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Discussion Starter · #1 ·
Recently had a woman come into my work who was in the process of selling her 17" wheels. They're coming off a 2002 Focus. I have stock 15" steelies and was wondering what I needed to do to adjust my speedo and odometer to match the new wheels. Is it a matter of plugging into the ECU and just setting different values?
 

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So mote be it
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You shouldn't have to do anything if they are 215.45.17 or 205.45.17 and your 15" ones are 195.60.15, which would be the stock size

You can use something like this to get an idea of the differences.
http://www.miata.net/garage/tirecalc.html
the difference from 195.60.15 to 215.45.17 is 1.7% difference, nothing that would cause any issues (even less with a 205 tire.) I went from 15" to 17" and the only thing I noticed was a decrease in mpg's due to the 17's being heavier and more unsprung mass. My speedometer matches what my GPS says at speed as well.
 

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Jetsetter
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the differences are minimal, my focus came with 15's and Ive been running 17's for years now, my spedo is maybe 1mph off from my gps. so there isn't too much need to reprogram the ecu, however a tune would be able to do that for you if its something you really want to do.
 

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Keep in mind if theybare heavy you will feel some drag. I lost tourqe going to the larger wheel. 17"x7.5" 215/45/17 tire. Wheel weighed about same as my 15" steelies but the tire weighed more due to being larger. All I all I like my wheels and would only change if I could find a place around me that sells the lightwhieght rotas.
 

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As long as you have tires that are overall about the same outer circumference as your original tires you do not have to change anything for speedo..
Go to "Tire Raack" and read up an the concept of "PLUS SIZING" and you will be able to better understand what you have to do.
If the lady is selling a wheel AND tire set, then justsee how much taller her wheels with tires are than yours. If less than a quarter inch taller, you should be OK.
 

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Moved to Wheels tires brakes and Suspension. Ford Focus Technical Chat is for technical discussions relating to general maintenance, electrical issues, engine trouble, and recalls.
Thanks for posting.
 

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Discussion Starter · #7 ·
You guys are fast >.>"
Anyways, thanks for the replies. I'm not too worried about it now that I've been able to plug in the numbers to the miata calulator.
 

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No Focus, except the SVT, came with 17" wheels. That said, if her car was not an SVT the wheels would have to be aftermarket. There's no downside to aftermarket wheels as long as fitment is OK. Some can get heavy as mentioned above. Since they came off of a Focus you don't need to worry about lug spacing. Do, however, check wheel width and offset. For a 17" wheel a 7 to 7.5" rim width is optimum along with a 45 to 49mm offset. 42mm also works on a car that's not dropped. If dropped, the 42mm (and lower) offsets can get "iffy" and more subject to possible rubbing.
 

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Aren't our speedometers off by +2 or 3 MPH in the first place? Every time Ive gone by a radar its off by a couple. Bigger would make it more accurate. lol
 

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Aren't our speedometers off by +2 or 3 MPH in the first place? Every time Ive gone by a radar its off by a couple. Bigger would make it more accurate. lol
The circumferential differences from a new tire versus a worn one will be enough to affect the speedo that much. A tire at full tread height (around 11/32'') will likely show you going 1-3 MPH slower than you actually are were a worn tire (3/32'') will show you're going faster. If you have a GPS unit in your car that tells you speed you'll be able to see this discrepancy.
 
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