The 1940 again saw major changes. Simplex continued to offer the direct drive model (pictured above), which was similar to the '39 model, but had floorboards instead of the kickstand/footpeg arrangement. This was referred to in dealer literature as a "non-clutch" model. However, these units were falling out of favor with the public, as the new clutch model was much more "user-friendly". In January of 1941, the company still had direct drive models in inventory.

In 1940, a clutch design was built which allowed the rider to disengage the drive belt by placing enough slack in the belt drive to cause it to slip on the pulley. This was referred to as the "G" model. The "G" continued to be built, with various updates and changes, from April 1940 through December of 1944.

The first "G" models used a clutch design which unfortunately failed quite rapidly. This design can be readily identified by the left heel-operated clutch pedal. In December of 1940, a replacement design was incorporated that used a rocker-pedal system operated by the toe and heel of the left foot.

ENGINE AND DRIVE SYSTEM

On the 1940 Direct Drive (non-clutch) models, the engine serial number begins with "40" followed by the sequential production order. "G" models will have a serial number beginning with "G" and followed by the production number. Towards the end of '40, Simplex began using the Wico Black Streak magneto. Thus, some G's and all "H" and "48" models have the Wico Black Streak. During production of the "G", a drive belt tensioner system was developed, which assisted in keeping tension on the belt between the "clutch" and the rear wheel pulley. This helped to prevent belt slippage in wet or muddy conditions, particularly since many military units were seeing this type of use.

CHASSIS

1940 was the first year for the new floorboard and kickstand arrangement. The old center stand which included the footrests was replaced by a folding sidestand located under the left floorboard. The floorboards are octagonal, where later models ("H" and later) have rounded corners. A heel-operated clutch pedal is used on the '40 model G, but was replaced by a rocker clutch by December of '40. The rear brake pedal was also heel-operated, and was located on the right side on the "G". The front brake was operated by a hand lever on the left handlebar. The throttle and compression release were offered both in twist grip or lever configuration on the right handlebar. By 1942, the compression release and throttle were again operated by a twist grip.
The Do-Ray Zephyr taillight appears as early as October 1940.

The US Military purchased a number of special Military-spec "G" models, which were designated the G-A-1. These models had a left twist throttle and a right handlebar compression release twist grip. Indian Motocycle had also adopted this design for military and police use where it might be desirable to shoot with the right hand while operating the throttle with the left.

Approximately 11,000 G Models were built over the five year period.