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Discussion Starter · #1 · (Edited)
Most posts here are for QV's and RWD cars.

So for AWD what is the widest wheel and tire that will fit?

Looking like using the stock rims for winter tires is the best bet and buying a wider rim/tire package for summer.

Sell the stock tires to offset cost.

Not looking for something huge but at least a 255 series? Will most likely get PS4's.

Car came with the 19x8 square setup.
 

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There a few threads related to your inquiry.. if u keep the stock rims you can go 245 all around but will either be gaining a bit in ride height or losing a minimal amount depending if you go with 35 or 40
 

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Will the speedo autocorrect?
Good question. I don't see anything about speedo/odo auto-calibration in any of the Giulia specifications. My $350 bicycle speedometer has it and uses GPS to make it work. I don't see anything that implies Giulia has GPS unless you get the optional Nav system.

Oh yeah, 255s might fit and I sure would like to hear from someone who tried it. Then the diameter change from 225s is minimal.
 

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Discussion Starter · #6 ·
Good question. I don't see anything about speedo/odo auto-calibration in any of the Giulia specifications. My $350 bicycle speedometer has it and uses GPS to make it work. I don't see anything that implies Giulia has GPS unless you get the optional Nav system.

Oh yeah, 255s might fit and I sure would like to hear from someone who tried it. Then the diameter change from 225s is minimal.
I hear 255's are too wide for a 8 inch rim. Audi's auto calibrate. The factory tire size is programmed into the ABS system and it uses wheel speed sensor to compare against a table of engine speed/gear/wheel speed sensor.

I would not mind going a bit shorter, low the car a bit and lower the final drive ratio.
 

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I hear 255's are too wide for a 8 inch rim. Audi's auto calibrate. The factory tire size is programmed into the ABS system and it uses wheel speed sensor to compare against a table of engine speed/gear/wheel speed sensor.

I would not mind going a bit shorter, low the car a bit and lower the final drive ratio.
Yes, but 245s are already not good on 8" rims because the sidewalls will be bowed inwards so that they may not handle well. 245s require an 8" rim minimum to stay safely on the rim. 9" and 10" rims are available from Alfa. 255s are best on 9.5" rims, but Alfa doesn't offer that size.

"As a general rule, Tire Rack recommends mounting Track & Competition DOT tires on the widest rim widths approved by the tire manufacturer (up to the widest permitted by the competition class rules)."

It is a little unclear if wider tires will result in improved performance. Use trial and error and stay fairly close to stock seems to be the best advice online, which is why I keep asking other people for their experiences. You may need to experiment with inflation pressures to find the best performance point as well. Wider tires will weigh more and possibly degrade acceleration and ride quality. They may also have a different shape contact patch that may improve lateral grip in exchange for a loss in longitudinal grip.

Wheel speed sensors (which measure wheel RPM), engine speed and gear ratios will not make a speedo auto-calibration system. You need something that can measure ground speed/distance for that. GPS can measure ground distance accurately under some conditions (moving enough distance in a straight line). RADAR/Lidar(sp) doppler or a wheel of known diameter can also measure ground speed/distance under a limited set of circumstances. Since forward collision protection usually includes RADAR it might be possible to use it to calibrate the speedo, I dunno. To get an accurate RADAR measurement to you need a reflector in front of the car that is going a known speed and that is at a known angle relative to the direction of travel (as close to 0 degrees as possible). An accelerometer can also judge speed, but I do not know if the reasonably priced units are accurate enough to use for calibration.
 

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Discussion Starter · #8 ·
Wheel speed sensors (which measure wheel RPM), engine speed and gear ratios will not make a speedo auto-calibration system. You need something that can measure ground speed/distance for that. GPS can measure ground distance accurately under some conditions (moving enough distance in a straight line). RADAR/Lidar(sp) doppler or a wheel of known diameter can also measure ground speed/distance under a limited set of circumstances. Since forward collision protection usually includes RADAR it might be possible to use it to calibrate the speedo, I dunno. To get an accurate RADAR measurement to you need a reflector in front of the car that is going a known speed and that is at a known angle relative to the direction of travel (as close to 0 degrees as possible). An accelerometer can also judge speed, but I do not know if the reasonably priced units are accurate enough to use for calibration.
If the ECU has a table for X MPH at Y Wheel speed sensor in a given gear or a given tire diameter, and selected gear with ratio then yes you can auto calibrate.

FCA used(well Chrysler did when I was there) wheel speed sensor data logs to determine odometer fraud. Know the tire diameter they can work distance. If you assume that the sensors are working properly if your over/under the expected amount you can compensate for the speedometer.
 

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Most posts here are for QV's and RWD cars.

So for AWD what is the widest wheel and tire that will fit?

Looking like using the stock rims for winter tires is the best bet and buying a wider rim/tire package for summer.

Sell the stock tires to offset cost.

Not looking for something huge but at least a 255 series? Will most likely get PS4's.

Car came with the 19x8 square setup.
In Europe the Giulia 2.0 280hp Q4 has staggered wheels 225/45 R18 front and 255/40 R18 rear or 225/40 R19 front and 255/35 R19 rear
 

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If the ECU has a table for X MPH at Y Wheel speed sensor in a given gear or a given tire diameter, and selected gear with ratio then yes you can auto calibrate.

FCA used(well Chrysler did when I was there) wheel speed sensor data logs to determine odometer fraud. Know the tire diameter they can work distance. If you assume that the sensors are working properly if your over/under the expected amount you can compensate for the speedometer.
The wheel speed sensor is reporting wheel RPM (rotations per minute) and could only correct for gearing changes (very unlikely to be an issue on a modern car), not tire diameter changes. Auto-calibrate needs to estimate the tire diameter from something.

Yes, if you have 2 measurements of the number of wheel rotations you can check them against each other to determine if one of them has been tampered with. It still does not provide a means for auto-calibration of the speedometer.

Also there is usually no need for a table to convert wheel speed sensor readings to MPH. The relationship is extremely close to linear (you just multiply the wheel RPM by the right factor and you get vehicle speed--this factor is published the tire manufacturers) except at very high speeds (greater than 150MPH or so). At very high speeds the tire diameter changes and tire slippage (which also varies with the pavement condition, tire temperature, etc) become a significant factor. Using non-driven wheel speed readings can minimize the effect of the later. Tire diameter changes with speed are tire specific, as are slippage rates. I expect that a low order polynomial fit would work better than a table in any case.
 

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