West Des Moines police say the two men hit a slick spot on the I-35/80 ramp, rolled the bikes and wound up in the ditch.
A passerby stopped to help, but their vehicle was hit by another car that slipped in the same spot.
Police shut down the busy ramp as the fire department and DOT cleaned it.
The driver of one of the cars went to the hospital as a precaution.
The out-of-state bikers were heading to Sturgis and say this accident will not stop them from making the rest of the trip.