|From Cycle World Nov. 1967. The date appears to be wrong.
In Kenzo Tadas own words- from a 1972 interview...
I began as a bicycle racer, and started that at the end of the Russo-Japanese War, in 1905. That first race was once around Shinobazu pond in Ueno Park, Tokyo, which was a 3 mile course, as the pond was bigger at that time. I was 18 years old and the prize was half a dozen beer glasses... Afterwards I trained for the Komiyama race as an apprentice, like a young sumo wrestler. I rode bicycles imported from America by the Ishikawa company in Yokohama. I joined their racing team in 1907. The pace car at that race was a Triumph motorcycle. Most bicycles were imported then and the Ishikawa company brought in American Pierce and British Triumph bicycles... I rode in a 250 mile bicycle race on 30 June 1907 and I won... In those days various stages of the race were reported by telegram to the finish line. I won several races after that and was reported on widely in the press. I was paid 3 yen per month by the Ishikawa company and I raced 3, 5 and 10 mile races. 10 miles races were the main event and if I won I was paid 10 yen and 5 yen for shorter races. I moved up to racing motorcyels in about 1921. In the the Taisho era I went to see the races at the Nakayama racecourse. I bought a Triumph motorcycle which cost about a 1000 to 1200 yen whereas a bicycle was only 120 to 170 yen. I managed a bicycle shop then whch made its own brand, Mates (as in "friends"), and sold it there on the premises. Later this brand became Shinbashi Bicycles. I raced again in 1924 but I got no prize money in that amateur race, only a trophy. At that time there were only about 20 motorcyle racers in the whole country.
I read three British motorcycle magazines all the time, Motorcycle, Cycling and Motorcycling and therein learned about the Isle of Man TT (Tourist Trophy) race. That was the age of ships, not of airplanes so I went to Korea, Harbin and then travelled to Europe by rail in the spring of 1930. From Paris I went to Dover and it took about 40 days in all to reach Man in May. I practised for a month for the race which was scheduled for June. I rode a British 350 Velocette motorcycle on the 420 km asphalt course. A racer on a Norton came in first place that year while I finished 15th and received a trophy... I had some western clothes but at the prize reception photo shoot I wore a Japanese haori (half coat), hakama (traditional loose fitting trousers), white tabi (socks) and felt zori (sandals). I went home via the Mediterranean sea, through the Suez canal to Singapore and then to Hong Kong before arriving home in Japan after a 41 day trip. Mine was the first overseas racing expedition to be completed and it it linked the racing community of Japan with the rest of the racing world.
From Japan's Motorcycle Wars by Jeffery Alexander, published by the UBC Press 2008
and more info here.