Rigga, you seem to have fallen into a common trap, which is to take the probability of something happening and then apply the worst severity to it to generate a risk.
If this was an aircraft with a large number of mainwheels (B52 or similar?), then the probability of a single tyre failing on landing may indeed be high, but the probable severity of that is unlikely to be a fatal accident. Of course you should consider the situation where a failing tyre does somehow result in a fatal accident, but the likelihood of that occurring will be much more remote. You will then have 2 risk factors, both of which would be closer to the real risk. IIRC, a fatal accident is always classed Catastrophic (happy to be corrected though), so anything higher than a Remote probability in this case would lead to the risk classification of A – Unacceptable. This would seem to rather overstate the actual risk of a single tyre failing on something like B-52 causing a fatal accident. That’s not to say it can’t happen (Concorde?), but that it is very unlikely.