Run two parameter sets side by side — spot the better design instantly
Comparison Mode — Side-by-Side Engineering Design Calculator (ISO 281 · Goodman · Roark)
The MechanixCalc Comparison Mode lets engineers run two design variants side by side across six mechanical component types — bearings (ISO 281), shafts (Goodman/Shigley), gears (contact and bending stress), beams (Roark deflection), helical compression springs (Wahl correction), and bolted joints (ISO 898-1 tensile stress area). Enter Design A and Design B, and the tool instantly shows every output metric, the absolute delta and which configuration is better — with no account or sign-up required.
It is built for early-stage design decisions: swap a bearing for one with a higher dynamic capacity, widen a gear face, increase a shaft diameter, or change a bolt grade — and the safety-factor impact appears in real time. The clean three-column layout (A | B | Δ) makes it straightforward to document a design-trade rationale before committing to the full per-tool calculation with its complete standards-cited PDF report.
What this calculator does
- Side-by-side A/B comparison for six mechanical component types in one view
- Bearing L10 life and equivalent dynamic load comparison (ISO 281 e/X/Y interpolation)
- Shaft bending stress, von Mises stress, and yield and fatigue safety factor delta (Goodman)
- Gear contact stress SH and bending stress SF comparison with gear ratio and tangential force
- Beam deflection and maximum bending stress for simply-supported and cantilever spans (Roark)
- Spring rate, deflection, Wahl-corrected shear stress and safety factor comparison
- Bolt preload, tensile stress area, clamp force and yield safety factor comparison (ISO 898-1)
Method & formulas
Bearing L10 life (ISO 281)
The bearing sub-calculator follows ISO 281: the equivalent dynamic load P is derived from the radial and axial forces using the interpolated e, X and Y factors from Table 11-1 based on the Fa/C0 ratio, with the ISO floor of P ≥ Fr always applied. L10 life in millions of revolutions is then the standard fatigue-life relation, and L10h converts that to hours at the given speed.
L10 = (C / P)^p × 10⁶ [revolutions]where C = dynamic load capacity (kN); P = equivalent dynamic load (kN), P = X·Fr + Y·Fa; p = 3 for ball bearings, 10/3 for roller bearings
L10h = L10 / (60 · n)where L10h = rating life (hours); L10 = rating life (revolutions); n = rotational speed (rpm)
Shaft stress and fatigue safety factor (Goodman / Shigley)
The shaft sub-calculator applies the Goodman mean-stress line to the combined bending and torsion state. Bending stress is amplified by the user-supplied fatigue stress-concentration factor Kf. Von Mises stress combines the normal bending component and the torsional shear component and is compared to yield strength for a yield safety factor. The corrected endurance limit is estimated at 0.45 Su (Shigley surface/size approximation), and the fatigue safety factor is the ratio of the endurance limit to the Kf-amplified bending stress.
σ_vm = √(σ_b² + 3·τ²)where σ_b = Kf · M · c / I = bending stress including stress concentration (MPa); τ = T·c / J = torsional shear stress (MPa); c = d/2; I = πd⁴/64; J = πd⁴/32
SF_fatigue = Se / σ_b where Se ≈ 0.45 · Suwhere Se = estimated corrected endurance limit (MPa); Su = ultimate tensile strength (MPa); σ_b already includes Kf
Beam deflection and spring stiffness (Roark / Wahl)
The beam sub-calculator uses the Roark closed-form solutions for midspan deflection: F·L³/(48·EI) for a central point load on a simply-supported span and F·L³/(3·EI) for a cantilever tip load, with the corresponding UDL terms superimposed. Bending stress at the extreme fibre follows σ = M_max·c / I. The spring sub-calculator applies the Wahl curvature-correction factor Kw = (4C+2)/(4C−3) to the shear-stress calculation; stiffness follows the standard coil-spring relation.
δ = F · L³ / (48 · E · I)where F = point load (N); L = span (mm); E = elastic modulus (MPa); I = second moment of area (mm⁴)
k = G · d⁴ / (8 · D³ · n)where G = shear modulus (MPa); d = wire diameter (mm); D = mean coil diameter (mm); n = number of active coils
Worked example
A designer is comparing two deep-groove ball bearings for a shaft rotating at 1500 rpm under a purely radial load of 10 kN. Design A has C = 30 kN; Design B has C = 40 kN. Determine the L10h life of each bearing and the percentage improvement.
