Duesenbergs Model X are very rare. It was a sportier version of the model A with a heavier and longer (136 in (3,500 mm) wheelbase) chassis and 100 hp (75 kW) engine that enabled it to reach 100 mph (161 km/h).
The most notable differences between the A and X were that the latter had hypoid differentials and all its valves were on one side; it sported the hydraulic brakes that Fred had originated on his 1914 racing cars.
This braking system could have earned him a fortune if he had obtained a patent.
According to Randy Ema, the top Duesenberg authority in the United States, only 13 were built. They fit in between the Duesenberg Model A and the famous J.
Only four were known to survive until comedian Jay Leno found a fifth X in a neighborhood garage in 2005.