18 to the 19 wheel swapping - circumference

[sergey]

I’m thinking about swapping 19 inches (like on gt2 summer) to 18 inches (like on gt2 all weather). Are circumference of those wheels the same? If not, will dealer reprogram it?

 

[MerlintheMad]

Obviously the circumferences of the rims (as you described it) are different: 18" and 19", a one inch difference. The A/S that go on the 18" have a lower aspect ratio (side wall height to tread width) to maintain the c. outside diameter of the rims and tires. In other words, the proper tire for the 18" rim has a higher side wall than the staggered tires on the 19"s do. Just match the same tire specs as the Bridgestone Potenzas that come OE with the 18"s. The speedometer will read within one MPH of accuracy.

 

[Waynerm002]

They are roughly the same, 26" in diameter for both 18 and 19" setup, front and rear. There may be a .1-.3" difference but that is fine.

 

[NS_Stinger]

Use this calculator to get the closest match and you should be fine.

Tire Size Calculator

 

[eflyguy]

They are roughly the same, 26" in diameter for both 18 and 19" setup, front and rear. There may be a .1-.3" difference but that is fine.

This.

You would not put the same dimension tires on the 18" and 19" rims, the overall diameter of the rubber meeting the road is effectively the same.