This paper describes a method of synthesis of asynchronous circuits with relative timing. Asynchronous communication between gates and modules typically utilizes handshakes to ensure functionality. Relative timing assumptions in the form "event a occurs before event b" can be used to remove redundant handshakes and associated logic. This paper presents a method for automatic generation of relative timing assumptions from the untimed specification. These assumptions can be used for area and delay optimization of the circuit. A set of relative timing constraints sufficient for the correct operation of the circuit is back-annotated to the designer. Experimental results for control circuits of a prototype iA32 instruction length decoding and steering unit called RAPPID (Revolving Asynchronous Pentium(R)Processor Instruction Decoder) shows significant improvements in area and delay over speed-independent circuits.