Spart

I've found quite a few discrepancies actually, hence the fine-tuner.

The nominal diameter for a given tire size is just that - a value in name only. The actual diameter varies by manufacturer and model of tire.

Also, many automakers intentionally program their speedometers to read fast. I assume this is the result of lawyers making sure the automaker can't be held at fault if someone caught speeding decides to sue.

That said, I noticed on the Mustangs in particular that some of the older cars seemed to use a different conversion factor, and it would have resulted in the speedometer reading fast. My 2017 Mustang reads dead on with the factory tires and factory setting.

tland4

I tried this out today on 2013 using the line given in the original post for the 11-14's and it did not work unfortunately

Spart

What was your original value on 726-45-01 and what did you try changing it to?

tland4

I'll double check when I get the chance, but I believe the as-built had the value at 09AC and after one of the options in your formula sheet, I changed it to 09AB for the tire size calculator

And 09B6 for the speed differential formula. (Indicated 75mph; actually 79mph)

tland4

Having a really hard time getting the speedometer to read differently at all. With both of the formula solutions entered in, nothing changed. And the "pre-loaded"(for lack of better words) options that Forscan has for the BCM read "error" under the tire size; really saying "incorrect value or not configured"

However, within that same data page that Forscan has built-in to the software for ease of access, so to speak, I've tried the biggest tire size as well as the smallest to see if there would be any changed on my speedo compared to my actual speed...none whatsoever.

I think line 726-45-01 does identify the tire size, but oddly has no effect on the speedometer reading

Spart

Interesting! Hopefully someone else with an 11-14 can jump in and confirm.

Did you try changing the gear ratio on the same line?

tland4

I didn't, but I did just find a Google sheet with several options to try.

Now, changing these gear ratios will, in reality, only "trick" my speedometer shouldn't it? Well, I hope it will lol

EDIT: tried all 4-5 gear ratio changes to no avail. I also noticed that whenever I tried to change the 4 digits that I'd like to change, when it write it in, the last 4 digits in the line are automatically changed as well

Spart

It only "tricks" your speedometer as much as telling it the correct tire size does.

I have no idea what's going on with the last four digits. The last *two* digits are check digits that FORScan should automatically recalculate for you. The last four digits on that line consist of two that I don't believe are identified in terms of function followed by the two check digits.

Have you managed to successfully change anything else on your truck with FORScan?

tland4

I apologize. It is only changing the last two digits whenever I change those other four. I have successfully added DRL's, as well as enabling remote start. So I'm not sure why this isn't working.. I'm running out of ideas at this point. And I really don't want to buy a tuner/programmer

Spart

Interesting. I look forward to hearing from another 2011-2014 owner to confirm if this issue is widespread.