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Old 04-03-2020, 01:04 PM   #1 (permalink)
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Math help......

I like math, but can't understand why I can't convert this formula. Maybe it's the 12 hour nights at the nuclear plant or the radiation scrambling my brain.

I need to convert this......

MPH = [60 / (transmission gear ratio x axle ratio)] x [engine RPM / tire revolution per mile]

into this.......

engine RPM = ????????

I don't need it for the Ranger in my signature, but for my project Triumph TR7. I need to decide what I want for a rear end to get a nice RPM highway cruising range. I already know the new tire size and new transmission ratios that go along with the engine swap I have planned.

Thanks

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Old 04-03-2020, 01:39 PM   #2 (permalink)
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Engine RPM = [MPH x (transmission gear ratio) x (axle ratio) x (tire revolutions per mile)] / 60
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Old 04-03-2020, 02:07 PM   #3 (permalink)
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Thank you. I haven't figured out what I was doing wrong, but the numbers I was coming up with were so far off I knew I had messed up someplace.
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Old 04-03-2020, 02:13 PM   #4 (permalink)
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After looking at what I had on paper I have come to the conclusion that it really helps if you write things in the SAME order as you type them. Really messes things up when you have RPM (engine speed) and confuse it with rpm (revolutions per mile). SMH
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Old 04-03-2020, 08:15 PM   #5 (permalink)
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Spicer also has an online calculator.

https://spicerparts.com/calculators/...rpm-calculator
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Old 04-04-2020, 06:46 PM   #6 (permalink)
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https://www.tremec.com/calculadora.php
1st: 3.72
2nd: 2.20
3rd: 1.50
4th: 1.00
5th: 0.79
Gear: 3.73
Tire: Whatever you have.

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