twobadfish

Does the weight of the rider or the weight of the bike contribute differently to how much power it takes to move a bike? In other words is a 160lb rider and 25lb bike the same as a 170lb rider and 15lb bike?

AEO

cross section surface area and wind drag are far more important than weight.

unless you start going up hill, then weight can add up.

Homebrew01

Yes, power requirement is the same. 185 lbs has to get from point A to point B. The 170 lb rider will have a theoretical advantage in the power to total weight ratio. And the 85 lb rider on a 100 lb bike is going to have a bad day.

revchuck 

If the riders are equally fit, yes. Aerodynamics plays a part in this too, as does the quality of the bike parts.

It's usually cheaper and more productive to lose weight off the rider than off the bike. It's just not as cool and blingy. A fitter rider with a heavier bike will clean the clock of a less fit rider on a lightweight bike.

Dellphinus

Where the weight is located is irrelevant, with a caveat-
Wheels and crankset- more weight in the rotating parts means more power is needed to change speeds, due to rotating mass.

The effects are small though, and for 99% of us make little to no difference. Crit racers, bike couriers, etc (lots of starts stops, lots of accelerations) would notice the difference in heavier vs lighter wheels.

gregf83 

If a 170lb rider with a 15lb bike decides to lose 10 lbs off his body but switches to a 25 lb bike he will generally be faster. Losing excess mass off your legs which are going up and down 90 times/min is going to be more efficient.

datlas 

The whole "rotating weight" issue gets hotly debated and I don't know enough about physics to say who is right.

I tend to believe that weight is weight and it doesn't really matter where it is, but I do also know that lighter weight on the bike and wheels especially "feels" lighter....but probably doesn't make much of a difference.

It's certainly cheaper to lose weight off your body, and unless you look like Rasmussen (or PCAD's latest incarnation) makes more sense....but if you push weight loss too much you will be losing muscle mass and that is bad and certainly may slow you down in the end.

I hope that helps, but probably not.

AEO

only matters in acceleration.
doesn't make much of a difference when maintaining velocity.


The car guys know more about this stuff, and lightweight flywheel it highly desirable for performance cars.
https://en.wikipedia.org/wiki/Flywheel
https://www.uucmotorwerks.com/flywhee...heel_works.htm

you might notice that the 'virtual weight lost' is an exponential decay type of chart, so the lightening of wheels only really matters at lower speeds. At higher speeds, when accelerating, there's less of an improvement, but it will be there.

M_FactorX19

its definitely cheaper to loose weight off your body! to bad i only weigh 120lb! ive got to loose weight off the bike and thats not cheap trust me! it matters more when you are <120lb how much your bike weights than if you were >200lb.
i would like to be bike + me < 135lb.. im close now and somedays am since my weight drops here and there a few lb.

pallen

not just flywheels, any rotational mass - lighter wheels, lighter pulleys, lighter drive shaft, etc...

BLR_0719

eat a hamburger

stien

While the above posters are correct, they forgot one thing.

A 25+ lb bike is usually not equal to a 15 lb bike in terms of components, so you might be able to wring some more speed out of the latter

datlas 

Wrong.

Creatre

Aerodynamics, rotational mass, and flex of the components are just as important as the actual weights. Most likely the 15lb bike is made of far superior quality, and while being lighter, would be faster. But it's hard to compare really, so many variables.

Debusama

There are a lot of variables. Is the 170 pound rider heavier because he is taller, does he have 5lbs more body fat, or is the 5 lbs due to having bigger quads and gluts? In general, I would say that a heavier bike is usually heavier because it is made of heavier materials that don’t necessarily take up more space and add to the surface area and drag of the bike. Realistically, if a 20 pound bike and a 15 pound are made on the same budget, the money that was not spent on weight reduction on the heavier bike was probably spent on aerodynamic improvements. An extra five pounds of rider body fat not only has to be pushed up the hills, but it also makes the rider bigger and less aerodynamic. An extra 5 pounds of muscle mass on the rider would not have as much volume as 5 pounds of fat, and would not contribute to drag as much, and the subsequent increase in power might justify the increase in weight and drag. (Fabian Cancellara, Thor Hushovd)

pallen

What about a 150lb rider that just lost 100lbs and built his muscles pushing 250lbs?

stien

Wrong.

DScott

= Right?

Phantoj

Can I crunch some numbers for you people?

datlas 

Maybe.

Shimagnolo

You need to carry 60 pounds of ballast to level the playing field.

twobadfish

This is an interesting idea. I'm trying to determine where I will see the greatest gains in weight reduction on a 25lb bike. Aside from my own weight I think I will - thanks to some of the info here - look into a lighter crankset, rear cassette and derailleur.

Phantoj

It's probably not worth getting all weight-weenie on a 25-lb bike. Just sell it and get something <20 to start with.

Grumpy McTrumpy

this is a goldmine of fallacies.

twobadfish

??