Ford Tech Won't Install Tires

[121gigawatts]

Hello,

I've got my car at a Ford dealership because the brakes got warped. Because they're under warranty for the first 12 months/18k miles they're taking care of it. While it's there I asked if they could get 255/50 r19's Michelin Primacy Touring A/S to upgrade the back tires. (OEM 225/55/R19, upgrade would have a difference of

The service guy reached back out and told me his certified MME tech won't upgrade the tires because the system won't allow it. He said I can't change anything other than to same size different brand because "the system is too complicated and could give errors and lock up which would prevent you from driving."

Has anyone heard of this? (Math attached if anyone would like to double check me)

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[RickMachE]

Yes, I've heard of dealers refusing to put in tires that don't match the original specification.

 

[Scooby24]

Your tech is right...you shouldn't put different sized tires front to rear unless the rolling diameter is exactly the same. Any difference can cause traction control problems. Hard to say what the threshold is but from their perspective, it's a liability issue.

Also, don't put 255 tires on a 7" wheel.

 

[121gigawatts]

Yes, I've heard of dealers refusing to put in tires that don't match the original specification.

Thanks for the reply. Yeah what had me pausing was that they're not willing to change anything other than same size different brand.

Your tech is right...you shouldn't put different sized tires front to rear unless the rolling diameter is exactly the same. Any difference can cause traction control problems. Hard to say what the threshold is but from their perspective, it's a liability issue.

Also, don't put 255 tires on a 7" wheel.

the 255s are rated for 7-9 inch wheels. The diameter is 0.3" bigger and the circumference is 0.9" bigger with a +7 difference in revs/mile.

Do you think this might be an issue?

 

[connoisseurr]

The larger rolling diameter might be the issue.

But, it's rather common that many dealerships won't install non-OE tire sizes to OE wheels. Some dealerships also won't mount or install aftermarket wheels and tires.

 

[ElectrifyCLT]

My bet is there is a decent shot this will cause issues. On top of traction control you've got the "AWD" system that is picking when to engage/disengage the motors on either axle and who knows what a slight variation in the rolling diameter may cause your motors to do.

 

[Maquis]

I definitely wouldn't have different size tires front vs rear if the car is an AWD.
Not knowing how traction control functions, I probably wouldn't do it for a RWD, either.

 

[Lord Polymath]

I've apparently had an "old school" mentality when it comes to tires, but thanks to this forum, have recently changed my way of thinking. Modern traction control is amazing.

 

[Scooby24]

the 255s are rated for 7-9 inch wheels. The diameter is 0.3" bigger and the circumference is 0.9" bigger with a +7 difference in revs/mile.

Do you think this might be an issue?

I do think it could be an issue...depending on how sensitive the traction control is....especially as you get going faster on the highway.

255 may be rated for a 7" wheel but you'll be extending the tread over the width of the wheel which will A) look worse and B) handle worse.

 

[markboris]

I am going to chime in here on the subject of not having different size (diameter) tires front and rear on AWD. If this were the case, why do Tesla, BMW, Porsche, Audi and so many others have OEM staggered sizes on their AWD cars? From what I have read about this is as long as you don't go over a 3% difference it is ok. I had a 2% difference on my Focus RS (AWD) for 20K miles with no issues when tracking the car or just normal driving. My staggered setup on the Mach-E has a 1% difference (255/45/20, 295/40/20). I have had them on for about 7000 miles with no issues. There are quite a few members here that have that same exact setup and some others more aggressive.

Just to name a few and all of these are AWD:

Tesla S Plaid 265/35/21, 295/30/21 1.1% difference
Tesa Model X 255/45/20, 275/45/20 2.4% difference
Porsche Taycan, Audi E-Tron 245/45/20, 285/40/20 1% difference
BMW X3M 255/45/20, 265/45/20 1.4% difference

I agree with Greg above and would get a wider wheel for a 255 tire even though it would fit on the 7" wheel. My front wheels are 8.5" with the 255.

 

[sotek2345]

I am going to chime in here on the subject of not having different size (diameter) tires front and rear on AWD. If this were the case, why do Tesla, BMW, Porsche, Audi and so many others have OEM staggered sizes on their AWD cars? From what I have read about this is as long as you don't go over a 3% difference it is ok. I had a 2% difference on my Focus RS (AWD) for 20K miles with no issues when tracking the car or just normal driving. My staggered setup on the Mach-E has a 1% difference (255/45/20, 295/40/20). I have had them on for about 7000 miles with no issues. There are quite a few members here that have that same exact setup and some others more aggressive.

Just to name a few and all of these are AWD:

Tesla S Plaid 265/35/21, 295/30/21 1.1% difference
Tesa Model X 255/45/20, 275/45/20 2.4% difference
Porsche Taycan, Audi E-Tron 245/45/20, 285/40/20 1% difference
BMW X3M 255/45/20, 265/45/20 1.4% difference

I agree with Greg above and would get a wider wheel for a 255 tire even though it would fit on the 7" wheel. My front wheels are 8.5" with the 255.

The issue isn't really the stagger, it is how it is programmed from the factory. If the factory setup is staggered then the control software reflects that and no issue. When you change off of the factory configuration, that is when problems developed because the software reads the front and back wheels as travelling at different speeds, indicating slip. What that threshold level is, is completely up to each vehicle's programming.

