3alarmer 

...I was never in a hurry to get to work, and going home, I was always stopping off somewhere along the way.

3alarmer 

...you got the full time, regular job ? Congratulations Larry. Now it's time to knuckle down and climb the promotional ladder.

HTupolev

They don't need to directly depend on bicycle mass to have implications on the performance effects of changing bike mass. Total ride effort with respect to various resistance forces is not a linear system where you can treat the contributions totally independently of each other.

It's true that gravitational potential energy will be returned to the bicycle on the descent. But due to the nonlinear and quite steep relationship between speed and aero drag, that gravitational energy generally gets cooked off as wind swirls while having relatively little impact on speed. It's therefore "returned" in a way which, for practical purposes, saves far less effort on the downhill than it had cost on the uphill.

I just plugged a few examples into my physics spreadsheets, using the simplified Martin model (i.e. power=((gradient+crr)*9.8*m+.5*airdensity*CdA*(v^2)*v)).
With 250W pedaling, a crr of .005, CdA of .32, and air density of 1.225kg/(m^3), an 86kg bike+rider does 10.96mph up a 5% grade versus 10.05 at 96kg. On a -5% grade, the numbers are instead 36.81 and 38.13. So the extra mass is costing a little over 8% in speed on the ascent, but giving back just 3.6% on the descent.
And think about what that means in times. If we're talking about a hill that's 5 miles each side, the 86kg bike+rider takes 1,642 seconds on the way up and 489 seconds on the way down. Meanwhile, the 96kg bike+rider takes 1,791 seconds up and 472 down. So the heavier bike+rider paid about two and a half minutes on the climb to save 17 seconds on the way down.

Very few people, whether they're "low-educational-level" internet debaters or professional physicists, use an English semantics where they'll look at that compromise and view it as an equal-effort tradeoff.

tomato coupe

How about that dude Einstein? Or Hawking? They both "bought into" that hammer / feather thing.

Trakhak

From quickie search:

The troy pound (lb t) consists of twelve troy ounces and thus is 5760 grains (373.24172 grams). (An avoirdupois pound is approximately 21.53% heavier at 7000 grains, and consists of sixteen avoirdupois ounces).

macattack71

The scientist in me wants to ride my Raleigh road bike with 32mm tires to work and compare versus the 25mm Cannondale SuperSix. I ride pretty hard to work when I do, currently 12 miles, Really no chance to hold back as its all on the road with traffic and thru a couple of school zones with buses. I am going to update the cockpit to match first, as the older narrow handlebars are annoying. Its maybe twice the weight.

PeteHski

The equation for aero drag force does not include mass as a parameter.

Maelochs

Oi .... here is where I would expect the engineers to shine ... but ...

No, the Equation for aero drag and its increase with speed does not include mass .... but even if you are neutrino ... You have mass. And any moving particle or bundle of particles will in fact be .... moving mass. If the matter which constitutes a thing does not move, the thing does not move ... and matter has mass (and takes up space .... )

The equations are models but the reality is my fat body and weak, skinny legs trying to drive that bike up some hill. I Do Not Get Back the energy I created with my muscles to move that mass.No matter how far I coast on the downhill .... the Muscular Energy Generated by Metabolism is not "returned to my system." The energy is transformed .... and I cannot use that transformed energy to move the bike again.

We All Know This. If you don't believe it, start doing hill repeats. You can coast down the back side in a frictionless vacuum ... I don't care, the Physical (physiological) energy you used to move the bike is not magically "returned" to your muscles.

Yes, the mass of the bike matters ... as someone mentioned above, hold a race. Have one rider on a 6-kg bike ... a normal racing bicycle ... and the other on a 600-kg joke bike with oversized tubes filled with depleted uranium. I doubt the rider on the heavier bike could even get the thing moving ... but weight doesn't matter!

At some point, if all the knowledge and education in the world causes you to ignore or forget Reality, which is supposed to the basis of all science ...

If the mass of the object doesn't matter, I will push my bike up a hill ... you push a fully loaded twenty-two car freight train. Let's wager on who gets there first.

Mr. Hski ... no disrespect intended. Equations describe (ideally) what they are modeling but they are models ... and if you focus on one equation which only describes one limited aspect of a thing, you cannot accurately predict the action of the thing.

I agree, calculating aero is a matter or area, shape, the resultant coefficient of drag, and the measurable density of the atmosphere .... but everything has mass, and @LarrySellerz was (as far as I understand it) trying to describe the concatenation of forces acting upon a bicycle ... his language might not have been as precise as yours (nor will mine be) but mass plays a role unless you are poised perfectly between gravity fields ... or at some portion of space time undistorted by nearby masses .... or well .... physicists have named gravity as a fundamental force and still don't even really know what it is ... but they have any number of equations for determining it in various systems ......

