Overflow formats were required in 1958 and 1959 when registrations exceeded 9999. A larger plate size was used from 1960 to 2003.

Confirmed serial ranges and break points:

Since 1976 all motorcycle plates have expired in April, and since 1990 two-year validations (prorated to even years only) have been used.

Confirmed serial ranges and break points:

The current series debuted in 1992; coinciding with 1994 expirations. New license plates were downsized in 2003 to a 4"x7" format; however, all earlier issues remain in use.

Confirmed serial ranges and break points:

Disabled Motorcycle

Motorcycle plates for disabled motorists have been available since the early 1990s. The current series started at D101 in 1992 (exp. 1994), and only a few hundred plates have been issued since.

Moped

Mopeds have been registered in Wisconsin since 1978, and since 1980 specially-captioned plates have been issued. Moped plates follow the same colors, replacement cycles, and registration intervals as those for motorcycles.

Snowmobile & ATV Dealer

These plates are a bit of an odd issue; but since they're motorcycle-sized, I'm including them here.

Snowmobile plates fall under the authority of the Wisconsin Department of Natural Resources (as opposed to the Department of Transportation), and aren't issued to snowmobiles per se as much as snowmobile dealers for use when demonstrating a vehicle. ATV and off-road motorcycle dealer registrations evidently fall into the same category, and the motorcycle-sized plate was succeeded in the 1990s by a smaller, bicycle-sized affair.