Calculation
Fu = F1 − F2
Only the difference F1 − F2 transmits torque, while the combined span forces load the shaft and bearings.
Ingenieurmäßige Vorbemessung
Belt Effective Tension Calculator
Only the difference F1 − F2 transmits torque, while the combined span forces load the shaft and bearings.
MINTSI
02
Result
Select a target and calculate.
Understand the inputs
- Effective tension Fu — Tangential useful force that transmits torque and power.
- Tight-side tension F1 — Force in the more highly loaded belt span during operation.
- Slack-side tension F2 — Remaining force in the less highly loaded belt span.
Example
A 1,000 N tight-side tension minus 400 N slack-side tension gives 600 N effective tension.
Assumptions and limits
Steady operation with span forces at the section considered. Centrifugal tension, tensioning method and dynamic peaks are not calculated independently.
Understand Belt Effective Tension Calculator
This calculator separates useful circumferential force from the larger forces carried by the two free spans of a belt drive. It finds Fu from tight-side tension F1 and slack-side tension F2, or rearranges the balance for either missing span force.
What does this quantity describe?
Effective belt tension Fu is the difference between span tensions: Fu = F1 − F2. It acts tangentially at the pulley pitch radius and produces transmitted torque. Common pretension added to both spans raises F1 and F2 without increasing their difference by the same amount.
If two people pull a rope in opposite directions with 1,000 N and 400 N, the resultant is 600 N. For a belt, that difference is the tangentially useful force, although both individual forces still matter to the belt, shaft and bearings.
Formula and variables
Fu = F1 − F2
Fu = F1 − F2F1 = Fu + F2F2 = F1 − FuP = Fu · vM = Fu · d/2
| Symbol / input | Meaning |
|---|---|
| Effective tension Fu | Tangential useful force that transmits torque and power. |
| Tight-side tension F1 | Force in the more highly loaded belt span during operation. |
| Slack-side tension F2 | Remaining force in the less highly loaded belt span. |
Choose the inputs correctly
F1 is the more highly loaded tight-side force and F2 the slack-side force. Both values must describe the same operating condition, pulley and convention regarding centrifugal tension. In driving operation F1 must be at least as large as F2.
How to use the calculator
Select Fu and enter measured span forces or values from a manufacturer calculation. To size one span, select F1 or F2 and enter the required effective tension plus the other span force. Then check traction, allowable belt tension and bearing load separately.
Worked example
For F1 = 1,000 N and F2 = 400 N, Fu = 1,000 − 400 = 600 N. At v = 12 m/s this would transmit 7.2 kW; on a 200 mm pitch-diameter pulley it would produce 60 N·m.
Understand the result and units
600 N is not the maximum belt force but the useful difference. The belt must carry at least F1, while shaft load follows from the vector combination of both span forces. A small Fu with large F1 and F2 indicates high pretension with low force utilisation.
Forces are evaluated in newtons. Power in watts follows from newtons times metres per second; torque in newton metres follows from newtons times metres. Use identical units for both span forces.
Effective pull is not shaft load
Fu acts tangentially and produces torque. The shaft instead experiences the geometric vector sum of the forces pulling along both spans. With nearly parallel spans, bearing load is on the order of F1 + F2 and can greatly exceed Fu.
Typical applications
Use the result to derive belt-drive power and torque, interpret span-force measurements, and check how much of the force predicted by a manufacturer selection actually transmits work.
Assumptions, limits and common mistakes
This force balance is not a complete belt rating. It does not determine required friction, pretension, centrifugal tension, dynamic factors, width or service life. Product-specific manufacturer data remains authoritative.
Common mistake: Do not use F1 + F2 as transmitted circumferential force. Do not mix operating forces with standstill pretension values. Tight and slack sides exchange roles when power flow reverses.
Frequently asked questions
What is effective belt tension?
It is tight-side tension minus slack-side tension. Only this difference produces transmitted torque.
Is Fu the maximum belt force?
No. The largest belt force is normally F1 and may also contain a centrifugal component.
How do I calculate power from Fu?
Use P = Fu·v when belt speed v is known. Divide watts by 1,000 for kilowatts.
How do I calculate pulley torque?
Use M = Fu·d/2 with pitch diameter d expressed in metres.
Why is there still tension on the slack side?
Pretension is required to create pulley contact pressure and traction, so the slack span does not become force-free.