Separate launch and running conditions
The selected ratio multiplies the chain reduction. An entered 2.5:1 converter ratio with 5:1 chain gearing produces 12.5:1 overall. A selected 0.9:1 operating point produces 4.5:1 overall. These values illustrate the method; they are not specifications for a particular converter.
Rtotal = Rchain × Rconverter at the selected operating pointFollow the worked comparison below for the input units and assumptions.
Work through an example
At 3,600 rpm and a 13-inch tire, 12.5:1 gives about 11.14 MPH, while 4.5:1 gives about 30.94 MPH. The examples hold RPM constant purely to isolate ratio changes.
Model more than one converter operating point
Create separate launch and running scenarios using documented converter ratios for your equipment. Hold tire dimensions and chain gearing fixed to see the isolated ratio effect. Then consider the engine RPM associated with each real operating point.
Distinguish ratio change from slip
A changing pulley ratio alters the geometric reduction. Slip changes how closely measured shaft speeds follow that ratio. A static worksheet evaluates your chosen reduction; it does not model belt forces, engagement or the converter shift schedule.
Compare launch and running converter scenarios
The example fixes chain reduction at 5:1, engine RPM at 3,600 and nominal tire diameter at 13 inches. Converter ratios below are illustrative input scenarios, not specifications for any product. Holding RPM constant is a deliberate way to isolate geometric ratio effects.
Rtotal = Rchain × Rconverter at the selected operating point- Find documented operating ratios for your exact converter and identify the convention used for reduction.
- Multiply each selected converter reduction by the complete chain and jackshaft reduction.
- Calculate wheel speed separately for each operating point rather than averaging the ratios first.
- Record the engine RPM associated with the operating point when moving from a comparison to actual observations.
| Selected converter (:1) | Overall reduction (:1) | Theoretical MPH |
|---|---|---|
| 2.5 | 12.5 | 11.14 |
| 1 | 5 | 27.85 |
| 0.9 | 4.5 | 30.94 |
The 0.9:1 scenario is an overdrive relative to the converter input, so overall reduction becomes 4.5:1. The selected converter ratio does not describe belt slip, engagement or the rate of shifting. A single static number cannot capture the complete acceleration process.
Check the inputs before interpreting a difference
Do not apply a launch ratio to every speed calculation, or assume that a no-load observed ratio holds under load. A converter description such as high or low range needs actual numerical ratios before it can be entered meaningfully.
Before you apply the result
Use documented ratios for your exact equipment and distinguish belt slip from ratio change. Engagement, load, belt condition and tuning affect the actual operating point. A static calculator cannot reconstruct converter behavior during acceleration.
Try the calculation
Enter your own values in the related calculators. Compare one input at a time and keep units and operating conditions visible with the result.
Frequently asked questions
Is the converter ratio always 1:1?
No. Use documented operating ratios for the actual converter rather than assuming direct drive throughout its range.
Should I multiply converter and sprocket ratios?
Yes. With the same reduction convention, 2.5:1 converter reduction and 5:1 chain gearing give 12.5:1 overall.
Does the calculated running speed include belt slip?
No. It assumes the selected ratio is transmitted without slip.
Can I average converter ratios to predict a complete acceleration run?
Not with this static worksheet. Acceleration also depends on how the ratio and engine output change with time and load. Evaluate clearly labeled operating points instead.
Reference and method
Angular speed and tangential speed. Gear reductions follow tooth engagement and conservation of rotation count.
OpenStax — University Physics: rotation with constant angular acceleration ↗These explanations and examples describe the documented model. No manufacturer testing, named expert authorship or independent professional review is claimed. Read the method policy or report a correction.