Rotational weight of equal weighing wheels diff depth though

Discuss light weight issues concerning road bikes & parts.
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JAX11
Posts: 39
Joined: Mon Jan 02, 2012 8:09 pm

by JAX11

A discussion at Superweek yesterday and this question was posed!

Wheel A is 58mm deep and weights 1450 grams

Wheel B is 38mm deep and also weight 1450 grams.

Is rotational weight the same or is it easier to spin up the shallower wheel due to cutting through the wind on acceleration?

Does it make no difference as to depth if their the same weight?

It almost seems like its hard to start a sprint or acceleration on deeper wheels of the same weigh!

by Weenie


denzity
Posts: 96
Joined: Sun Mar 27, 2011 10:01 pm

by denzity

I would've thought that the deeper wheel is easier to spin since less of the weight is on the outer edge (hence less force required to rotate it). However, since the weight distribution is so small (12mm) the extra depth might be causing a drag effect that overpowers the beneficial effect from having the weight closer to the hub.

HillRPete
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Location: Pedal Square

by HillRPete

Not enough information to do the calculation, you need to know where the mass is. Imagine one wheel having internal nipples, then the spoke bed would be farther out, meaning more inertia.

Not that I think it would make a difference in real world.

bricky21
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Joined: Tue Sep 14, 2010 3:28 pm

by bricky21

Rollers are the best way for someone to see for themselves how much impact wheel inertia is having on there accelerations. Try out a few different wheels using the same protocol, and then the next time wheel inertia comes up you'll find yourself doing :roll:

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bobbyOCR
Posts: 1838
Joined: Sun Sep 03, 2006 1:55 pm
Location: Western Australia

by bobbyOCR

It's likely that the deeper wheel will have a lower moment of inertia. Wassertreter is 100% correct though. Not enough info.


However, the difference in practice would be so small and the aero advantage with a deeper set would be greater that the better choice really is the deeper set. All things considered, unless a shallower set is significantly lighter, aero is better.
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