to counter the initial fall & remain in equilibrium in the new orientation.

A rider who has mastered this skill can change his line mid turn or make any necessary course or balance adjustments at speed & remain in full control keeping the desired line of travel under the apparent center of gravity (or not) of the rider as desired.

Bikes wheels have a lot less inertial mass than motorcycles, but proportionally more in relation to the body (bike frame) they are acting upon. Ie: Bikes are nimble enough most people don't realize how it works & do ok. Motorcycles OTOH, a failure of understanding & mastery can have disastrous consequences.

Between seeing a pile of sand in the middle of a high speed corner and hoping for the best & seeing a pile of sand in a corner & readjusting my line on the fly to avoid it, I'll choose adjusting my course every time. Indeed, I counter-steered forcefully to avoid a 30mph vehicle collision just today.

Paraphrasing my thoughts on the debate raging in the other thread:
The forces involved don't have to be big. Just strong enough to act upon the bike frame. It's the "why" behind why light wheels feel nicer & heavy wheels feel like pigs. With lighter wheels less effort is required to change the wheels plane of rotation. So, although the moment of inertia is essentially insignificantly different in terms of forward motion of the bicycle, the lighter wheel requires less input effort to act upon the frame.

(I'm sure I've mis-typed something, somewhere. But that is the gist of it, anyway.)

wolfchild

Here is a little challenge for you. Take a carbon seat post and an aluminum seat post and bang them hard against a rock and see which one will break first....or put them both on a vice then put a long pipe on one end and try to bend them and see which one will snap first.

Eric F 

I'll take that test when you provide me 1 CF seat post and 1 aluminum seat post where the shaft sections weight the same. Hell, I'll even do it if they have the same ID and OD.

3alarmer 

...I have made no "big claims" in this thread. I have simply stated what seems obvious to me, that limiting your examples to small differences gives you a very different picture of the experimental results. And that it's probably unwise to generalize, unless you state that limitation as part of your argument.

...OK, you don't agree with 1.85, even though it sounds reasonable to PeteHski . Fine with me. Among the three of you, nobody seems to agree on much, except that the handling of my bicycle is secondary in importance to my elapsed times.

...do you recall any of the basic math you took as an introduction to differentials, or do you just use the formulas ? The brilliance of differential calculus lies in exactly this use of smaller and smaller differences in values as we approach certain "limits", to the point where we can consider them as unimportant.
...anyway it's a simple linear plot on an xy axis. Draw one line with a rise of 1, and run of 1. Draw another with a rise of 2 (or 1.5, since that's the number you prefer),and run of 1. What should happen, is that they diverge. That divergence represents the difference between weight on the frame, and weight on the wheels, as those values increase. I'm sorry, but maybe this explanation is too basic for your skillset ? Feel free to once again insult me. I'm kind of immune to it, by now, and it probably helps you to vent.



....once more, only within defined limits.


...OK, whatever you say.






...OK, you don't agree at all, you think it's zero. And the tomato guy doesn't agree, and wants it to be less, at 1.5. I stand corrected in thinking there was any sort of agreement at all. World peace is difficult because of just such misunderstandings.

Trakhak

That's true. And another problem you just reminded me of: when they came out with Biopace, they didn't yet have a full-fledged U.S.-based marketing department. I don't remember the time line, but they hired Wayne Stetina, a former Olympian cyclist and winner of multiple national championships, to head their U.S. operations around that time.

Which, in turn, reminds of a conversation I witnessed at a Shimano presentation to bike shop owners and employees in the Baltimore area that was conducted by Stetina.

He'd finished talking up a bunch of the current and forthcoming Shimano products and asked for questions. Alex, the owner of a chain of bike stores in the Baltimore area, stood up.

"Wayne, did I understand you to say that any Shimano-equipped bike we order from any of our brands next year will come with a Biopace crankset? No exceptions?"

"Yes, that's right."

"So---a customer comes in one of my shops. Wants a bike. Cash in hand. Doesn't want Biopace chainrings. What do I do?"

"Well, I hope you'll explain to the customer the advantages of Biopace compared to conventional rings."

"Wayne. Listen. I said: cash in hand."

Wayne [looking uncomfortable]: "Well, I guess you'll have to sell the customer a bike with some other component group."

wolfchild

That's not a myth, that's the truth.

tomato coupe

The more you write about math (and physics), the more apparent it becomes that your understanding is much less than you think it is.