Given
- Radial load Fr (both designs)10 kN
- Speed n (both designs)1 500 rpm
- Load exponent p (ball bearing)3
- Dynamic capacity C — Design A30 kN
- Dynamic capacity C — Design B40 kN
Result
- L10h — Design A300 h
- L10h — Design B≈ 711 h
- Improvement (B vs A)+137 %
- For a purely radial load, P = Fr = 10 kN (no axial component, so X = 1, Y = 0).
- Design A — L10 life in millions of revolutions: L10_A = (C/P)^p = (30/10)^3 = 3^3 = 27 Mrev.
- Design A — L10h life in hours: L10h_A = 27 × 10⁶ / (60 × 1 500) = 27 000 000 / 90 000 = 300 h.
- Design B — L10 life: L10_B = (40/10)^3 = 4^3 = 64 Mrev.
- Design B — L10h life: L10h_B = 64 × 10⁶ / (60 × 1 500) = 64 000 000 / 90 000 ≈ 711 h.
- Percentage improvement: Δ = (711 − 300) / 300 × 100 ≈ +137 %. Design B wins.
Illustrative only — assumes purely radial load (Fa = 0). The full Comparison Mode tool uses ISO 281 Table 11-1 interpolation for combined radial + axial loads. Verify against your own bearing catalogue data.
Frequently asked questions
Which standard does the Comparison Mode use?
Each sub-calculator applies the standard native to that discipline: bearings use the ISO 281 equivalent dynamic load and basic rating life; shafts use the Goodman mean-stress criterion with Shigley endurance-limit corrections; beam deflection follows the Roark closed-form solutions; spring shear stress uses the Wahl correction factor; and bolt tensile stress area follows ISO 898-1. There is no single governing standard because this is a multi-discipline meta-tool.
Is the Comparison Mode free?
Yes — the Comparison Mode is fully free with no sign-up required. You can also use every other MechanixCalc tool during a free 30-minute preview with no account, and a 14-day account trial (no credit card) unlocks the full suite. Saving calculations to your account and generating branded PDF engineering reports are available on a paid plan.
Which component types can I compare?
The current release supports six component types: deep-groove ball bearings (ISO 281 L10 life), solid circular shafts (bending, torsion, Goodman fatigue), spur/helical gear pairs (contact stress SH, bending stress SF, gear ratio), beams (simply-supported or cantilever, point load + UDL), helical compression springs (stiffness, deflection, shear stress), and metric bolted joints (preload, clamp force, stress area, safety factor).
How is the delta calculated and what does it mean?
For each output metric the tool computes Δ = (B − A) / |A| × 100 %. It then labels a metric green for the configuration that is better — for safety factors, stiffness, life, preload and clamp load, higher is better; for stress, deflection and load, lower is better. A positive Δ means Design B is higher than A; the colour and label tell you whether that is an improvement.
When should I use Comparison Mode rather than a dedicated calculator?
Use Comparison Mode for rapid early-stage trade studies — comparing two bearing sizes, two shaft diameters, or two spring wire gauges — where you need a quick delta before committing time to a full standards-cited calculation. For a final design sign-off, use the dedicated per-tool calculator: it applies the complete standard method, stress-concentration factor libraries, material databases and generates a reviewable PDF report with the governing standard cited on every output.
Related calculators
- Bearing Analysis (ISO 281)Full ISO 281 bearing selection with combined radial/axial loading, L10m modified life and heat generation.
- Shaft Analysis (DIN 743)Complete DIN 743 shaft fatigue safety factor, multi-segment deflection and critical speed.
- Beam AnalysisRoark beam deflection, slope and bending stress for standard load cases with section library.
- Spring DesignHelical compression and extension spring design: Wahl stress, fatigue life and clash clearance.
- Bolt / Fastener AnalysisFull VDI 2230 bolt-joint analysis: preload, clamp force, thermal delta and fatigue safety factor.
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