Flopshot,

I found that my car got about 2-3 more MPG's after I reached 5000 miles, I just passed 12K on it and my mileage has improved. My driving habits have improved somewhat as well which has given me even more increased MPG. I will say that when I first got mine I was not doing as well on fuel economy until I reached around 5000 miles. I was seeing numbers even a little below yours. Maybe your car took its time breaking in and you changed the rims out before you got a true sense of what your FE would have been after break-in?

It does seem odd that the steel wheels that are heavier would actually help your mileage. I will say that you did not mention what pressure your 16" tires were on the alloys vs. the steel rims. Was/is there a difference in tire pressure?

Like you I cannot imagine that the TPS sensors or lack thereof has anything to do with it.

 

Also, when was your first oil change and do you use 0w-20 synthetic now? My first oil change was dino and on the second one, I switched to synthetic. That has increased my FE about 1-2 MPG.

 

Tegster, my FE over the first ~48k miles was very consistent. I never saw an increase in FE after the break-in period like other owners did. With the stock 16" wheels/tires, I was averaging just about 35mpg(thru 5k+ miles). After I switched to the 18" wheels, my FE dropped to about 34.5mpg, and it remained there for the next 43k miles. It is really a line-in-the-sand where I saw a sudden and instantaneous 3mpg increase in FE on the same tank of gas where I put on the 16" steel wheels/tires.

I didn't even think about tire pressure until you mentioned it, but turns out it didn't matter and actually makes the case even weirded. The original alloy wheels and tires were always kept at 36psi, and I just measured the new steel wheels and tires at 34psi. So once again, I should be seeing a lower FE, not a greater FE. Too weird! (If you want to blur the line in between, my 18" wheels/tires were set to 40psi, which is probably why I didn't see a large drop in FE when I had them on the car).

To answer your last post, I have never used synthetic, and I change my oil every 5k using 0W20, so that is not a variable in this equation.

 

That's interesting. You put enough miles on the car that you should know the MPG's better than anyone. At any rate, I suppose the MPG's went up so at least the change was positive!!

I am stumped on that one. Sorry I could not help.

 

If I read the complete post it actually appears quite simple as to what you are experiencing as I am noticing the same thing with my car.

In the first 5000k you were driving with low rolling resistance michelin tires and your vehicle was not quite broken in, and you got around 35 mpg.

You then switched to 18" rims and BFG tires which would cause a reduction in mileage however you bumped the pressure up to 40 psi and the car was proably just about broken in, which increased your mpg, however due to the bigger wheels and less rolling resistant tires you only saw a drop in mpg of about .5 mpg.

Now after 43k miles you switched back to the low rolling resistance michelin tires and you see an increase of 2-3 mpg.

You are seeing the improvement because of the michelin tires, the steel wheels have nothing to do with it. The car is now broken in properly and you are using the ultra efficient mileage low resistance rolling tires, on your vehicle.

I have a new set of 4 alloy wheels with the michelin tires and I doubt they would differ more then a pound from the steel wheels with the same tires.

so if we take the wheels out of the equation, that leave us with the changing of the tires from bfg to the original factory michelins.

the improvement is because of returning the factory tires to your vehicle which is why you see the 2-3 mpg in gasoline.

I bought my 09 with the alloy wheels and within 6000k switched out to 19" rims with 225/35/19 michelin pilot tires which stick like glue, however only last 20k tops and are about $368 each from the tire rack.

Even running at 38 psi I saw a reduction im mileage from 3-4 mpg. This reduction was then overcome by the vehicle breaking in and I now see a reduction of about 1 mpg.

I will only use these tires from april to september at which point I will swap the factory tires and rims back on, and I will see the exact change in mpg which you are describing.

The michelin energy are extremely good mileage tires and according to michelin they are the best mileage tires out there, however in the summer I just can't stand the "wishy washy" ride they give and until they come up with some performance sway bars, I will swap the tires and rims back and fourth twice a year.

I hope this helps you out

Tim

ps

what do the steel wheels look like, and if you want a weight for alloy wheel with michelin tire let me know and I will weigh one for you to compare.

 

Everything you say makes a lot of sense. The only thing is that based on my spreadsheet, I had a very consistent FE during the first 5k while on the original Michelin tires, and then a very consistent FE during the 43k which I was on the BFG tires. So we would have to assume that my engine got broken in at precisely the same time that I switched out my 16" wheels for the 18' wheels. This would not necessarily be a bad assumption since it was right around the 5k mark, but it would still be highly coincidental. But it's the first theory that I've heard which makes sense to me. Thanks!