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I bought a new 2012 Focus 4dr S w/manual trans about 3 weeks ago. I like the extra zip over the 2010 I had and am considering changing out the 15” factory wheels and going up to 16 or 17” with 225/55R or greater tires, mainly to provide better handling/cornering but also to improve the look with sport wheels.
Are there any issues I should consider prior to investing in these new “shoes”? ……I heard someone mention that the speedometer calibration may be affected. Are there issues with wheel clearances or other tolerances? What’s the significance of the offset and backspacing?
 

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For a much greater understanding of wheels, tires, and drops, check out this sticky located at the top of the forum.

Size and subsequent speedometer changes can be found out using a tire/wheel calculator.
I use this one. Just put in your stock tire size as tire A, the size you are looking at as Tire B and select compare tire A to tire B.

On a stock suspension, you should not have any fitment issues on wheels with standard FWD offsets and backspacing. Shop around on the Tire Rack for wheels and you will get an idea on typical aftermarket fitment size and offset combinations.

As to your want to fit a taller tire than stock with larger wheels goes, the +/- diameter change over the stock tire diameter, the greater affect on gearing. Basically a taller diameter tire compared to stock will increase mid-top end power and a smaller diameter tire compared to stock will increase low to mid range power. So with a taller tire, low end speed suffers, and with a shorter tire top end speed suffers. This may or may not be of much significance to you.

The Tire Rack Tech Center has a wealth of information worth checking out too.
 
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