i have a 98 svt and i have 18in konig toxxins on it. i have 215/35's on right now. but i want to put like a 225/35 or a 225/40 or a 215/40. i know the 215/40 will work. but my car has eibachs on it. i also need to know what is the best autocross tire of 18's. my falken's just aren't working??

98 svt t-red
kkm,bassani cat-back, superchip,pulley,B&M,18" konig toxxins w/ 215/35zr18 falkens, stock rims with 215/45 falken azenis for auto-x,limo tint, 3-12" alpine type S's and a A6001 xtant amp,XM radio,alpine cd,xtant a4004,alpine type R 5 1/4 components up front,boston acoustics highs out back, eibachs, kyb gr2's,sub frames,bat high flow y-pipe, street glow underbody (red)
new-quaife,grizzley clutch and fidanza flywheel-plans to come nitrous,stut bar