I am a student for automotive and have a print out of the conversion chart for tires. it says I can go from 215/70r15 to 244/55r16 and only lose 1mph on speedometer, but found some 245/50r16 will that be a too much of a conversion?

  • how do you figure 5 inches? In any case youll likely have clearance issues.
    – agentp
    Feb 25, 2016 at 2:33
  • 5
    Tyre sizes are width(mm)/profile(percentage)r(in). 245*50% gives 122.5mm tall, 215*70% gives 150mm. Both tyres have a final radius of not quite 21". with Circumference = pi*diameter, I get a grand total of .3" difference. The 217/70r15 is a whole inch narrower than the 245/50r16 though. In short, where are you getting 5" from.
    – Leliel
    Feb 25, 2016 at 3:15

1 Answer 1


245/50r16 tyres are 30mm (just over 1") wider than 215/70r15. More of a difference is the diameter - 215/70r15 gives 26.85" or 682 mm, 245/50r16 is 25.65" or 651mm - just over 1", or 4.5% smaller - your speedometer will over-read by nearly 5%.

Also bear in mind that you'll need new wheels for the 16" tyres (though that might be the whole reason you're asking?), so make sure they will fit correctly - check the offset and PCD (bolt pattern) of the new wheels before buying.

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