Help 2002 Corvette
Thread Starter
Cruising
Joined: Sep 2011
Posts: 10
Likes: 0
From: Lathrop Ca
Help 2002 Corvette
I recently purchased this vehicle and it has a set of Z06 Wheels on the car except they are all 18 inch wheels. The tire size in the rear is a 295/30/R18 and the Front tires are 275/35/R18. I took the car into the dealership for the car shaking for a few seconds when I give it gas anywhere above 60 mph. After that few seconds it goes away. They told me that the owner before me put wrong size tires on the car which is why the car shakes. Has anyone had this issue before? Are these tires too big for the non Z06 Corvettes? Please let me know if you have any information.
Thanks Derrick
Thanks Derrick
Melting Slicks
Joined: Oct 2000
Posts: 2,491
Likes: 1
From: prescott AZ
That certainly is not the reason the car shakes!
Maybe the wheels are not true or the tires slipped a ply.
How many miles on this car?
Bushings, shocks or balance of tires can be a factor but not the size or 18: wheels all around.
I was thinking of putting 18" tires all around onn my C5 Z06 and my 2001. Do they stck out of the fender wells?
A photo would be appreciated.
I also agree alankb -- stay far, far away from that dealer.
Maybe the wheels are not true or the tires slipped a ply.
How many miles on this car?
Bushings, shocks or balance of tires can be a factor but not the size or 18: wheels all around.
I was thinking of putting 18" tires all around onn my C5 Z06 and my 2001. Do they stck out of the fender wells?
A photo would be appreciated.
I also agree alankb -- stay far, far away from that dealer.
Pro
Joined: Aug 2009
Posts: 537
Likes: 4
From: Roseville Ca.
Hey Derrick....good answers above, could be a bent rim or alignment as well. The idea of larger wheels making any kind of an affect like that is bs. A lot of people both here and that you saw at the Abels toy run have plus1 or plus2 sizing on their wheels. As stated above a good tire shop will usually determine the cause.
Safety Car
Joined: Apr 2004
Posts: 3,729
Likes: 10
From: Austin, Texas
OP, if you do in fact have 295-30-18's out back, you should really replace them with 295-35-18's to work properly with the size you are running on the front...
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 28
From: Van Buren Arkansas
Wounded Warrior Escort '11
Unless the wheel size was changed in the computer, the system will indeed cause problems with the AH and traction systems. People cannot just change the wheels and go on their merry way. The software was written in specific ways for specific reasons and the wheel size ratios were done for a specific reason...and no, I don't know the reason but I do understand the engineering of the supporting systems. The OP needs to see the programming of the computers first to determine if a change was made in there.
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Melting Slicks
Joined: Sep 2011
Posts: 2,252
Likes: 542
From: Appleton WI
I disagree with both of the above responses.
Are you certain the rear tire is 295/30-18??? Might it be 295/35-18???
If the tire sizes you stated are in fact what is on the car then there IS a problem that the tire sizing would be causing.
A general rule of thumb is that for C5's that have both AH and TC (all C5's 2001 and newer) the rear tire overall diameter should be at least 1/2" larger overall diameter than the front tire. The 295/30-18 is 25.0" OD. The 275/35-18 is 25.6". So your car has indeed got the wrong size (overall diameter) tire on it. The vibration that you are feeling is the AH trying to take control because the rear tires are spinning from it's point of view.
A 295/35-18 rear tire has an overall diameter of 26.1" so it would eliminate tha AH/TC issue.
Are you certain the rear tire is 295/30-18??? Might it be 295/35-18???
If the tire sizes you stated are in fact what is on the car then there IS a problem that the tire sizing would be causing.
A general rule of thumb is that for C5's that have both AH and TC (all C5's 2001 and newer) the rear tire overall diameter should be at least 1/2" larger overall diameter than the front tire. The 295/30-18 is 25.0" OD. The 275/35-18 is 25.6". So your car has indeed got the wrong size (overall diameter) tire on it. The vibration that you are feeling is the AH trying to take control because the rear tires are spinning from it's point of view.
A 295/35-18 rear tire has an overall diameter of 26.1" so it would eliminate tha AH/TC issue.
Last edited by 3sACROWD; Jan 25, 2012 at 10:03 AM. Reason: added clarification
Thread Starter
Cruising
Joined: Sep 2011
Posts: 10
Likes: 0
From: Lathrop Ca
The AH is active almost all the time according to the DIC. I can't confirm the car tire size until the morning because I need to go pick up the car from the shop in Stockton. I am going to try again with the AH off. Also I will take it by a tire shop and have them look at the tires. Any idea about tire shops in the Manteca area? One thing I notice that look fishy is the tire height for the front tire is a 35 while the back is a 30. I didn't think I will be able to rotate the tires because of how wide the back tires are. The back tire is a 295 and the front is a 275. Let me know if you have any other suggestions.
Thread Starter
Cruising
Joined: Sep 2011
Posts: 10
Likes: 0
From: Lathrop Ca
Can you change the tire size in the system AH system? If I went to a tire that was about a inch taller in the rear will it fix this issue. Why are the front tires taller then the rear tires?
