So then , soften the gear and go with the taller tire, 60ft does not mean crap as long as its consistent, and throw some blower at it till the et is where you want it. Make laps and log all info like track condition ,time ,temp, alt, humidity,car peramiters,so as to have all the info one needs to dial in properly.
Dial-in or Index is all about consistency and equipment need not be the latest go-fast thing-a-gobob.