OK, guys, let me try to explain what is what with regard to rolling resistance in tires.
Mass (weight) = rolling resistance. The heavier the tire, the lower the fuel economy.
Since the tread is the heaviest component in a tire, the tread compound has a great effect on RR.
There are three things that can get traded off when it comes to tread compound: treadwear, rolling resistance and traction (especially wet traction). So if you want low RR values, you have to sacrifice traction and / or treadwear. For example, OE tires, which the OEM's want to have low RR values, are generally low treadwear and / or low traction. Read the ratings on OE tires and that's always what the complaints are about.
BTW, this does not mean that tires with low treadwear ratings have low RR - might be true, might not. Same for low traction.
But there are things that affect wet traction and wear that don't affect RR. For example, lots of sipes is good for wet traction, but bad for wear, and RR is pretty much the same.
So how do you pick tires with low RR values?
First stay away from high speed rated tires - more material = more mass = higher RR. That also eliminates that problem of confusing high grip/low treadwear with high RR
Second, find a tire line that specifically mentions fuel economy. But be aware that most tire manufacturers don't publish RR ratings. Why? It doesn't help sell tires (except for those few interested in the subject).
So if you can't find a tire that is designed for low RR, then your best bet is to find an OE tire (note - that size has to be OE, not part of the line)
BUT!!!
There is something that everyone has control over that has more effect on RR than the tire itself - inflation pressure. Higher is better.
So in this particular case:
1) The change in tire size isn't going to have a major effect on RR, especially since a P175/70R13's aren't OE anymore and the comparable 75 and 80 series tires are more likely to be produced in the cheap versions only, meaning that the tires won't have the exotic, and expensive, tread compounds.
2) S speed rating. This means that the "20 over the limit" has got to go!! (more fuel consumed and a larger risk relative to the speed rating)
3) Use as high an inflation pressure as you can feel comfortable about the traction (which means some tests doing panic stops).
Hope this helps.
[ December 22, 2004, 08:54 AM: Message edited by: CapriRacer ]