Sounds like they were over-inflated.

 

That's what I was thinking

 

What air pressure are you running?

 

A 10 mpg difference seems excessive, but I do think rolling resistance can make a big difference especially on a hybrid. According to this report, rolling resistance can differ 30-40 % between brands and types of tires
http://www.greenseal.org/resources/r...resistance.pdf

They say a 10% difference corresponds to about 2% difference in FE, but that's for a normal car. It could be more for a hybrid, at least counting in percent. (And probably less for a 5.7L V8 with carburators, where most of the fuel is spent on just turning the crankshaft around.)

A lot of people also reports low FE with new tires, it could improve after a while.

 

I got my tires replaced today. At 88,000 miles the OEM were worn down to the top of the tread bar.

I've ran all 4 at 51PSI all that time and in my case have warn evenly across the tires. I've had them rotated every 10,000 miles and an alignment done every 15,000 miles.

I was lucky enought to get the original model: Dunlop SP-20FE and was suprised how smooth the ride was. It was almost like driving through soft sand. I noticed my MPG had dropped as well.

Then I got to work and realized something, and checked- sure enough they're deflated to 33PSI. I had my pump with me and ran them up to 51.

I'll see tonight if I can get the same MPG as the set I just replaced.

 

The smoother ride comment is very common for new tire owners. As tires wear they obviously are losing rubber that insulates you from the road. It's very gradual over 88k miles.

An interesting point that that brings up with FE. You have just added unsprung weight to each wheel and that can definately affect your FE. It's not much weight, but it's unsprung AND you are dealing with rotational inertia with tire weight.

So, even with the tire pressure set correctly, I'll bet you could see a 1 mpg loss, just from the added rubber of the new tires. Of course, you'll gradually gain it back over the next 88k miles.

 

I highly doubt non-LLR tires will reduce mileage that much. I would check to see if any mechanical components are binding since your last visit...the FIRST thing I would check is what the mechanics may have done to your vehicle...no joke.

 

I'm getting about the same FE with my new tires vs old.

I'm not sure if this angle was covered but Shine5555 if your car needs new tires that early and get that low MPG with new ones, I'd say almost certainly it's a wheel alignment problem.