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How Many Rpms An Automatic Turns At 55Mph?


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Automatics have the same top-end gear ratio as 4-speed manuals.  The rpm depends on such things as tire size and diff gear ratio.


My '75 automatic with 185/60 x 14 tires and a stock 3.64:1 rear end turns about 2800 rpm @ 55 mph.  At 80 mph I'm just under 4K rpm, but wife's '76, with a 3.91:1 rear end turn about 400 more rpm at 80 mph than my car.  She also has 185/60 x 14 tires, which are a little smaller than the OE 165/80 x 13s that came on our cars.


Bob Napier

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you  ...."Have a 1975 auto.....seems like a lot of RPMs

going on at 55mph. Just curious."


you don't have a tachometer to tell us what RPM at what MPH your

gauging this by ?  Automatics come from factory with clocks,

no tach, unles PO's have changed cluster


your bmw Owner's handboof from 1975 states:


Permitted Maximum Top Speed :

Auto Gear Selector Position 1 = 39 mph (65 kph)

............................................  2 = 69 mph (110 kph)

............................................ A = 103 mph (165 kph)

all at 6,200 RPM


Permitted Maximum Sustained RPM = 6,000


if your car has tires other than 165x13" then expect some

variance from above specs


happy Automatic'ing


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