1961 Indianapolis 500

The 45th Indianapolis 500 was held at the Indianapolis Motor Speedway on Tuesday, May 30, 1961. For the first time since 1949, the Indianapolis 500 was not recognized on the World Championship calendar. The race celebrated the 50th anniversary of the first Indy 500 in 1911.

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1966 Indianapolis 500

The 50th International 500-Mile Sweepstakes was held at the Indianapolis Motor Speedway on Monday, May 30, 1966. The official program cover for the race celebrated both the 50th running of the race, and sesquicentennial (150th anniversary) of Indiana statehood.

Eddie Sachs and A. J. Foyt were battling for 1st-2nd in the latter stages of the race. On Foyt's final scheduled pit stop, his crew is unable to properly engage the fuel mechanism, and his car does not take on a full load of fuel. Foyt returns to the track, and is pulling away from Sachs. Foyt's car is running faster due to the light fuel load, but his crew signals him that he will be unable to make it to the finish without another pit stop. The crew borrowed a fuel tank from Len Sutton's team, and signaled Foyt to the pits.

Foyt gives up the lead on lap 184 for a splash-and-go. That hands the lead to Sachs, who is now leading by 25 seconds. With three laps to go, the warning tread shows through on Sachs' rear tire and Sachs decides to play it safe. Rather than nurse the car around, he pits to replace the worn tire on lap 197. Foyt takes the lead with three laps to go and wins his first (of four) Indy 500 victories by a margin of 8.28 seconds.

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Tire

Wear bars (or wear indicators) are raised features located at the bottom of the tread grooves that indicate the tire has reached its wear limit. When the tread lugs are worn to the point that the wear bars connect across the lugs, the tires are fully worn and should be taken out of service. Most wear bars indicate a remaining tread depth of 1.6 millimetres (0.063 in) and are deemed "worn out" at that point.

(Source: Wikipedia)