The Similarly Stimulated Saturn is rolling on 4 Michelin HARMONY Radial X P185/70R14 tires. Running them at 40 psi. They are rated at maximum loaded weight of 1201 pounds each and maximum pressure is 44 psi.
Wondering what tires are the best, as far as [[rolling resistance coefficient]] ([[RRC]]) and how do my tires fare? How much difference is there between the best tires and worst? Does RRC effect efficiency as much as other drags? How do tire pressure effect rolling resistance?
[[http://saturn.lynnautorepair.com/2009%20Rolling%20Resistance%20Efficiency%20Ratings%20for%2077%20Tires|Which tires are the most efficient? See this chart]]
Best and worse tires? California has done lots of reports and studies on tire rolling resistance and have passed some laws (Assembly Bill 844) to require more efficient tires like their California Fuel Efficient Tire Program . [[Rolling Resistance Force]] (RRF) is a newer rating term some use instead of RRC. Most new passenger tires have reported RRCs ranging from .007 to .014, the lower the better. Although a different (larger) size, a study in 2002 by Ecos Consulting showed the Harmony at around .010, around the median. Tire Rolling Resistance Coefficient does not allow comparing different sized tires. Smaller tires have lower resistance.
According to this Michelin Chart 20% of the energy consumed on a level drive, after reaching cruising speed, is caused by tire rolling resistance. They dramatically say “Today, it is true to say that one out of every five tanks of fuel, is used to overcome rolling resistance”
So if an EV is…………………..
• Using 500 watts per mile
• Tire rolling resistance accounts for 20% of the energy used
• The best tires are rated at .0070 and the worst at .0140
• My tires are rated .0107
• If I changed my tires to the best .0070’s
• I would increase efficiency 35% of the 20% that RRC effects energy usage.
• So 500watts X 35% X20% =
• Final Answer 35 watts less per mile or 7% increase in power or distance from the better, lower resistance tires.
Tire pressures Inflation affects tire deformation. The more a tire at a given pressure is loaded the more it deforms and rolling resistance increases. For conventional passenger tires and increase in inflation pressure from 24 to 29 pounds per square inch (psi) will reduce rolling resistance by 10 percent. For a tire inflated to pressures between 24 and 36 psi, each drop of 1 psi leads to a 1.4 percent increase in its rolling resistance. the response is even greater for pressure changes below 24 psi.