Mustang Speedometer Correction - Please Help

[EutectoidAndroid]

I've been happily using my intune for about 3 years now. On older versions of the inTune firmware, I could easily adjust/calibrate the speedometer using tire revolutions per mile. However, now that only the sidewall tire dimensions, or tire diameter can be used for speedometer adjustment, I can't get the speedometer dialed in.

My current tune is from BAMA, and it reads 120 km/h when I'm travelling at 130 km/h (per accurate GPS). I tried running "Adjust Parameters" in the inTune, and inputting the stock sidewall size of 255/40 R19, the speedometer only shows about a third of my speed. Note that the screen indicated that the tire size was not previously set in the tune when I entered these values. I checked the rear end gear ratio, and it is correctly set at 3.31. I've played around with tire sizes to get the speedometer to show correctly but I can't even get it close.

In order to have the speedometer show something close to the correct speed, I have to run the BAMA tune as is, so it's showing higher than actual. I would like to get it to read the correct speed for obvious reasons. I tried searching to find if others have had similar issues but can't find anything. Is there anything else I can try to get this corrected? Is there a way to access the tire revolutions per mile setting to easily get things dialed in? Thanks for your help.

[mikel]

post the tune file and tell us what the previous setting was for circumference.

[EutectoidAndroid]

Tune is attached. In the "Adjustable Parameters" menu, for both sidewall and diameter, there is a statement similar to "not previously set". It was only when I entered values into these fields that the speedometer got extremely incorrect.

[EutectoidAndroid]

I was going to PM this to you Mike, but I see you have PMs disabled. I hope you are able to help.

Hello,

I am the mustang owner with the speedometer problem that posted a couple of weeks ago. I posted the tune as you asked. For the speed correction, I had used the tire sidewall, as I stated in the original post.

You had asked what circumference I had used. I thought the interface asks for a diameter? Do you suggest I try this setting, inserting circumference for diameter, rather than the sidewall size and report back?

The revolutions per mile worked way better, I used that setting with no issue in the past. I see on the forum I'm not the only one with that opinion.

If you can please help me resolve this issue I'd appreciate it because I have a long trip coming up in a few weeks, thanks.

Chris

[EutectoidAndroid]

Update:

Today I used the "tire height" adjustable parameter to try to adjust my speedometer. I set it to 26", which is what I physically measured on the car. The speedometer shows only a third (or 1/pi?) of my actual speed as measured by GPS. I confirmed again that the correct gear ratio of 3:31 was in the tuner, which it was. Mike, you'd asked earlier if I'd entered the tire circumference in your previous reply. I cannot see anywhere to enter circumference, and also, with the tire height scale ending at 57" at the upper end, I wouldn't be able to put in the actual circumference anyway.

In summary:
1. The tune I previously uploaded is only off by a bit (130 km/h at actual 120 km/h).
2. When using the tire sidewall calculator for speedometer correction, the shown speed is only about a third of my actual speed.
3. When using the tire height for speedometer correction, the shown speed is only about a third of my actual speed.
4. The old tire revolutions per mile adjustment feature worked perfectly, but this is no longer available. If you were to bring this back I'm sure you'd have some appreciative customers.

Apologies for the quality of the attached pictures.