Need Definitive Y/N - Tire diameter diff F/R - Computer Issues?
Thread Starter
Melting Slicks
Joined: Sep 1999
Posts: 2,305
Likes: 86
From: Richmond, BC, Canada
Need Definitive Y/N - Tire diameter diff F/R - Computer Issues?
We know the front and rear tires have a diameter difference.
I have "heard" that the difference in diameter is monitored (via revolutions) by the computer,
AND,
If that difference is NOT within certain minimum/maximum,
it will put the vehicle into "limp" mode.
But I have never actually heard of any person who has experienced this.
I would like a definitive Yes or No that this does happen.
And, if so, what are those minimum and maximum values.
I have "heard" that the difference in diameter is monitored (via revolutions) by the computer,
AND,
If that difference is NOT within certain minimum/maximum,
it will put the vehicle into "limp" mode.
But I have never actually heard of any person who has experienced this.
I would like a definitive Yes or No that this does happen.
And, if so, what are those minimum and maximum values.
Instructor
Joined: Nov 2014
Posts: 114
Likes: 3
From: Mandeville Louisiana
I recently put 305/35/20's on the rear of my car and yes, the car goes into a sort of "limp" mode, but it's not what you think. The car still has all of the engine power, although you lose all of you traction and stability control, along with the steering becoming extremely stiff as if not having power steering. As far as the percentage difference you're looking for I have no idea, but I also know that if you change the tire size and this happens that you can bring your vehicle to the dealer and they will recalibrate it for the new tire size. Hope this helps.
PS, I do not recommend the use of 305/35/20 tires due to rubbing issues.
PS, I do not recommend the use of 305/35/20 tires due to rubbing issues.
Dazed Confused & Verklemp
Joined: May 2008
Posts: 1,392
Likes: 106
From: Naples, FL & Clear Lake, IA
The key is to keep the ratio of tire size between fronts and rears close to the same. So if you raise the diameter of the rears by .5 you need to raise the fronts by close to the same... maybe .45.. all relative to the original diameter comparison.
Thread Starter
Melting Slicks
Joined: Sep 1999
Posts: 2,305
Likes: 86
From: Richmond, BC, Canada
EcoBrick Bob,
Sorry... not true.
I have installed (for the time being) 265/35/19 front and 285/35/20 rears,
for a diameter difference of 1.4"
No discernible difference in any performance.
Sorry... not true.
I have installed (for the time being) 265/35/19 front and 285/35/20 rears,
for a diameter difference of 1.4"
No discernible difference in any performance.
Safety Car
Joined: May 2000
Posts: 4,808
Likes: 344
From: Albuquerque NM
People have said the same thing about the C5 and the C6, that you have to keep the rears taller than the fronts. I found that not to be the case. I ran tires that were the same diameter, front and rear, for years with no computer glitches. I suspect the C7 will prove to be the same.
Heel & Toe
Joined: Feb 2015
Posts: 16
Likes: 0
I don't have actual experience with the C7 yet, still on the stock tires.
But I have a 2013 ZL1 Camaro that that has raced on 6 different tire sizes including drag racing with various drag radials and not matching fronts. My experience with the Camaro comes to this. You can vary stock ratio about 1 inch without throwing the stabilitrac code. Since the C7 has a 0.7 inch difference from front to rear that would come to roughly you could run a front about 1.7 inches shorter to about 0.3 inches taller than the rear without electronic issues. Haven't actually tested it on the stingray but what Dangerous Don describes is exactly the response I get in the Camaro and usually drag race with no stability and a stiff power steering feel because I run taller drag radials for better times on my Camaro. I'm guessing he is running the 305 Pirelli p zero which would be about 2.6 taller than the front.
