Taller Tires & Cruise Control

[Ken H.]

Does your car have adaptive cruise control?

Also, may be difference in DH HP vs GT vs GT PP. The non-DH HP wheels/tires may be taller so that 285/35/20s are closer to stock

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[Ken H.]

Since there is some mention that there hasn't been any feedback, I figured I’d share some real world feedback for anyone considering a taller tire setup on a GT PP car with adaptive cruise.

I’ve got a '24 GT PP with adaptive cruise, and a little over two years ago I moved away from the stock PP wheel/tire setup. I’m currently running:

• Rear: 315/35R20
• Front: 275/35R20

I did not change anything in Forscan or adjust tire size settings in any module. Just bolted them on and been rolling ever since.

For context, I use adaptive cruise all the time. Both on highway trips and daily driving. In 2+ years and about 38K miles, I’ve had zero issues. No warning lights, no weird cruise behavior, no ABS complaints, nothing noticeable in drivability.

I was actually planning to go in and update the tire size with Forscan this afternoon just to make everything technically “correct.” My Windows laptop is currently out of commission, so I needed to load Windows onto my MacBook Pro first before diving in. Life got busy… and honestly, since everything has been working flawlessly, it hasn’t felt urgent.

Thanks for that info. I’m not sure how your new setup compares to your GT PP stock setup. Good to know someone isn’t having trouble.

 

[Ken H.]

If you wouldn’t mind the hassle… perhaps you could try mixing the stock fronts and aftermarket rears and see if the problem exists? Not as a permanent solution obviously but just to see whether it is the fronts or rears that cause the issue.

Now that’s what I’m talking about. Great idea. That’s why I turn to you guys. I’ve been racking my brain & didn’t think of that.
Still 2 issues that I’ll have to work around.
1. The stock rears in the garage are Trofeo RS’s & too cold right now to try them
2. May have to get a dealer reset with the stock rears on to see if will take. Would not reset with the 20’s on before with 285/35/20 (now has 285/30/20 & haven’t tried dealer reset due to salted roads)
If it resets with the stock rears, then I just need to new rear A/S Michelins to match that diameter.
BRILLIANT! I have a plan.

 

[Ken H.]

Now that’s what I’m talking about. Great idea. That’s why I turn to you guys. I’ve been racking my brain & didn’t think of that.
Still 2 issues that I’ll have to work around.
1. The stock rears in the garage are Trofeo RS’s & too cold right now to try them
2. May have to get a dealer reset with the stock rears on to see if will take. Would not reset with the 20’s on before with 285/35/20 (now has 285/30/20 & haven’t tried dealer reset due to salted roads)
If it resets with the stock rears, then I just need to new rear A/S Michelins to match that diameter.
BRILLIANT! I have a plan.

Wouldn’t reset with
285/35/30 front
305/35/20 rear
Still has 305/35/20’s on the rear
285/30/30’s on front
Clarification

 

[MidwayJ]

Since there is some mention that there hasn't been any feedback, I figured I’d share some real world feedback for anyone considering a taller tire setup on a GT PP car with adaptive cruise.

I’ve got a '24 GT PP with adaptive cruise, and a little over two years ago I moved away from the stock PP wheel/tire setup. I’m currently running:

• Rear: 315/35R20
• Front: 275/35R20

I did not change anything in Forscan or adjust tire size settings in any module. Just bolted them on and been rolling ever since.

For context, I use adaptive cruise all the time. Both on highway trips and daily driving. In 2+ years and about 38K miles, I’ve had zero issues. No warning lights, no weird cruise behavior, no ABS complaints, nothing noticeable in drivability.

I was actually planning to go in and update the tire size with Forscan this afternoon just to make everything technically “correct.” My Windows laptop is currently out of commission, so I needed to load Windows onto my MacBook Pro first before diving in. Life got busy… and honestly, since everything has been working flawlessly, it hasn’t felt urgent.

That's good to know you aren't having issues. The diameter changes were greater for @Ken H. with his DH handling pkg setup, so maybe you are below the threshold.

