.:HSTuners::

05-02-2002, 11:59 AM

I think I remember this, but someone correct me if I'm wrong. The first number is the max tire width (mm) - call it W. The second number is the sidewall height as a % of the width - call it H. The third number is the ID of the tire in inches - call it D.

OD can thus be calculated (in mm) as
OD = 25.4*D + 2*H*W

For your 195/65/15 :
OD = 25.4*(15)+2*0.65*195 = 634.5 mm

For a 215/xx/18, the profile you need (to be the same OD as the 15s) would be :
H = (OD-25.4*D) / (2W) = 0.412 => so a 215/40 would be close

For a 225/xx/18, the profile you need would be :
H = (634.5-25.4*18) / (2*225) = 0.394 => a 225/40 is still the closest you can get

Of course, you can put it all in 1 equation, but I thought subscripts might be confusing.

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05-02-2002, 11:59 AM	#2
Mushroom Posts: n/a	I think I remember this, but someone correct me if I'm wrong. The first number is the max tire width (mm) - call it W. The second number is the sidewall height as a % of the width - call it H. The third number is the ID of the tire in inches - call it D. OD can thus be calculated (in mm) as OD = 25.4D + 2HW For your 195/65/15 : OD = 25.4(15)+20.65195 = 634.5 mm For a 215/xx/18, the profile you need (to be the same OD as the 15s) would be : H = (OD-25.4D) / (2W) = 0.412 => so a 215/40 would be close For a 225/xx/18, the profile you need would be : H = (634.5-25.418) / (2*225) = 0.394 => a 225/40 is still the closest you can get Of course, you can put it all in 1 equation, but I thought subscripts might be confusing.