A waiver can only waive the rights of the person signing it (and can't always waive all of those rights.)

Your business could easily be subject to claims from someone other than the person who rented the bike, for example:

* A third person who rides the bike that your customer rented
* The other party involved in a collision, if they think you were negligent in letting that customer rent a bike, or in the maintenance or equipment of the bike.
* The health insurance company covering either your customer or the other party involved in a collision.
* The spouse, partner, or children of customer who is killed or incapacitated, for loss of the breadwinner's income, or loss of consortium, or wrongful death, or mental anguish, or the cost to care for an invalid...

Your customer could also claim the waiver is invalidated by fraud or misrepresentation on your part, or is contrary to public policy.

Even if you can defend against all those claims, who pays your attorney costs?