tire diameter difference
Thread Starter
Cruising
Joined: Mar 2014
Posts: 11
Likes: 0
From: Valparaiso indiana
tire diameter difference
what is the greatest difference in diameter you can go from front to rear and not have issues with the AH on a c6? some places on here I am seeing 1.1-1.2 inches is the highest, and somebody else said between 1-1.5 inch difference.
Le Mans Master
Joined: Sep 2004
Posts: 5,118
Likes: 122
From: Madison (Huntsville) Alabama
CI 6-7-8 Veteran
St. Jude Donor '09
I've never seen wheels or tires sold in tenths-on-an-inch diameter increments; they all are in whole inches to the best of my knowledge.
Burning Brakes
Joined: Jul 2013
Posts: 823
Likes: 7
From: Rosewood Heights IL
^^ wow....really? There is a difference in sidewall height.
Overall tire diameter is different than wheel diameter. The rear tire diameter must be 1.04" larger than the front. So no matter what size the front is, the rear tire must be that much bigger.
Every tire manufacturer is different for a given size. Example: Pirelli 305/30-19 may be slightly bigger or smaller than a Michelin 305/30-19. So compare all brands for the specific info and make sure the rear is 1.04 bigger.
Failure to maintain that difference will result in Active Handling problems at speeds near 100mph because of the difference in tire speed.
Overall tire diameter is different than wheel diameter. The rear tire diameter must be 1.04" larger than the front. So no matter what size the front is, the rear tire must be that much bigger.
Every tire manufacturer is different for a given size. Example: Pirelli 305/30-19 may be slightly bigger or smaller than a Michelin 305/30-19. So compare all brands for the specific info and make sure the rear is 1.04 bigger.
Failure to maintain that difference will result in Active Handling problems at speeds near 100mph because of the difference in tire speed.
Burning Brakes
Joined: Jun 2013
Posts: 867
Likes: 26
From: SW Ohio
GS are equipped with 18"/19" with 275/35 and 325/30 profile specs F/R. Z06/ZR1 come with 19"/20" but with lower profile specs (30/25). Your best measure of whether a tire combo is comparable to OE would be circumference or revs/mile. Data can be found on the TireRack site in the Specs page. I would guess that as long as you keep the F:R circumference delta to within a percent or two of stock, the TC nannies wouldn't get too riled up. At a minimum, you can figure that the TC MUST be able to account for a change in tire circumference related to max vs min tread depth--somewhere on the order of 7/32" to 9/32" delta--over the life of a tire.
Le Mans Master
Joined: Aug 2006
Posts: 5,292
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From: San Antonio, TX
Either way the gap is still the 1".
Race Director
Joined: Mar 2005
Posts: 10,399
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From: Austin Texas
I don't know what the maximum difference is. But C6 coupes come with 19" diameter wheels on the back, and 18" on the front. So it's set up for a 1-inch delta. I'm fairly certain GS's are 19" front, 20" rear.
I've never seen wheels or tires sold in tenths-on-an-inch diameter increments; they all are in whole inches to the best of my knowledge.
I've never seen wheels or tires sold in tenths-on-an-inch diameter increments; they all are in whole inches to the best of my knowledge.
There's a huge range of tire diameters (by playing with the width and aspect) that will fit either 18" or 19" wheels.
Racer
Joined: Feb 2014
Posts: 304
Likes: 19
From: Valley AL
I would think I could get by with the rear being 1.7" more but not sure about the 2.2" more.
What is everyones opinion on this? Thanks
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Race Director
Joined: Mar 2005
Posts: 10,399
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From: Austin Texas
Bear in mind that the diameter given on the various sites IS NOT a measured diameter. It's calculated from the dimensions given by the manufacturer and those dimensions vary a lot. Seem like every tire manufacturer has their own ruler scale and their own % scale for aspect ratio.
A 285/35/19 tire from one manufacturer will not measure the same as a 285/35/19 from a different manufacturer.
A 285/35/19 tire from one manufacturer will not measure the same as a 285/35/19 from a different manufacturer.
Le Mans Master
Joined: Nov 2007
Posts: 6,413
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From: Wilkes-Barre Pa
CF Senior Member
Joined: Feb 2006
Posts: 23,313
Likes: 25
From: Tucson Arizona
I've often read where different diameter tires (front vs. rear) could at a certain point cause problems. Being an avid road racer my friends and I often experiment with different brand (and size) track tires. Virtually all serious Corvette road racers use 18" wheels all-around...usually 11" x 18" wheels on the front and 12" or 13" x 18" wheels on the rear. The difference in diameter of tires (front to rear) can vary greatly from only 0.1" with Hoosier R100 racing slicks to 1.4" with Kumho 710 track tires.
