SHELBY GT 350 Member
Joined: Jan 2011
Location: Central Massachusetts
I really don't know what is going on but here are some thoughts:
255/40-19's are about 27.1" diameter; 305/35-20 are about 28.4 . . . that is about 5% change so it probably does need to be recalibrated (speedometer will read 5% low, if nothing else)
I don't understand how the system can automatically recallibrate, if nobody tells it that the tire diameter has changed . . . does it check speed versus GPS or something? If you reload the tune I would expect that it will just reload the old diameter, unless you change it in the parameters before loading. I would definitely update the tire diameter (actually revolutions/mile) and reload the tune, to make sure that is not the issue.
Can you tell if the light is traction control or stability control? Could be stability control because it thinks it is seeing a difference in speed between the front and rear tires?
| 2010 GT coupe | Daily Driver with some Steeda and GT500 take-off stuff for the occasional track day