I just had 20x15 16gr Dr Pulley rollers put in. I've gone through a tank and a half of gas. The first tank I got 83mpg, and the second tank I got 85.4. The 85.4mpg tank was with the new rollers for the entire tank of gas.
My travel conditions are 75-100 miles round trip, daily, on roads that are posted at 50mph.
I've noticed my take off speed is better. No shutter at all at slow speeds, just really nice and smooth. My mid-range to top end is soooo much more responsive.
Here's the confusing part: My top end speed has increased! My MPG have increased! I've noticed that I was never able to pass the 8k rpm before. Now I can zoom right by it if I need to, which increases my speed.
My only explanation for improved gas mileage (if it wasn't just a fluke thing, which I will find out when I go through several more tanks), is that the engine through all RPM's (regardless if low or extremely high), just doesn't have to work as hard as it ever has. I can feel this, because the Yager just FEELS lighter and more responsive.
I'm not a tech guy or a mech guy, though, so my opinion is just that - an opinion. But I can say that I've been more than pleased so far.