"That is really cooking, for 335 miles," Johnson said.

Factoring in stops, a rider will have to average 14 mph for all 24 hours to reach Dubuque in time. But Johnson really doesn't recommend stopping. Some RAID participants will ingest foods and gels while riding.

"You just have to keep going...You have to have your nutrition dialed in. It is basically an eating contest," Johnson said.

The conditions will also determine how riders fare over the day, and for now the forecast has a 40 percent chance of rain in the morning and 12 mph buffeting winds to push riders east, with temps into the mid-70s by afternoon.

"A tailwind will make or break a lot of guys," Johnson said.

There are RAID volunteers who traffic control in limited places, so participants have to arrange their own support with a following vehicle.

Riders leave Sioux City at 4 a.m. Sioux City will be dozens of miles behind by the time the sun rises Saturday.

The participants also have the choice of riding a half-RAID of 167 miles to Webster City, or the last half, from Webster City to Dubuque, leaving on that piece at 11 a.m.