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Discussion Starter · #1 ·
I am changing tires for the summer and will go larger than the 225/40/19's now on the car. Probably up to 245/45/19's. A small amount of increased height, approx 20mm. Can the speedometer be calibrated for the new size? Since it is all computerized, I would think so.
 

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I am changing tires for the summer and will go larger than the 225/40/19's now on the car. Probably up to 245/45/19's. A small amount of increased height, approx 20mm. Can the speedometer be calibrated for the new size? Since it is all computerized, I would think so.
It should be ~1%, well within margin of error, don't worry about it.
 

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I am changing tires for the summer and will go larger than the 225/40/19's now on the car. Probably up to 245/45/19's. A small amount of increased height, approx 20mm. Can the speedometer be calibrated for the new size? Since it is all computerized, I would think so.
Drive 1% slower than the what speedo say and you should be good. :grin2:
 

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I am changing tires for the summer and will go larger than the 225/40/19's now on the car. Probably up to 245/45/19's. A small amount of increased height, approx 20mm. Can the speedometer be calibrated for the new size? Since it is all computerized, I would think so.
Check this out and put both tire sizes in the calculator. https://www.tacomaworld.com/tirecalc?tires=225-40r19-245-45r19
According to this, it's more like a -6% speedometer reading error (not 1%). Which means that you would be travelling at 63.67mph when the speedo (if accurate) reads 60mph.
 

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Check this out and put both tire sizes in the calculator. https://www.tacomaworld.com/tirecalc?tires=225-40r19-245-45r19
According to this, it's more like a -6% speedometer reading error (not 1%). Which means that you would be travelling at 63.67mph when the speedo (if accurate) reads 60mph.
I did this already on my 18" wheels. 225/45/18 to 245/40/18. According to GPS speed on Waze there's essentially no difference from before (as it should be - 1% should be <1mph at any normal speed). This is within the error bars for different manufacturers.

Edit: My bad!! OP is really proposing 225/40 to 245/45. That's ridiculous. I'm the one who misread because I assumed sanity :) The correct size to go to 245 wide on 19" wheels would be 245/35, not 245/45. That'll have a 1% error.

Sorry!
 

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2018 Q4 with Fiamenghi Ti exhaust, Race Mod, and Tecnico wheels.
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I am changing tires for the summer and will go larger than the 225/40/19's now on the car. Probably up to 245/45/19's. A small amount of increased height, approx 20mm. Can the speedometer be calibrated for the new size? Since it is all computerized, I would think so.
245 45R19 is pretty large for Giulia. Check to see if it will fit before worrying about the speedometer accuracy.

Call me Al (wide tires, lowered car) discovered that if the front wheels rub the wheel well they tend to hit a spot that has a major wiring harness on the other side.
 

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Discussion Starter · #7 ·
Here's the question " can the speedometer be recalibrated"
 
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