Speedometer Recalculation for 35" Tires

[NH-RCSB]

I'm swapping out my OEM 265/70 R17's for 35/10.5 R17's How do I recalculate / program the speedo ?

Thank you.

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[Boyk1182]

I have 295/65R20 ties that are 35.1” in diameter so this is probably a good starting point for you. I did it with FORScan and after some reading online and trial and error with a GPS, I changed the old measurement from 2547mm to 2686mm and it’s spot on now.

 

[NH-RCSB]

Perfect, Thank you !
Now,.. what is FORScan and how / where do I get this ?

 

[Boyk1182]

I bought it for like $20 on Amazon and only used it for that but it can do lot of other things. You plug it into a laptop and the OBD port on the truck to access the computer. I found some forums and YouTube videos to learn the process, but you’re just changing the tire circumference that’s programmed into your truck’s computer. I spent a lot more time reading about it than actually doing it. I think it took less than 5 minutes to do.

 

[12Lariat21]

Here you go, good luck with this rabbit hole!
https://www.f150gen14.com/forum/threads/2021-f-150-forscan-list-database-spreadsheet.1578/

 

[NH-RCSB]

I bought it for like $20 on Amazon and only used it for that but it can do lot of other things. You plug it into a laptop and the OBD port on the truck to access the computer. I found some forums and YouTube videos to learn the process, but you’re just changing the tire circumference that’s programmed into your truck’s computer. I spent a lot more time reading about it than actually doing it. I think it took less than 5 minutes to do.

I just went on Amazon. There's dozens of these FORScans. What PN. did you get ? I want to make sure I have the correct one. 2025, F-150.

Thank you

 

[Boyk1182]

I just went on Amazon. There's dozens of these FORScans. What PN. did you get ? I want to make sure I have the correct one. 2025, F-150.

Thank you

Please confirm this will work for your truck in the rabbit hole but mine is ELM327.

 

[NH-RCSB]

Thank you

 

[NVRANUF]

@NH-RCSB You will need the ForScan software... Go to the ForScan website and download the software... I think it's still free for a month or two... But a 1-year subscription is only like $20. Also on the Forscan website is the link to the right OBDLink product. I prefer the USB connection one versus the Bluetooth one. I don't trust a wireless Bluetooth connection when changing programming on my truck.

Then check out the thread linked in the other post above and make sure you understand what you are doing before you start using the spreadsheet and changing things.

 

[NH-RCSB]

@NH-RCSB You will need the ForScan software... Go to the ForScan website and download the software... I think it's still free for a month or two... But a 1-year subscription is only like $20. Also on the Forscan website is the link to the right OBDLink product. I prefer the USB connection one versus the Bluetooth one. I don't trust a wireless Bluetooth connection when changing programming on my truck.

Then check out the thread linked in the other post above and make sure you understand what you are doing before you start using the spreadsheet and changing things.

Thank you very much for this info. When I have everything set up, I'm sure that I'll have more questions !!

 

[Boyk1182]

Thank you very much for this info. When I have everything set up, I'm sure that I'll have more questions !!

If I remember right I had a website to follow as well as a YouTube video and did it one step at a time and it worked fine. I’m far from being computer savvy so getting a good handle on it first is what I did. It’s actually very easy and only a few steps.

 

[Jdsnowman]

I agree with the responses above. Get ForScan and the OBDLink adapter and you will be able to do it yourself. There are lots of articles on this forum about using ForScan and you'll be able to tweak more than your tire size if want to. I tried calculating the new circumference and the speedometer was still off so I had to adjust based on the GPS speed.

 

[Graygoose2021]

Or see if there is someone close that has Forscan, and knows how, pay em $150 to make changes for you.

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