terrymorse 

Uh uh. Added mass will increase rolling resistance. Not by a lot, but it's not zero.

Nope. See wind drag. A hilly course always requires more energy expenditure than a flat course, because going faster increases wind drag.

Physics don't care.

ofajen

There is no such thing as a conservative bike route. Gravity is the only conservative force involved. All the rest are non-conservative and the biggest one is non-linear. So it really won’t work out that way.

Extra weight will add a proportional amount to the work done by the rider climbing (when most of the work is being done against gravity).

On the downhill, it will not make a corresponding energy benefit because riders, especially non-racers such as commuters, will be sensible enough to coast downhill (assuming a freehub).

Either you will brake a tad more to hold a comfortable speed or coast a very tiny bit faster. No positive effect on total cycling work done during the ride and some net negative effect on overall average speed. That’s because the extra benefit of the weight downhill makes less difference in speed against the much higher air drag at high speed downhill.

Even for racers there won’t generally be much of a benefit because they will quickly speed up and then tuck and coast downhill once they spin out. So most of a downhill will still be zero pedaling effort regardless of weight.

Otto

LarrySellerz

This. Some people take the commute very seriously and there are some contested segments with heavy hitters etc.

AndreyT

... and the only force we are talking about here. Since the topic is how the bicycle mass affects the effort. So, yes, there is such thing as conservative bike route.

... and irrelevant, since none of them are bicycle-mass-related in any sufficiently significant way.

Um... Given the above, I don't know what to make out of this strange statement.

Precisely.

... and that is exactly "a corresponding energy benefit". Everything spent climbing will be returned ~100% on the downhill. The only problem is that you cannot convert that returned effort into "uneffort": you can't pump it back into your stamina or use it to restore your blood glucose level. (But this, as I have already stated above, is beyond physics.)

All you can do on the downhill is make sure the returned energy benefit is used purely mechanically to accelerate you and your bike as much as possible.

AndreyT

Compared to the forces being discussed, the contribution of rolling resistance is so disappearingly small as to be completely irrelevant. Its contribution is below the noise floor. The ultra-precise measuring equipment capable of detecting its existence seem to be kept in deep underground chambers under seven seals in some companies' marketing departments

It must be that mysterious relationship between bicycle weight and wind drag: everyone knows it does not exist, yet for some reason it periodically pops up in low-educational-level internet debates

ofajen

Ok.

Otto

SurferRosa

You haven't ridden through Texas.

RCMoeur 

They're very strong hamsters. And they're unionized.

RCMoeur 

I have a range of bicycles from my light full-531 Raleigh Pro to my Chicago-forged, Wald-basketed neighborhood cruiser, and quite a few in between. I'd estimate the Pro or my "speedy" cruiser use about half the effort of my more-substantial bicycles, but I enjoy riding all of them. I look at it this way: the heavier bikes give me a "quality workout" on a per-mile basis, and I do notice the speed boost when I switch to a lighter machine.

tomato coupe

There are four basic forces that oppose the forward motion of a bicycle, and three of those depend on the mass of the bicycle. You are imposing unrealistic constraints to eliminate those three forces so that you can make a blanket statement about the mass not making a difference. At best, that's sloppy and misleading physics.

AndreyT

As it is virtually always the case, such aggressively assertive statements lack any specifics. It wouldn't be that difficult to name those "forces" (that "depend on the mass of the bicycle"), would it? But alas, we are seeing only smoke here... Ordinary weaseling, you say? Might be... But I'd guess it is simply because most of these "fundamental forces" have already been more than satisfactorily taken into account, analyzed and accounted for above.

In other words, same thing as with the previous trolling/smoke-pumping attempt

terrymorse 

It's a simple yet subtle relationship (too subtle for some, apparently ).

Why does it take more energy to move a heavy bike up and down a hilly course? Because of wind drag.

Holding everything else constant (rider, power, position, etc), a heavy bike will be slower on the uphill, but only a little faster on the downhill.

Consider a 5 km 6% course. Rider goes up it, turns around and coasts back down to the start. Default bike weighs 9.5 kg, heavy bike weighs 19.5 kg.

The heavier bike will be 10.1% slower on the climb, but only 6.0% faster on the descent. Why the difference? Wind drag. That extra potential energy of the heavier bike at the top of the hill is spent pushing through the air, and since wind drag increases as the velocity squared, it wastes a bunch of that energy.

shelbyfv

Larry has a knack for bringing them out.

CAT7RDR

Bike commuting has nothing on tree trimming without power tools. Just sayin'.

retswerb

I know right?? I was reading through this thinking what a success Larry had on his hands.

tomato coupe

No, it's not difficult to name the four forces, but I assumed that I wouldn't have to list them for someone with such a deep understanding of physics. The four forces are well known and arise from: aerodynamic drag, rolling resistance, acceleration, and change in potential energy due to gravity. All but aerodynamic drag depend on the mass of the bicycle.

Steve B.

Very dependent on the level of traffic and congestion. I was 18-27 miles one way in Brooklyn, then the beach area, then endless turns and short local streets. Too many traffic lights in Brooklyn, too many pedestrians and other cyclists elsewhere, as well as too much vehicle traffic to want to push for speed. It was simply too dangerous. I had 54 turns and local streets in the last 8 miles. I wasn’t using those as hard training efforts. I really needed to pay attention on this commute, doing hard efforts was impossible, but YMMV

PeteHski

I was joking, but what I said was still true.

PeteHski

A heavier bike will require more rider effort if any of the commute is uphill or requires any accelerations.

Steve B.

No argument, really depends on circumstances, road traffic, how busy, etc,,,,

HTupolev

Not only that, but because the descent takes far less time than the climb, the time costs and benefits are even bigger than the difference in the ratios of speed.

LarrySellerz

Friction internal to the bicycle system (drivechain inefficiencies, wheels rubbing on brakes) is another force that is sometimes dominant. Aerodynamic drag not depending on mass? Sounds like you buy into that obviously farcical test where they dropped a hammer and feather on "the moon" and they fell at the same speed.

RCMoeur 

Cheaper than the gym...

tomato coupe

Those forces don't oppose the forward motion of a bicycle; they just affect the efficiency with which power reaches the rear wheels of the bicycle.
Aerodynamic drag does not depend on mass. Ask some of the people you work with.

LarrySellerz

They also buy into the hammer/feather thing and now that I'm full time and making $$ I don't bring it up