Go Back   EcoModder Forum > EcoModding > Hypermiling / EcoDriver's Ed
Register Now
 Register Now

Reply  Post New Thread
Submit Tools LinkBack Thread Tools
Old 01-13-2012, 07:22 PM   #1 (permalink)
Master EcoModder
Join Date: Dec 2011
Location: Boise Idaho
Posts: 842
Thanks: 39
Thanked 89 Times in 69 Posts
Tire diameter and coast down

Heavier tires and wheels will contain more energy as a function of the square of the speed.

When doing coast down testing to determing CDA and CRR, how do you eliminate the effects or rewards of heavier wheels and tires?

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

Old 01-13-2012, 08:09 PM   #2 (permalink)
needs more cowbell
dcb's Avatar
Join Date: Feb 2008
Posts: 5,038

pimp mobile - '81 suzuki gs 250 t
90 day: 96.29 mpg (US)

schnitzel - '01 Volkswagen Golf TDI
90 day: 53.56 mpg (US)
Thanks: 158
Thanked 267 Times in 210 Posts
Good question, especially when comparing tires. The momentum they store is also a function of their diameter(was in the title, but road speed is the same, so clarifying), i.e. more mass farther out in some tires. Holding the road speed the same may cancel out the effect of diameter, I haven't run any numbers. But even different pressures imply (slightly) different masses.

What Darin did if I recall is to start from a stop, on a hill, so that seems like it would take into account the extra energy needed to spin up different wheels (or wheels with more or less air), and return it on coast out, maybe.


probably best to measure the force needed for rolling with some fixture, but for most folks that is probably overkill. Or measure the momentum, torque needed to achieve a certain road speed within a given amount of time on the bench and factor it in somehow.


Last edited by dcb; 01-14-2012 at 04:57 AM..
  Reply With Quote
Reply  Post New Thread

Thread Tools

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com