Ford Mustang Forum - View Single Post - 2012 Tire diameters, gearing & tuning. Stock ECU conflicts?
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post #1 of (permalink) Old 09-12-2013 Thread Starter
fullsail's Avatar
Joined: Jul 2013
Location: Los Angeles
Posts: 69
Question 2012 Tire diameters, gearing & tuning. Stock ECU conflicts?

I currently drive a 2012 Mustang V6 Premium auto. I traded in my 4.0 Ranger and my gas milage has doubled! I have been saving so much money at the pump that now have the itch to modify!

One item I would like to do is put new wheels on. I have my eye on some TSW 20" Panoramas but I want to fill my wheel well. I currently run a stock 215/65-17 that has a 28" overall diameter. What is best to my eye is a 275/40-20 in the rear and a 245/40-20 up front on 9.5s and 8.5s respectively. These diameters come in 28.66 and 27.75 respectively. With 27" being the ideal diameter, my desired rear size is 6% larger I don't know if I can handle bogging down the car down even more.

So my problem is compensating the gearing. I already have an auto and 2.73 gears. So here a few questions I hope some of you may be able to help with...

If I swap out my gears for 3.15 or 3.31 ratio can I maintain a 2.73-3.00 gearing with this tire/wheel size? I still need the mpg to be reasonable and 30 mpg at 80 is a beautiful thing.

Can I swap the gears and correct/compensate with a tune? Will a tuner be able to make the car's ECU compensate that much or will my ECU get stuck in a Ford safe mode?

Will I be wearing or stressing the transmission or any other components quicker as a result?

Any good websites to figure out overall gearing ratios?

I could go with /35 sidewalls but I want the car to sit tucked on a tad more rubber.

Thanks in advance for your thoughts.

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