When your car gets a puncture (increasingly called a “flat tyre” in the non-American parts of the English speaking world) in India, you open the “dicky” (“boot” in British-influenced countries), (“trunk” in America) and get the “stepney”.
What’s a stepney? No, not some suburb of London or Adelaide, but the spare wheel (and its fully-inflated tyre). Try to search for it in Google and at least in Australia, you’ll not find the Indian meaning of stepney, namely, the spare tyre. Even the car-related results are simply car dealerships and service stations in Adelaide. (The definition in the Urban Dictionary is most unkind and we won’t go there.)

Origin of “Stepney” as a spare tyre

The explanation is that a mechanic in Llanelli, Wales had a shop on Stepney Street and he was the first to sell spare tyres when cars did not come with them. The coat of arms of Llanelli Borough Council (not the current city’s coat of arms) even had a spare tyre on it!
For an excellent article on its origins, please visit the entry for Stepney at World Wide Words.