| Abbreviation | Definition |
|---|---|
| IROC | International Race of the Champions |
| IROC | International Racing of Champions |
| IROC | nternational Race Of Champions |
| IRR | Infinity Random Race |
| IRRC | International Road Racing Championship |
| IRS | Internet Racer's Supply |
| IRTA | International Racing Teams Association |
| ISR | International Snowmobile Racing |
| ISRA | International Sim Racing Association |
| ISRA | International Slot Racing Association |
| ITM | Instrumentation Trace Macrocell |
| ITRA | International Tricycle Racing Authority |
| ITS | International Tracing Service |
| IVTM | Influenza Virus Traceability Mechanism |
| JBR | James Barone Racing |
| JFR | John Force Racing |
| JFRT | Jack Frost/Big Boulder Race Track |
| JFRT | Jesus First Racing Team |
| JFRT | Jesus Fish Racing Team |
| JGR | Joe Gibbs Racing |