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Hallelujah! A tire size programming breakthrough!


Madlock

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After realizing long ago that most dealers' service departments tend only to be coincidental experts in any given aspect of any particular vehicle they're tasked with supporting, the most important lesson I've learned is to never accept as gospel any technician's "can't be done" to the exclusionof ever asking any other(s).

 

So it was today when I jail broke my GT500 from winterstorage to enjoy the 50-degree sunny skies and treat it to a fresh tank of Sunoco 99 at $8.99/gallon – but I digress.

 

When servicing my Taurus SHO last week, I asked to speakwith whomever the dealer considered to be its Mustang "expert". I explained my desire for alternative wheelsand tires to the SVTPP and that I'd been repeatedly told Ford had locked-out thewheel revs/mile setting from being changed for all 2010 and newer vehicles makingit impossible to change without a ProCal or aftermarket tuner.

 

He suggested I bring-in my GT500 when convenient so he couldtry-out something he had in mind which would take only 15 minutes to test byaccessing the ABS parameters through ROTUNDA. So I did. And Hallelujah!

 

It's a little arcane, but the ABS module has severalpre-stored tire size settings paired to what Ford offers in OE fitments. It also has an "OTHER" setting which acceptsa parameter between 725 and 792 revs/mile – or tire diameters roughly between25.5" and 27.8" with a 3.73 final drive ratio.

 

A parameter also exists for Final Drive Ratio which can beset to anything within a specific combination of ranges depending upon the tiresize that's been programmed. Apparently,the PCM looks to the ABS module for this data to begin with, which it thenpasses along to the instrumentation to keep the speedo and odometer in-check.

 

It may not be as convenient as hooking-up an SCT, but forthose who don't do their own wheel swaps at home, it may be both quicker andcheaper to have them done this way through a dealer. Anyway, I thought people who may be tryingto accomplish the same thing would appreciate knowing it can be done – and how.

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After realizing long ago that most dealers' servicedepartments tend only to be coincidental experts in any given aspect of any particularvehicle they're tasked with supporting, the most important lesson I've learnedis to never accept as gospel any technician's "can't be done" to the exclusionof ever asking any other(s).

 

So it was today when I jail broke my GT500 from winterstorage to enjoy the 50-degree sunny skies and treat it to a fresh tank of Sunoco99 at $8.99/gallon – but I digress.

 

When servicing my Taurus SHO last week, I asked to speakwith whomever the dealer considered to be its Mustang "expert". I explained my desire for alternative wheelsand tires to the SVTPP and that I'd been repeatedly told Ford had locked-out thewheel revs/mile setting from being changed for all 2010 and newer vehicles makingit impossible to change without a ProCal or aftermarket tuner.

 

He suggested I bring-in my GT500 when convenient so he couldtry-out something he had in mind which would take only 15 minutes to test byaccessing the ABS parameters through ROTUNDA. So I did. And Hallelujah!

 

It's a little arcane, but the ABS module has severalpre-stored tire size settings paired to what Ford offers in OE fitments. It also has an "OTHER" setting which acceptsa parameter between 725 and 792 revs/mile – or tire diameters roughly between25.5" and 27.8" with a 3.73 final drive ratio.

 

A parameter also exists for Final Drive Ratio which can beset to anything within a specific combination of ranges depending upon the tiresize that's been programmed. Apparently,the PCM looks to the ABS module for this data to begin with, which it thenpasses along to the instrumentation to keep the speedo and odometer in-check.

 

It may not be as convenient as hooking-up an SCT, but forthose who don't do their own wheel swaps at home, it may be both quicker andcheaper to have them done this way through a dealer. Anyway, I thought people who may be tryingto accomplish the same thing would appreciate knowing it can be done – and how.

 

 

Great to know, I will print this and show it to my Mustang guru at Ford. Thanks for the info.

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Great to know, I will print this and show it to my Mustang guru at Ford. Thanks for the info.

 

 

You're welcome.

 

I don't know what more your technician would need to know than it can be done by accessing the ABS module, but print away.

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When servicing my Taurus SHO last week, I asked to speakwith whomever the dealer considered to be its Mustang "expert". I explained my desire for alternative wheelsand tires to the SVTPP and that I'd been repeatedly told Ford had locked-out thewheel revs/mile setting from being changed for all 2010 and newer vehicles makingit impossible to change without a ProCal or aftermarket tuner.

