FORScan Speedo/Tire adjustment size correction for those running 37's - solution for 2021 Tremor

[Sparkie2413]

For anyone interested in calibrating the speedo correctly I was able to do so with no dash lights and no PCM relearn on my 2021 Tremor.

I used version 2.3.38 (FORScan), went Bdycm not as built (Plain English), scrolled down to tire circumference and changed the stock value of 2689 to 2770. After writing the new information to the truck, I went for a 10+ mile freeway trip and found everything to be spot on per WAZE GPS all the way up to 87mph. I didn't check any higher than that because there is no need for me to drive that fast or faster.

Note: I had been showing +3mph at 70 - 75 mph per GPS when compared to the speedometer prior to the change. Now it seems to be perfectly adjusted.

I have Fuel 18x9 wheels with +20 offset, running Toyo 37" AT3's. Toyo's website shows the tire to actually measure 36.5" with 569 revolutions per mile.

I had been hearing of problems with the 20's and 21's when trying to adjust speedo with FORScan and had not tried anything until this evening.

The credit goes to ZooDad on the Ford Truck enthusiast web page and one of his beta postings.

Hope that helps someone.

Cheers!

 

[22F250]

For anyone interested in calibrating the speedo correctly I was able to do so with no dash lights and no PCM relearn on my 2021 Tremor.

I used version 2.3.38 (FORScan), went Bdycm not as built (Plain English), scrolled down to tire circumference and changed the stock value of 2689 to 2770. After writing the new information to the truck, I went for a 10+ mile freeway trip and found everything to be spot on per WAZE GPS all the way up to 87mph. I didn't check any higher than that because there is no need for me to drive that fast or faster.

Note: I had been showing +3mph at 70 - 75 mph per GPS when compared to the speedometer prior to the change. Now it seems to be perfectly adjusted.

I have Fuel 18x9 wheels with +20 offset, running Toyo 37" AT3's. Toyo's website shows the tire to actually measure 36.5" with 569 revolutions per mile.

I had been hearing of problems with the 20's and 21's when trying to adjust speedo with FORScan and had not tried anything until this evening.

The credit goes to ZooDad on the Ford Truck enthusiast web page and one of his beta postings.

Hope that helps someone.

Cheers!

I would like to revive this thread. Anyone else try this change with success?

 

[banthos]

I would like to revive this thread. Anyone else try this change with success?

Also curious

 

[banthos]

I might try it out today, of course saving current settings before modifying. Might save a couple hundred bucks on a calibrator. I'll report back if I do it. Also running 37s on 18s.

 

[banthos]

For anyone interested in calibrating the speedo correctly I was able to do so with no dash lights and no PCM relearn on my 2021 Tremor.

I used version 2.3.38 (FORScan), went Bdycm not as built (Plain English), scrolled down to tire circumference and changed the stock value of 2689 to 2770. After writing the new information to the truck, I went for a 10+ mile freeway trip and found everything to be spot on per WAZE GPS all the way up to 87mph. I didn't check any higher than that because there is no need for me to drive that fast or faster.

Note: I had been showing +3mph at 70 - 75 mph per GPS when compared to the speedometer prior to the change. Now it seems to be perfectly adjusted.

I have Fuel 18x9 wheels with +20 offset, running Toyo 37" AT3's. Toyo's website shows the tire to actually measure 36.5" with 569 revolutions per mile.

I had been hearing of problems with the 20's and 21's when trying to adjust speedo with FORScan and had not tried anything until this evening.

The credit goes to ZooDad on the Ford Truck enthusiast web page and one of his beta postings.

Hope that helps someone.

Cheers!

Where did you get your value of 2770? I'm trying to dial my value in before making any changes. Converting 37/12.5r18, circumference is 2951mm so I'd just like to understand.

 

[Sparkie2413]

Where did you get your value of 2770? I'm trying to dial my value in before making any changes. Converting 37/12.5r18, circumference is 2951mm so I'd just like to understand.

Tires are labeled 37" diameter, but they are actually a bit smaller. 2770 was recommended for my tire on the Ford enthusiast site and it works on my truck.

Some people report they can not get the computer to recognize anything over 2745 without a dash warning light. This number will not correct the speedo perfectly for 37's.

Trial and error on the number input and validate with GPS.

 

[22F250]

Tires are labeled 37" diameter, but they are actually a bit smaller. 2770 was recommended for my tire on the Ford enthusiast site and it works on my truck.

Some people report they can not get the computer to recognize anything over 2745 without a dash warning light. This number will not correct the speedo perfectly for 37's.

Trial and error on the number input and validate with GPS.

Did you do the plain English section, tires, then change it to 2770? Did you have to relearn the pcm etc? Thanks in advance

 

[Sparkie2413]

Did you do the plain English section, tires, then change it to 2770? Did you have to relearn the pcm etc? Thanks in advance

Yes, plain English. No PCM relearn for my truck. It worked with that simple change. No dash lights, GPS verified as correct.

I have read some must do the PCM relearn. Give it a try. If it works then your all set, if not, try the PCM relearn. Good Luck.

 

[22F250]

thank you!

 

[22F250]

I might try it out today, of course saving current settings before modifying. Might save a couple hundred bucks on a calibrator. I'll report back if I do it. Also running 37s on 18s.

did you try this method?

 

[banthos]

did you try this method?

I did with no success on my '22. Couldn't get past both the wrench and CEL on any circumference setting other than stock. So I ordered a speedo calibrator to fix it instead.

 

[22F250]

Bummer. looking like that’s the solution.

 

[CalTremor2020]

Some of you may have seen the other thread but, if you are getting a CEL with the larger tire diameter, just tell the truck the differential gearing is lower than actual (for diesel, try 3.31) and then calculate the equivalent tire circumference. I’m running 37s and I’m dead on with no CEL/DTC.

 

[22F250]

Considering this too

 

[Nyvall]

Yep just did mine and the CEL is on. Changed it back to the original number and the light stayed on. So I switched it back. So now I’m stumped on what to do.

 

[Rockshot]

I've heard that 37s without speedo recalibrate, like rough country's, can cause issues with shifting. Any truth to this? Rough country's unit says it updates ecu for shift points and recalibrates electronic stability control along with adjusting speedometer.

 

[Sparkie2413]

Yep just did mine and the CEL is on. Changed it back to the original number and the light stayed on. So I switched it back. So now I’m stumped on what to do.

I did not experience a CEL, but from what I have read I would try the PCM/TCM relearn after switching it back to original numbers if you have not tried that yet. Hope it helps.

 

[DieselDawg88]

Yep just did mine and the CEL is on. Changed it back to the original number and the light stayed on. So I switched it back. So now I’m stumped on what to do.

I did the gear ratio & tire mm change and generated CEL with relearn on PCM/TcM. Then set it back to factory and did relearn, CEL was gone.

 

[jred225]

I did with no success on my '22. Couldn't get past both the wrench and CEL on any circumference setting other than stock. So I ordered a speedo calibrator to fix it instead.

Which calibrator did you order?

 

[banthos]

Which calibrator did you order?

Speedometer Calibrator | Ford Bronco/Bronco (2 Door)/F-150/F-250/F-350

Speedometer Calibrator | Ford Bronco/Bronco (2 Door)/F-150/F-250/F-350

www.roughcountry.com

Works great, would order again