Modern Triumph Bonneville and Thruxton parallel-Twins are cooled by both air and oil. As such, they are fitted at the factory with a supplemental oil radiator of, ahem, questionable appearance. Here’s a more-attractive, less-complex and an even-better-functioning option: the In-Frame Oil Cooler ($849; $749 with core exchange). Oil circulates through a replacement 4130-chromoly subframe, which, [...]