Just FWIW....my friend used to use a combination of Michelin racing slicks that had a 2.2" difference in diameter from front to rear. When I asked if he had any 'computer' or ABS issues with that great of a difference he said "No problems whatsoever." I was somewhat surprised he could get away with such a great variance but evidently it worked out well for him.
Just FWIW....my friend used to use a combination of Michelin racing slicks that had a 2.2" difference in diameter from front to rear. When I asked if he had any 'computer' or ABS issues with that great of a difference he said "No problems whatsoever." I was somewhat surprised he could get away with such a great variance but evidently it worked out well for him.
Safety Car
Joined: May 2011
Posts: 3,807
Likes: 508
From: Oshawa, Ontario
M/T Drag Radial II
On my 2008 Corvette the front Bridgestone 245-40R 1897W tire dia. is 25.7" my rear GoodYear P285-35 ZR19 tire dia. is 26.9".the dia. is 1.2" more on the rear.I am thinking about going to a Nitto Drag Radial with a dia. of 27.44" the rear tire dia. then will be 1.7" more.I would really like to go with the M/T Drag Radial with a dia. of 27.9" which will be 2.2" more.
I would think I could get by with the rear being 1.7" more but not sure about the 2.2" more.
What is everyones opinion on this? Thanks
I would think I could get by with the rear being 1.7" more but not sure about the 2.2" more.
What is everyones opinion on this? Thanks
Racer
Joined: Feb 2014
Posts: 304
Likes: 19
From: Valley AL
PS and thanks to 08kody88 I hope you did not mind me asking a few questions on your post.
Race Director
Joined: Oct 2007
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From: Edgewood Washington
St. Jude Donor '11-'12-'13-'14-'15
For street/road course use the anecdotal evidence posted in the past suggests that if you are within about 6% of the OEM front-to-rear tire diameter relationship, you should not have any AH intervention issues.
I am not a drag racer, but on the strip wouldn't you turn all the nannies off, allowing you run pretty much whatever tire combo you wanted, within reason?
I am not a drag racer, but on the strip wouldn't you turn all the nannies off, allowing you run pretty much whatever tire combo you wanted, within reason?
Race Director
Joined: Mar 2005
Posts: 10,399
Likes: 25
From: Austin Texas
I've always used this to compare https://www.1010tires.com/Tools/Tire-Size-Calculator
Race Director
Joined: Sep 2007
Posts: 16,557
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From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
For street/road course use the anecdotal evidence posted in the past suggests that if you are within about 6% of the OEM front-to-rear tire diameter relationship, you should not have any AH intervention issues.
I am not a drag racer, but on the strip wouldn't you turn all the nannies off, allowing you run pretty much whatever tire combo you wanted, within reason?
I am not a drag racer, but on the strip wouldn't you turn all the nannies off, allowing you run pretty much whatever tire combo you wanted, within reason?
Most C6 guys run smaller diameter rear tires than front at the track.
Racer
Joined: Feb 2014
Posts: 304
Likes: 19
From: Valley AL
I am not planning on running mind at the track but maybe once are twice just to see what it will run,but the Drag Radial might be the only choice on getting a tire that will come close to holding mine.More than likely that is the same thing 08kody88 is looking for.
With the Traction Control on it is useless it's like not having it on should I turn it off to keep from hurting anything?
Which of the two does everyone thinks will be best the M/T or Nitto?
Le Mans Master
Joined: Feb 2007
Posts: 8,514
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From: Currently somewhere in IL,IN,KY,TN,MO,AR,MS,AL, or FL
What seems to be getting totally lost here is that it isn't the exact tire diameter measurement difference but the ratio that is important. The stock ratio is about 4.7% larger in the rear or 1.2". But if you were to go crazy and double the size of the front then you would need a rear that was 2.4 inches larger. That should keep the TC happy but the AH might still complain in turns. And TC might decide there was an issue during turns under power so...
And it is the actually running diameter and not the off the car measurement so tire pressure can make a difference.
None of this actually answers the real question which was (should have been) what is the allowable range of ratios of tire diameters between front and rear. Knowing something about controls, however, I would GUESS that you should be safe between equal and the rear being 10% larger.
And it is the actually running diameter and not the off the car measurement so tire pressure can make a difference.
None of this actually answers the real question which was (should have been) what is the allowable range of ratios of tire diameters between front and rear. Knowing something about controls, however, I would GUESS that you should be safe between equal and the rear being 10% larger.
