On the face of it, it would ideally be only a leasing of cars and not a sale, since there is no "transfer of ownership" as you have rightly mentioned. There is no specific provision in the service tax laws, which makes this sort of a transaction liable to service tax. However, you would need to check the VAT laws of the concerned state, since under the Karnataka VAT, this is a deemed sale and accordingly VAT is levied. Just see the below provision of the Karnataka VAT, where transfer of right to use is included in definition of "sale" (have highlighted the relevant portion in yellow)
"Sale" with all its grammatical variation and cognate expressions means every transfer of the property in goods (other than by way of a mortgage, hypothecation, charge or pledge) by one person to another in the course of trade or business for cash or for deferred payment or other valuable consideration and includes,-
(a) a transfer otherwise than in pursuance of a contract of property in any goods for cash, deferred payment or other valuable consideration;
(b) a transfer of property in goods (whether as goods or in some other form) involved in the execution of a works contract;
(c) a delivery of goods on hire purchase or any system of payment by installments;
(d) a transfer of the right to use any goods for any purpose (whether or not for a specified period) for cash, deferred payment or other valuable consideration.