Is Tire mileage proportional to FE,

[ystasino]

The title says it all I guess. just curious if it's only the initial wear that brings about FE increase or is it a continuing thing?

[jdenenberg]

<div class='quotetop'>QUOTE(ystasino @ Jun 14 2007, 09:57 PM) [snapback]462037[/snapback]</div>

The title says it all I guess. just curious if it's only the initial wear that brings about FE increase or is it a continuing thing?
[/b]

Some of the increase in MPG as your tires wear is continuous, but artificial. As the tread wears, the tire circumference decreases so that the number of revolutions per mile increases. Since a worn tire has lost about 3/16 inches in radius and our tires start at about 24.5 inches in diameter, the apparent increase in MPG is about 0.375/24.5 = 1.5% (about 0.75 MPG in a Prius). This increase is not real, but due to mis-calibration of the odometer.

There is a small factor due to decreased rolling resistance as less tread material is left to bend as the tire rolls. This part is real.

JeffD

[Tempus]

There are a couple of ways FE increases with tire wear.

1) Sizing - They put gummy stuff in the molds to make the tires release. It wears off pretty quickly.

2) Tread Block Squirm - There is resistance and thus lost energy in the Tread Blocks wiggling. Even more so on corners. As the Tread Blocks get shorter, they squirm less.

3) Tire Diameter Decrease - as the tire wears it gets smaller. Since the Odometer counts tire revolutions to show you the mileage, you get more miles per mile. In other words, it's not really increasing your actual fuel economy, but it looks like it from the math. If your tread blocks are 10MM deep, when you're half done your tire diameter is 10mm less, so the tire has to rotate more times to go a given distance.

[ystasino]

And is this small increase in FE due to less resistance measurable if say one compare a tire that has 5k miles on it vs one that has 25k miles on it?

And are we talking something like 0.3 MPG or 3 MPG for these mileage marks?

[Charles Suitt]

If you take a close look at a brand new tire, you will note that the edges of the tread pattern are sharp from the mould and there are hundreds of small 'tits' of rubber on the tire from the injection holes on the mould. These wear off with use and thus decrease to a small degree the rolling resistance of the tire - thus increasing the FE a bit.

There are numerous posts in PriusChat documenting losses in FE for awhile after new tires are installed. Also, as posted, tire pressures and driving habits are much greater factors in MPG.

[hill]

<div class='quotetop'>QUOTE(ystasino @ Jun 14 2007, 09:57 PM) [snapback]462037[/snapback]</div>

The title says it all I guess. just curious if it's only the initial wear that brings about FE increase or is it a continuing thing?
[/b]

I noted that after the 1st 200 miles, the new michelins we got ~ started getting way better mileage. In fact I just got my best tank (over 700 miles) on the new tires. Some here have written that once tires seat / become "less-new" this phenomena seems to happen.