Changing tire size, regearing and computer update

[poppastar]

My '25 GT manual has 255/40x19 all around which are 27" in diameter. In time I'd like to go wider (and likely as a result ending up with summer tires).

I'm reading that the computer can be updated with Forscan for a change in tire diameter but all 4 have to be the same diameter and that there's no workaround to this? I'm thinking that can't be right so looking for some guidance here.

This might be the wrong forum to ask but I'm also looking to regear from 3.55 to 4.09. I've got a shop capable of it and my research indicates since I have a manual only Forscan is needed to updated the vehicle. Sound about right? Below is a screenshot from a Gemini search and my Iconic Silver Gt Nite Pony.

Thanks!

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[Sofa King]

Same size front and rear are not required... DH and GT PP cars have 27" front and rear is 27.7.

Edit: biggest thing is to have the correct rear tire size in the computer.

 

[GooberDH]

You'd have to use forscan to change it. The three closest dealers to me insisted it couldn't be done and talked to me like I'm crazy unless my dealers just suck.

 

[Nik691]

Also asked my dealer about this. They said it wasn’t possible. I just think they didn’t want to look into it

 

[MNPony]

I used a Ford Procal 4 for adapting the car to a new tire size and a change from 3:15 gears to 3:55. It worked for flawlessly and took all of 5 minutes to do.

 

[A.alansari]

you can do it in forscan use this calculator

https://roketgamer.dev/mustangtools

 

[Skye]

A dealer would not want to get involved because it changes the vehicle's baseline, what the car was sold as. It creates a series of liabilities they'd not want to be associated with.

The OP has a connect for the physical replacement of the gears. Another shop in the area specific to tuning or speed mods might assist with tire size and gear ratio changes via FORScan, if assistance is needed.

The following threads discuss several of these topics.

https://www.mustang7g.com/forums/th...ist-database-spreadsheet-by-livinitup.159997/

https://www.google.com/search?q=mus...cwMzdqMGoxNagCArACAQ&sourceid=chrome&ie=UTF-8

https://www.google.com/search?q=mus...HYXWJ2kQrQIoAnoECB8QAw&biw=1460&bih=740&dpr=2

 

[poppastar]

Understood and thank you everyone.

I read conflicting info that staggered from the factory is programmed that way but going from square to staggered, if not the same diameter, could be a problem. Conversely, if within 3% (front to rear) there wouldn't be an issue. The latter makes more sense especially given all the aftermarket offerings.

I'm likely to have the regear done 1st later this year will post results.

 

[Sofa King]

Understood and thank you everyone.

I read conflicting info that staggered from the factory is programmed that way but going from square to staggered, if not the same diameter, could be a problem. Conversely, if within 3% (front to rear) there wouldn't be an issue. The latter makes more sense especially given all the aftermarket offerings.

I'm likely to have the regear done 1st later this year will post results.

Whatever tire is installed on the REAR from the factory, is the tire size programmed into the computer...(GT 27", PP or DH 27.7", DH HP 26.5") the fronts have nothing to do with it.. square/staggered also has nothing to do with it. If you replace the REAR tire with something less than a 3% increase/decrease you could probably get away without changing tire size in the computer.

My car came with 27" tires front and rear. I put a 27.3 in front and 28.1 in the rear... the only issue was speedo was off by a couple mph. Like @MNPony, I used a procal4 device to set the tire size correctly... everything perfect.

 

[poppastar]

Perfect, thanks man.

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