Thread: Prius 75-91mpg
View Single Post
Old 04-22-2019, 10:30 AM   #24 (permalink)
Master EcoModder
Ecky's Avatar
Join Date: Dec 2011
Location: Vermont
Posts: 4,416

Gaptooth (retired) - '00 Honda Insight
Team Honda
Gen-1 Insights
90 day: 54.26 mpg (US)

Such Fit - '07 Honda Fit Sport
90 day: 41.27 mpg (US)

Connect - '15 Ford Transit Connect XL
90 day: 21.26 mpg (US)

K-sight - '00 Honda K-sight
Team Honda
90 day: 46.5 mpg (US)

Aerocivic - '92 Honda Civic CX
90 day: 64.49 mpg (US)
Thanks: 2,251
Thanked 2,015 Times in 1,261 Posts
Originally Posted by Vman455 View Post
You mean angular momentum? Rotational inertia is independent of speed.

All that as a prelude to saying, I don't get that result using representative tire dimensions and weights from Tire Rack--for the 185/55R14 and 185/75R14 I compared just now (they don't list any 165/xxR14), the larger tire still has higher angular momentum....
Maybe I'm confused by the terms, but the math works out that the energy stored in a spinning tire is very slightly less in the tire with a larger diameter, all else being equal, if you want to be traveling at the same speed. It's counter-intuitive but the reduction in RPM is worth more (slightly) than bringing the mass closer to center and spinning it faster.

Angular momentum is likely the term I wanted.
  Reply With Quote