Complex sentence: Both the 2009 Triumph Thunderbird and the "Donington" Norton Commando 961 are 270 ° designs, and arguably, the 270 ° crank is becoming the optimum configuration for large parallel-twins.
Split into simpler sentences: Both the 2009 Triumph Thunderbird and the "Donington" Norton Commando 961 are 270 ° designs. Arguably, the 270 ° crank is becoming the optimum configuration for large parallel-twins.