The Wisconsin State Patrol said five people were injured, one of them critically, in the crash that developed when traffic in front of the cyclists slowed down.
One of those injured, a 47-year-old from Denmark, suffered life-threatening injuries and was transported by Med Flight helicopter.
The State Patrol said that 60 members of an international motorcycle group were traveling on the interstate. The State Patrol said the bikers were speeding and following too closely in their group.
"They were traveling in excess of the speed limit and they were following way too closely. Traffic had slowed a little in front of them due to heavy traffic volume, (and) they weren't able to react in time to that," said Lt. Brad Altman, of the Wisconsin State Patrol. "Whether it's one motorcycle or 100 motorcycles, they need to be operating responsibly on the roads and following the traffic laws by wearing the appropriate safety equipment that's available to them. None of the cyclists had helmets on."
The crash happened at about 10:30 a.m. in the westbound lanes of the interstate. All lanes were blocked for more than an hour, but traffic got moving again shortly before noon Friday.
Traffic was backed up for 10 to 15 miles Friday after the crash.
Jeff Martin, a member of the motorcycling group that was heading to Onalaska for an annual picnic, said group members are "people who enjoy riding motorcycles and a clean and sober lifestyle."
Some members headed for the hospital to support those injured in the crash.
Motorcycle fatalities in Wisconsin are on the rise. The state Department of Transportation said it has seen a major jump in deaths this year compared to last year.
In 2009, there have been 46 motorcycle fatalities from January to June. There were 28 motorcycle fatalities in the same period last year.
The Department of Transportation said that unlike Friday's crash, most crashes involve just one motorcycle.
"A lot of those riders just need to make sure they understand the properties of the motorcycle and what it takes to operate it. And another disturbing trend that we see is a lot of motorcyclists are not properly licensed," said Maj. Daniel Lonsdorf, of the Wisconsin Department of Transportation.
The DOT said it has found that many motorcycle crashes are a result of control problems.
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