I'm trying to get an idea of why I'm getting worsening mileage and what to do about it. First off, I've had my '03 HCH since March '03 and I had been averaging 42-45 per tank. Last Nov I had air induction service done and new tires installed at the dealer; then I noticed I couldn't get it above 39. I found the following thread:

https://www.greenhybrid.com/discuss/...g-36mpg-13356/

I seriously doubt it was my driving habits since I haven't changed the way I drive. I do wonder if using E10 has a really noticeable effect. And do tires make that much difference (assuming they're always properly inflated and regularly rotated)?

 

What was your mileage like at the beginning of ownership? I think it might be the tires, having more tread. Are the replacement tires the same type?

 

Come to think of it, I do remember being disappointed when the overall milage of my trip from DC to Atlanta and back of being <41; I had had the car for 5 months. So the treading is a possibility...

 

I believe the tire rubber gets harder as it ages- decreasing it's footprint on the road, decreasing rolling resistance and increasing efficiency.

I had my original Dunlops replaced at 88,000 miles with the same tire and noticed perhaps 3-4MPG decrease.

There are also other factors to consider: My dealer offered several tires, and since I've had such good luck with the Dunlops I renewed them.
Other tires offered were not LRR.

Tire pressure is another question: My dealer always deflates them to 32PSI unless I specify 51. I've always ran mine at max cold sidwall pressure (51PSI) for maximim efficiency.

-Steve

 

My dealer had Pirellis available so that's what I went with. I seem to recall Ferrari owners don't care much for milage...

I thought the recommended tire pressure was 30 (so I inflated mine to 32). I know overinflating causes uneven tread wear, but does it also cause accelerated tread wear?

 

the tires could possibly be underinflated, but i also suspect the E10. there is one station on my way to work that has only E10, and the time i used it, there was a definite reduction in my FE. there has been a lot of press lately on the fact that is does indeed decrease mileage.

http://www.sunjournal.com/story/2669...duces_mileage/

 

I'm not so sure about the E10 part. I've only had my '03 HCH1 for a little over a month, but I'm on my third tank of gas and getting really decent milage. I've learned that driving habits REALLY matter, but I agree with the OP that I doubt she's "unlearned" how to drive well on the HCH.

I'm currently geting 49.9 with 340 miles on this tank (one tick under half tank) and here in Ohio we use E10.

 

My last set was replaced when worn almost to the bar at 88,000 miles, and wore evenly. I've driven the car with the higer pressure and am so used to it now that lower pressure seems overly soft, defninetly sluggish.
Feels like I'm driving on a soft sandy beach at 32PSI.

-Steve

 

My car (~60K miles) does not have the original tires; I bought it used and they had been replaced by some more generic ones, and I've never gotten below 42mpg...sometimes getting as high as 47. I keep the pressure inflated to a little over 30psi. I have read that the increased tire wear doesn't happen until about 6 psi over the recommended amount.

I'm a grandma driver though. Maybe that's why I get good mileage.

 

It's a known fact that Ethanol contains approx. 34% less energy per unit volume than gasoline, so blending it with gasoline has got to be lowering the energy per unit of the fuel. As for the tires, I am running OEM Bridgestone 381s with 60 psi and they look great. My mpg is great with these tires as can be seen below.