Tire Size Change - '14 C7 Z51
 

Hey,

Looking to get some better tires for street class SCCA autocross this year on the '14 Z51 Stingray. Considering running 255/35/19 Bridgestone RE71R fronts because I have seen those as the most competitive tire thus far available for the Stingray, but I am struggling with finding a good rear tire because of the 20" wheel size.

I am leaning toward running the 305/35/20 Hankook R-S3 V2 on the rear to get some more meat back there, but am unsure if I will experience either loss of performance due to the added height of the tire or due to potentially putting too much width on too narrow of a wheel.

Further reading has lead me to conclude that changing the ratio of tire diameter front to rear may mess with the computer systems in the C7, most specifically the PTM functionality and the stability control items. While I kill most or all of these systems while on the track, it would be a shame to have to kill them for street utilization or experience the vehicle going into a limp mode. I have made the following chart of the ratios on the tire sets I am interested in using:

STOCK

ratio 1.027131

25.8" front diameter
26.5" rear diameter

.7 difference, 2.7131% diameter different front to rear

RE71R

255/35/19
26" diameter
ratio w/ 285 -> 1.073076 (7.3076%)
ratio w/ 305 -> 1.096153 (9.6153%)

245/40/19
26.7" diameter
ratio w/ 285 -> 1.044943 (4.4943%)
ratio w/ 305 -> 1.067415 (6.7514%)

R-S3 V2

285/35/20
27.9" diameter

305/35/20
28.5" diameter

I am concerned that the larger ratio of diameter in going to wider rubber in the rear may have negative implications from ranging from slight computer interference to full blown limp mode dependent on how drastic the ratio is. Any feedback?

Khumo has just released a new tire that may be worth taking a look at. One of my sons has just put a set on his BMW M3. I don't know the name of it off hand...