 

[Pushrods&Capacitors]

I am going to chime in here on the subject of not having different size (diameter) tires front and rear on AWD. If this were the case, why do Tesla, BMW, Porsche, Audi and so many others have OEM staggered sizes on their AWD cars? From what I have read about this is as long as you don't go over a 3% difference it is ok. I had a 2% difference on my Focus RS (AWD) for 20K miles with no issues when tracking the car or just normal driving. My staggered setup on the Mach-E has a 1% difference (255/45/20, 295/40/20). I have had them on for about 7000 miles with no issues. There are quite a few members here that have that same exact setup and some others more aggressive.

Just to name a few and all of these are AWD:

Tesla S Plaid 265/35/21, 295/30/21 1.1% difference
Tesa Model X 255/45/20, 275/45/20 2.4% difference
Porsche Taycan, Audi E-Tron 245/45/20, 285/40/20 1% difference
BMW X3M 255/45/20, 265/45/20 1.4% difference

I agree with Greg above and would get a wider wheel for a 255 tire even though it would fit on the 7" wheel. My front wheels are 8.5" with the 255.

The cars you listed are offered from the factory with chassis tuning/ESC programming specific to the OEM staggered figment. The MME isn’t.

I’m upgrading our 4X from the OEM 225 summer tires option to 20”s with 245/45s but I’m keeping it square just like OEM for reasons:

1. OEM like chassis balance with regards to understeer/oversteer tendencies. I really like the MME’s inherent balance towards a bit of exit oversteer in certain situations and fairly neutral feel overall. It would lose some of that with a staggered fitment with a wider rear tire. Those that never drive past 5-6/10ths may never notice it, however.

2. Tire warranty- We’re probably going with the Goodyear Exhilarate or Pirelli P Zero A/S and want to retain the full rated warranty mileage rather than have it cut in half as a staggered fitment dictates.

3. Rolling mass. The 20” wheel/tire package we're looking at is a total of 7 lbs per corner lighter than the OEM setup, so, the weight savings may end up
making up for the addition frictional losses due to the wider contact patch. It will definitely help the handling though.

 

[Scooby24]

I am going to chime in here on the subject of not having different size (diameter) tires front and rear on AWD. If this were the case, why do Tesla, BMW, Porsche, Audi and so many others have OEM staggered sizes on their AWD cars? From what I have read about this is as long as you don't go over a 3% difference it is ok. I had a 2% difference on my Focus RS (AWD) for 20K miles with no issues when tracking the car or just normal driving. My staggered setup on the Mach-E has a 1% difference (255/45/20, 295/40/20). I have had them on for about 7000 miles with no issues. There are quite a few members here that have that same exact setup and some others more aggressive.

Just to name a few and all of these are AWD:

Tesla S Plaid 265/35/21, 295/30/21 1.1% difference
Tesa Model X 255/45/20, 275/45/20 2.4% difference
Porsche Taycan, Audi E-Tron 245/45/20, 285/40/20 1% difference
BMW X3M 255/45/20, 265/45/20 1.4% difference

I agree with Greg above and would get a wider wheel for a 255 tire even though it would fit on the 7" wheel. My front wheels are 8.5" with the 255.

Glad to hear it's not been an issue for you. It's all a matter of how and when the OEM's setup their nannies.

One concern I would have is while it may be perfectly fine under normal driving conditions...that stability control they've setup for when you're losing traction, will it work as well or as predictably?

What happens on the track, or in inclement weather, or if you get squirrely on a turn? Is it going to be as predictable in those conditions as it would be with the stock sized tires or at least stock difference in sizing front to rear to account for rotational differences?

I'm imagining a scenario where you are taking a hard turn and where you'd normally be fine pushing it a little bit, now the car sees more wheel spin than anticipated and engages nannies sooner...hurting the fun and performance? Dunno, spit balling.

 

[Timelessblur]

the 255s are rated for 7-9 inch wheels. The diameter is 0.3" bigger and the circumference is 0.9" bigger with a +7 difference in revs/mile.

Do you think this might be an issue?

The short answer is yes it will.
I had an even closer match (+4 per mile) on a former car of mine and I had to throw the spare on it. The car quickly screamed that something was wrong. It disabled traction control, ABS, lane centering, cruise control very quickly and threw a lot of errors until it was fixed.

On the mach E I can see it screaming even more and this goes double if it is AWD

 

[SnBGC]

I don't blame the dealer for not wanting to do this. It probably would be fine but I wouldn't want to take chances with a customer's car by installing a different size tire.

Later on, you might get some fault notices that are completely unrelated to tire size but the tech won't be able to trouble shoot because of the non-standard tire size.

Every once in a while I get a message saying something like brake assist and adaptive cruise not available but it goes away pretty quick so I never bothered taking it in for service. Other folks get a 1PD not available message etc. If I am a tech and someone brings in a car with an issue like that then I would want the correct tire size on the car just to rule that out as a possible cause.

Based on that rationale, I wouldn't install non-standard tire sizes on a customer's car even if they asked for it. You can try a neighborhood tire shop....they might be less concerned about it.

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