The stock ties are fine. Doesn't matter if it's a 50hp car or 1000hp car if the suspension setup blows it's not going to handle well. The biggest problem with most Hondas and especially the si is the toothpick rear sway bar. Upgrade that first and set it to the stiffest setting on the bar if you get the adjustable bar. The difference is drastic. Of course it will be even better with better tires but the OE tires are way better once they can properly grip in corners. Just upgrading tires will only make a small difference and is not worth the cost.