 

 

While in the process of buying my car I asked my salesman (also the SVT & Truck Sales Mgr.) if they can recal the speedo when I change my wheels. Being a GM Trained Tech, I *know* all dealerships are capable of doing that and have been since at LEAST the early 90's.

 

He said, "Yeah, no poblem. Just bring it into our Service Dept and they can flash it." I asked him how much and he just said "it'll be minimal".

 

I don't know who you talked to that said they couldn't do it, but I know for fact that they CAN (and might be that they HAVE to be able to).

 

One legal defense for a speeding ticket is if you were depending on the Speedo for your speed indicator. I mean obviously, if you're speedo shows you're doing the posted limit and you're passing everyone on the road like they're standing still, you'll lose in court but if you are going the limit as indicated by your OEM speedo, it's a viable defense.

 

But you WILL be required to have it recalibrated and it would be smart to have it calibrated (to show it WAS off when you got the cite) before going to court.

 

On earlier GM's we had what we called a "Comb". It looked like a little comb and you removed a tooth for X inches you added of tire diameter, or got a new comb to add teeth. It plugged into the back of the speedo head and that was.......shhheeeeesh, at least....hmm, 1988 or 89?

 

My local Ford Dealer is a SVT Certified (or whatever Ford calls it) shop but still......it's a freakin' MUSTANG fer chripes sake so you shouldn't need a SVT Certified shop to calibrate your speedometer.

 

 

Lesson for today: Talk to the right people at your dealership,

Phill

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While in the process of buying my car I asked my salesman (also the SVT & Truck Sales Mgr.) if they can recal the speedo when I change my wheels. Being a GM Trained Tech, I *know* all dealerships are capable of doing that and have been since at LEAST the early 90's.

 

He said, "Yeah, no poblem. Just bring it into our Service Dept and they can flash it." I asked him how much and he just said "it'll be minimal".

 

I don't know who you talked to that said they couldn't do it, but I know for fact that they CAN (and might be that they HAVE to be able to).

 

One legal defense for a speeding ticket is if you were depending on the Speedo for your speed indicator. I mean obviously, if you're speedo shows you're doing the posted limit and you're passing everyone on the road like they're standing still, you'll lose in court but if you are going the limit as indicated by your OEM speedo, it's a viable defense.

 

But you WILL be required to have it recalibrated and it would be smart to have it calibrated (to show it WAS off when you got the cite) before going to court.

 

On earlier GM's we had what we called a "Comb". It looked like a little comb and you removed a tooth for X inches you added of tire diameter, or got a new comb to add teeth. It plugged into the back of the speedo head and that was.......shhheeeeesh, at least....hmm, 1988 or 89?

 

My local Ford Dealer is a SVT Certified (or whatever Ford calls it) shop but still......it's a freakin' MUSTANG fer chripes sake so you shouldn't need a SVT Certified shop to calibrate your speedometer.

 

 

Lesson for today: Talk to the right people at your dealership,

Phill

 

 

It has been my experience that if you change anything on you car so it no longer fits the mold of what the dealership understands you are hooped.

If the work does not involve breaking a part that was not broken, spilling lubrcant of some sort on the car, or looking you straight in the face and lying. The local dealers in my town do not have the skills to do it. It is worth the cost and effort to buy the aftermarket tool and set the spedo yourself.

Just my 2cents.

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While in the process of buying my car I asked my salesman (also the SVT & Truck Sales Mgr.) if they can recal the speedo when I change my wheels. Being a GM Trained Tech, I *know* all dealerships are capable of doing that and have been since at LEAST the early 90's.

 

 

That may be true, but the straightforward PCM setting has been locked-out for 2010 and newer vehicles. Perhaps the tech you were speaking with was referring to a prior model year - or he already knew of the ABS backdoor, or perhaps even another.

 

As it was explained to me by more than one shop manager, it's something Ford did for several reasons - first to try to influence people to stay with OE fitments (perhaps a marketing agreement?) and to discourage people who had deliberately gone to larger diameters on non-performance lease vehicles as a means of lowering the amount of wheel revs and therefore mileage compared to what had actually been driven at a time when Ford was taking huge baths on lease residuals it had to eat.

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