Your reading comprehension is poor. I explained where the 1.85 estimate comes from, why the estimate can differ from 1.85, and under what situation it would be closer to 1.5.

Regardless, the 1.85 factor is a red herring. You can use any number up to the maximum factor (= 2) and it doesn't change the fact that the effect of the rotating mass is insignificant.

Koyote

I'm hoping to be shot by a jealous husband. When I'm 95 years old.

Maelochs

I am not an engineer, ro even particularly smart, but ...

My understanding is that the differences with CF As A material is that it damps vibration better than steel or aluminum. CF is "deader" somehow, which means a whack on the end of the forks doesn't travel to the other end so much. This made CF a very attractive material for forks because steel, to take the stress, will either be be heavy or exceedingly springy, whereas CF forks can have all the strength and much less weight---and while the CF forks won't dissipate impacts with harmonic vibration, they simply damp it out through lack of resonance. (AL forks .... beat your palms, but they are lighter than steel.)

Steel is springy, and will do some sort of harmonic resonance thing which transmits the feeling but takes the edges off---a sharp impact is fully felt but not as a sharp impact. The fork quivers which dissipates some the the energy and spaces out the impact over a span (admittedly very short) of time ... in essence, you feel many smaller impacts but each is smaller.

Aluminum, usually being stiffer in bike applications (because "springy" aluminum is aluminum using u its fatigue life in a hurry) so Aluminum forks transmit every impact and doesn't damp it at all .... one hit at one end, the same hit at the other end, just as short and sharp.

However .... as many (including Sheldon Brown) have noted, it is what you make, not what you make it out of. Carbon can be formed across a wide range of parameters, with different weaves, orientation of weaves, number of layers, and amount of epoxy. CF is probably the most customizable material .... the down tube/seat tube juncture can be rock solid while the chain stays and seat stays act as springs, the seat tube can get slimmer so it offers some minor flex, whatever ... and since CF doesn't fatigue from flex or vibration, all kinds of characteristics can be built into the bike's parts, and all of them could last a very long time (but they will eventually assplode ---- i know, because I read it here.)

Steel and aluminum can be formed pretty extensively now if people want to pay the money for hydroforming or olio-forming or whatever the latest, best, tech might be ... but it is still a lot harder to form than CF. Still, metal is generally more accepting of minor abuse than CF (gasp! I admitted it!) not because CF is brittle, generally, but it is less forgiving from point-impacts than most metals. Most metal bikes, if whacked with the peen of a ball-peen hammer, will dent. I invite everyone else who has a CF frame to do the same test at home .... be sure to video it. I might be wrong, but I am pretty sure that more times than with a metal frame, the CF frame will sustain serious (though probably patchable) damage.

That said, I have dropped or seen knocked over my CF bikes, have crashed them, have dropped other bikes against them .... CF is really tough. But I am not recommending it to people who disagree ... those folks are completely correct that CF will assplode and kill them.

It will be amusing to see what BF makes of all this mess.

PeteHski

The big claims were made by someone else in relation to the myth, not you. I'm not limiting my examples to small differences either. The only generalisation I made was that we are discussing bicycle wheels.

Maelochs

Whoops ... i see that a number of others have weighed in more rationally than I on the issue of materials and their properties.

And some, shockingly, as irrationally as I. I suggest a hammer test, another opts for the vice-and-pipe test.

Jeff Neese

Certainly enough for this topic, I assure you.

Maelochs

Alos ... is cycling "dangerous"? Which is the undefined term?

As for insurance actuaries .... they are weighing the fact that A.) most bike injuries are non-fatal, B.) medical insurance, not life insurance, therefore covers most bike injuries, C.) people who don't get hurt riding often improve their health and longevity. So sure, ride a bike, get a good rate. Also, cyclists are a lot less likely to be smokers, and by definition are not sedentary, which generally increases lifespan.

US cycling deaths as far as I have seen have remained right around and just under 1000 per year for quite a while. That is a tiny number.

People who ride on the road might think cycling is dangerous because it can Feel dangerous---lot so drivers, lots of idiot drivers---but I think it is safe to say that no one who is reading this thread has been killed by a driver---though many of us might have been hit, or run off the road, or been the target of thrown projectiles---I was even shot by a loser with a BB gun---but is it 'dangerous" if we almost never get hurt due to the actions of others and always get back up and ride again, eventually? Not to a life insurance salesman.