Having worked in the urethane casting industry I can tell you that durometer readings are not directly related to grip. Case I point: Many race tires are harder at cooler ambient temperatures than street tires, yet they get considerably gripper when brought up to temperature. Yes, they get softer, but that is when they are heated by warmers or use. So checking durometer readings of various tires at ambient temps is of no value. By the way, you do know that the A13 is a multi compound tire right? So where you take your durometer readings would make a difference in the result.
As for the A13 SPs I am using them on my endurance bike. They work ok, but they aren't as good as the Pirelli Supercorsas. We are winning on the A13s but if the competition got tougher I'd go to the Pirellis in a heartbeat. They are a more confidence inspiring tire for me. And absolutely no need to run the 150 width on a 250. 140 works great.
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