E38 Computer ~ EFI Live Speedometer Calibration?

[pmkls1]

Yes, someone does take that into account..........................

There is a lot of interesting info there Shannen. I knew that if anyone had a decent answer it would be you. I was hoping that although slightly OT, my question might yield answers containing valuable info like that.

Understood. Your theory sounds reasonable but the values in the screenshot do not agree with it. 36 for pulses per TOS revolution vs 32 for driven wheel pulses per rev while fdr is 3.42. More investigation is in order imo. These values may be for two different inputs where there are separate speed sensors on each wheel and a speed sensor at the trans. Or, is this controller responsible for providing ABS functions or providing signals to the ABS computer?

I noticed the value of 32 for driven wheel pulses per rev and thought it seemed funny at the time, but I thought that perhaps Dave had begun to make changes already. After reading your reply and studying the screenshot again I do have some more info to add. I confused myself by looking at the speedo calculations to the right of the screenshot and based my answer off of that. There are in fact individual wheel speed sensors at all 4 wheels as well as an output shaft sensor on the transfer case on the donor vehicle. The wheel speed sensors are still wired directly to the EBCM and the VSS is wired to the ECM. The ECM does not provide ABS functions or wheel speed signals to the EBCM, but does reference the wheel speed sensor data from the EBCM for reasons that I cannot recall. So, the true answer to Dave's question would be that those values are based off of the reluctor tooth count on the wheel speed sensors. What he needs to do with those values depends on how you eliminate the EBCM in standalone drivetrain transplants which is beyond my realm of expertise. The calculations that I provided would be correct for speedometer calibration though.

What are typical tread depths new and worn for a motorcycle tire? What's a typical tire diameter?

Typical sport bike rear tires are right at 25 inches in diameter and average tread depths are ~7/32 new & 1/32 at the wear indicators.

The standards for speedometer accuracy are wide. OE speedometer accuracy errs on the high side and tends to read higher above 65 mph. I'm not a conspiracy theorist but I've always wondered about that one. Odometers are generally fairly close, though.

It is well known in the biker community that the speedometers consistently read on the high side. Funny thing is that I just checked the site where the online calculator was for making speedo adjustments and they have removed the option to compensate for tire wear but the factory speedo error option is still there which is set at a fairly generous 5.5%. What makes this error seem so deliberate is that there are confirmed instances of the odometer being accurate despite the speedometer error. Once the error was corrected with a signal modifier the speedo was then correct, but the odometer was then incorrect.

BTW, I based all of my answers under the assumption that this screenshot was taken while trying to calculate the speedometer for the drivetrain transplant that Dave is assisting with currently.