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Discussion Starter #1
I have searched the Wheels, Tires, Brakes & Suspension forum and there is no answer to this question that I can find.

All other factors being egual, if I change wheels and thereby increase the width of the wheel by .5 inch, will this change the diameter of the tire enough to introduce an odometer error?

I switched from the stock 16 x 6 inch wide alloy wheels on my 2005 Focus ST to SVT 16 x 6.5 inch wheels. I just tested my car against 20 miles of Interstate mile markers and find that the odometer reads 2% slow. While I realize there are normal factory variations in the speedometer and odometer readings, did I create an error myself by changing wheel widths?

Thank you for any feedback.
 

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wheel width has nothing to do with odometer readings...the new tire might be slightly larger in diameter thus creating more contact per revolution but a wider tire of the same diameter doesnt effect anything
 

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It means... a mile is just a mile
 

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Not so on the two previous posts. Your tires' sidewall height is determined in part by the width of the tire. Say you have a 215/40 17" tire.....then you increase width to say....235/40 17" tire....not only does your tire width increase, but by not going with a lower profile number...your sidewall height also increases by 0.8cm therefore throwing your odometer off by a tad. The sidewall height is determined by the percentage (2nd number on tire size) of the width (1st number in tire size) with the width being in millimeters. Now....you might could put the same tire size on your new rims, and then again you may not can...every tire has it's max mountable rim width...

final answer...the .5" in width increase...whethere you have to get a different width tire or not...shouldn't affect your speedo much...but if you do have to get a slightly different width tire and keep the same profile it will affect it...but only slightly.
 

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And i just noticed something......you have a 16" svt wheel??? SVT's are 17's bro.
 

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Discussion Starter #6
Hondaluver and SVT-gEEK,

Thank you both for your replies.

According to the Pirelli website, my P6 tires are a P205/50R16 TL 87 HM+S and will fit on rim sizes from 5.5 inches to 8.0 inches. The stock Ford ST rims are 6.0 inches wide and the new rims I have are 6.5" wide. I thought the extra .5 inch would slightly change the overall diameter, hence the the lower odometer reading.

By the way, I do have 16 X 6.5 " SVT rims, but not from a Focus. The SVT Contour from 2000 has wheels that fit the Focus and look similar to the SVTF rims. They weigh only 18lbs each and were inexpensive. I wanted to keep the P6s and the same ride and handling, so I stayed with the smaller wheels. See my picture gallery.
 

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So I am assuming you are using the same tires from your 6" wheel on your 6.5" wheel.

Depending from tire to tire, but in theory, the 6.5" could stretch your sidewall making the cross section more trapazoidal instead of rectangular. But if Pirelli says the 205 can stretch to an 8" wheel, I don't see the 0.5" doing much stretching thing.

However, I think they are crazy saying a 205 tire can fit on a 8" wheel. That is some massive stretch.
 

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Dayna2.3 said:
Hondaluver and SVT-gEEK,

Thank you both for your replies.

According to the Pirelli website, my P6 tires are a P205/50R16 TL 87 HM+S and will fit on rim sizes from 5.5 inches to 8.0 inches. The stock Ford ST rims are 6.0 inches wide and the new rims I have are 6.5" wide. I thought the extra .5 inch would slightly change the overall diameter, hence the the lower odometer reading.

By the way, I do have 16 X 6.5 " SVT rims, but not from a Focus. The SVT Contour from 2000 has wheels that fit the Focus and look similar to the SVTF rims. They weigh only 18lbs each and were inexpensive. I wanted to keep the P6s and the same ride and handling, so I stayed with the smaller wheels. See my picture gallery.
Ok, I understand now. If you use the same size tire, wheel width won't matter.
 

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Dayna2.3 said:


According to the Pirelli website, my P6 tires are a P205/50R16 TL 87 HM+S and will fit on rim sizes from 5.5 inches to 8.0 inches.

That doesn't seem right, or safe at all, to have a 205 on a wheel as small as a 5.5 or as large as an 8.0


[???:)] [???:)]
 
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