Tires: Mix Michelin and BF Goodrich?, michelin energy mxv4, michelin tires

Question
Hi,

thanks for your advice.

I replaced the four old Michelin tires with Goodrich Traction.
After four weeks/1000 miles running, My 02 accord MPG decreased more than 10%. It runs 27 MPG
instead of 32 MPG.

Any idea what may cause this problem? new tire break-in time?

I notices the new BFG Traction is heavier than  Michelin.

thanks.
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The text above is a follow-up to ...

-----Question-----
I need to replace Michelin Energy MXV4+ for my Honda Accord, however, one of four tires is kind of new, under 10,000 miles. Should I buy a set of new four tires, or only three tires.

Can I mix the bands, same size and speed?
Is that ok if I mix three new BFgoodrich and one Michelin?

thanks,
-----Answer-----
Jim,

It's always best to have 4 of the same tire on your vehicle.  If you don't, the vehicle may behave in unpredictable ways during emergency maneuvers - just when you need predictability.

The more different the tires, the worse this is.

I certainly wouldn't recommend 1 odd tire on a vehicle.

Answer
Jim,

There are a couple of things that may be going on:

1)  Rolling Resistance is a function of the amount of rubber in a tire, especially tread rubber.  A new tire will have a lot more tread rubber than a worn out tire, so just putting new tires on, even if they are the same, will result in more fuel consumption.

2)  Original Equipment tires are designed will improved RR because that's what the vehicle manufacturer wants.  But what usually happens is that wet traction and tread wear are sacrificed in order to get good RR.  This is unacceptable to the consumer, so replacement tires generally don't have as good of fuel economy. But I think in the big scheme of things this is more economical for the consumer as he doesn't have to buy tires as often.

Hope this helps.