I feel this apparent recommendation could be misleading. The Michelin XWX (not XAS as stated) was built specially for the 6.9 and a Ferrari of the time. It is a V-rated tyre with immensely strong sidewalls to cope with the power and torque being transmitted. They are expensive, but for the full performance of a 6.9 W116, the only type suitable. Compromising with cheap tyres is not only potentially dangerous but could have implications with insurers.