Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Over-inflating tires

GreenHornet · 07-24-2013, 01:53 PM

I would like to share some data with all of you on testing that was performed for the Shell eco marathons. This data is out of the book by W.S. Affleck and G. B. Toft Fuel economy of the gasoline engine. While the book was published back in 1977 the research that was done into the science of fuel economy is very relevant today as well as pertains to this thread!

Chapter 12 Mileage Marathons

Under rolling resistance it states that

"Rolling resistance is, in a properly prepared vehicle, largely determined by tyre size,profile,structure and inflation pressure. Increasing inflation pressure on a conventional cross-ply 14" tyre from 25 to 40 1b/in2 reduces Cr from 0.018 to 0.015. Changing from cross-ply to a radial-ply tyre, inflated to 40 lb/in2, will further reduce Cr to 0.011. Investigation with the Wood River Fiat 600 showed further reductions in rolling resistance as tyre pressure was increased to 100 1b/in2. Increasing from 20 to 100 1b/in2 increased the 16.5 to 0 mile/h coast distance by 50%."

It went on to further say

"Large wheels show useful reductions in rolling resistance over small ones, thin sectioned tyres over thick sectioned ones, and treadless tyres over fully treaded ones. TRC specials have used high-pressure racing bicycle tyres and probably achieve values of Cr of 0.003."

"For a 'modified' car a reduction in Cr to 0.01 appears plausible, with a significant further reduction available to the special builder. Recalculating equation 12.1 with these data for a 2000 lb vehicle,

at 10 mile/h, bhp = 0.0267(20 + 2.08) = 0.59
Fuel economy at 0.08 bsfc = 212 mile/gal

at 30 mile/h, bhp = 0.08(20 + 18.72) = 3.09
Fuel economy at 0.08 bsfc = 121.0 mile/gal "

So from this data and research, improvements can be seen up to 100 lb/in2
However at these inflation pressures I don't know if a cush air ride would even help a street car LOL

I doubt 100 lb/in2 would be safe for every day road use. But it is interesting test data none the less.

Hope some of you find it interesting.

GH..

07-24-2013, 01:53 PM	#14 (permalink)
GreenHornet Master EcoModder Join Date: Feb 2013 Location: Oregon Posts: 429 Thanks: 41 Thanked 108 Times in 68 Posts	I would like to share some data with all of you on testing that was performed for the Shell eco marathons. This data is out of the book by W.S. Affleck and G. B. Toft Fuel economy of the gasoline engine. While the book was published back in 1977 the research that was done into the science of fuel economy is very relevant today as well as pertains to this thread! Chapter 12 Mileage Marathons Under rolling resistance it states that "Rolling resistance is, in a properly prepared vehicle, largely determined by tyre size,profile,structure and inflation pressure. Increasing inflation pressure on a conventional cross-ply 14" tyre from 25 to 40 1b/in2 reduces Cr from 0.018 to 0.015. Changing from cross-ply to a radial-ply tyre, inflated to 40 lb/in2, will further reduce Cr to 0.011. Investigation with the Wood River Fiat 600 showed further reductions in rolling resistance as tyre pressure was increased to 100 1b/in2. Increasing from 20 to 100 1b/in2 increased the 16.5 to 0 mile/h coast distance by 50%." It went on to further say "Large wheels show useful reductions in rolling resistance over small ones, thin sectioned tyres over thick sectioned ones, and treadless tyres over fully treaded ones. TRC specials have used high-pressure racing bicycle tyres and probably achieve values of Cr of 0.003." "For a 'modified' car a reduction in Cr to 0.01 appears plausible, with a significant further reduction available to the special builder. Recalculating equation 12.1 with these data for a 2000 lb vehicle, at 10 mile/h, bhp = 0.0267(20 + 2.08) = 0.59 Fuel economy at 0.08 bsfc = 212 mile/gal at 30 mile/h, bhp = 0.08(20 + 18.72) = 3.09 Fuel economy at 0.08 bsfc = 121.0 mile/gal " So from this data and research, improvements can be seen up to 100 lb/in2 However at these inflation pressures I don't know if a cush air ride would even help a street car LOL I doubt 100 lb/in2 would be safe for every day road use. But it is interesting test data none the less. Hope some of you find it interesting. GH..