- Well they are brand new tires, properly inflated ( got 215/60/17 since not many replacements for stock size)
- Running good from what I can tell only 26k on it, but like isaid in anothee post, that 5 speed auto just acts funky to me
- trunk empty except for a small tool box
- I use cruise about 35-40 % of the time when I can
- Commute is... gulp.... about 130 miles round trip everyday, 80 % hwy
- A/C was running most of the summer... im in Texas and so I'm sure TheMAN can vouch for why lol. But does it kill it that bad with the 3's horrible A/C performance ?
- Windows usually closed...cept on a cool evening
Tire size is your problem. That tire size may only be ~2 in. wider in overall diameter, but that translates to ~6.5 inches more distance for it to roll in a single revolution, which will add up fast at 700-800 RPM. That means your speedometer reading with those tires is 8.32% too slow. So, when your speedometer is reading 60mph you are actually traveling 64.61mph. This also means you're ticking fewer miles onto the odometer for a given number of miles travelled. For example, I'm betting your trip is actually closer to 140 actual miles travelled (you can check this with Google Maps; it's certainly close enough for this purpose).
Fewer apparent miles travelled / gallons used = your lost mileage.
Try multiplying the miles travelled on your most recent fill-up by 1.0832 (to add 8.32% more miles) and then do the calculation using that number of miles. I'm willing to bet it'll be more like what you're expecting to get. In fact, just multiplying 27MPG by 1.0832 yields 29.25MPG, which is what I get on straight highway trips.
If you haven't had the tires more than 30 days, it's possible you can still get the shop to take them back and get a different set that's the right size if they offer a 30-day money-back guarantee. Otherwise, you'll just have to do the math differently when calculating your mileage.. And, BTW, less miles on the car means
less miles on the car at resale/trade-in time, too.
If you
can return them for a different set, check out TireRack (and Consumer Reports, if you have a subscription (at ~$20/yr. for access to the ratings on the web site it's totally worth it)) to help you decide which tires are best for your purposes. There are more out there now in 205/50R17 than there used to be.
(I got all my calculations from
www.tiresizecalculator.info. I was looking for a different calculator that does more, but this one works well enough.)
