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Old 09-26-2012, 10:40 PM   #10 (permalink)
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Originally Posted by MetroMPG View Post
Barry's Tire Tech

(That site is maintained by an EcoModder member & tire engineer.)
Thank you Metro.

I only repeated my question to everyone because this site should have substantiated claims instead of pages worth of speculation.

It was my understanding that FE generally increases as a tire wears, and your link suggests the same.

Here is what I found from Tirerack:
Tire rolling resistance gradually drops by about 20% during the life of a tire as the tread wears from its original molded depth to worn out. This can be attributed to the reduction in tread mass and rubber squirm, as well as subtle hardening of the tread compound during years of service and exposure to the elements.

While this gradual reduction in tire rolling resistance and minor increase in fuel economy may be too subtle to register during the tire's life on a tank-by-tank basis, the virtually instantaneous switch from worn tires to new tires (even if they are the same brand, type and size) will typically result in an increase in rolling resistance of about 20%. Since the automotive industry estimates a 10% increase in tire rolling resistance will result in a 1% to 2% decrease in vehicle fuel economy, drivers should expect to experience a potential 2% to 4% decrease in mpg.
The page also goes on to discuss how worn tires affect the odometer reading. On a test car fitted with 205/55R16 tires, a 100 mile test showed a 1.5% difference in odometer distance with worn tires when compared with new tires. This would directly affect the accuracy of MPG calculations taken from the odometer or trip meters.

On a 30mpg car, new tires might actually decrease FE by 1mpg, and the change in odometer reading might show another 0.5mpg "loss".
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Last edited by redpoint5; 09-26-2012 at 10:46 PM..
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arcosine (09-27-2012), MetroMPG (09-26-2012), Tango Charlie (09-26-2012)