Not common. 8.1 Allsion combo truck speedo issue.

[04blackgmc]

It'd probably be prudent for people to go look up the formula for the diameter of a circle.

What is that from is the question?
I'll try this all again but that file screenshot doesn't look like the file from the 8.1/Allison trucks.

I have the revs set to 607.3 and tried various swings in numbers from there and nothing changed. Such a simple thing made so hard lol.

[DSteck]

It's from the exact file you posted using 2.25.

I suspect this is more an issue of not knowing how the numbers are used.

[Road]

I am sure I will get proved wrong but this is what I think is going on. First off back in the LS1 days we could change tire size with tech 2 on pretty much everything except for the LS1/Allison TCM combination. The LS1 is a PCM meaning it has a transmission segment in it and that transmission segment is not used in the LS1/TCM Allison combination that the 8.1 uses. I believe there is something in the hard code that is keeping you from correcting the speedometer. I am attaching a screenshot of OS 12587603 which allows speedo corrections and you make changes to trans/revolutions per mile. I will share the OS if you think it will work for you. That where I made my mistake when I posted my didn't what I doing dumbass help.
Mike

[DSteck]

Start with the fact that the VSS is on the output shaft of the transmission. Multiple things get calculated to correct a speedometer.

[Road]

Yea and HP Tuners not putting the speedo calculator in the OS and GM not supporting tire size calibration makes me believe it's not supported.

[DSteck]

Why do you need a calculator?

[Road]

Why do you need a calculator?

I guess HP Tuners added it for us Dumbass tuners.
You must be living a miserable life because you never have anything positive to say.
I want be responding to anymore of your bull shit.

[DSteck]

It's a genuine question. Yes, the calculator is nice and quick, but IMO people should understand what things do so they aren't just relying on some tool to make things work. Far too many people don't want to invest the time to know what the PCM is actually doing. If that shoe fits you, then I don't know what else to tell you.