Speedo Recalibration

[BQuiz]

Have a new '25 Bronco Outer Banks....new to the Bronco world. (It's my wife's, but she's going to let me do what I normally do, as Director of Automotive Modifications for our household. )

Our OBX has the 2.7L V6 and all the buttons.

It has the 255/70-18 OE street tires (Dueler AT) that make it look "less than cool."

I want to put 275/70-18's on it, as many have attested will fit and function just fine.

Dealer says they can't recalibrate the speedo on a '25, the Superchips FlashCal says it only works up to 2024 model year, and it would appear that a Ford Performance ProCal is my old option, for stupid money.

For those that have upsized tires, is it really necessary to recalibrate the speedo for an additional 1" of rubber? I'm not talking about 35's or 37's here - Just some Load Range C 275/70-18's that will weigh 10'ish pounds heavier than the OE tires. If I couldn't care less about the speed reading 2-3mph slower than I'm actually running, is anybody noticing anything else with the 2.7L that would make me want to spend $600 on the ProCal just to change the tire size?

Thanks! I'll be seeing you all around and posting a bit, I'm sure.

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[RagnarKon]

We can math this.

• 255/70R18 = 2558mm circumference
• 275/70R18 = 2644mm circumference

Granted those circumferences numbers are probably not exactly what Ford is using, I'm sure they have a buffer. But your speedometer will be off by around 3-4%.

Or said another way... if your speedometer reads 70 MPH, you are actually going ~73 MPH.

 

[BQuiz]

We can math this.

• 255/70R18 = 2558mm circumference
• 275/70R18 = 2644mm circumference

Granted those circumferences numbers are probably not exactly what Ford is using, I'm sure they have a buffer. But your speedometer will be off by around 3-4%.

Or said another way... if your speedometer reads 70 MPH, you are actually going ~73 MPH.

Yep, I came up with the same - I’ve got no issue with that.

Any other reason to recalibrate the system for it? Transmission shift points or anything drivability related?

Thanks!

 

[RagnarKon]

Yep, I came up with the same - I’ve got no issue with that.

Any other reason to recalibrate the system for it? Transmission shift points or anything drivability related?

Thanks!

I was going to say “No”, but that’s a good point on the transmission. I’ve only ever driven manual transmissions so obviously that part doesn’t apply to me, and truthfully I’ve never looked into that. My hunch is the change is too small for it to really matter, but that’s only a hunch.

On the non-drivability side of things: you’ll be messing with your odometer obviously. Which effectively means you’ll be shorting yourself on the warranty side by a few thousand miles.

Edit: err.. wait… did I think about that backwards? Hold up… brain not functioning.

Edit2: Yup, I thought about this backwards initially. Your odometer would be reading less than the actual mileage. Still something to keep in mind though for when you go to sell the Bronco or get warranty service. Laws/contract terms can vary.

 

[Ducati1098]

Any other reason to recalibrate the system for it? Transmission shift points or anything drivability related?

It won’t affect the transmission at all

 

[Brian_B]

Forscan should be able to do the recal

 

[BQuiz]

On a 2025? I understood that it couldn’t yet.

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