C5 Corvette wheels Cast Aluminum
Front: 17 x 8.5 Tire size: P245/45ZR-17
Rear: 18 x 9.5 Tire size: P275/40ZR-18
Bolt pattern 5x4.75" (same as 5x120.65mm)
Front offset=58mm, Rear offset=65mm
C5 Corvette wheels Cast Aluminum
Front: 17 x 8.5 Tire size: P245/45ZR-17
Rear: 18 x 9.5 Tire size: P275/40ZR-18
Bolt pattern 5x4.75" (same as 5x120.65mm)
Front offset=58mm, Rear offset=65mm
Melting Slicks
Joined: Jun 2010
Posts: 2,809
Likes: 3
From: Yorktown Virginia
Unless the wheel size was changed in the computer, the system will indeed cause problems with the AH and traction systems. People cannot just change the wheels and go on their merry way. The software was written in specific ways for specific reasons and the wheel size ratios were done for a specific reason...and no, I don't know the reason but I do understand the engineering of the supporting systems. The OP needs to see the programming of the computers first to determine if a change was made in there.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 28
From: Van Buren Arkansas
Wounded Warrior Escort '11
I was thinking that you can change the tire sizes in there but I'm not positive. If not, then the OP is stuck with 17's and 18's, F and R...at least its that way for mine. The AH is looking at the wheel speed sensors and measuring the spin frequency as such. The AH expects certain spin results for the front vs the rear and when someone deliberately changes things as far as the wheel diameters, there's going to be problems.
Burning Brakes
Joined: Jul 2010
Posts: 835
Likes: 4
From: Los Angeles CA
For the tires specified by the OP, the front tire is 2.4% larger than the rear tire.
The OEM tires, which are 265/40/17 and 295/35/18, the rear tire is 3.0% larger than the front.
Generally, a 2.4% difference should be big enough to keep the computer happy, but I'm not sure how it feels when the bias is shifted from the back to the front. My guess would be that based on the fact the AH is constantly on, that this is the cause of the problem.
My suggestion is to turn of AH and see if it persists. If it does, than you know that it is most likely the tire size that is causing this issue. If the rear tire is changed to 295/35/18, the diameter difference will now shift to the rear tire being 2.4% larger than the front, which should be large enough to allow active handling to operate correctly.
Le Mans Master
Joined: Feb 2002
Posts: 6,937
Likes: 21
From: Waldorf MD
Looks like the Dealer was right ! You must have a minimum size difference (with rear being taller) for Traction Control and AH to function properly.Good catch 8VETTE7 !
Mrleeks, you won't believe the performance of your car once you get this fixed. I suspect the TC is "holding" the throttle back during your acceleration because it thinks your tires are spinning !
Last edited by Oldvetter; Jan 27, 2012 at 09:33 AM.
Melting Slicks
Joined: Mar 2008
Posts: 3,328
Likes: 40
From: Orangevale California
St. Jude Donor '10
I'm thinking these might be aftermarket Z06 replica wheels. Many of these were made in made in China and are pure junk. If they're garbage wheels, this could be the problem.
Take the wheels off and see what it says on the inner barrel. Should be some markings if they're Speedlines or Alcoas.
Regardless, you do need the proper tire stagger or you'll have computer issues.
Take the wheels off and see what it says on the inner barrel. Should be some markings if they're Speedlines or Alcoas.
Regardless, you do need the proper tire stagger or you'll have computer issues.
Thread Starter
Cruising
Joined: Sep 2011
Posts: 10
Likes: 0
From: Lathrop Ca
I turn off the AH and it fix the issue.
Wheels/Tires Stock Specs
Corvette
Front P245/45ZR-17 = 25.68
Rear: P275/40ZR-18 = 26.66
Z06
Front P265/40ZR-17 = 25.34
Rear P295/35ZR-18= 26.12
Here is my tire size and diameter of the tire with the wheels on my car.
Back 295/30/zr18 = 24.96
Front 275/35zr18= 25.57
This is what I think I am going to change to.
Front: 255/30zr18=24.02
Back: 295/30zr18=24.96
This will give it 3.9% difference from the front to back or I can go to
Front: 265/30zr18 24.25
Back: 295/30zr18=24.96
This will give me a difference of 3% from front to back. which do you guys believe will work best?
Wheels/Tires Stock Specs
Corvette
Front P245/45ZR-17 = 25.68
Rear: P275/40ZR-18 = 26.66
Z06
Front P265/40ZR-17 = 25.34
Rear P295/35ZR-18= 26.12
Here is my tire size and diameter of the tire with the wheels on my car.
Back 295/30/zr18 = 24.96
Front 275/35zr18= 25.57
This is what I think I am going to change to.
Front: 255/30zr18=24.02
Back: 295/30zr18=24.96
This will give it 3.9% difference from the front to back or I can go to
Front: 265/30zr18 24.25
Back: 295/30zr18=24.96
This will give me a difference of 3% from front to back. which do you guys believe will work best?
Last edited by Mrleeks; Jan 30, 2012 at 09:07 PM.
Le Mans Master
Joined: Feb 2003
Posts: 6,682
Likes: 144
From: Memphis Tennessee
If at all possible, contact the previous owner and ask the important questions. This could NOT be a new problem, rather one that has been going on for a while and not likely to be noticed in most test-drives.
If it is tires, it can be fixed. Even if it is the wheels, there are many lesser-expensive options to get her back to normal.
Be calm, you and us here on the Forum can get you through.
Good Luck
If it is tires, it can be fixed. Even if it is the wheels, there are many lesser-expensive options to get her back to normal.
Be calm, you and us here on the Forum can get you through.
Good Luck
