View Single Post
Old 06-08-2008, 04:36 PM   #101 (permalink)
Master EcoModder
Join Date: May 2008
Location: Auburn, NH
Posts: 451

Wicked Wanda - '99 VW Beetle GLS
90 day: 29.59 mpg (US)

Green Monster - '99 Ford Explorer Sport
90 day: 16.73 mpg (US)

Dad's Taxi - '99 Honda Odyssey EX
90 day: 24.23 mpg (US)
Thanks: 0
Thanked 2 Times in 2 Posts
Originally Posted by CapriRacer View Post
NO!! - If I am reading the graphic right.

What this is saying (I think) is that the RRC (Rolling Resistance Coefficient) is lower for larger tires.

RRC is RR divided by the load on the tire. I've been searching for the source document to see how they tested the tires - and haven't found it (so far). But Smithers is well known and well respected in the tire industry, so I'm going to take an educated guess that they tested all these tires at the rated conditions - the logical way to do this.

So a P215/70R15 - which has about 50% more load carrying capacity also has about a 30% lower RRC - which means that the P215/70R15 has more RR - just like you'd think.

But what I think this graphic points to is that large tires could be used in such a way that they would generate lower RR.
The other factor is sidewall height. Low aspect ratio tires have stiffer sidewalls = less RR. Look at the tires on mileage contest cars: tall, skinny, short sidewall. The tricky part is balancing low RR vs handling requirements.

  Reply With Quote