But I have a 2013 ZL1 Camaro that that has raced on 6 different tire sizes including drag racing with various drag radials and not matching fronts. My experience with the Camaro comes to this. You can vary stock ratio about 1 inch without throwing the stabilitrac code. Since the C7 has a 0.7 inch difference from front to rear that would come to roughly you could run a front about 1.7 inches shorter to about 0.3 inches taller than the rear without electronic issues. Haven't actually tested it on the stingray but what Dangerous Don describes is exactly the response I get in the Camaro and usually drag race with no stability and a stiff power steering feel because I run taller drag radials for better times on my Camaro. I'm guessing he is running the 305 Pirelli p zero which would be about 2.6 taller than the front.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 326
From: CA.
St. Jude Donor '13-'14-'15
You shouldn't notice any codes ABS or otherwise when altering the difference between the stock difference in heights between the front and rear---HOWEVER your ABS system will NOT be at 100% efficiency--- That is a hard thing to prove as the only time you will notice that the ABS is NOT working correctly is when you need it the most---on a panic hi-speed stop !!!! It's your life do what you like---But I would never gamble changing the stock height split regardless how much the car looks better with larger wheels--The "split" difference is built into the ABS controller and cannot be changed--
Safety Car
Joined: May 2000
Posts: 4,808
Likes: 344
From: Albuquerque NM
You shouldn't notice any codes ABS or otherwise when altering the difference between the stock difference in heights between the front and rear---HOWEVER your ABS system will NOT be at 100% efficiency--- That is a hard thing to prove as the only time you will notice that the ABS is NOT working correctly is when you need it the most---on a panic hi-speed stop !!!! It's your life do what you like---But I would never gamble changing the stock height split regardless how much the car looks better with larger wheels--The "split" difference is built into the ABS controller and cannot be changed--
Now the TCS is another matter. I know if you install too tall rear tires the TCS can intervene and ADD some throttle when it thinks the rears are slipping from throttle shut down.
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Heel & Toe
Joined: Feb 2015
Posts: 16
Likes: 0
You shouldn't notice any codes ABS or otherwise when altering the difference between the stock difference in heights between the front and rear---HOWEVER your ABS system will NOT be at 100% efficiency--- That is a hard thing to prove as the only time you will notice that the ABS is NOT working correctly is when you need it the most---on a panic hi-speed stop !!!! It's your life do what you like---But I would never gamble changing the stock height split regardless how much the car looks better with larger wheels--The "split" difference is built into the ABS controller and cannot be changed--
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 326
From: CA.
St. Jude Donor '13-'14-'15
How do you know the ABS is set for the split? I believe the ABS operates independently, on each wheel, keeping each wheel from locking, again, independently.
Now the TCS is another matter. I know if you install too tall rear tires the TCS can intervene and ADD some throttle when it thinks the rears are slipping from throttle shut down.
Now the TCS is another matter. I know if you install too tall rear tires the TCS can intervene and ADD some throttle when it thinks the rears are slipping from throttle shut down.
Safety Car
Joined: May 2000
Posts: 4,808
Likes: 344
From: Albuquerque NM
The ABS and TC both use wheel speed sensors for input to control various functions--- The ABS system uses the wheel speed sensors from keeping the tires from skidding on a hard stop--The TC uses the wheel speed sensors from keeping the tires from spinning on a hard launch---So both are affected by altering the stock split of 1" from rear heights to front--- as I said you can do whatever you like--But it has been my experience that the TC issue is no bid deal--however the ABS issue may save your life---
Heel & Toe
Joined: Feb 2015
Posts: 16
Likes: 0
Running tires of significant size differences from stock will not affect Engine performance or ABS. They both work fine. After you roll about 50 feet it gives a stabilitrac warning and then says stbilitrac disabled, then you get a power steering warning. The power steering system continues to function but at reduced boost.
Thread Starter
Melting Slicks
Joined: Sep 1999
Posts: 2,305
Likes: 86
From: Richmond, BC, Canada
And this is why I'd like a DEFINITIVE Answer from someone at GM.
We are getting all sorts of answers here.... many in conflict with one another,
based on experience and/or heresay.
We are getting all sorts of answers here.... many in conflict with one another,
based on experience and/or heresay.