 

[Dark Sprite]

Wouldn’t reset with
285/35/30 front
305/35/20 rear
Still has 305/35/20’s on the rear
285/30/30’s on front
Clarification

Would love to see the look of those R30 fronts

 

[mp390]

When I was sorting out new wheels and different tire sizes, a friend warned me that the diameter of the front wheel should always be smaller than or equal to the rear one. Apparently this used to be an issue on the BMW E46, where it caused problems with ABS and ESP. He said it’s important to keep the ratio of front‑to‑rear wheel close to the factory setup.

Tomorrow I’m switching from 255/40 R19 and 275/40 R19 to 275/35 R19 and 295/35 R19, so I’ll let you know if anything happens with the cruise control. According to the calculators, the new wheel sizes are smaller than the stock setup, the ratio between the axles stays the same as from the factory, and the car will sit 6 mm lower at the front and 6 mm lower at the rear. So the camera angle shouldn’t change.

 

[MidwayJ]

He said it’s important to keep the ratio of front‑to‑rear wheel close to the factory setup.

Factory setups vary in that regard. My performance package is like yours, 255/40 front, 275/40 rear, but many factory setups are square with the front and rear diameters the same. It would be interesting to know if the camera angles are actually calibrated differently at the factory for staggered setups. I want to switch to a square setup.

 

[mp390]

So, new wheels fitted and no problems with adaptive cruise control. It seems that the problem only occurs when the front wheels are larger in diameter than the stock ones.

 

[MidwayJ]

So, new wheels fitted and no problems with adaptive cruise control. It seems that the problem only occurs when the front wheels are larger in diameter than the stock ones.

Originally I wanted to go with either 20x10 or 19x10 square, but this has me thinking about 19x10 with 285/35 front and 19x11 with 305/35 rear.

I would have to live with the smaller selection of tires in 305/35, higher cost, and the inability to rotate. On the positive side, wider tires in back will look great.

 

[agreywolfe]

chiming in to complicate things more for yall: ive been running 20x10 fronts and 20x11 rears, 285/35 and 315/35 for over a year now upsized from my 19x9 and 19x9.5 255/40 and 275/40. roughly 1 inch larger all around, absolutely zero issues with cruise control, adaptive cruise, speed limiting, etc. your issues are probably electrical.

 

[Ken H.]

chiming in to complicate things more for yall: ive been running 20x10 fronts and 20x11 rears, 285/35 and 315/35 for over a year now upsized from my 19x9 and 19x9.5 255/40 and 275/40. roughly 1 inch larger all around, absolutely zero issues with cruise control, adaptive cruise, speed limiting, etc. your issues are probably electrical.

Do you ha

chiming in to complicate things more for yall: ive been running 20x10 fronts and 20x11 rears, 285/35 and 315/35 for over a year now upsized from my 19x9 and 19x9.5 255/40 and 275/40. roughly 1 inch larger all around, absolutely zero issues with cruise control, adaptive cruise, speed limiting, etc. your issues are probably electrical.

Why me, Lord. Now I’m totally confused. Off to the dealership. I’m off to see the wizard.

 

[ChitownStang]

chiming in to complicate things more for yall: ive been running 20x10 fronts and 20x11 rears, 285/35 and 315/35 for over a year now upsized from my 19x9 and 19x9.5 255/40 and 275/40. roughly 1 inch larger all around, absolutely zero issues with cruise control, adaptive cruise, speed limiting, etc. your issues are probably electrical.

Well that does throw a wrench in our theory… wtf

 

[Dark Sprite]

Could it be the angle the car sits at affect the forward facing adaptive cruise sensor? Perhaps if the car remains at the same angle (or within 1-2 degrees) post wheel/tyre change everything is fine… can someone work out using agreywolfe’s before and after diameters if there would have been any change?

 

[ChitownStang]

Ok, just got back from highway drive and I got cruise control and adaptive cruise control working. Normal mode with traction control on.
My custom mode is Sport with traction control off and this must of been the issue, not the taller tires.
I’m running 285/35r20 & 315/35r20
Mystery solved

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