s10 front tires

what is the largest diameter tire that can be run on the front of an s10 without having to modify the fire wall?

I'm running a 18 x 8 front 20 x 9 rear with Nitto Extreme 215/35/18 front 255/35/20 rear. Lays frame but tires with rub slightly on the passenger side when draggin.

a 225/40/18 doesnt hit firewall either