Changing tire size
Thread Starter
Intermediate
Joined: Aug 2020
Posts: 29
Likes: 10
From: SE Pennsylvania
Changing tire size
I've read through some threads, and I'm sorry to ask yet again, but I see many answers to this. To avoid the active handling message, ratios need to stay the same. How far apart can the ratio be though? Stock size tires for z06, based on tire measurements on door jam, but with toyo r888r, fronts are 25.6" and rear 26.7". So if I go to 345 rears, 27.2", and stay with 25.6" fronts, will that trigger the active handling? I can't seem to find r888r in the 26.1" range to keep ratios even. I'm pretty set on the r888r but also would like to go to 345 rear AND use r888r for front as well.
Race Director
Joined: Sep 2007
Posts: 16,557
Likes: 2,106
From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
The simple method is a 1 to 1.04 ratio front to rear. However, to be more precise, you need to know the OEM tire diameter when new and when bald for both the front and rear. Then create a ratio using bald fronts and new rears along with a ratio of new fronts and bald rears. Obviously, you need to know the original tread depth for each tire. Those two ratios are the worst case that would still fit within the limits that GM programmed as acceptable. If your new tires fit within those same limits using the same worst case scenario, you're good to go. Otherwise, find the average ratio and limit the tire wear to stay inside of the worst case ratio.
Race Director
Joined: Mar 2011
Posts: 13,262
Likes: 3,150
From: SW Florida
2021 C6 of the Year Finalist - Modified
Right now, I have a set of 285/40 -17 (26.0" diameter) in front . . . And a set of 305/45 -17 (27.8" diameter) drag radials in the rear
That's a difference of 1.8" front to rear
No problem with the active handling or any of the nannies ... no warning lights
Attachment 48333851
That's a difference of 1.8" front to rear
No problem with the active handling or any of the nannies ... no warning lights
Attachment 48333851
Last edited by Turbo6TA; Oct 31, 2020 at 06:37 AM.
Thread Starter
Intermediate
Joined: Aug 2020
Posts: 29
Likes: 10
From: SE Pennsylvania
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,684
From: Southeast TX
My experience says you're more likely to get into traction control issues when your rears are too short compared to the fronts. 305/30 19's in the rear triggered traction control at the 3/4 shift when I tried running stock fronts. Got shorter fronts and all was good.
Instructor
Joined: Aug 2003
Posts: 249
Likes: 1
From: Round Rock TX
I've been running Nitto NT05 245/40R18 97W - Front, 305/35ZR19 120W - Rear. I occasionally get engine drag control on the display, but other than that I haven't had any issues.
They are worn out so I was checking this forum to see if there were any new favorite tires for my 2007 with 670 RWHP.
They are worn out so I was checking this forum to see if there were any new favorite tires for my 2007 with 670 RWHP.
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