How it unfolded
To mark the TT's fiftieth anniversary, the 1957 Senior race was extended from its usual seven laps to eight, about 486 km. The Scottish rider Bob McIntyre entered on Gilera's transverse four-cylinder machine, having already swept the Junior 350cc race days earlier. In the Senior he pushed the pace from the first lap and became the first rider ever to lap the Mountain Course at over 100 mph, with the record set at 101.12 mph. At the time the course had rough surfaces and poor sightlines over long stretches, so a 100 mph lap had long been considered physically out of reach. McIntyre completed the extended distance and finished the Junior-Senior double. The record stood for a decade. Later that year the Italian manufacturers, Gilera, Moto Guzzi and Moto Parilla among them, agreed to a joint Grand Prix withdrawal over rising costs, and McIntyre's ride became Gilera's last major achievement with its four-cylinder machine.
Why it still matters
The 100 mph lap broke a psychological limit the sport had set for itself, and became the reference point for every speed-record discussion since. It coincided with Gilera's withdrawal to mark the moment premier-class leadership passed to MV Agusta, the start of a seventeen-year single-manufacturer dominance.