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Old 09-19-2012, 12:50 AM   #26
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Location: Marion, IA
What I Drive: 2012 Ford Focus S Ingot Silver

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Originally Posted by Joey D View Post
Why would you get something so vastly different over the OEM size? It's really going to mess with your suspension geometry not to mention your transmission, odometer, and speedometer.

A 195/55/15 would make your speedometer read 8% to fast.
the S model came factory with a 195/65/15... when i went to my 215/50/17's the overall tire diameter was only half inch in difference... at 30MPH difference between the two tires is about 1 MPH... in my case fast.. when i show 30MPH on the speedo.. my actual speed is 31 MPH....

Comparing the 195/55/15 to the 195/65/15 the difference is 3/4 inch overall tire diameter.. which at 30 MPH is about 1.2MPH difference...

As far as being 8 year old tires... that is getting kinda old, but as long as they were stored correctly, out of the sun and the elements, they should be ok..

For reference..

195 x 55% = 107.25mm
107.25mm divided by 25.4mm = 4.22 inches + 15 inch rim = 19.22 inches

19.22inches x 3.14 gives you a rollout of 60.35 inches per tire revolution

for the 5 speed cars... (if i remember right in 5th gear with a 3.85:1 axle ratio at 30 MPH indicated on the speedometer is 506 axle revolutions per minute..)

so 60.35 inches x 506 = 30541 inches divided by 12 = 2545 feet per minute
2545 divided by 5280 = 0.48 Miles per minute x 60 = 28.92 MPH meaning with these tires over his stock tires his speedo will read about 1.5 to 2 MPH fast.. which is negligable...
as far as suspension geometry and handling... it shouldn't handle any differently than an S model with 15 inch factory wheels/tires.. it wont handle as well as his 17's.. but.. still should be quite drivable.

and with the narrower treadface.. they'll handle snow better than the 17's..
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