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Old 07-26-2008, 12:31 PM
koldei koldei is offline
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Join Date: Jun 2008
Posts: 3
scary math time
(aka me thinking out loud)

when my speedometer reads 60mph I'mshowing 3100rpm on the tach

3100 RPM * 60 = 186,000RP-hour (engine)
if final transmission ratio is 1:1
186,000RP-hour (driveshaft) / 2.88 =
64583.3 RP-hour rear axle

195/70R14 tires get either 852 or 836 revs per mile dep. on brand

64583/852 = 75.8 miles in that same hour

for better or worse the above seems to work out to what i *thought* was happening..when taking real- world measurements.
(my odo would show 60 miles...80% of the 75miles the interstate said i'd traveled

i am assuming the tach is right

brain = ow

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