35" tires and speedometer correction ?

[NH-RCSB]

What is required to have the speedo accurate when I switch to the 35" tires ??

Thanks.

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[Ricksc]

You will feed Forscan and go in and change tire size. Search this site I can’t remember there’s a formula to get it. I did it and it worked great

 

[ThumperF150]

I have a (probably irrational) fear of messing up my truck’s computer so I did not want to use ForScan. Instead I got and installed the Hypertech in line Speedometer correction module. Worked well for me but most will use ForScan.

 

[Ricksc]

Don’t fear Forscan. I did at first, but you take your time and it’s cake walk. Always save as built or changes each time just to be safe.

 

[Magellan]

Just did it a few days ago. Not too difficult in forscan. What you will need is the circumference of the new tires. After reading the manufactures site I used Michelin’s numbers for circumference but the speedo and the GPS were not matching so I did it the old fashion way with math. Still not match the GPS. The final time I took a ride with forscan connected and decreased the circumference by 10mm each time until I got it spot on with the GPS. I used Waze on my CarPlay which made it easy. So, if Waze GPS is off then so is my truck but i got them to match up exactly.
By the way the circumference is measured in (mm). I believe i ended up 50 mm under what Michelin’s chart said.

 

[NH-RCSB]

So,..
If I change out my OEM tires and put on the 35x10.5 R17's will it be drivable until I can get the Forscan / speedo re calibrated, or will there be drivability issues and error codes ?

Thank you.

 

[ThumperF150]

It will drive just fine. Speedo will be 10% slow at all speeds. Indicated 60 will be an actual 66 for example.

 

[NH-RCSB]

It will drive just fine. Speedo will be 10% slow at all speeds. Indicated 60 will be an actual 66 for example.

Thank you !

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