Q: We own a couple of dirt bikes. Do we need insurance for these?
A: Dirt bikes need comprehensive and collision coverage, just like you would have on a car. You should probably also get med pay or medical payments coverage. That way if someone is injured while riding the bike, you will have insurance to pay their medical bills. (This assumes you let friends ride the bikes and you do not know if they have health insurance.)
You also need liability insurance. While it is unlikely that the bike is going to hit a car, it is possible that someone riding the bike could be injured and allege that they were injured by a result of your failure to maintain the bike.
Check with your homeowners policy because some homeowners policies provide this coverage, but not all of them. (That includes both coverage for theft/fire and liability coverage.)
Also, if you are just riding your bikes on dirt tracks, you can probably skip the comprehensive and collision coverage. It is unlikely you will have a collision (although you may hit another bike) and do substantial damage. The comprehensive coverage may be a good idea in case the bike is stolen, but again, check with your homeowners coverage.