# Torsion spring or flywheel cars: what says the dope?

**URL:** <https://boards.straightdope.com/t/torsion-spring-or-flywheel-cars-what-says-the-dope/590563>\
**Category:** In My Humble Opinion\
**Created:** [July 28, 2011, 12:29am UTC](https://boards.straightdope.com/t/torsion-spring-or-flywheel-cars-what-says-the-dope/590563 "2011-07-28T00:29:40Z")\
**Posts on this page:** 1\
**Page:** 2

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**Author:** ![SCSimmons](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@SCSimmons](https://boards.straightdope.com/u/SCSimmons)\
**Post date:** [July 29, 2011, 8:22pm UTC](https://boards.straightdope.com/t/torsion-spring-or-flywheel-cars-what-says-the-dope/590563/21 "2011-07-29T20:22:04Z")

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> [@allyn](#):
>
> A couple of examples of flywheel power in use:
> 
> [Parry People Movers - Wikipedia](http://en.wikipedia.org/wiki/Parry_People_Movers)

Can someone check my math here? That link has some actual specs on their flywheel–a 1m diameter disc weighing about 500 kg, designed to rotate at up to 2500 rpm. I calculate that out as storing about 2 million joules of energy at maximum speed. That may sound like a big number–but [a liter of diesel stores over 38 million joules](http://en.wikipedia.org/wiki/Energy_density) … Did I drop a decimal point somewhere? Even with increased efficiencies, I don’t see 50 ml of gas taking your tram up a hill.

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