Originally Posted by upflying
and a speedometer reading that will read slower than actual
No. If you go down in aspect ratio while going up in wheel diameter to end up with a similar overall tire diameter as the previous post described, you do not change final gear ratio. Also you would not change the speedometer reading.
It's simple. To convert metric to old school US floatation tire size you need to know some 4th grade math.
A millimeter is 25.4 inches.
A metric tire is described as follows:
Millimeters wide, aspect ratio and wheel diameter.
This is shown like this...
That tells you that the tire is 315 mm wide.
It is 70% as tall from wheel bead to tread surface. This occurs twice, road surface to wheel and then wheel to top of tire.
Then you have the wheel diameter.
So 315/70-17 is:
12.4" × 0.70 is 8.68" from tread to bead. This is doubled to be 17.36".
The wheel is 17" so it's 17" wheel + 17.36 = 34.36" tall and 12.4" wide.
You can repeat this over and over with different sizes too get a diameter and width that you desire.
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