Here is where, for me ignorance is bliss, not stupidity . I am too ignorant not to realize that a bike has to have External power added to its total mathematical/physical system if it is to move (Mr. Newton told me.) The power is not destroyed, but transformed ... from peanut-butter sandwiches to forward motion. it never turns back into peanut-butter sandwiches. Isn't that, like, the fifth law of thermodynamics?

I like peanut-butter sandwiches. This makes me happy. Science!

Reynolds 

DonkeyShow

Does she want to get to work or get a work out in? **** sake just ride around the block for an extra 15 min when she gets home.

better yet road bike to work, extra 15 on the heavy bike loaded with anchors. She'll be yoked in no time. And might not even be losing time out of her day considering the road bike is faster.

staehpj1

This morning I saw a guy with one of those sleds you put weight plates on and push or pull. It had maybe a couple hundred pounds on it. He wasn't moving it when I went by, but he was a few hundred yards from the parking area so he went at least that far with it.

DeoreDX

The weight of a bike matters, but to what degree does it matter? The bike has to be thought of as part of a whole system, bike + rider. Take a 170lbs rider on a 20lbs bike v a 30lbs bike pedalling to the top of a hill. 190lbs v 200lbs. All things being equal that's a 5% difference in energy required to pedal to the top of the hill. That's not an insignificant difference but its still pretty small. If you are chasing marginal gains to squeeze out that last few seconds in a racing situation yeah that's pretty important. What about. 120lbs rider? That 10lbs is now a 7% instead of 5%. For the smaller rider that's slightly more significant. Heavier rider? Less important.

But what of the metabolic cost of doing this cycling thing? If you were at a low effort level when your body is primarily burning fat for fuel the metabolic cost is pretty darned low so you won't notice much difference in total energy expended. If you are like most of us, that fat is an almost infinite energy source. Imagine walking around you city all morning with a backpack with your laptop, water bottle , snacks, and a spare jacket. Taking the backpack off isn't going to make you walk faster and for most decently fit people won't effect how much they can walk during the day. Now change the scenario to running around the city. Now your body is anaerobic. Each step produces lactic acid your body has to flush away. Your are burning a finite amount of stored muscle glycogen and carbs in your system. The metabolic cost in this scenario is going to be much more significant. Now all out sprint where you a at max metabolic capacity the effect of that extra weight will be more dramatic.

There was a question about mass and wind resistance. No mass doesn't come into play when calculating the total force of the wind resistance. But recall our first basic equation in physics f=ma. With identical force the larger mass will accelerate less. Intrinsically people tend to think of this as momentum. Sum of forces, conservation of momentum, conservation of energy. Think of it however you will they all tell the same story. Headwind will slow down a lighter object more rapidly than a heavier object all things being equal. Again in terms of total system we're are talking single digit percentage points in effect. And all things are never equal.

PeteHski

I was just clarifying the indisputable fact that aerodynamic drag does not depend on mass. Larry appeared to be questioning this specific point.

Of course there are other forces acting that are mass dependent, but this isn’t one of them.

tomato coupe

I think Larry was actually implying the moon landings were fake.

terrymorse 

Now wait just a minute -- which engineers you talking' about?!

LarrySellerz

IDK, I've been crushing on her for a while so I gave her a bike. Her longterm bf that ive met twice doesn't seem to like me very much

LarrySellerz

Its not indisputable, who wrote these equations? My lived experiences tell me that heavier things fall faster

shelbyfv

Not surprising! I'm sure he recognizes a formidable rival for her affection.

ofajen

I have to laugh at myself. After so many years riding drop bars and not quite feeling comfortable, I discovered that my new TRP RRL levers on some old, narrow GB rando bars are actually quite comfortable for me. This despite my shoulders being fairly broad (that acromion measurement is 50 cm).

All this time thinking I had to have wide bars to feel right. Mind you, I notice a loss of leverage and they are maybe more of a handful out of the saddle, but it’s by far the best for hand comfort. Even better than my touring bars on the MTB and they are very good.

So it’s hard to know what works until you try it. YMMV.

OK, back to wherever this thread is now.

Otto

PeteHski

LOL. I’m going to presume you are taking the p**** rather than being dumb.

wheelreason

Yeah, but your lived experiences tell you to zip tie bottom brackets, so....

wheelreason

LOL, "She's caught the scent of a lesser stallion"...

tomato coupe

Why, does he participate in this forum?

tomato coupe

I guess that means every physicist on the planet is wrong. That's gonna cause some problems ...

DonkeyShow

I'll be in sf thanksgiving, I can come wingman you. Imagine us rolling up on some sick bikes while they are dining at some outdoor cafe. Leave her urs then hop on my peg stands and we ride off into the sunset...