The course was shaved with specially adapted road equipment and the 13-mile stretch was really as smooth as any surface could be. In fact, among experts, the course at Bonneville Salt Flats is considered the best for speed trials of any in the world, so far as surface is concerned.
What the instrument board on the Thunderbolt looked like, carrying the following devices:
The first official attempt was made by Captain Eyston on August 24th. On his North run he turned 345.15 m.p.h. On the South run the timer failed to register. Reflected light from the very white salt was such that it prevented the sensitive eye from registering the fleet passage of the car.
Mr. H.T. Plumb, one of the nation’s foremost authorities on light, and district engineer for the General Electric Company was called in. He made certain recommendations and following that a black strip was painted on the salt at the location of the eye. Black boards were put behind the light source and a black strip was painted on the car. This corrected the timing difficulties.
On August 27th the Captain tried again. On his North run he turned 347.49 m.p.h. and on the South run he turned 343.51 m.p.h. This gave him an average of 345.49 m.p.h. and increased the old record by a little over 32 m.p.h.
Then on Tuesday morning, August 30th, John Cobb made a trial. No figures were released to the public, but expert observers estimated that he had traveled about 325 m.p.h. He announced that after making some changes he would try again.
At that point the weather stepped in and rain prevented another trial until September 12th.
The salt beds are approximately 45 miles long and are from about 25 to 40 miles in width. The thickness of the salt varies considerably, the deposit resting upon the undulations of an old ocean bed. Rain falling on the beds soaks into and through the salt to the mud flats below. Each day, after the rains are over, the sun draws a percentage of this moisture to the surface. Around noon many parts of the beds are covered with a brine. As the sun moves on the moisture that has not been absorbed into the air works back into the salt. But in the process, salt from the brine forms a deposit in weird designs over the flats. Locally this is spoken of as “bloom.”
This action goes on even in fair weather and that is why the course must be worked every day with drags and occasionally scraped. Following rains the amount of work necessary for a good course is increased and thus the long delay until September 12th before Cobb was able to run again.
That time his first run was South and he turned 341.25 m.p.h. On the run North he turned 343.8 m.p.h., or an average of 342.5 m.p.h. He missed by approximately 3 m.p.h. and possibly that is the only figure out of most that came from the salt beds that the ordinary laymen could understand. But even when thinking of the lowly 3 m.p.h. it is doubtful if Mr. John Public stopped to realized that at that speed it represents but nine hundredths of a second on the watch. It takes the long Thunderbolt at 350 m.p.h. 1/16th of a second to pass before the eye. Thus Captain Eyston had beat John Cobb by slightly more than a length of the Thunderbolt. It was a close struggle for world supremacy and little wonder the experts, accustomed to thinking in small fractions of time, high speeds, and who fought so valiantly to add even one mile per hour to the speed of either car, should thrill at this “battle of the century.”
Another interesting factor at this stage was that the above run was made with the highest wind of the trial, a velocity of 5 m.p.h. The wind was on his tail during the North run.
Then on September 15th Cobb made another attempt and set the average of 350.2 m.p.h. It was a new record and he was the champion of the world.