Installing Larger Diameter Tires (Ford mechanic input needed)

[T Fades]

Hi,

My '23 base GT has the 235/50/18 (27.3" diameter) square with 18x8 wheels. I am considering larger size tires/wheels, maybe 275/40/19 square (27.7" diameter).

Are there any Ford mechanics/specialists on here that can help me understand:

- What other areas would be impacted by taller tires (other than speedometer, ABS, traction control)?

- Does changing the width of the tires cause any concern, or just diameter?

- Would I be able to take my car into the Ford dealer to have the computer tuned to the new tire size? Is it that simple?

- I know other GT's with performance packages come stock with a similar tire as what I want to run. Is the computer the same on my base GT compared to the GT's with PP, and the only difference is a tune that is loaded onto that computer?

I appreciate any guidance, or pointing me to another thread that already discusses this.

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[K4fxd]

That small of a change shouldn't need any tweaking. The car is smart enough to self correct.

 

[I Bleed Ford Blue]

You are correct, the PP1, bullitt and Mach 1 come with a 275/40/19 so fitment will not be a problem. The factory calibrates the speedo for an average tire size and the speedo is never spot on, but real close. You can tweak the calibration to get it perfect if you want, but why bother, the factory cal isn't that close.

You can always get some 19x11's and some 305/35/19's they are closer in diameter to your stock 18's around 27.3-27.4 depending on brand.

 

[T Fades]

The speedo being off a bit does not concern me. I am comfortable that the tires I want to run will fit no problem.

What I am really concerned with is if I go with a taller tire, what other things can be impacted, and what is needed so the car isn't confused. I have read that traction control and ABS could be impacted with changing tire diameter, and I don't want those things doing unwanted things when driving.

If a simple re-tune at Ford dealer is what I need to do, I have no problem paying an hour of labor. I want this car to last my lifetime and don't want premature wear or unexpected driving assistance.

 

[sukhoi_584th]

Nothing needs updated for a change that small.

 

[T Fades]

That small of a change shouldn't need any tweaking. The car is smart enough to self correct.

Not saying I don't believe you, please understand that, but do you have a source that states the car will 'self correct'?

 

[T Fades]

Nothing needs updated for a change that small.

Assume it was a big enough change, what would be impacted and what would need to be updated?

 

[K4fxd]

If you want I can post a screen shot of the relevant section in the tuning software.

Not sure you will understand it but it shows the car will self correct for a range of tire sizes. This includes all stock sizes and slightly out of stock ranges.

 

[SheepDog]

Assume it was a big enough change, what would be impacted and what would need to be updated?

If you are that concerned over such a small increase (which won't actually make any difference to the way the car behaves) Get FORscan and change the tire size in the BCM. (and TCM if your car is an automatic)
https://forscan.org/forum/viewtopic.php?t=15994

 

[K4fxd]

Assume it was a big enough change, what would be impacted and what would need to be updated?

 

[K4fxd]

The key to the above is "Learn from" Stock is is set to learn from the BCM so any tire in the min and max range will cause the car to self adjust.

If you want a tire outside of the stock range you will need a tuner to change the min or max setting.

 

[T Fades]

Yes, mt GT is a 6sp (BCM).

Thanks Dan, SheepDog, sukhoi, and Mike for the responses. I understand what I am changing is very small compared to some on the forum.

@K4fxd Here is the comparison between my stock size and the 275/40/19 I am considering. Looks like the cc on the 275 is just outside the max range of the tuning software. Is that tuning software you show from FORscan?

 

[K4fxd]

No it is from HP tuning software. What year is your Mustang?

 

[T Fades]

2023 base GT 6spd with active exhaust (manufactured 2/2023)

 

[K4fxd]

I was wrong.

As long as the switch is learn from BCM it will self adjust. The min and max are only
used if the switch is set to calibration.

I am posting a pic with it set to cal and also a stock 2023 PP1 cal

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