Gear Shift RPM Drop Calculator (Where the Revs Land After an Upshift)
Engine speed just after you change up (or down) a gear, how much the revs fall, and the road speed at which it happens, from the two gear ratios.
Results
The dashed line marks the value you entered.
What this tool does
Because the wheels keep turning at the same speed during a shift, the engine speed changes in proportion to the ratio of the two gears: rpm after = rpm before × next ratio ÷ current ratio. Shifting from a 2.0 ratio to a 1.4 ratio drops the revs by 30 %, however high you started. Tuners use this to check that a shift from the redline lands the engine back near the power peak, so the next gear pulls hard straight away, and that gaps between gears are not too wide. Ratios are the total gearbox ratio of each gear; the final drive and tyre size only enter the road-speed figure.
Formula
rpm after = rpm before × (next ratio ÷ current ratio) · speed = rpm ÷ (gear ratio × final drive) × tyre circumference × 60 ÷ 1000
Variables
| Symbol | Meaning | Unit |
|---|---|---|
r1 | Ratio of the gear you shift from (gearbox ratio) | — |
r2 | Ratio of the gear you shift to (gearbox ratio) | — |
rp | Engine speed when you shift | rpm |
fd | Final drive ratio | — |
tc | Tyre rolling circumference | m |
pk | Engine speed of peak power | rpm |
RA | Engine speed just after the shift | rpm |
RD | Drop in engine speed | rpm |
RQ | Drop as a share of the shift speed | % |
SP | Road speed at the shift | km/h |
PV | Engine speed after the shift minus the power peak (negative = below the peak) | rpm |
Worked example
- Ratio of the gear you shift from (gearbox ratio)2
- Ratio of the gear you shift to (gearbox ratio)1.4
- Engine speed when you shift6500 rpm
- Final drive ratio3.9
- Tyre rolling circumference1.95 m
- Engine speed of peak power5500 rpm
- Engine speed just after the shift4550 rpm
- Drop in engine speed1950 rpm
- Drop as a share of the shift speed30.0 %
- Road speed at the shift98 km/h
- Engine speed after the shift minus the power peak (negative = below the peak)-950 rpm
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.