Thread: Prius 75-91mpg
View Single Post
Old 04-22-2019, 10:30 AM   #24 (permalink)
Ecky
Master EcoModder
 
Ecky's Avatar
 
Join Date: Dec 2011
Location: New Zealand
Posts: 4,691

ND Miata - '15 Mazda MX-5 Special Package
90 day: 36.7 mpg (US)
Thanks: 2,562
Thanked 2,275 Times in 1,410 Posts
Quote:
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