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spacemanspif · 08-23-2013, 04:46 PM

What you want to do is increase the TOTAL diameter of the wheel and tire combo.

Assuming your tire size is 225/45/16:

Tires on your stock 16s could go up a size or 2 to 225/55 or 65/16. These sizes give you more sidewall which also induces more sidewall flex and can affect handling characteristics.

Your new 18s will help a little because of being lighter and also reducing the size of the sidewall to achieve the same total diameter of the aforementioned 225/65/16 tires. Less sidewall means less sidewall flex and better handling characteristics.

Keep in mind that tire size is a balancing act. Shorter total diameter tires require less power to get rolling, but taller total diameter tires are better for highway eco. If you go too tall, your car will accelerate like crap and possibly negate any gains made on the highways depending on your commute.

Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

Rims and tires is a good place to understand aspect ratios and tires sizes and can help you pick a larger tire.

HTH

08-23-2013, 04:46 PM	#3 (permalink)
spacemanspif Spaced out... Join Date: Jul 2013 Location: Dirty Jersey Posts: 748 The New Focus - '07 Ford Focus ZX5 90 day: 32.44 mpg (US) Thanks: 142 Thanked 205 Times in 149 Posts	What you want to do is increase the TOTAL diameter of the wheel and tire combo. Assuming your tire size is 225/45/16: Tires on your stock 16s could go up a size or 2 to 225/55 or 65/16. These sizes give you more sidewall which also induces more sidewall flex and can affect handling characteristics. Your new 18s will help a little because of being lighter and also reducing the size of the sidewall to achieve the same total diameter of the aforementioned 225/65/16 tires. Less sidewall means less sidewall flex and better handling characteristics. Keep in mind that tire size is a balancing act. Shorter total diameter tires require less power to get rolling, but taller total diameter tires are better for highway eco. If you go too tall, your car will accelerate like crap and possibly negate any gains made on the highways depending on your commute. Custom rims, wheel tire packages for your ride - RIMSnTIRES.com Rims and tires is a good place to understand aspect ratios and tires sizes and can help you pick a larger tire. HTH __________________ -Mike 2007 Ford Focus ZX5 - 91k - SGII, pending upper and lower grill bocks - auto trans 1987 Monte Carlo SS - 5.3/4L80E swap - 13.67 @ 106 2007 Ford Focus Estate - 230k - 33mpg - Retired 4/2018 1995 Saturn SL2 - 256K miles - 44mpg - Retired 9/2014 Cost to Operate Spreadsheet for "The New Focus"