On This Date: In 1904 the First Isle of Man Tourist Trophy Race

BUT, it was with automobiles. The "Royal Automobile Club Tourist Trophy," as it was called then, featured GT-type cars. That was the start which shortly thereafter led to motorcycles racing at the event - and they have ever since (with a few years off during the War). So, Happy 105th Birthday, Isle of Man TT!

http://tinyurl.com/kl6hl2

P.S. So, it's not exactly official, but it was the start of the tradition...