Potential Lesson Learned?

[BlueSteele]

I finally purchased a set of front tires for my car. I wanted a more aggressive look so I went with a lower profile tire and a taller tires in the back.I purchased the Hankook Ventus Evos 255/40R19s.

In the rears I have Yokohama YK580s that are 255/50R19s. Here is a pic of the setup:



Here is the problem:

As soon as my car hits 24mph, my "service stabilitrak" message, ABS light, parking brake light, and all traction control lights come on. Also, my rear park assist stopped working and the car is not logging trip mileage, avg mpg, fuel range, or avg mpg.

Before hitting the Onstar button I theorized that with all these lights, it was a wheel speed sensor disagreement issue. The codes they gave back were:

C0245 - PCM-to-EBCM correlation issue and

P0856 - Traction Control Input issue

Fronts: 255/40R19 (4.5mm higher than stock)
Rears: 255/50/R19 (20.5mm lower than stock)

There is a 25mm difference between the fronts and rears (roughly 1") in height. Ironically, the speedo is still accurate

In summary, I would like to forewarn anyone thinking of doing this about the light show that lies ahead. Also, I would like to highlight just HOW dependent the car is on these abs speed sensors.

And, does anyone know if a calibration will fix this?

[Rangore]

Sorry I can't answer your question...I don't know.

I've been thinking of doing 255/50 on all 4 corners. I like matching all 4 to be able to rotate. Can I ask how the tire on the back looks from the side...too much bulge? Got any pics from that angle?


Thanks for the FYI on the size diff issue.







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[BlueSteele]

Just came home from the Van Chevrolet and they said there is no way to calibrate these tires through GM. The car is designed to have a specific circumference (with a small tolerance) and anything above or below this circumference will give you the symptoms I am now facing.

Key phrase is calibrating through GM. There is a way to calibrate it with an aftermarket tuner but those cost like $500 unless you have a buddy who can hook you up.

So, long story short, follow the recommended tire size chart sticky thread and "don't be like me kids!"

[BlueSteele]

Oh, and I'll post pics before I go to work tonight

[Rangore]

Originally Posted by BlueSteele

Oh, and I'll post pics before I go to work tonight

Thanks...much appreciated.


So...if you would have matched all 4 corners your issue would not exist...it's the large difference in front vs rear that caused the problem?

[CamaroDreams07]

I can't believe you found a tire shop who would install those. They should've told you that you'd run into those problems, it's commonly known on these cars.

[11TexaSS]

Yup, I believe if the difference between tires is more then .5 the computer senses the difference and thinks your spinning out. Your difference is probably about 2.1. Simply put, your rears are 2.1 inches taller then the front. .5 is the limit. You're probably gonna need to change your tires to within that limit and your problem should be fixed.
I'm learning too so I could be wrong but think that's it.

[Scalded Dog]

I appreciate the heads up, too... wouldn't have considered the staggered setup to have the potential to confuse the almighty computer... gotta keep this stuff in mind (back in the day, the cars I drove had muscle, and a rear bumper a foot higher in elevation than the front, thanks to some skyjackers and giant rear tires!).

Hey, here's your solution... light those rears up, maybe even powerbrake for a while... eventually, you'll wear off enough rear tread to match the circumference of the fronts!

"But officer, it's a repair I'm performing!"

[bannonm]

The height of your tires must be nearly the same as pointed out earlier. The way to properly check how much the difference would be is look for the revolutions per mile in the tire specs. Divide the front and back and the difference has to be less than 5% I believe or you'll start throwing errors.

Just had this discussing two days ago with a guy at the shop i work with that ran into the same issue on his Camaro. He decided to attempt a wheel and tire fitment on this own with custom wheels and screwed himself.

[BlueSteele]

Here are the pics. As for the tire shop not knowing, well, they did tell me up front it might set off the speed sensors but said the dealer should be able to calibrate it. The tires are 100Y weight rated so that was what they were most concerned with.

Anyway, here are some pics for you Rangore:

[Rangore]

Thanks BlueSteele...you have done me a great service.