My son lent his bike to a friend. My son keeps the bike tightly chained with a combination lock to a pipe in the back yard of our building. He told his friend the combination on the lock and told him to return the bike to the place he found it when he finished using it, which he says he did. However, when my son returned, the bike was gone. One of the neighbors says he saw an Arab who entered the building and after about fifteen minutes left with a bike which now we realize was my son’s. When my son spoke with his friend the cause became apparent. In order to prevent theft one must wrap the chain tightly around the pipe since otherwise it is possible to slide the chain off the pipe and take the bike along with the chain. When his friend borrowed the bike he found it wrapped tightly but his friend, who was unaware that this was necessary, failed to do so which allowed the thief to steal the bike. Is his friend liable for the loss?
You left out an important detail: the age of the children. We will see that the age of your son is probably not important but the age of his friend is.
When one allows someone to ride his bike the borrower assumes the legal status of a sho’eil, a borrower, for as long as he is allowed to use the bike. When the borrower informs the owner that he finished using the bike, or the time period for which he was allowed to use the bike ends (See CM 340, 8), the borrower assumes the status of a socheir, a renter, until he returns the bike. Even though he no longer is allowed to ride the bike, he still has the status of a socheir and not the status of a shomeir chinom, one who watches for free, since he did benefit from the bike when he drove it. Finally, when he returns the bike the borrower is totally absolved from all responsibility.
Since a sho’eil is liable even for oness (circumstances that were beyond the control of the borrower), if the theft had taken place when the friend was allowed to drive the bike he would certainly be liable. Even after the period when he was allowed to drive the bike ended, the friend is liable for ordinary theft since a socheir is liable for theft.
Therefore, there are only two possibilities that absolve the friend from liability. One possibility applies even if the theft took place before the bike is legally considered to have been returned. Specifically, if the theft was a result of an oness, some opinions (See Tosafos BM 42A and CM 303, 2-3) absolve the borrower from liability. However, this certainly was not the case here since the chain could have been wrapped tightly and this was not done. Thus, the only possibility to absolve the friend is if we consider the bike as having been returned to your son, in which case the borrower has no liability.
As we mentioned at the outset, the age of the friend is crucial. The reason is that if the friend was under bar mitzvah he is certainly not liable since it is clear from the Gemara (BB 87B) that a minor never assumes the legal status of any kind of shomeir. The Pischei Choshen (2, Chapter 1 Note 34) rules that even those who maintain that it is proper for a minor who damages to pay when he grows up, agree that a minor who was negligent with an object that he was entrusted with does not need to pay when he becomes of age, since the owner himself acted negligently when he entrusted a minor with his object. Thus, your question is only relevant if his friend was over bar mitzvah.
In theory, the age of the owner of the bike is also quite significant since there is a dispute among the Rishonim whether one who is entrusted with an object that belongs to a minor assumes the status of a shomeir. The opinion of the Rambam (Sechirus 2, 7), which is followed by the Shulchan Aruch (96, 1), is that he does assume the status of a shomeir. However, the Ramo follows the opinion of many (Rashba, Ran on Shavuos 42A) that he does not assume this status and even if a person who was paid to watch over a minor’s possession was negligent he is not liable for an ensuing loss.
There is an additional dispute in the case of one who, like your son’s friend, borrowed an object. The opinion of the Machane Efraim (Shomrim 9-10) is that all agree that one who borrows an object from a minor assumes the status of a sho’eil. However, many Acharonim (including the Imrei Binah To’ein 37, Nachal Yitzchok 96, 1, Minchas Pitim in Sheyorei Hamincha 302) disagree and maintain that those who disagree with the Rambam maintain that even one who borrows an object from a minor is not liable.
However, the reason this issue is irrelevant is that when one gives a present to a minor who lives with his parents (See Money Matters Page 214) it is considered as if he gave the present to the father. Moreover, even if the father himself (See the notes of R. Akiva Eiger on CM 270 in the name of the Nemukei Yosef who is the source of this halachah) gave a present to his son, the father retains ownership.
There are two reasons for this ruling. The Rishonim (Ran on BM 12) who are the source for this ruling say that an underage child who is not financially independent does not have the ability to acquire presents even from his parents due to his lack of independence. (The Gra (note 6) finds this explanation quite difficult.) The Sema (note 6) gives his own reason for this ruling, namely, that when people give a present to a minor child they really intend to give it to his parents since children tend to act irresponsibly. Therefore, if your son was past Bar Mitzva when he received the bike it was his, but if he was under bar mitzvah it was your bike. In either case the bike was not owned by a minor. Therefore, from a practical standpoint, your son’s age is irrelevant.
Thus, if the boy who used the bike was over bar mitzvah the only way that he can be absolved from liability is if the way he placed the bike is considered a return of the bike. We should note that usually when one borrows a bike he must: 1-inform the bike owner that he returned the bike and, 2-return it to a safe place. The standards of what is called a safe place are quite high and according to some (Darkei Moshe 340 and Sema 340, 12) relate to the relationship that the borrower had with the object prior to its return. Since one who borrowed the object had the status of a shoeil the standard is very high. The Ramo (340, 8) rules that when one borrows an object from the husband it does not suffice to return it to his wife! This is not true for our women who have permission to transact business with their husband’s money but it illustrates the high standard of what is called a safe place. Certainly, chaining the bike loosely to a pipe where it can be slid off does not qualify.
However, when an owner tells the borrower explicitly to place the borrowed object in a specific place when he finishes using it, the Mishpatei Hachoshen (Ohr Efraim 340, 26) proves that once the borrower follows his instructions he is considered as having returned the object even if he did not inform the owner and even if the place is not totally safe. The reason is because we view the owner as having waived his right to require return to a totally safe place. Since in your situation, we cannot say that the boy who returned the bike in a significantly different manner complied with the instructions he was given, we cannot classify the borrower as having returned the bike and he is liable for the theft.
In conclusion: The friend, if he is post-bar mitzvah, must pay you for the loss of your son’s bike. Bear in mind that he only must pay the value of the bike when it was stolen, which is less than the price of a new bike unless your son’s bike was brand new.