Issues with AlfaOBD and changing tire size

[Irongoats]

I measured tire installed from ground to top of tire (flat ground) no surprise it was off whatever internet says now within 1 or exact in Alfa.

 

[John Jensen]

Best way to measure diameter is to mark a spot on the ground and the tire, roll the tire one revolution, mark again, and measure the distance between the spots on the ground.

 

[Justin33]

So I've only done the tire change procedure to it. Went into BCM and ran that procedure, disconnected, cycled key off waited a minute, turned it back to run. Then connected into ABS and did ECU initialization, cleared CELs, disconnected, cycled off and back to run, then did clearing rolls information, cleared CELs in ABS, BCM, then PCM. All standard procedure we've done before. When turned on power steering was locked up and multiple CELs for implausible data. Repeated for multiple types of common values including the stock option in the drop-down which is the Goodyear Wrangler SR-A 275/60r20 which set the value of 2750mm. It didn't like it, same results. Went to my truck and pulled the value on mine and my truck said 65535mm and used that value into his so it could be drivable again but off by 4 again. 65535mm (max value according to AlfaOBD is 65534mm) sounds outrageous and never showed that before on either truck.

I don’t get how your number is so high you shouldn’t even need a value that high where you were at sound like ballpark. I had a tablet at a circle K and made adjustments and it took out my power steering and speedo ect. I think I needed to give it more time to take. I have a 15 and never even have done the abs side of things although I’ve seen it done with the wheel change. Mine has worked without that step.

 

[Dean2]

So out of curiosity, what did Alexie have to say about this issue and the oddball max value you are having to use.

Also, the values are actually circumference, so inflation and load factor can have an effect on the value and accuracy of the speedo if you are trying to get within 1 mph. So a 33" tire should have a circumference of 2633.3 MM, 35" is 2792.9