So it's been 2 weeks with new LRR tires...no improvement in mpg!

So have you come back to have the Re - Balance and Rotation? If so at what mileage? If you haven't done so it's about time to do it, 1,100 miles is a good time to work on.

BTW, did you check battery air vent?

 

Puzzling because of your final declaration. Which is that you had excellent MPG the moment before the new tires. Which would suggest it's NOT related to anything that isn't tire or suspension.

Michelin Fuel Savers as a "brand" of tire should not cause- even as new, the mileage drop you are presenting.
Which leads me back around to it HAS to be something suspension or alignment related.

But I'll admit....if your alignment and suspension are OK, I'm stumped.
Sure a LOT of things can affect your mileage, BUT most of those peripheral things would NOT coincide or manifest exactly when you change tires.

Let us know if you solve this mystery.

 

I hate to say it but I agree with the OP. I know tyre brands and types differ in Europe and the US but the Micheline Fuel Savers have a variety of different types here, from A rated for economy to E rated! On a scale that runs A to F. I fear the OP has purchased the tyre thinking they would save fuel and got the wrong one.

If I recall I had two non LRR tyres put on my Prius after about 6 months and the economy dropped, as seen on Fuelly stats, and then went back up when the non LRR tyres were removed. If just two tyres made that difference, that four would be worse still. I looked it up on Fuelly and my mpg's fell to a low of 43 mpg UK (36 mpg US). After replacement, the economy went back up to 47/51 mpg UK.

 

Interesting idea.
But why would Michelin market a tire named "Fuel Savers" and then produce one (or more) that actually are horrible at promoting fuel economy?
I'm really discounting the idea that it's the tires causing the drop off, as everything I've ever read (most of it here on Prius Chat) is that Michelin Fuel Savers are an excellent choice if fuel savings is a priority.

I'd be surprised and disappointed in Michelin if they slap the moniker "Fuel Saver" on a tire that is manufactured with a low ranking for fuel economy. A lot of people aren't going to look at ratings, "maybe" a review or two, but they are probably going to go on the "name".

I would be so basic as to assume "Fuel Savers" are designed to save fuel.

 

I keep harking back to Bridgestone, with their Ecopia EP422: they're manufactured in two different countries, in 195/65R15 one version has 3 row, widely spaced tread, the other has 4 row more tightly spaced. Maybe quality control. That's really frustrating if the case.

 

Just looked up the various Michelins and there are Energy Savers and Energy Saver+ tyres, which range from E to B ratings. Strange that just two tyres have such a variety, but it appears the load rating as well as well as the reinforced tyres for heavier vehicles affects the economy ratings.

It appears the new Eco tyre rating we have here helps narrow down the best tyre for the wheel size. Just sticking to 'Ecopia' or 'Energy Saver' isn't as clear cut as you'd hope.

 

Even worse economy, but usually better than winter tyres.

Try this link, I know it's a UK link and the tyres are probably different, but search the size you need and then select the option for Michelin. Then see how many varieties they have and the difference in fuel economy rating. A is good, F is not good at all.

Blackcircles.com - Buy Car Tyres Online UK, Click & Fit Today!

Do Michelin offer the "Energy Saver +" tyre in the US? That seems to get come economy reviews here.

 

Bald tires are more efficient so new tires, even new LRR tires like the Energy Savers, are going to appear less efficient at first or maybe just not show any improvement.

The efficiency during the first 2 weeks of use are not that important. The important point is the long-term average efficiency while retaining other important tire performance measurements like traction and noise.

When I put Michelin MXV tires on my car it dropped my mpg and EV range by 10% and that only very gradually improved until I reached near parity with my old Goodyear Fuel Max tires after about 20,000 miles.

That was disappointing to me at the time and next time I will get different tires (since they no longer make MXV4's...) but the upside was that all other aspects of the tire design were excellent and it has a long tire life so I'm getting good efficiency and my tires are still in good shape after 63,000 miles on them.

You are not going to find better tires than the Energy Saver A/S for all around efficiency on the Prius.

 

i thought they were fuel savers?

 

I recently put Michelin Energy Saver a/s on my 2013 C2. They initially seemed to drop the mpg's and I was disappointed. After at least some few hundred miles on them I took the car on my favorite fall colors drive. Last year on that same drive with Ecopia 422's I got 60 and change mpgs. This year on the Michelins on the exact same drive I got 61 and change. I am re-assured that the Michelins are LRR indeed.
Just a side note the Ecopias were clearly better on snow. The Michelins may be "mud / snow" rated but they are pretty weak on snow, as many commenters on Tire Rack will mention.