How to use this calculator
- Enter shift RPM. Use the RPM where the shift begins.
- Enter both gear ratios. Set the current gear and the next gear.
- Set minimum useful RPM. Use the low end of the engine power band.
- Read margin. Check after-shift RPM and power-band margin.
How it works
Road speed is nearly unchanged during a quick shift, so engine RPM follows the gear-ratio change: after-shift rpm = shift rpm x next gear / current gear.
Pair this with the vehicle speed calculator or final drive ratio calculator when selecting an overall gearing package.
Worked example
Verified against the live calculator
Shifting at 6,500 rpm from a 2.10 gear into a 1.45 gear lands at about 4,488 rpm, a 2,012 rpm drop.
Frequently asked questions
How do you calculate RPM drop after a shift?
Multiply shift RPM by the next gear ratio divided by the current gear ratio.
Does final drive ratio affect RPM drop?
No. If tire and final drive stay the same, the RPM drop only depends on the two transmission gear ratios.
What is a good RPM drop?
A good RPM drop lands the engine above the useful torque or power band after the shift.
Can this be used for downshifts?
It is intended for upshift spacing. For downshifts, swap the gear ratios and interpret the RPM change accordingly.
Method & assumptions
- Assumes vehicle speed does not change during the shift event.
- Does not choose the optimal shift point; it only checks gear spacing against a target RPM band.