yes, a 215/50 will FIT, but I think a 205/55 will fit better...people have gone up to 225 on the stock s14 rims, but I don't think that is a good idea at all.
I'm using and am very happy with falken azenis in 205/55/16 (about 85 each, lasted me about a year)
I've heard a few things about kumho MX tires, but don't really know anything about them...maybe someone else will reply on those.
kumho ecsta supra 712's last seemingly forever (compared to my falkens atleast...200 treadwear vs 320 or so) but are as hard as a rock, stay away.
Its nice to have matching tires front and rear for better balance, but if i had to change it up, i'd put the sticker ones up front...most will agree that understeer is much more scary than over.
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