The Detroit News is in the middle of a series of articles on speed limits. One of their articlese, excerpted below, gives a good overview of how to fight a speeding ticket in Michigan:

But motorists often lose their cases because they aren’t aware of a recently enacted state law that opens the door for challenges of many speeding tickets, [NMA Michigan Activist Steve] Purdy said.

Michigan Public Act 85, which took effect in November 2006, changed the way municipalities may set speed limits. It gave them three choices:

Communities may set speed limits based on the frequency of driveways and cross streets on a particular stretch of road.

If a community conducts an engineering and traffic study, it may post a speed limit by using the 85th percentile of free-flowing traffic, meaning the speed at which 85 percent of drivers are traveling during the traffic study.

If communities don’t use either of those two methods, a 55 mph limit applies by default, except in platted subdivisions and in business districts, said Lt. Gary Megge of the Michigan State Police Traffic Service Section.

“There are many roads in Michigan where the speed limit isn’t in compliance with the law,” said Megge, who travels the state helping communities set proper speed limits. “A lot of speed limits are set artificially low.”

And if the speed limit isn’t in compliance with the state regulations, any ticket written for violating it is invalid.