Propshaft Critical Speed Calculator

Calculate the critical (whirl) speed of a driveshaft to ensure safe operating RPM margin per SAE J1722.

Input Parameters

Results

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Critical Speed
RPM
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Max Safe RPM
RPM
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Moment of Inertia
in⁴
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Safety Factor @ 6000
Note: Operating above 75% of critical speed risks catastrophic driveshaft failure. Two-piece shafts with a center bearing reduce effective length. Carbon fiber provides the best strength-to-weight. SAE J1722.

Reference

I = pi/64 × (Do⁴ − Di⁴) A = pi/4 × (Do² − Di²) Nc = 4.71 × sqrt(E×I×g / (w×L⁴)) × 60/(2pi) Max Safe RPM = Nc × 0.75 (25% margin) Steel: E=30 Msi, rho=0.283 lb/in³ Aluminum: E=10 Msi, rho=0.098 lb/in³