3.73 Gears and next Mods

[junits15]

Well I can tell you this for sure, when i changed my wheels and tires from 18 inch to 19 inch and the circumstance of the tires was a little different, the car did not learn the difference. The speedo remained off until I changed it using forscan

Tires are not gears.

The car knows how fast the axle is spinning so it knows the gear ratio, it doesn't know how fast the edge of the tire spins because the sensor is in the middle on the hub.

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[TonyT930]

Tires are not gears.

The car knows how fast the axle is spinning so it knows the gear ratio, it doesn't know how fast the edge of the tire spins because the sensor is in the middle on the hub.

Um, no. Nevermind

 

[2015 Silver GT]

Tires are not gears.

The car knows how fast the axle is spinning so it knows the gear ratio, it doesn't know how fast the edge of the tire spins because the sensor is in the middle on the hub.

Yea you couldn’t be more wrong. Tires have an affect on the the speedometer and odometer. I just swapped to taller than stock tires and both are now off.

 

[TonyT930]

Yea you couldn’t be more wrong. Tires have an affect on the the speedometer and odometer. I just swapped to taller than stock tires and both are now off.

Thank you. I gave up. Sometimes you have to step back and just let someone be wrong.

 

[junits15]

@2015 Silver GT and @TonyT930

I don't appreciate the condescending tone, especially because you guys weren't even bold enough to reply to me, and also because you're both wrong and have no clue what you're talking about

See these two sections? One for tires and one for final drive. They're different, and they're handled differently. The final drive ratio is used for ABS, Stability control, and the speedometer. The tire diameter is only used for the spedometer. The ECU performs plausibility checks between the speed of the motor and the speed of the axle using the wheel-speed sensors. If it can't figure it out it freaks out.

Look at the field that says "Use Final Ratio". It is by default set to "Learn from BCM" the BCM detects the final drive ratio, the ECM reads that data and uses it for its calculations. It can only learn values within the range defined below by "Max ratio" and "Min ratio".

This is why i said if its working then it's done, if you put in gears inside this range (3.31 to 3.77) the ECU can just learn what the gear is and it will all work. This doesn't happen with tires, thats why your speedo is off when you switch tire sizes. Its not physically possible to "learn" the tire size, its completely possible for the BCM to instantly learn the rear gear ratio.

TLDR: The car can learn rear gears above 3.31 and below 3.77, the car can't learn your tire size.

As I said before, tires are not gears.

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