Thanks to Google books, I picked up the following graphs from:Gyenes, L. and Mitchell, C.G.B., "The Effect of Vehicle-Road Interaction on Fuel Consumption," Vehicle-Road Interaction, ASTM STP 1225, B.T. Kulakawski, Ed., American Society for Testing and Materials, Philadelphia, 1994, pp. 225-239. Tire inflation lookup table:kN/m**2 - psi 200 - 29 225 - 33 250 - 36 275 - 40 300 - 44 325 - 47 350 - 51 375 - 53 Speed lookup table:km/h - miles per hour 80 - 50 90 - 56 100 - 62 110 - 68 120 - 75 Vehicle drag is a function of rolling resistance and drag times the velocity squared. However, tire rolling resistance is not a linear function with speed and these charts give a clue. Bob Wilson
Thanks Bob. For those of us that digest information better visually this is excellent. It would appear that tire pressures have a negligible advantage as pressures increase greater than 60 psi , but the difference between 29 and 60 seems signifigant. That would correlate with what Wayne said in his talk videotaped at Hybridfest. My question is what is the impact of the rolling resistance coefficient at speeds less than 56 mph? It seems small to me between the types of tires. Is this correct or does the small difference have a signifigant impact? Since my tires are new I am staying with the Turanza's as they seem to be handling the snow well so far, but at some point down the line I will have to choose new ones, and the choices for 16" are far less than for the 15" from what I've seen. Thanks again for posting this.
I wish there were a graph, or a web site that gives the rolling resistance for the different brands of tires sold. Does anyone know of one?
One source claimed it was an inverse square function, A - (k/(psi**2)), and the shape of the curves are consistent with that relationship where A is a lower limit and k is a parameter that is tire dependent. It holds a constant drag. This is why the drag in Newtons for an NHW11 Prius is expressed as: 190 + (0.42*(V**2)) 190 - tire drag of the OEM tires at OEM pressure My reading from the graph projected on the NHW11, OEM tire: 190 - .013 - radial - 100% 241 - .0165 - bias tires - 127% 263 - .018 - cross belted - 138% It is a significant impact especially at low speeds. Bob Wilson
You are asking for info that tire manufacturers guard close to their chest. California will force tire manufacturers to cough up their deep dark secret rolling resistence info in 2009. I had a chart about a year ago ... when we had to replace the cheezy stock Goodyears. Consumer reports did an article not too long ago on the topic. For the money, the Michelin hydroedge was hard to beat.
hi Hill, yeah, i got a set of hydroedges, but a got a wider size, 205 instead of the OEM 185 that came on my Prius. It has really hit my MPG... hard.
