Tire size variations

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Aug 27, 2014
Hi guys, My 2004 Buick Lesabre has the original Michelin Symmetry tires on it w/48k miles. Tread on them is not bad but will be replacing them after winter. I have a set of two Cooper Weather-Master ST2's from another car that I would like to put on the Buick for the winter(and buy another set of two so that I have a complete set). Standing up the Coopers & Michelins side by side, the Coopers are shorter. The Coopers measure approximately 26.25" and the Michelins 26.5". The Michelins have 47k miles while the Coopers only have a couple winter seasons on them. Both are 225 60 R16. Is this difference in diameter to be expected when buying across different tires and manufacturers? This seems like quite a big different given the tread wear of the smaller tire is less. It's a little annoying because my Buick has the Gran Touring package with the shorter final drive ratio, so it already turns enough RPMs. Thanks
Originally Posted By: Brybo86
softer sidewalls? flex more and so end up measuring shorter?
They are both on rims, properly inflated, and were measured off of the vehicle.
Are they the same width wheels? What size wheels did the manufacturer measure them on for the data sheet? Some variation between tire models(and manufacturers) is normal that seems abit much. for example a HTR A/S P01 235/55R17 is 776 revs per mile diameter 27.2" The kumho 4x in the same size also measures 27.2 but 764 rev/mile. Firestone winterforce 27.2 767 rev/mile. I spot checked 3-4 more tires and they were all in a similar range.
Differences in diameter for tires of the same nominal size are common between different manufacturers, and even between different models by the same maker. In your case, the current difference is 1/4" with both diameters over 26", or less than 1%. Just keep 'em on the same axle, you'll never notice the difference.
Black Friday is a few days away. Look to Sears or Walmart for a good deal on some tires. Buy a new amd same size set of 4 tires and either save the others for a problem or let them go. That way you know the tires are the same and equivalent
If I did the math right, the variance in circumference is less than 1% - so one tire would read 99 MPH on the speedo, and the other 100 MPH. Or, drive 100 miles - one tire will be off by a mile compared with the other on the odometer. I think they're close enough to not really make a difference in practical usage.
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