Tire size - speedometer adjustment '06

[N2STC]

I am considering 235/50 -17 tires because I found a good deal and it would effectively lower the gear ratio slightly. Does anyone know of a way to adjust the speedometer to compensate? I know the error will be small, but there is already an error in that direction.

 

[06 T-RED S/C GT]

If you have an SCT X3-X4 hand-held programming device? there's a revs per mile menu you can make adjustments. Select 782 revs per mile for your 235/50/17" size tires. If 782 isn't listed? then select 780 which is close enough. If you don't have a hand-held tuning device? then don't worry about it, as there really isn't much difference between 235/50/17" and stock 235/55/17" size tires, to begin with anyhow.

 

[stkjock]

/\ pretty much what is said above.

you need a hand held tuner to make an adjustment or the dealer IIRC can make an adjustment

 

[N2STC]

Thanks! Sounds like a great excuse to get one. Any recommendations on Brand/model/source?

 

[DieHarder]

You can find them at SCT online https://www.sctflash.com/ or look at the used market. Just make sure you're getting a model (7015) for a Mustang. Many of us have the X4. If you get one on the used market just ensure it's not married and ask for number of unlocks left on it. They come with 5 unlocks stock.

If you get one that's still married it'll cost you around $150 to get it unlocked by SCT. Better to buy a new one (~$400) than a used one and have to pay to get it unlocked.

 

[stkjock]

Thanks! Sounds like a great excuse to get one. Any recommendations on Brand/model/source?

do you want to have a tune on the car as well?

 

[JEWC_Motorsports]

SCT sends them with canned tunes now. About as good as a procal.

 

[stkjock]

SCT sends them with canned tunes now. About as good as a procal.

yea, however, for the same money I think you can buy one from a tuning shop with a better canned tune

 

[Juice]

If there is no tune on the car now, Forscan maybe able to adjust tire size and even gear ratio. It is under VID block programming, if available for your car. Or a Ford dealer could do it with ids.
I said no tune, because tunes usually override the VID block.
If you have the tire size set in the tune, changing it in the VID block has no effect.

 

[06 T-RED S/C GT]

JDM engineering, VMP, Steeda and Brenspeed all include their own custom/preloaded calibration tunes on their SCT X3-X4 hand-held tuning devices. IMHO, they are in fact much better canned tunes than what SCT has. Just make certain to stay away from SCT X3-X4 hand-held tuning devices from Bama performance, as their preloaded/canned tunes suck horribly lol.

 

[N2STC]

I appreciate all your input. Thanks guys.