I'm going to say harshness/stiffness on the ride are 80% RFT, the bottoming out is 75% suspension. You'll have to change them both out to realize the benefits.
I changed out my tires first and was pretty happy. Suspension a month later after taking a light sweeping corner on the freeway when I hit a deep pot hole at 65Km/h that almost flipped the f'n car over.
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