Michelin X Radials and Poor Gas Mileage

[evil_attorney]

I purchased the Michelin X Radials from Costco a short time ago and have taken a serious MPG hit.

I have had the tires for about 4 weeks and 4 tanks of gas for about 1200-1300 miles. I was averaging about 49 mpg and now I am averaging about 42. I'm surprised that they caused that large of a MPG change. I haven't noticed any improvement or "break in" since I've had them. I'm running them at 40/38 psi. I thought these had relatively low rolling resistance.

Should I just suck it up and be patient or try to return them to Costco for something else? Is there any way that Costco messed something else up that would decrease mileage so drastically?

What exactly does "breaking in" do to the tires?

[Sufferin' Prius Envy]

I doubt the new tires are contributing much to your decreased gas mileage. I too have Michelin X Radials from Costco, use the same inflation pressures you indicate, and maybe, maybe, noticed a one MPG decrease for the first couple of weeks. I drove over two hundred miles to and from San Francisco yesterday . . . 53.3 MPG.

I notice you did not include your location in your profile, you should add it so we can possibly tell you things like, "ah, yes, your temperature there in Nome, Alaska is no longer conducive to higher MPGs", or, "yes, driving uphill into those Southern California Santa Anna winds will ruin your mileage."

"breaking in" smooths down the rough spots on the tires and loosens them up for smoother, lower rolling resistance operation.

[evil_attorney]

<div class='quotetop'>QUOTE(Sufferin' Prius Envy @ Nov 5 2007, 04:42 PM) [snapback]535046[/snapback]</div>

I doubt the new tires are contributing much to your decreased gas mileage. I too have Michelin X Radials from Costco and maybe, maybe, noticed a one MPG decrease for the first couple of weeks. I drove over two hundred miles to and from San Francisco yesterday . . . 53.3 MPG.

I notice you did not include your location in your profile, you should add it so we can possibly tell you things like, "ah, yes, your temperature there in Nome, Alaska is no longer conducive to higher MPGs", or, "yes, driving uphill into those Southern California Santa Anna winds will ruin your mileage."
[/b]

I'm in Los Angeles and have a 2004 Prius, so I know what to expect. Since changing my tires I have mostly driven my usual route to and from work (almost all highway). The weather has been between 60-75 degrees. Even when it's cold here (50 degrees at worst) I don't notice much difference.

When I got my new tires, I had half a tank of gas, so I didn't notice the change until a few days later after I had filled up again. But I haven't made any other changes to the car.

[evil_attorney]

Assuming the tires themselves aren't causing my mileage problem, is there anything else the Costco tire people could have done to cause the problem? The prius drives exactly as it did before the tires. The only difference I notice is that the ride is slightly less bumpy with the tires inflated to the same PSI as the OEM tires.

Could the problem be a combination of two problems? Maybe tire break in and a change in fuel used by the stations (winter grade)?

[saechaka]

what size tires did you get? i put on some 195/60 goodyear assurance comfort treads and saw a 5mpg hit and no improvement on my speedometer gauge which still reads about 2mph too fast. i'm going to go with 185/70 on my next set of tires.

[evil_attorney]

<div class='quotetop'>QUOTE(saechaka @ Nov 5 2007, 07:19 PM) [snapback]535132[/snapback]</div>

what size tires did you get? i put on some 195/60 goodyear assurance comfort treads and saw a 5mpg hit and no improvement on my speedometer gauge which still reads about 2mph too fast. i'm going to go with 185/70 on my next set of tires.
[/b]

I have p185 65r15. I believe that is the same size as the OEM's (Goodyear Integrity I think).

[member]

<div class='quotetop'>QUOTE(evil_attorney @ Nov 5 2007, 01:30 PM) [snapback]535042[/snapback]</div>

Should I just suck it up and be patient or try to return them to Costco for something else?
[/b]

Patience.

[H2OSkier]

I drive about 45 miles on the 405 every day. I was averaging around 48 mpg when I purchased my X radials. I just filled up and my last tank was 50 mpg. I have almost 5k on the X radials. Overall I think I might have gained just a touch on my mileage.

Ken

[evil_attorney]

<div class='quotetop'>QUOTE(H2OSkier @ Nov 6 2007, 12:39 PM) [snapback]535536[/snapback]</div>

I drive about 45 miles on the 405 every day. I was averaging around 48 mpg when I purchased my X radials. I just filled up and my last tank was 50 mpg. I have almost 5k on the X radials. Overall I think I might have gained just a touch on my mileage.

Ken
[/b]

Thanks Ken. I'll wait it out and see if things improve. I'm almost ready to refill the tank, so I'll see if things improved. What do you keep your tire pressure at?

[evil_attorney]

<div class='quotetop'>QUOTE(evil_attorney @ Nov 6 2007, 12:46 PM) [snapback]535540[/snapback]</div>

Thanks Ken. I'll wait it out and see if things improve. I'm almost ready to refill the tank, so I'll see if things improved. What do you keep your tire pressure at?
[/b]

Ok, it's been just under 3k miles or so on the new tires and the mileage has slowly improved. It is now almost to where it was with the OEMs. I guess the break in period for these was longer and more dramatic for me for some reason. Just happy it's almost back to normal with gas prices coming back up.