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2006 outback 2.5i
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If you have tires that are 225/55/17, what size would you need for 16 inch rims to keep your speedometer and odometer just as accurate?

According to my GPS (if its accurate?) my speedometer is 2 MPH slower than what i am actually going, and id like to keep it that way.

ANd i need a quick and easy guide to understanding the sizes, which one is width and which one is height? The R16 and R17 and R so on, ive got that down.
 

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There's a page in the Owners Manual with the different size tires that the car can be used on the car without significantly affecting the speedometer. (In my 2007 Manual, it's on the very last page.)

There are "tire calculators" on the Internet where you can choose different tire sizes and see what the effect will be. One is: Tire Size Calculator - Compare Tire Sizes. You can use this to try different 16 inch tires that will not introduce a change in the speedometer. Note however, that not all tires will fit in the wheel well space properly, so even if a tire seems to have no effect on the speedometer, it might not fit the car.

Also, there's no shortage of sites that provide good explanations of what the numbers on the tire mean. See, for example: Tire code - Wikipedia, the free encyclopedia, or, How to Read A Sidewall - Tires - Coast Tire & Auto Service
 

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2005 3.0 R n totaled
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7,529 Posts
If you have tires that are 225/55/17, what size would you need for 16 inch rims to keep your speedometer and odometer just as accurate?

According to my GPS (if its accurate?) my speedometer is 2 MPH slower than what i am actually going, and id like to keep it that way.

ANd i need a quick and easy guide to understanding the sizes, which one is width and which one is height? The R16 and R17 and R so on, ive got that down.
TireRack has a calculator on their website with all the answers....
 

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2012 4LT Centennial Edition Grand Sport Corvette convertible
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225 is the tread width in millimeters
55 is the aspect ratio - the sidewall height is 55% of the tread width
So, to get the theoretical tire height, you:

225/25.4 (converts mm to inches) X 0.55 X 2 sidewalls = tire height in inches = 9.744". ADD the rim diameter - 17+9.744 = 26.744" tire height.

This gives you the theoretical height based strictly on the numbers. Manufacturers don't always manufacture tires to the theoretical heights. Tire Rack many times has information on the actual manufacturer tire height.
 
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