Pheonix, I've just been through this tire-size decision process, and I can confirm that you can be drowned by the options. Tire width and height, rim size and mass, rolling resistance, traction, speed, load and temperature ratings; there certainly are a lot of variables.
Trebuchet and the racers are correct that less mass is easier to accelerate. But I ruled out light-weight alloy wheels, as it would probably take forever to recover their cost in fuel savings. So what is left for FE? Friction, aka rolling resistance. And as you and StanleyD noted, skinnier tires are usually more FE. So I looked for skinnier tires with a low rolling resistance.
DracoFelis and StanleyD's comments about changing the tire diameter are significant, because this also changes your effective final gear ratio. I don't have overdrive, and I considered larger diameter tires. But I decided to keep my tire diameter the same and only change the tire width. ( I am double thinking this decision, as changing tire size is much cheaper than a gear or transmission swap to achieve higher gearing... but too late)
My Cavalier came with 195/65R15 tires (the "big 15's") though most Cavaliers came with 14" wheels. I could not find 185/70 15" tires, but I did find 185/75R14's. They are not common, but available online. This size maintains the same diameter as the stock tires within 2 rev's per mile. I found 175/80r14 tires online in Europe, but not in the USA. This is interesting to me since they are more into mileage than the U.S.A. See the pictures below for a comparison of my old and new tires. Remember, the new tire is not inflated, so were not comparing apples to apples here. But I wanted to show them anyway - they look like bicycle tires compared to my old tires. I hope, when mounted, they maintain that rounded cross section at the tread, instead of being flat like the old ones. That would reduce road contact even more. I'll post another shot once I get them mounted.
These are the General Ameri G4S. I only found two sources of RR data online. The data from
2002 lists the Continental Ameri G4S as having the second lowest RRC at 0.0078. Since Continental makes the General tires, I'm hoping it is the same tire with just a different branding slapped on. I've written Continental asking if this is the case. My tires have a treadwear rating of 520 and a 60,000 mile tread warranty. So they should last a little longer that the Prius OEM tires, which have a treadwear rating of 160.
When I tell my friends that I got some tall, skinny, LRR tires, many respond with "won't that affect your traction". Well, here's where I get to rant. <standing on soap box> The current fad of wide, low-profile tires is silly. That style of tire is only good for traction on dry pavement. ie, racing or trying to pull 1g in the turns. Narrow tires concentrate the weight of your car on a smaller footprint, giving better traction in rain and snow. And THAT's when I'm concerned about traction. < off the soap box now> The 195's on my Cavalier hydroplane easily and were terrible in the snow. I expect much better performance from the new, narrower tires. I will report my findings as soon as I get some 14" wheels.
??? Thanks for the input!
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