Rotating Mass vs. Static Mass (Wheel Specific)

[livingminimal]

Ok.

How important is hub weight?

Does it matter for the overall gravitational/static mass of the bike?

Or, so close to the axle, does it actually play a roll in rotational mass?

Inquiring minds gots to know (and my search turned up bumpkins)

[steamer]

Hub weight plays almost no role in determining the wheel's moment of inertia since it is so close to the axis of rotation. Think of it as no different than frame, or handlebar, or seatpost (etc) weight. And it's a minor contributor, at that.

Heading a little bit OT, wheel rotational inertia is way overblown, as it plays a fairly small role in the bike / rider system's overall inertia. And acceleration, outside of a few very specific riding situations (yoyo at the back of a crit pack, city riding in traffic, etc.), consumes very little energy compared to aero drag, rolling resistance, and overcoming gravity (when climbing).

So yeah, anyways, hub weight is pretty unimportant.

[ergott]

For the purposes of cycling, it doesn't matter where the weight is. There are online calculators that will approximate hill climb times based on total mass and power output. Where that weight is distributed on the bike/rider won't significantly change the result.

Wheels with lighter rims do feel different when accelerating and cornering. Just don't mistake that for significant differences in speed.

Here's an experiment.
1) place your bike on a trainer, but don't connect the resistance unit.
2) put your bike in the biggest gear and apply power to the pedals.
3) notice how little effort is needed to accelerate a wheel to max speed.
4) try with multiple wheels that have different mass at the rim/tire.
5) notice how you won't notice any significant difference.

It's you that needs all your power to get moving (and continue moving).

[oldpotatoe]

Ok.

How important is hub weight?

Does it matter for the overall gravitational/static mass of the bike?

Or, so close to the axle, does it actually play a roll in rotational mass?

Inquiring minds gots to know (and my search turned up bumpkins)

Rotational mass, 'flywheel effect' is almost not measureable. A test I read, wish I could find it, somebody doubled the weight of a bike rim and measured energy to spin to a certain speed and it increased about .1 of 1%.


Weight is weight, still gotta lift it up hill. The energy required to move a bike is determined by the mass of the bike and rider.

When people say carbon wheels ,'spin up faster', that's mostly due to stiffness, not weight.

[ultraman6970]

"5) notice how you won't notice any significant difference."... that means that I suck then! :D

[livingminimal]

Rotational mass, 'flywheel effect' is almost not measureable. A test I read, wish I could find it, somebody doubled the weight of a bike rim and measured energy to spin to a certain speed and it increased about .1 of 1%.


Weight is weight, still gotta lift it up hill. The energy required to move a bike is determined by the mass of the bike and rider.

When people say carbon wheels ,'spin up faster', that's mostly due to stiffness, not weight.

And so then...based on what we've learned about flex and rim deflection, that's really more about spokes than rims...

[ergott]

I have rims about as light as you can make them (220g). Trust me, they feel lighter when you accelerate the bike. Thing is, it doesn't make me appreciably faster than if I lost that same amount of weight elsewhere.

[Black Dog]

I have rims about as light as you can make them (220g). Trust me, they feel lighter when you accelerate the bike. Thing is, it doesn't make me appreciably faster than if I lost that same amount of weight elsewhere.

If you know they are on the bike then you may be feeling a placebo effect. :D

[redir]

When people say carbon wheels ,'spin up faster', that's mostly due to stiffness, not weight.

I think you meant to say it's due mostly to marketing, not weight :D

[oldpotatoe]

I think you meant to say it's due mostly to marketing, not weight :D

Reality, what a concept:D

[MadRocketSci]

https://www.youtube.com/watch?v=OTjqt24oH3U

[martl]

Here's an experiment.
1) place your bike on a trainer, but don't connect the resistance unit.
2) put your bike in the biggest gear and apply power to the pedals.
3) notice how little effort is needed to accelerate a wheel to max speed.
4) try with multiple wheels that have different mass at the rim/tire.
5) notice how you won't notice any significant difference.


Another experiment:
1) turn your bike upside down and let it rest on handlebars and saddle
2) spin the crank with your hand as fast as you can
3) stop the rear wheel using your palm
4) the heat generated on your palm is the amount of energy that was stored in the rotating wheel
5) if your palm didn't suffer at least 2nd degree burns, the amount of energy was insignificant

;)