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I got my 718 C with the standard 18" wheels. I am thinking about getting 19" wheels, but to keep the ride civil, going with tires that are the same sidewall profile as the 18s. That will increase the circumference of the tires. I didn't see a setting anywhere where you could enter the tire's measurements. So, if I go with my plan, what would that do to the speedometer and odometer in the car? I tried to math it out myself, but quickly came to the conclusion that it is a good thing that I became a lawyer.

Thanks.
 
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Just DON'T do it.

It will mess up the speedo and the odo, not to mention by raising the height of the car the handling will suffer.

Roughly the front diameter would increase by 0.8 inches which would raise the front of the car 0.4 inches, and the rear diameter would increase by 1.0 inches which would raise the rear of the car 0.5 inches.
 

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I got my 718 C with the standard 18" wheels. I am thinking about getting 19" wheels, but to keep the ride civil, going with tires that are the same sidewall profile as the 18s. That will increase the circumference of the tires. I didn't see a setting anywhere where you could enter the tire's measurements. So, if I go with my plan, what would that do to the speedometer and odometer in the car? I tried to math it out myself, but quickly came to the conclusion that it is a good thing that I became a lawyer.

Thanks.
The reason you won't see anywhere to enter the tyre measurements is because you've had a bad idea. No matter the size of wheel fitted to your 718 the overall circumference should stay the same, ie Large wheels, small tyre/tire walls & small wheels, large tyre/tire walls & you shouldn't attempt to mess with it. You also won't be able to get any Porsche approved tyres/tires with an N rating for a 718 in those sizes. On top of that you'd be affecting the final drive ratio & would decrease acceleration & your speedometer will under read your true speed. Speedo error calculator ? speedometer error as a result of tyre size change ? Speedometer calibration
 

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I tried to math it out myself, but quickly came to the conclusion that it is a good thing that I became a lawyer.
That just made me laugh out loud, which prompted my wife to start questioning why I was laughing on the toilet :laugh:
 
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Simple solution: buy the same tire size you read on the 19's Porsche offers for the 718 form the factory. I have owned and continue to own several slightly modified to heavily modified cars. I would personally not do what you're suggesting. There's simply no reason in my opinion. 19's on the the 718, with the tires Porsche has on the car, drive very compliant...
 

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Pasm on 20" summer tires compared to S-Pasm on 19"winter tires, the 19" runs Way smoother.
So its gonna be new rims and tires next spring :)
 
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