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So I'm needing new tires, and I'm looking at some times that might better suit my needs, and while they're same width and rim specs, the sidewall ratio is different. Current is 235/50 r18 and the one I'm looking at is 235/60 r18. I'm in an AWD Volvo V60 CC. I understand I don't want to run a tire with a different ratios mixed in, but if I change them all at once, could that be OK?

  • What range of sizes do Volvo specify for that car & rim? – Solar Mike Jul 4 at 21:49
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I would advise against doing this. This will remove 6.4% from your speedometer reading. Usually speedometers show 5% above your current speed with the stock tire size. By removing 6.4% from your speedometer reading, your speedometer will become 100% illegal, because it shows a speed below your actual speed.

Not only that, but the tires are 6.8% larger. There may not be enough room for the larger tires.

Usually you'll find that you can change the aspect ratio if changing the width too. For example, 235/50R18 is nearly the same as 195/60R18 when considering the tire diameter. Similarly, 215/55R18 might be fine too. When doing this change, you need to be certain that the rim can accommodate the tire width.

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  • In all places I'm familiar with, it's illegal to drive above the posted speed limit. the law doesn't care about the speedometer. – jwh20 Jul 5 at 11:32
  • Thanks, that's what I was afraid of. And the car manual only has alternatives based on the different rim sizes they offered, so no go for this. sigh Ah well. – Drizzt321 Jul 5 at 19:43

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