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I have 255/45/18 instead of 245/45/18. on my 02Q45
THe diamiter is 3.4% more than the 245. my mileage did infact increase with the increase in diameter. the 255 is also about 3/4 inch wider than the 245.
the hieght increase was just under 1/2 inch.
THe issue is complex.
If you do alot of short distance driving then the increased diameter can hurt mileage (ignoring the cd issue) because of the extra effort to get the car moving each time you stop
If you do alot of freway, then you'll see results because of the lower rpm at cruise.
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