The ACU had insisted on a minimum of 30 entries for each race before agreeing to a resumption of the TT in 1920, and decided to introduce a new Lightweight class for 250 cc machines, which would be incorporated within the Junior race.
The Mountain Circuit was extended to its current length of 37 3/4 miles, with the riders turning left at Cronk-ny-Mona, and taking in Signpost, Bedstead and Governor's Bridge before reaching the new start-and-finish area, just a few yards down the road from the present grandstand.
Nineteen Junior and just four Lightweight machines shattered the post-war depression as they continued the TT story after the enforced six-year lay-off.
The 1914 winner, Eric Williams, soon established a new Junior lap record of 51.36 mph, but retired with mechanical failure. Cyril Williams, riding a similar machine, took up the challenge and built up an impressive 20-minute lead before hitting severe transmission problems at Keppel Gate, four miles from the finish.
A combination of freewheeling and pushing brought the exhausted Williams to the line for a well-earned victory over the Blackburne of Watson-Bourne. His winning margin was still nine minutes, but the outcome could have been very different. Veteran campaigner R. O. Clark, riding a Lightweight Levis, crashed just before Keppel Gate on the last lap and had to nurse his machine home. He eventually finished fourth (first in the Lightweight class). Had it not been for the accident, he could easily have won the Junior overall, but how many times has that been said in the history of the TT races.
The six-lap Senior was not so dramatic, with just four factory teams (Sunbeam, AJS, Indian and Norton) in the 31-strong entry.
Local man Dougie Brown took over on his Norton, but was overhauled by the eventual winner, Tommy de la Hay, riding another Sunbeam. De la Hay and Brown, who was second, became the first riders to average over 50 mph for a complete race.